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Review

Electrospinning of Nanofibers for Energy Applications

1
Institute of Functional Materials, Faculty of Chemistry, Northeast Normal University, Changchun 130024, China
2
National & Local United Engineering Lab for Power Battery, Northeast Normal University, Changchun 130024, China
*
Authors to whom correspondence should be addressed.
Nanomaterials 2016, 6(7), 129; https://doi.org/10.3390/nano6070129
Submission received: 29 April 2016 / Revised: 9 June 2016 / Accepted: 22 June 2016 / Published: 2 July 2016
(This article belongs to the Special Issue Electrospinning of Nanofibres for Energy Applications)

Abstract

:
With global concerns about the shortage of fossil fuels and environmental issues, the development of efficient and clean energy storage devices has been drastically accelerated. Nanofibers are used widely for energy storage devices due to their high surface areas and porosities. Electrospinning is a versatile and efficient fabrication method for nanofibers. In this review, we mainly focus on the application of electrospun nanofibers on energy storage, such as lithium batteries, fuel cells, dye-sensitized solar cells and supercapacitors. The structure and properties of nanofibers are also summarized systematically. The special morphology of nanofibers prepared by electrospinning is significant to the functional materials for energy storage.

1. Introduction

Energy conversion and storage devices have drawn significantly attention with fossil fuels depleting, climate change, and environment deterioration. Although some devices have realized commercialization, new breakthroughs are needed to improve their performance, including durability, harvest efficiency, power density and conversion efficiency.
Nanofiber (NF) materials have been extensively studied as constituent parts of energy conversion and storage devices. Currently, much effort has been devoted to developing nanostructured materials synthesized by different methods, including chemical vapor deposition [1], wet chemical synthesis [2], sol-gel templating [3], self-assembly [4], the molten salt method [5,6,7,8,9,10,11,12,13,14,15,16,17], the polymer precursor method [18,19,20,21,22,23] and electrospinning. Among these methods, electrospinning, as a versatile, efficient and low-cost method, has been used widely to synthesize many special NFs with different morphologies, including core-shell [24], hollow [25], multilayer [26], porous [27], etc. Combined with the high surface area, controllable porosity and ease of accessibility, the electrospun NFs have come to have important roles in various energy storage fields.
In this review, we focus specifically on the application of electrospun NF materials in lithium-based batteries, fuel cells, dye-sensitized solar cells and supercapacitors.

2. Electrospinning

The electrospinning technique is a versatile, efficient, and low-cost method for NFs’ fabrication, which traces its roots back to an initial patent on the fabrication of textile yarns by Formhals in 1934 [28]. However, electrospinning did not become a popular technique. This technique was not revived until the 1990s, when several research teams (especially that of Reneker) found that it could be used to prepare NFs from many organic polymer solutions [29]. After that, the electrospinning technique has been further developed.
A general electrospinning apparatus consists of a high voltage power supply, a syringe with a metallic needle with blunt-tip, and a grounded conductive collector, as shown in Figure 1. A high voltage electrostatic field is used to charge the surface of the polymer solution droplet. When the electrical forces overcome the surface tension and viscosity of the fluid, a liquid jet is ejected through the needle tip. The shape of the Taylor cone is influenced by the applied voltage. Within the evaporation of the mobile solution from the fluid jet to the collector, uniform NF mats form on the collector [30,31,32]. The types of collectors include a rotating drum, a metal frame, and a rotating mandrel, which can influence the alignment of electrospun NFs [33].
The properties of the fabricated NFs depend on the operating parameters, such as applied voltage, solution feed rate, spinning distance, environmental temperature, humidity, air velocity in the chamber, polymer molecular weight, solution conductivity, viscosity and surface tension. By adjusting the parameters, different morphologies of the NFs can be obtained [34,35,36]. The industrial development of electrospun NFs is at the starting stage. The NFs have potential in some fields, such as high temperature filtration, efficient catalysis, biology, tissue engineering, optoelectronic devices, and aerospace equipment [37].

3. Applications

Electrospun NF materials were applied widely in many fields due to their high surface area, good crystalline structure and superior kinetic property. In this section, we discuss the applications of electrospun NFs in lithium-based batteries, fuel cells, dye-sensitized solar cells and supercapacitors. The influences of the structures and the properties for NFs on these applications are also systematically summarized.

3.1. Lithium-Based Batteries

According to the development course of lithium-based batteries, there are three critical battery systems, including Li-ion batteries (LIBs) (Figure 2a), lithium-sulfur batteries (LSBs) (Figure 2b) and lithium-oxygen (Li-O2) batteries (Figure 2c). As one of the most important energy storage systems, the Li-ion battery (LIB) has been used not only in portable electronics [38], but also in power batteries for electric vehicles now. Simultaneously, to meet the demands of all-electric vehicles in the long term [39], researchers have been devoted to developing other battery systems with lithium metal as the anode material to improve the energy density, such as LSB and Li-O2 batteries. Certainly, the application of NF materials on these three lithium-based batteries plays a fundamental role to improve the energy density. In this section, we focus on the application of NFs on the LIB, LSB, and Li-O2 battery systems.

3.1.1. Li-Ion Batteries

At present, for the commercial LIBs, the electrode materials usually are based on powder materials. The long migration pathways for the Li+ of powder materials may lead to the large volume expansion occurring during cycling, resulting in the low rate of performance and poor cyclability [38]. NF materials are promising materials for LIBs because of their good electrochemical activity, high mechanical strength, and large specific surface area. In this section, recent advances in the areas of electrospun NFs as cathodes, anodes, and separator materials for LIBs are briefly summarized.

3.1.1.1. Cathode Materials

LiCoO2 is the first commercial cathode material for LIBs [40]. Jiao et al. [41] synthesized LiCoO2 NFs via the sol-gel and electrospinning technique. The LiCoO2 NFs delivered first cycle discharge capacities of 182 mAh/g (powder-based electrodes with first cycle discharge capacities of 140 mAh/g). However, LiCoO2 NF electrodes exhibited a poor cyclability. In order to solve this problem, the core-shell LiCoO2-MgO NFs were prepared through a coaxial electrospinning [42]. The first cycle discharge capacity of core-shell LiCoO2-MgO NFs was close to that of the bare LiCoO2 NFs. After 40 cycles, the discharge capacity of the core-shell LiCoO2-MgO NFs electrode still remained at 90.0% of the initial value (bare LiCoO2 NFs with a capacity retention of 52.0%). LiCoO2-MgO NFs can effectively avoid the increasing of the impedance result from passive surface film formation during cycling.
As a ternary layered material, Li-Ni-Co-Mn-O has attracted considerable interest as the cathode material for LIBs to replace the commonly-used material LiCoO2 due to its high capacity, good thermal stability and excellent rate capability [43]. Currently, most prepared Li-Ni-Co-Mn-O have the Li+/Ni2+ cation mixing structure, resulting in depressing of the Li+ mobility, which leads to the poor cyclability of the cells [44]. In order to overcome this obstacle, electrospun LiNi1/3Co1/3Mn1/3O2 was fabricated, which was proven to be able to largely improve the cell performance [45,46,47,48]. Xiong et al. [45] prepared LiNi0.5Co0.2Mn0.3O2 with a particle size of 300 nm by the electrospinning method and LiNi0.5Co0.2Mn0.3O2 with a particle size of 1 um by the sol-gel method. The electrospinning material exhibited better performance than the sol-gel material, which is mainly attributed to the shorter Li+ and electron migration distance of the electrospinning material. LiNi1/3Co1/3Mn1/3O2 NFs were obtained by electrospinning poly(vinylpyrrolidone) (PVP) and MNO3 (M = Li, Ni, Co, Mn). The resulting LiNi1/3Co1/3Mn1/3O2 NFs showed a high first charge and discharge capacity of 217.93 mAh/g and 172.81 mAh/g, respectively [46]. Electrospun PVP and M(CH3COO)2 (M = Li, Ni, Co, Mn) fibers can yield a Li-rich Li1.2Mn0.54Ni0.13Co0.13O2-encapsulated carbon nanofiber (CNF) network (Li1.2Mn0.54Ni0.13Co0.13O2/CNF) that exhibited a high coulombic efficiency of 83.5% and a discharge capacity of 263.7 mAh/g [47]. The Li-rich Li1.2Ni0.17Co0.17Mn0.5O2 were also synthesized by the electrospinning technique, with PVP and polyvinyl acetate (PVAc) as different polymer sources [48]. The morphology of Li1.2Ni0.17Co0.17Mn0.5O2 NFs has depended on the different heat temperatures and the polymer used. The result shows that the porous nanostructure morphology can enhance the initial discharge capacity of the electrospun samples.
LiFePO4 was discovered by Goodenough in 1997, which possesses high discharge potential, large specific capacity (170 mAh/g) and good thermal stability [49]. However, LiFePO4 has low conductivity (~10−9 S/cm) and low rate capability due to the one-dimensional twisted channel of Li+ [50]. Particle nanocrystallization is supposed to be an effective method to shorten the diffusion channels. Thus, the LiFePO4/C composite NFs were prepared via electrospinning, with polyacrylonitrile (PAN) as polymer additives, which showed a good cyclability [51]. Interestingly, a slight increase of capacity was exhibited rather than the capacity fading after several cycles, which could be attributed to slow electrolyte penetration into the electrode or the crack formation on the amorphous carbon layer during cycling that increases the surface area of NFs and improves the electrode-electrolyte interaction. LiFePO4/carbon nanotube (CNT)/C composite NFs also were obtained via the combination of electrospinning and sol-gel methods, with PAN as the electrospinning media and carbon source [52]. The result shows that electrospinning is an effective method for minimizing the aggregation of LiFePO4 particles and promoting the formation of a conducting carbonaceous layer on the LiFePO4 surface. CNTs were well-dispersed in the carbonaceous matrix, which can help increase the electrochemical performance of the LiFePO4 cathodes by forming conducting bridges between LiFePO4 particles and enhancing the electron transport of the system. In another format, triaxial LiFePO4 nanowires (NWs) with a multiwall CNT core column and an outer shell of amorphous carbon were successfully synthesized with the electrospinning method [53]. The model image of the material is demonstrated in Figure 3. The CNT core oriented in the direction of the wire played an important role in the conduction of electrons during the cycling; the outer amorphous carbon shell suppressed the Fe2+ oxidation.
At the current stage, for a commercial battery, the cathode materials usually participate in a one-electron reaction, which inevitably limits the practical capacity [54]. Therefore, one promising approach to increase the delivered capacity is to develop a material that involves a two (or more)-electron reaction. Vanadium pentoxide (V2O5) has attracted particular attention because of the availability of the two-electron V5+–V3+ couple and its low cost, ease of synthesis, rich abundance, as well as its relatively high theoretical capacity (about 294 mAh/g with 2 Li+ insertions/extractions per unit formula) [55]. V2O5 NFs were synthesized by a hydrothermal treatment of electrospun PMMA and vanadium oxide NFs [56]. The delivered discharge capacity for the first cycle in an LIB with V2O5 NFs was 350 mAh/g. In addition, the capacity was maintained above 240 mAh/g after 25 cycles. The hierarchical V2O5 NFs with diameters of 200–400 nm were obtained via electrospinning combined with annealing, with PVP as the electrospinning media [57]. After 100 cycles, the specific capacity of the V2O5 NFs retains 133.9 mAh/g at a current density of 800 mA/g, corresponding to a high capacity retention of 96.05%. The ultra-long hierarchical V2O5 NWs with diameters of 100–200 nm were also prepared using PVA and low-cost raw materials by electrospinning combined with annealing [58]. The initial discharge capacities of the ultra-long hierarchical V2O5 NWs were up to 390 within a potential range of 1.75–4.0 V. In another study, electrospun PVP and a low-cost inorganic vanadium precursor can yield porous V2O5 NTs that showed good cycling performance; the capacity retention is 97.4% after 200 cycles at 50 C [59].
LiMn2O4 [60], Li3V2(PO4)3 [61,62] and LiNi0.5Mn1.5 [63,64,65] NFs as cathode materials were also prepared by electrospinning, which exhibited high capacity and good cyclability. This indicates that the NFs with a shorter Li+ and electron migration distance can provide fast Li+ intercalation and de-intercalation channels. The overview of some electrospun fibers as cathode materials of LIBs and their electrochemical performances is presented in Table 1.

3.1.1.2. Anode Materials

Electrospun CNFs are popular anode materials for LIBs due to their low cost, easy availability and long cycle life [38]. However, LIBs with electrospun CNFs as the anode exhibited relatively low specific capacity and rate capability [66,67]. Therefore, flexible highly porous CNFs (HPCNFs) [68] and hollow CNFs (HCNFs) [69] were prepared by the electrospinning method. The HPCNFs delivered a reversible capacity as high as 1780 mAh/g after 40 cycles at current densities of 50 mA/g [68]. Controlling the mesopores in HCNFs is an effective means to improve the electrochemical performance of HCNFs [69]. HPCNFs and HCNFs with excellent electrochemical and mechanical properties result from the novel porous structure, which can provide the good access of the electrolyte to the electrode surface. Moreover, CNFs complemented with the high lithium storage capacity transition metals and transition metal oxides were used as anode materials for LIBs, which can result in a higher electrochemical performance; for example, Ag/CNFs composite by electrospinning PMMA/PAN and AgNO3 solution in DMF, where Ag NPs were embedded into the hollow CNFs [70]. The LIBs with Ag/CNFs composite as the anode delivered a capacity of 739 mAh/g at 50 mA/g, with 85% capacity retention after 100 cycles. Similarly, GeOx NPs were encapsulated into hollow carbon shells using co-axial electrospinning [71]. This core-shell structure can alleviate the volume change of GeOx during cycling, decrease the contact area between electrolyte and GeOx to form a stable solid electrolyte interface film and increase the electrical conductivity. Cho et al. [72] prepared carbon-coated Fe3O4 hollow NFs (Fe3O4/C hNFs) and Fe3O4 hNFs via the electrospinning method, annealing and hydrothermal processing using PVP and Fe(NO3)3. The Li+ diffusion coefficient of the Fe3O4/C hNFs (8.0 × 10−14 cm2/s) is 60-times higher than that of Fe3O4 hNFs (1.33 × 10−15 cm2/s). The Fe3O4/C hNFs exhibit superior electrochemical performance compared to that of the Fe3O4 hNFs. CNF and transition metal oxide composites were also reported, such as Co3O4/CNF core-shell NWs [73], Mn3O4/CNF [74], GeO2/CNFs [75] and γ-Fe3O4/CNFs [76]. All of the composites are promising materials, which have important implications for developing high performance anodes for next-generation LIBs.
Among anode materials for LIBs, silicon (Si) is the most promising candidate because of its high theoretical lithium storage capacity (~4200 mAh/g) [77]. Nevertheless, the pure Si anode, with the format of a nanoparticle (NP), NW or membrane, has faced adverse issues on electrode pulverization and capacity loss during frequent charging/discharging cycles [78]. Carbon/silicon composite was proved to exhibit a synergistic effect [79]. For example, Si/CNFs with mesopores were prepared by electrospinning PVA, aluminum acetylacetonate (AACA) and Si in DMF solution [80]. The mesoporous structure was generated by foaming NFs via AACA sublimation. The LIBs with Si/CNFs as the anode showed a superior high first discharge capacity of 1639 mAh/g and a good capacity retention of 83.6%. Xing et al. [81] synthesized pyrolytic carbon-coated Si/C NF (Si/C-CNF) composites by electrospinning and carbonization, which exhibited a high retention capacity of 1215.2 mAh/g after 50 cycles. An amorphous carbon layer covering the surface of Si/CNFs (prepared by electrospinning and sintering PAN and Si) can limit the volume expansion of the exposed Si NPs and prevent Si/CNF;s direct contact with the electrolyte. It also can create connections between the fibers that are conducive to Li+ ion transport. In other formats, a core-shell silicon/carbon fiber (Si/po-C@C) was prepared by simultaneously electrospinning polystyrene (PS)/PAN/Si as the core and electrospinning PAN as the shell then carbonization [82]. The structural design of the Si/po-C@C composite fiber is demonstrated in Figure 4. The LIBs with Si/po-C@C composite fiber as the anode exhibited a high initial discharge capacity of 997 mAh/g and a capacity retention of 71% after 150 cycles at a current density of 0.2 A/g. A novel flexible 3D Si/C fiber paper electrode was also fabricated via simultaneously electrospraying nano-Si/PAN clusters and electrospinning PAN fibers then carbonization [83]. The as-prepared Si/PAN paper and the carbonized Si/PAN paper (3D Si/C fiber paper) exhibited good flexibilities, as shown in Figure 5a,b, respectively. Figure 5c–f is the SEM micrographs of 3D Si/C fiber paper. When the novel structure of the 3D Si/C fiber paper was used as an anode for LIB, the LIB exhibited a high capacity (1600 mAh/g), an excellent rate capability performance and a low capacity loss (0.079% after 600 cycles).
As an anode material for LIBs, tin (Sn) has attracted considerable interest due to its high theoretical capacity (990 mAh/g) [84]. However, the volume changes during cycling and the tin NPs aggregate during the discharging process, resulting in the Sn-based materials’ poor cyclability [85]. To address these problems, Sn NP-loaded CNF (Sn NP/CNF) [86] and Sn NP-loaded PCNF (Sn/PCNF) [87] composites were fabricated. The discharge capacity for LIB with Sn/PCNF composite was 774 mAh/g at a high current density of 0.8 A/g after 200 cycles [87]. Wang et al. [88] prepared Sn@carbon NPs encapsulated in bamboo-like hollow CNFs (see Scheme 1) by pyrolysis of coaxial tributyltin (TBT)/PAN electrospun NFs, which contained Sn and C with a weight ratio of 7:3. The LIBs with the composite material as the anode displayed a high discharge capacity of 737 mAh/g after 200 cycles at 0.5 C. The high cyclability and capacity retention ratio could be attributed to providing the appropriate void volume of the composite to respond to the large volume change and to prevent pulverization of the Sn NPs. The 3D Sn/C hybrid core/shell NFs with micro-/nano-channels were also prepared by electrospinning, annealing and glucose-hydrothermal processing, with PAN as the electrospinning media and carbon source [85]. The LIBs with the obtained Sn/C hybrid NFs as the anode displayed a high initial discharge capacity of 1090.8 mAh/g at a current density of 40 mA/g and a high coulombic efficiency of nearly 100%. The advantages of this particular 3D core/shell architecture result from the greatly enhanced lithium storage from enlarging the electrode-electrolyte contact area, shortening the Li+ migration pathways and enhancing the Li+ and electrolyte diffusion of the active materials during cycling processes.
As a promising candidate to replace graphite, metal oxide is believed to contribute to increasing energy density and decreasing cost [89]. TiO2 is one of the most exciting anode candidates for LIBs due to its high abundance, nontoxicity and structural integrity during cycling [90]. Nevertheless, TiO2 possesses low intrinsic electronic conductivity, which limits its application [91]. In order to improve the shortcoming, the TiO2 NFs were synthesized by electrospinning [91,92,93,94,95]. Sigmund et al. [91] obtained the electrospun TiO2 NFs with anatase and anatase-rutile mixed phase crystallites without carbon coating and then calcined the electrospun TiO2 NFs under different atmospheres. The results show that argon-calcined TiO2 NFs exhibited several orders of magnitude higher electronic conductivity. The anatase TiO2 NF with a fiber-in-tube structure was also reported, with the formation mechanism as shown in Scheme 2, which exhibited high structural stability during cycling [92]. Ramakrishna et al. [96] studied electrospun TiO2 nanostructures and their composites with multiwalled CNTs for rechargeable LIBs. The TiO2/CNT composite showed enhancement in the capacity retention (10–800 cycles) by increasing the retention from 81% to 92%. To improve the rate capability of TiO2 NFs, the metal oxide/TiO2 was prepared via electrospinning, such as Co3O4/TiO2 [93], which exhibited high discharge capacity and an excellent rate capability, resulting from the synergetic effect between Co3O4 and TiO2, as well as the unique feature of hierarchical heterostructures.
The Nb2O5 was also used as the anode material for LIBs [97]. The polymorphs of Nb2O5, including pseudohexagonal (H-Nb2O5), orthorhombic (O-Nb2O5) and monoclinic (M-Nb2O5), were synthesized by electrospinning [98]. After annealing, the H-Nb2O5 and O-Nb2O5 phases maintained the fibrous morphology, whereas the M-Nb2O5 phase adopted a distorted nugget structure. The M-Nb2O5 delivered the highest capacity and exhibited the highest capacity retention compared to the other two phases. The Li+ diffusion coefficients of H-Nb2O5, O-Nb2O5 and M-Nb2O5 were also studied, which were in the ranges of 10−17–10−16, 10−15–10−14 and 10−13–10−12 cm2/s, respectively [99]. The overview of some electrospun fibers as anode materials of LIBs and their electrochemical performances is presented in Table 2.

3.1.1.3. Separator Materials

The traditional commercial separators for LIBs are microporous membranes, whose low porosity, unsatisfactory thermal stability and poor wettability in liquid electrolytes inevitably limit the battery performance [100]. In this regard, fiber-based membranes and fiber-coated membranes have been developed [101]. Electrospun poly(vinylidene fluoride) (PVdF)-based membranes as separators for LIBs have been reported and show advantages in electrochemical performances [102,103]. Owing to the softening of PVdF fibers at high temperatures, the electrospun PVdF-based membranes can form an interconnected web structure by annealing. The interconnected web structure greatly improves the physical properties and electrochemical performance [102]. Porous PVdF fiber-based membranes possess good electrochemical properties, such as a high ionic conductivity of 1.0 × 10−3 S/cm and a wide electrochemical stability window up to 4.5 V vs. Li+/Li at room temperature [103]. Furthermore, the electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) membranes possessed high electrolyte uptake and ionic conductivities (10−3 S/cm) [104]. However, PVdF and PVdF-HFP separators also have their disadvantages, such as the inferior thermal stability and intrinsically hydrophobic character. Wei et al. [105] prepared cellulose/PVdF-HFP membranes by coaxial electrospinning with superior thermal stability and a hydrophilic property. Other electrospun PVdF-based materials, such as P(VdF-HFP)/SiO2 [106,107], PVdF-HFP/PMMA [108], P(VdF-co-HFP)/PAN [109] and PVdF/SiO2-Poly(acrylic acid) lithium (PAALi) [110] as separators for LIBs, all delivered high ionic conductivity, good tensile strength and high uptake/leakage. These results show that the physical properties and electrochemical performance of the membranes can be improved by adding SiO2, PMMA and PAN [106,107,108,109,110]. Electrospun PAN-based NF membranes are another common host separator for LIBs due to their high ionic conductivity, electrolyte uptake and electrochemical stability window [111,112]. Sui et al. [113] prepared PMMA/PAN NF membranes with a core-shell structure by electrospinning. The LIBs with the PMMA/PAN NF membranes as the separator exhibited excellent initial discharge capacities, as well as remarkable cycle performance, resulting from the unique electrospun core-shell structure of PMMA/PAN NF membranes. Electrospun SiO2/PAN [114,115], PAN/Al2O3-TEGDA-BA [116] (triethylene glycol diacetate-2-propenoic acid butyl ester (TEGDA-BA)), PAN/TEGDA-BA [117], PAN/PEO [118] (polyethylene oxide (PEO)), oxy-PAN [119] and LLTO/PAN (lithium lanthanum titanate oxide (LLTO)) [120] NF membranes were used as separators for LIBs, which showed remarkably good physical properties and electrochemical performance. The overview of electrospun fiber membranes as separators of LIBs mentioned above is presented in Table 3.

3.1.2. Li-S and Li-O2 Batteries

3.1.2.1. Li-S Batteries

Sulfur possesses the characteristics of high natural abundance, low cost and environmental friendliness. Equally, as a promising electrode material for lithium secondary batteries, sulfur has attracted attention because of its high theoretical specific capacity (1675 mAh/g) and high theoretical specific energy (2600 Wh/kg) [122]. Sulfur, working as the cathode of Li-S batteries, has an insulating property [123]. In recent years, though some progress has been made in LSBs, the dissolution of intermediates (Li2Sx, 3 ≤ x ≤ 8) and the rapid capacity decay limit the future application of LSBs [124,125]. In order to overcome the above disadvantages, various kinds of carbon materials were used to composite with sulfur. Electrospinning is an effective method to obtain carbon materials with a special morphology for the storage of sulfur. The porous carbon NF (PCNF)/S nanocomposites were fabricated by carbonization of electrospun PAN/PMMA NFs and the subsequent chemical reaction-deposition strategy [126]. The as-prepared nanocomposites have a high electrical conductivity and extremely high surface area. The LSBs with the PCNF/S nanocomposites as cathodes showed high reversible capacity, good discharge capacity retention and an excellent rate capability because the sulfur was dispersed and immobilized on the porous structures of CNFs, alleviating the polysulfide shuttle phenomenon. A hierarchical structure carbon/sulfur composite is fabricated based on electrospun CNF matrices [123]. The CNF matrices were obtained by removing Ni NPs of Ni/CNF, which was synthesized by electrospinning PAN and Ni(AC)2 H2O. The cell with the carbon/sulfur composite as the cathode exhibited an initial discharge capacity of 845 mAh/g at 0.25 C, with a retention of 77% after 100 cycles. Guo et al. [127] prepared the ordered mesoporous carbon fiber/sulfur (OMCF)/S composite via electrospinning. The OMCF/S composite with a weight ratio of 3:7 delivered a stable discharge capacity of 690 mAh/g after 300 cycles at 0.3 C. In situ synthesis is the most preferred preparation method of cathode materials for LSBs, particularly in synthesizing precursor mixture materials by electrospinning [128]. PAN NFs were fabricated in situ firstly with a porous structure by electrospinning, and then, the final product, PCNFs, was obtained by the following carbonization [129]. The prepared PCNFs were both mesoporous and microporous with large surface areas, which can store much sulfur and were utilized as conductive matrices for sulfur to form PCNFs/S nanocomposites. The LSB with the PCNFs/S nanocomposites as the cathode showed an initial discharge capacity of 1155 mAh/g at 0.02 C.

3.1.2.2. Lithium-O2 Batteries

Recently, a rechargeable Li-O2 battery has attracted significantly attention due to its high theoretical energy density (11,680 Wh/kg) [130]. The Li-O2 battery involves a distinct operating mechanism (typically, 2Li+ + O2 + 2e ↔ Li2O2, E0 = 2.96 V vs. Li/Li+) on the O2 electrode, which relates to the Li2O2 formation during the discharging process (oxygen reduction reaction = ORR) and the Li2O2 decomposition during the charging process (oxygen evolution reaction = OER) [131,132]. To date, the O2 electrode is porous, which can provide the solid-liquid-gas tri-phase and electron migration regions for the ORR and OER. Therefore, the performances of the Li-O2 battery depend on the material and architecture of the O2 electrode [133]. Electrospinning is an attractive method for fabricating the materials of the O2 electrode for Li-O2 batteries [134].
In recent years, numerous electrospun electrocatalyst have been explored to enhance the performance of Li-O2 batteries. For example, Kim et al. [135] prepared the 1D Co3O4 NFs (obtained by electrospinning and calcination of PVP and Co precursor) immobilized on both sides of 2D non-oxidized graphene nanoflakes as a bifunctional composite catalyst for an O2 electrode in Li-O2 batteries. It showed the first discharge capacity of 10,500 mAh/g and a stable cyclability of 80 cycles with a limited capacity of 1000 mAh/g. 1D porous La0.5Sr0.5CoO2.91 NTs were synthesized via electrospinning and sintering PVP and La(NO3)3·6H2O, Sr(NO3)2 and Co(CH3COO)2·4H2O [134]. The resulting La0.5Sr0.5CoO2.91 NTs as O2 electrode catalyst exhibited a high initial discharge capacity of 7205 mAh/g at a current density of 100 mA/g and a stable cyclability of 85 cycles with a limited discharge depth of 1000 mAh/g. A hierarchical mesoporous/macroporous La0.5Sr0.5CoO3 − x NTs (HPN-LSC) was also prepared by electrospinning PVP and La(NO3)·6H2O, Sr(NO3)2 and Co(NO3)2·6H2O [136]. The Li-O2 battery with HPN-LSC as the O2 electrode catalyst enhanced the reversibility and round-trip efficiency.
The O2 electrode architecture also influences the performance of Li-O2 batteries. To avoid the negative influence of the binder on the long-term stability, a novel “binder-free” design has been proposed [137]. Typically, electrospun PAN and Co(NO3)2·6H2O can yield the Co3O4/CNF composites, that as the O2 electrode exhibited a high initial discharge capacity of 760 mAh/g [137]. In another study, a Co3O4-based binder-free O2 electrode was reported for Li-O2 batteries [138]. Scheme 3 illustrates a typical procedure for the fabrication of the Co3O4-based binder-free O2 electrode. The Co3O4 nanoparticles formed nanoflakes by the aggregation in O2 electrode, which can provide a large amount of catalytic active sites for ORR/OER. The Co3O4 spheres embedded in the TiO2 fiber mesh may function as anchors to prevent the detachment of the Co3O4 layer from the current collector, resulting in excellent structural and cycling stability.

3.2. Fuel Cells

Fuel cells are energy conversion devices that can convert chemical energy into electrical energy through electrochemical oxidation of fuel (hydrogen or hydrogen-rich fuel). Fuel cells include proton exchange membrane fuel cells (PEMFCs) [139], direct methanol fuel cells (DMFCs) [140], alkaline fuel cells (AFCs) [141], phosphoric acid fuel cells (PAFCs) [142], solid oxide fuel cells (SOFCs) [143] and molten carbonate fuel cells (MCFCs) [144].

3.2.1. Electrode Materials

The catalyst is the key material in fuel cells. It has been proven that the employment of a catalyst can largely influence the fuel cell performance [145]. Currently, electrospun NF materials have been used as catalyst and catalyst supporting materials for fuel cells because of their high poisoning resistance, high activity and good durability [146]. The PVP/Pt composite fibers were synthesized via electrospinning. After calcining, the Pt NWs with a high surface area were obtained, which displayed large electrochemically-active surface areas (ESA) of 6.2 m2/g and a high specific activity toward a methanol oxidation reaction (MOR) of 1.41 mA/cm2 in DMFCs [140]. Pt/Rh NWs [145] and Pt/Ru NWs [147] were further synthesized, which exhibited higher catalytic activities in fuel cells than that of the traditional NP catalyst. It has been also reported that the bimetallic NWs electrocatalysts showed better stability than the bimetallic NPs [147]. Nanoporous Pt/Fe alloy NWs [148] and Pt/Co alloy NWs [149] were synthesized and studied. The Pt/Fe alloy NWs’ overall wire diameters are about 10–20 nm, which showed a high specific activity (2.3-times that of conventional Pt/C catalyst) [148]. Pt/Co alloy NWs’ average diameters are 28 nm, which showed excellent stability activity to the ORR in acidic electrolytes [149].
It has been proven that the catalytic activity of the catalyst depends not only on the shape, size and distribution of the catalyst materials, but also on the categories and properties of the catalyst support [150]. The catalyst particles are dispersed on various supports, including CNFs, SnO2 and TiO2. Among them, CNFs are the most widely used catalyst supports. For example, Pt/CNF mats were prepared by electrospinning [146]. The catalytic peak current on the optimum Pt/CNF mat electrode reaches 420 mA/mg (the catalytic peak current of methanol oxidation on a commercial catalyst of 185 mA/mg). The results suggest that the electrospun CNF mats are favorable to enhance the performance of the catalyst. However, the cost and scarcity of Pt limit its application in fuel cells. Therefore, the low-cost N-doped CNFs were synthesized to replace Pt/CNFs [151,152,153]. Yu et al. [151] investigated the effect of different nitrogen sources (including melamine, aniline, urea and polyaniline) and nitrogen content on the activity of electrocatalyst, indicating that the best electrocatalytic activity was obtained with an aniline/PAN with a mass ratio of 20:3. You et al. [152] and Huang et al. [153] used NH3 as the nitrogen source to prepare the N-doped CNFs by carbonizing electrospun polyacrylonitrile (PAN) NFs in NH3. Metal-/alloy-doped CNFs were also used as catalysts for fuel cells, such as Ag [154], Co/N [155,156], Cu/Co [150], Fe/Co [157,158], Ni/Cu alloy [159], Fe/N [160,161] and Ni/Co [162] -doped CNFs. For example, Smirnova et al. [154] fabricated Ag/CNFs with different Ag loading amounts of 11, 15 and 25 wt %. The well-dispersed Ag NPs were attached to the surface of the electrospun CNFs. The results show that the mass activity of the 15 wt % Ag/CNFs system was the highest (119 mA/mg).
The transition metal oxides possess high chemical stability, good corrosion resistance and strong metal support interaction, like SnO2 and TiO2, which can enhance the activity of the catalysts. As catalyst supports, they are able to stabilize and disperse adequately a number of active phases [163]. Electrospun Pt/SnO2 NFs were used as the anode electrocatalyst material for PEMFCs [164], which exhibited a high electrochemically-active surface area (81.17 m2/g-Pt). A diffusion-limited current was achieved at 0.07 V. Cavaliere et al. [165] prepared the Pt supported on the electrospun Nb-SnO2 with a loose-tube (fiber-in-tube) morphology (Figure 6), which exhibited a higher electrochemical stability than conventional Pt/C electrodes. Cavaliere et al. [166] also synthesized Pt supported on electrospun Nb-SnO2 with a loose-tube structure as the cathode material for fuel cells, who studied in situ fuel cell operation under accelerated stress tests and confirmed that the voltage loss was negligible degradation. Electrospun Pt/TiO2 NFs were also synthesized by electrospinning and the reductive impregnation method, which were used as electrocatalysts and exhibited high activities for methanol oxidation [167]. Electrospun Nb-TiO2 NFs were investigated as electrocatalyst supports for PEMFCs [168]. The Pt/Nb-TiO2 NFs showed a high stability after accelerated stress tests, retaining 73% of the electroactive Pt area (the value of Pt/CNFs was 8%).
The membrane electrode assembly (MEA) is one of the important parts for fuel cells, which consists of the membrane and electrocatalyst [169]. Electrospinning is a straightforward method to prepare NFs of MEA for fuel cells. Electrospun nafion/polyphenylsulfone (PPSU) mats were synthesized for the H2/Br2 fuel cell [169], which exhibited good selectivity and high ionic conductivity. Shul et al. [170] fabricated electrospun SiC webs as membranes. The functionalized SiC webs (by introducing the hydroxyl group and phosphoric acid) showed a 70% better ion-exchange capability than that of the conventional membrane. The Pt NWs deposited on electrospun carbon film with a hierarchical structure were also used as MEA for fuel cells [171], which can induce the catalytic reaction toward formic acid electrooxidation.

3.2.2. Electrolyte Membrane

The proton exchange membrane (PEM) is an electrolyte that behaves as an important indicator of the performance of fuel cells [172]. Nafion has been regarded as the most commonly-used polymer electrolyte membrane, which showed excellent chemical and physical stabilities and high proton conductivity [173]. However, the pure nafion is not a good candidate for electrospinning due to its low viscosity [174]. Aiming at the enhancement of the mechanical strength of the composite membrane, matrix polymers, such as PEO/Nafion [175] and PVA/Nafion [174], have been studied. To improve the proton conductivity, Na et al. [176] fabricated the sulfonated poly(ether ether ketone ketone) (SPEEKK) membrane with a spherical structure by electrospinning. The sulfonated SPEEKK membrane exhibited a high proton conductivity (0.37 S/cm), which is 37-times higher than that of the common SPEEKK membrane. The Nafion and PVdF composite membranes were fabricated by electrospinning [177]. They studied the Nafion NFs embedded in a PVdF matrix (N(fibers)/PVdF) and PVdF NFs embedded in a Nafion matrix (N/PVdF(fibers)). Both membrane structures exhibited similar in-plane conductivity, where the conductivity scaled linearly with the Nafion volume fraction. Hybrid organic-inorganic membranes were also prepared by electrospinning, which exhibited good thermal stability and a high proton conductivity of 15 ms/cm at 120 °C [178]. Shanmugam et al. [179] fabricated TiO2, CeO2 and ZrO1.95 NTs with mesoporous structures as fillers in the composite membranes, which were then incorporated in a Nafion ionomer to increase the water retention capability in the Nafion membrane.

3.3. Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) as the third generation of solar cells have attracted much attention due to their high energy efficiency, clean energy source and low cost, which can be applied to many portable and mobile ubiquitous power sources [180]. DSSCs consists of a photoanode, counter electrodes, dye and electrolyte [181]. NFs have been considered to be the most important material for DSSC photoanodes, counter electrodes and electrolytes.

3.3.1. Photoanode

In the DSSCs, the photoanode is a transparent conducting oxide coated with a film of a high band gap metal oxide (TiO2, ZnO, SnO2 and Nb2O5) [182,183]. Electrospun metal oxide NFs as the film coated with photoanode have been studied due to their high specific area [184,185,186]. Leung et al. [187] fabricated an innovative bilayer TiO2 NF photoanode by electrospinning. The bilayer TiO2 NF photoanode can offer excellent dye-loading, light harvesting and electron-transport properties, which improved the power conversion efficiency. Figure 7 shows the schematic diagram of the fabrication procedure for the bilayer TiO2 NF photoanode. In general, the photoanode with high specific surface area can improve light-scattering effects and facilitate electrolyte diffusion [188]. In this regards, Jang et al. [189] synthesized the multiscale porous TiO2 NFs via electrospinning, which were used as photoanodes of DSSCs. In another study, CNT/TiO2 NF [190] was fabricated by electrospinning. When 5 wt % of hollow CNTs was added into TiO2 NFs, the energy conversion efficiency of DSSCs reached 3.39%. Ko et al. [191] prepared a novel nanostructured PVdF NFs/TiO2 NP composite by electrospinning. The composite showed an outstanding bending stability because the PVdF NFs can reinforce the photoelectrode. Electrospun hollow TiO2 NFs were also obtained to enhance the conversion efficiency of ZnO-based DSSCs [192]. The results show that the weight of TiO2 influences the performance of the TiO2/ZnO composite photoanode. The maximal energy conversion efficiency reached 4.59% by adding 10 wt % of hollow TiO2 NFs, which is 62% higher than that of pure ZnO NPs-based DSSCs.

3.3.2. Counter Electrodes

In the DSSCs, the counter electrode is a transparent conducting oxide coated with a thin layer of Pt, which plays an important role on transferring the electron to the external circuit and regenerating the I3 into I by reduction in the electrolyte system [193]. However, Pt is an expensive metal, and the corrosive I/I3 redox couple can reduce its catalytic activity [194]. To address these issues, many studies have been carried out on the alternatives to replace the Pt. For example, Qiao et al. [195] fabricated CNFs by electrospinning using an electrocatalyst and low-cost alternative to Pt for I3 reduction in DSSCs. The short circuit current density and open circuit voltage of CNF-based cells were comparable to Pt-based cells, while the conversion efficiency was slightly lower than that of Pt-based cells. The hollow activated CNFs with a mesoporous structure were reported, which can promote the electron and ion transfer, decrease the resistance of charge transfer and increase the contact area between the liquid electrolyte and the electrode [196,197]. The resulting overall conversion efficiency of hollow activated CNF-based cells is comparable to that of Pt-based cells. To enhance the electrocatalytic activity, some of the teams prepared transition metals/CNFs [198,199,200,201,202] and transition metal carbides/CNFs [203,204]. The overview of electrospun NFs as a counter electrode material of DSSCs is summarized in Table 4.

3.3.3. Electrolytes of DSSCs

The electrolyte is an indispensable component in the DSSCs, which plays an important role in reduction of the oxidized dye by a suitable redox couple and the assistance of the charge transfer from the counter electrode to the photoanode [205]. In the DSSCs, the traditional organic liquid electrolytes and ionic liquid electrolytes exhibit a poor long-term stability because of their being prone to leakage and volatility [206]. Therefore, polymer electrolytes have been developed due to their high ionic conductivity, high thermal stability and good permeability [207]. Kim et al. [208] prepared the PVdF-HFP via the electrospinning method, which showed high electrolyte uptake and ionic conductivity of 653 ± 50% and 4.53 ± 1.3 × 10−3 S/cm, respectively. Electrospun PVdF-HEP NFs with different diameters were further discussed [206]. The PVDF-HFP NFs prepared from a 15 wt % spinning solution showed high ionic conductivity (1.295 S/cm) and electrolyte uptake (947%). Dyson et al. [209] soaked electrospun PVdF-HFP membrane (es-PM) in the ionic liquid electrolyte containing 0.5 M 1-butyl-3-methylimidazolium iodide (BMImI), 0.5 M LiI, 0.05 M I2 and 0.5 M 4-tert-butylpyribine to obtain the electrospun PVdF-HFP membrane electrolyte (esPME). The 0.5 M BMImI-esPME exhibited better performance than 0.5 M BMImI containing liquid electrolyte (LE), as shown in Figure 8. The poly(vinylidenefluoride-cohexafluoropropylene)/polystyrene (PVdF-HFP/PS) [210] and PVdF-HFP/cobalt sulfide (CoS) [211] were also prepared by the electrospinning method, which showed the good photovoltaic performance in DSSCs. SiO2 NF/PEO-(PVdF-HFP) was also synthesized via electrospinning, which possesses high ionic conductivity of 9.9 × 10−4 S/cm [212]. In addition, SiO2 NF/PEO-(PVdF-HFP) as the polymer electrolyte can enhance the stability of the interface between the electrolyte and the semiconductor electrodes. The photovoltaic performances of electrospun NFs electrolytes are summarized in Table 5.

3.4. Supercapacitors

As a promising novel energy storage device, electrochemical capacitors (supercapacitors) have been used in various fields because of their high power density, fast charging and discharging times and long cycle life [215]. According to different energy storage mechanisms, supercapacitors are classified into pseudocapacitors and electric double-layer capacitors (EDLCs) [216]. The pseudocapacitors involve a faradic charge storage process that was facilitated by a redox reaction at the interface between electrode and electrolyte [217]. The EDLCs store electrical energy via the accumulation of electric charges at the electrical double layer formed at the electrode-electrolyte interface [218].
In the EDLCs, the capacitance depends on the surface area accessible to the electrolyte, and porous carbon has been investigated because of its high surface area [219]. Electrospinning techniques are one of the most facile methods to fabricate high PCNFs [27,220,221,222,223]. Yan et al. [224] prepared a light-weight CNF/graphene nanosheet (CNF/GNS) composite paper by electrospinning. The CNF/GNS composite paper showed a high specific capacitance of 197 F/g, about 24% higher than that of pure CNF paper. CNT/CNFs [225] and graphene-beaded CNFs (G/CNFs) [226] were synthesized via electrospinning techniques. The performance of pure CNFs is significantly improved after adding CNT and graphene. Song et al. [227] fabricated nitrogen-enriched PCNF by electrospinning. The nitrogen-enriched PCNF possessed a high specific surface area, good thermal stability and high electrical conductivity, which exhibited the maximum specific capacitance of 251.2 F/g. The transition metal oxide encapsulated on electrospun CNFs, including Fe3O4/CNFs [228], Co3O4/CNFs [229], Fe/CeO2/CNFs [230], MnO2/CNFs [231,232], MnOx/CNFs [233], NiO/RuO2/CNFs [234], RuO2/ACNFs [235], ZnO/ACNFs [236] and V2O5/CNFs [237], was synthesized via electrospinning, and all exhibited good electrochemical performance.
Besides, transition metal oxides are also promising pseudocapacitors electrode materials, due to their high electrical conductivity, several possible oxidation states and electrochemical stability. Kim et al. [238] fabricated electrospun RuO2 NF mats to support the RuO2 NPs. RuO2 NF mats with RuO2 NPs displayed high specific capacitance of 886.9 F/g at a scan rate of 10 mV/s and a low capacity loss of only 30% from 10 to 2000 mV/s. Electrospun V2O5 NFs [134] and Mn3O4 NFs [239] were also demonstrated to be promising electrode materials for pseudocapacitors. Wang et al. [240] fabricated the NiO NFs modified by citric acid (NiO/CA) with a hollow tube via electrospinning techniques. The pseudocapacitors with NiO/CA as electrodes displayed superior capacitive performance with large capacitance (336 F/g) and excellent cyclic performance (the capacitance decreases only by 13% of the initial capacitance after 1000 cycles). α-Fe2O3 with porous fiber and α-Fe2O3 with nanograin structures were prepared by the electrospinning technique [241], which were used as electrode materials in supercapacitors. The supercapacitors with both showed high capacitance retentions even after 3000 cycles. Electrospun 1D porous bimetallic ZnCo2O4 NTs showed a much higher specific capacitance of 770 F/g at 10 A/g and good cycling stability of only a 10.5% loss after 3000 cycles [242]. Lin et al. [243,244,245] reported LaxSr1 − xCu0.1Mn0.9O3 − δ (0.1 ≤ x ≤ 1) NFs, LaxSr1 − xCoO3 − δ (0.3 ≤ x ≤ 1) NFs and LaxSr1 − xNiO3 − δ (0.3 ≤ x ≤ 1) NFs, which exhibited excellent electrochemical performance. The supercapacitors with LaxSr1 − xCoO3 − δ (0.3 ≤ x ≤ 1) NFs as the electrode exhibit the highest specific capacity of 747.75 F/g at a current density of 2 A/g.

4. Conclusions

In this review, we summarized some progress in electrospun NFs for energy applications, such as lithium-based batteries (LIBs, LSBs and Li-O2 batteries), fuel cells, dye-sensitized solar cells and supercapacitors. As the materials for electrodes and separators in lithium-based batteries, electrospun NFs exhibited high power capabilities and good kinetic properties because of the decreasing length of Li+ diffusion pathways, which is mainly attributed to their high specific surface areas and high porosities. In fuel cells, electrospun NFs were used as the electrode materials and electrolyte membranes. Being electrocatalysts for electrode materials, electrospun NFs showed high activities and good durabilities. As electrolyte membranes, electrospun NFs exhibited high electrolyte uptakes and ionic conductivities. Equally, in terms of the application in dye-sensitized solar cells, the photoelectrodes prepared by electrospun NFs demonstrated high photoelectric conversion efficiencies due to their unique fiber morphologies. Supercapacitors with NFs exhibited high specific capacities and good electrochemical performances, which result from the high specific surface areas, good thermal stabilities and high electrical conductivities of NFs. As a promising synthesis technology for NFs with various morphologies, electrospinning has been largely explored. Nonetheless, the improvement of the accuracy of the experimental parameters and the development of NFs with multiple structures are currently being undertaken.

Acknowledgments

This work was supported by Changbai Mountain Scholar Project by the Education Department of Jilin Province.

Author Contributions

The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Li, M.; Wu, X.; Zeng, J.; Hou, Z.; Liao, S. Heteroatom Doped Carbon Nanofibers Synthesized by Chemical Vapor Deposition as Platinum Electrocatalyst Supports for Polymer Electrolyte Membrane Fuel Cells. Electrochim. Acta 2015, 182, 351–360. [Google Scholar] [CrossRef]
  2. Balde, C.P.; Hereijgers, B.P.; Bitter, J.H.; Jong, K.P. Sodium Alanate Nanoparticles-Linking Size to Hydrogen Storage Properties. J. Am. Chem. Soc. 2008, 130, 6761–6765. [Google Scholar] [CrossRef] [PubMed]
  3. Clark, M.D.; Walker, L.S.; Hadjiev, V.G.; Khabashesku, V.; Corral, E.L.; Krishnamoorti, R.; Cinibulk, M. Fast Sol-Gel Preparation of Silicon Carbide-Silicon Oxycarbide Nanocomposites. J. Am. Ceram. Soc. 2011, 94, 4444–4452. [Google Scholar] [CrossRef]
  4. Li, S.; Huang, J. Cellulose-Rich Nanofiber-Based Functional Nanoarchitectures. Adv. Mater. 2016, 28, 1143–1158. [Google Scholar] [CrossRef] [PubMed]
  5. Reddy, M.; Beichen, Z.; Nicholette, L.J.E.; Kaimeng, Z.; Chowdari, B. Molten salt synthesis and its electrochemical characterization of Co3O4 for lithium batteries. Electrochem. Solid State Lett. 2011, 14, A79–A82. [Google Scholar] [CrossRef]
  6. Reddy, M.; Yu, C.; Jiahuan, F.; Loh, K.P.; Chowdari, B. Molten salt synthesis and energy storage studies on CuCo2O4 and CuO·Co3O4. RSC Adv. 2012, 2, 9619–9625. [Google Scholar] [CrossRef]
  7. Reddy, M.; Khai, V.; Chowdari, B. Facile one pot molten salt synthesis of nano (M1/2Sb1/2Sn)O4 (M = V, Fe, In). Mater. Lett. 2015, 140, 115–118. [Google Scholar] [CrossRef]
  8. Wu, Y.; Reddy, M.; Chowdari, B.; Ramakrishna, S. Long-term cycling studies on electrospun carbon nanofibers as anode material for lithium ion batteries. ACS Appl. Mater. Interfaces 2013, 5, 12175–12184. [Google Scholar] [CrossRef] [PubMed]
  9. Reddy, M.; Quan, C.Y.; Teo, K.W.; Ho, L.J.; Chowdari, B. Mixed Oxides,(Ni1 − xZnx) Fe2O4 (x = 0, 0.25, 0.5, 0.75, 1): Molten Salt Synthesis, Characterization and Its Lithium-Storage Performance for Lithium Ion Batteries. J. Phys. Chem. C 2015, 119, 4709–4718. [Google Scholar] [CrossRef]
  10. Reddy, M.; Cherian, C.T.; Ramanathan, K.; Jie, K.C.W.; Daryl, T.Y.W.; Hao, T.Y.; Adams, S.; Loh, K.; Chowdari, B. Molten synthesis of ZnO. Fe3O4 and Fe2O3 and its electrochemical performance. Electrochim. Acta 2014, 118, 75–80. [Google Scholar] [CrossRef]
  11. Reddy, M.; Sharma, N.; Adams, S.; Rao, R.P.; Peterson, V.K.; Chowdari, B. Evaluation of undoped and M-doped TiO2, where M = Sn, Fe, Ni/Nb, Zr, V, and Mn, for lithium-ion battery applications prepared by the molten-salt method. RSC Adv. 2015, 5, 29535–29544. [Google Scholar] [CrossRef]
  12. Reddy, M.; Teoh, X.V.; Nguyen, T.; Lim, Y.M.; Chowdari, B. Effect of 0.5 M NaNO3: 0.5 M KNO3 and 0.88 M LiNO3: 0.12 M LiCl molten salts, and heat treatment on electrochemical properties of TiO2. J. Electrochem. Soc. 2012, 159, A762–A769. [Google Scholar] [CrossRef]
  13. Nithyadharseni, P.; Reddy, M.; Ozoemena, K.I.; Balakrishna, R.G.; Chowdari, B. Low temperature molten salt synthesis of Y2Sn2O7 anode material for lithium ion batteries. Electrochim. Acta 2015, 182, 1060–1069. [Google Scholar] [CrossRef]
  14. Reddy, M.; Tung, B.D.; Yang, L.; Minh, N.D.Q.; Loh, K.; Chowdari, B. Molten salt method of preparation and cathodic studies on layered-cathode materials Li(Co0.7Ni0.3)O2 and Li(Ni0.7Co0.3)O2 for Li-ion batteries. J. Power Sources 2013, 225, 374–381. [Google Scholar] [CrossRef]
  15. Reddy, M.; Beichen, Z.; Loh, K.; Chowdari, B. Facile synthesis of Co3O4 by molten salt method and its Li-storage performance. CrystEngComm 2013, 15, 3568–3574. [Google Scholar] [CrossRef]
  16. Reddy, M.; Rao, G.S.; Chowdari, B. Synthesis and electrochemical studies of the 4 V cathode, Li(Ni2/3Mn1/3)O2. J. Power Sources 2006, 160, 1369–1374. [Google Scholar] [CrossRef]
  17. Reddy, M.; Jie, T.W.; Jafta, C.J.; Ozoemena, K.I.; Mathe, M.K.; Nair, A.S.; Peng, S.S.; Idris, M.S.; Balakrishna, G.; Ezema, F.I. Studies on Bare and Mg-doped LiCoO2 as a cathode material for lithium ion batteries. Electrochim. Acta 2014, 128, 192–197. [Google Scholar] [CrossRef]
  18. Sakunthala, A.; Reddy, M.; Selvasekarapandian, S.; Chowdari, B.; Selvin, P.C. Synthesis of compounds, Li(MMn11/6)O4 (M = Mn1/6, Co1/6, (Co1/12Cr1/12), (Co1/12Al1/12), (Cr1/12Al1/12)) by polymer precursor method and its electrochemical performance for lithium-ion batteries. Electrochim. Acta 2010, 55, 4441–4450. [Google Scholar] [CrossRef]
  19. Reddy, M.; Sakunthala, A.; SelvashekaraPandian, S.; Chowdari, B. Preparation, Comparative Energy Storage Properties, and Impedance Spectroscopy Studies of Environmentally Friendly Cathode, Li(MMn11/6)O4 (M = Mn1/6, Co1/6, (Co1/12Cr1/12)). J. Physi. Chem. C 2013, 117, 9056–9064. [Google Scholar] [CrossRef]
  20. Prabu, M.; Reddy, M.; Selvasekarapandian, S.; Rao, G.S.; Chowdari, B. (Li, Al)-co-doped spinel, Li(Li0.1Al0.1Mn1.8)O4 as high performance cathode for lithium ion batteries. Electrochim. Acta 2013, 88, 745–755. [Google Scholar] [CrossRef]
  21. Zhao, X.; Reddy, M.; Liu, H.; Ramakrishna, S.; Rao, G.S.; Chowdari, B. Nano LiMn2O4 with spherical morphology synthesized by a molten salt method as cathodes for lithium ion batteries. RSC Adv. 2012, 2, 7462–7469. [Google Scholar] [CrossRef]
  22. Reddy, M.; Raju, M.S.; Sharma, N.; Quan, P.; Nowshad, S.H.; Emmanuel, H.-C.; Peterson, V.; Chowdari, B. Preparation of Li1.03Mn1.97O4 and Li1.06Mn1.94O4 by the Polymer Precursor Method and X-ray, Neutron Diffraction and Electrochemical Studies. J. Electrochem. Soc. 2011, 158, A1231–A1236. [Google Scholar] [CrossRef]
  23. Reddy, M.; Cheng, H.; Tham, J.; Yuan, C.; Goh, H.; Chowdari, B. Preparation of Li(Ni0.5Mn1.5)O4 by polymer precursor method and its electrochemical properties. Electrochim. Acta 2012, 62, 269–275. [Google Scholar] [CrossRef]
  24. Du, P.; Song, L.; Xiong, J.; Yuan, Y.; Wang, L.; Xi, Z.; Jin, D.; Chen, J. TiO2/Nb2O5 core-sheath nanofibers film: Co-electrospinning fabrication and its application in dye-sensitized solar cells. Electrochem. Commun. 2012, 25, 46–49. [Google Scholar] [CrossRef]
  25. Hu, L.; Deng, Y.; Liang, K.; Liu, X.; Hu, W. LaNiO3/NiO hollow nanofibers with mesoporous wall: A significant improvement in NiO electrodes for supercapacitors. J. Solid State Electrochem. 2014, 19, 629–637. [Google Scholar] [CrossRef]
  26. Wang, G.; Xiao, W.; Yu, J. High-efficiency dye-sensitized solar cells based on electrospun TiO2 multi-layered composite film photoanodes. Energy 2015, 86, 196–203. [Google Scholar] [CrossRef]
  27. Kim, B.H.; Yang, K.S.; Woo, H.G.; Oshida, K. Supercapacitor performance of porous carbon nanofiber composites prepared by electrospinning polymethylhydrosiloxane (PMHS)/polyacrylonitrile (PAN) blend solutions. Synth. Met. 2011, 161, 1211–1216. [Google Scholar] [CrossRef]
  28. Wu, J.; Wang, N.; Zhao, Y.; Jiang, L. Electrospinning of multilevel structured functional micro-/nanofibers and their applications. J. Mater. Chem. A 2013, 1, 7290–7305. [Google Scholar] [CrossRef]
  29. Wang, H.G.; Yuan, S.; Ma, D.L.; Zhang, X.B.; Yan, J.M. Electrospun materials for lithium and sodium rechargeable batteries: From structure evolution to electrochemical performance. Energy Environ. Sci. 2015, 8, 1660–1681. [Google Scholar] [CrossRef]
  30. Inagaki, M.; Yang, Y.; Kang, F. Carbon nanofibers prepared via electrospinning. Adv. Mater. 2012, 24, 2547–2566. [Google Scholar] [CrossRef] [PubMed]
  31. Zhang, C.L.; Yu, S.H. Nanoparticles meet electrospinning: Recent advances and future prospects. Chem. Soc. Rev. 2014, 43, 4423–4448. [Google Scholar] [CrossRef] [PubMed]
  32. Zhang, B.; Kang, F.; Tarascon, J.-M.; Kim, J.-K. Recent advances in electrospun carbon nanofibers and their application in electrochemical energy storage. Prog. Mater. Sci. 2016, 76, 319–380. [Google Scholar] [CrossRef]
  33. Shi, X.; Zhou, W.; Ma, D.; Ma, Q.; Bridges, D.; Ma, Y.; Hu, A. Electrospinning of Nanofibers and Their Applications for Energy Devices. J. Nanomater. 2015, 2015, 1–20. [Google Scholar] [CrossRef]
  34. Thavasi, V.; Singh, G.; Ramakrishna, S. Electrospun nanofibers in energy and environmental applications. Energy Environ. Sci. 2008, 1, 205–221. [Google Scholar] [CrossRef]
  35. Agarwal, S.; Greiner, A.; Wendorff, J.H. Functional materials by electrospinning of polymers. Prog. Polym. Sci. 2013, 38, 963–991. [Google Scholar] [CrossRef]
  36. Kumar, P.S.; Sundaramurthy, J.; Sundarrajan, S.; Babu, V.J.; Singh, G.; Allakhverdiev, S.I.; Ramakrishna, S. Hierarchical electrospun nanofibers for energy harvesting, production and environmental remediation. Energy Environ. Sci. 2014, 7, 3192–3222. [Google Scholar] [CrossRef]
  37. Cavaliere, S.; Subianto, S.; Savych, I.; Jones, D.J.; Rozière, J. Electrospinning: Designed architectures for energy conversion and storage devices. Energy Environ. Sci. 2011, 4, 4761–4785. [Google Scholar] [CrossRef]
  38. Pampal, E.S.; Stojanovska, E.; Simon, B.; Kilic, A. A review of nanofibrous structures in lithium ion batteries. J. Power Sources 2015, 300, 199–215. [Google Scholar] [CrossRef]
  39. Jaguemont, J.; Boulon, L.; Dubé, Y. A comprehensive review of lithium-ion batteries used in hybrid and electric vehicles at cold temperatures. Appl. Energy 2016, 164, 99–114. [Google Scholar] [CrossRef]
  40. Goodenough, J.B.; Park, K.S. The Li-ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167–1176. [Google Scholar] [CrossRef] [PubMed]
  41. Gu, Y.; Chen, D.; Jiao, X. Synthesis and electrochemical properties of nanostructured LiCoO2 fibers as cathode materials for lithium-ion batteries. J. Phys. Chem. B 2005, 109, 17901–17906. [Google Scholar] [CrossRef] [PubMed]
  42. Gu, Y.; Chen, D.; Jiao, X.; Liu, F. LiCoO2-MgO coaxial fibers: Co-electrospun fabrication, characterization and electrochemical properties. J. Mater. Chem. 2007, 17, 1769–1776. [Google Scholar] [CrossRef]
  43. Shaju, K.M.; Bruce, P.G. Macroporous LiNi1/3Co1/3Mn1/3O2: A High-Power and High-Energy Cathode for Rechargeable Lithium Batteries. Adv. Mater. 2006, 18, 2330–2334. [Google Scholar] [CrossRef]
  44. Chen, Z.; Wang, J.; Chao, D.; Baikie, T.; Bai, L.; Chen, S.; Zhao, Y.; Sum, T.C.; Lin, J.; Shen, Z. Hierarchical Porous LiNi1/3Co1/3Mn1/3O2 Nano-/Micro Spherical Cathode Material: Minimized Cation Mixing and Improved Li+ Mobility for Enhanced Electrochemical Performance. Sci. Rep. 2016, 6. [Google Scholar] [CrossRef] [PubMed]
  45. Liang, C.; Liu, L.; Jia, Z.; Dai, C.; Xiong, Y. Synergy of Nyquist and Bode electrochemical impedance spectroscopy studies to particle size effect on the electrochemical properties of LiNi0.5Co0.2Mn0.3O2. Electrochim. Acta 2015, 186, 413–419. [Google Scholar] [CrossRef]
  46. Kang, C.S.; Son, J.T. Synthesis and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 cathode materials by electrospinning process. J. Electroceram. 2012, 29, 235–239. [Google Scholar] [CrossRef]
  47. Ma, D.; Zhang, P.; Li, Y.; Ren, X. Li1.2Mn0.54Ni0.13Co0.13O2-Encapsulated Carbon Nanofiber Network Cathodes with Improved Stability and Rate Capability for Li-ion Batteries. Sci. Rep. 2015, 5. [Google Scholar] [CrossRef] [PubMed]
  48. Min, J.W.; Kalathil, A.K.; Yim, C.J.; Im, W.B. Morphological effects on the electrochemical performance of lithium-rich layered oxide cathodes, prepared by electrospinning technique, for lithium-ion battery applications. Mater. Charact. 2014, 92, 118–126. [Google Scholar] [CrossRef]
  49. Padhi, A.K.; Nanjundaswamy, K.; Goodenough, J. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J. Electrochem. Soc. 1997, 144, 1188–1194. [Google Scholar] [CrossRef]
  50. Li, M.; Sun, L.; Sun, K.; Yu, S.; Wang, R.; Xie, H. Synthesis of nano-LiFePO4 particles with excellent electrochemical performance by electrospinning-assisted method. J. Solid State Electrochem. 2012, 16, 3581–3586. [Google Scholar] [CrossRef]
  51. Toprakci, O.; Ji, L.; Lin, Z.; Toprakci, H.A.K.; Zhang, X. Fabrication and electrochemical characteristics of electrospun LiFePO4/carbon composite fibers for lithium-ion batteries. J. Power Sources 2011, 196, 7692–7699. [Google Scholar] [CrossRef]
  52. Toprakci, O.; Toprakci, H.A.; Ji, L.; Xu, G.; Lin, Z.; Zhang, X. Carbon nanotube-loaded electrospun LiFePO4/carbon composite nanofibers as stable and binder-free cathodes for rechargeable lithium-ion batteries. ACS Appl. Mater. Interfaces 2012, 4, 1273–1280. [Google Scholar] [CrossRef] [PubMed]
  53. Hosono, E.; Wang, Y.; Kida, N.; Enomoto, M.; Kojima, N.; Okubo, M.; Matsuda, H.; Saito, Y.; Kudo, T.; Honma, I.; et al. Synthesis of triaxial LiFePO4 nanowire with a VGCF core column and a carbon shell through the electrospinning method. ACS Appl. Mater. Interfaces 2010, 2, 212–218. [Google Scholar] [CrossRef] [PubMed]
  54. Murphy, D.; Christian, P.; DiSalvo, F.; Waszczak, J. Lithium incorporation by vanadium pentoxide. Inorg. Chem. 1979, 18, 2800–2803. [Google Scholar] [CrossRef]
  55. Liang, S.; Hu, Y.; Nie, Z.; Huang, H.; Chen, T.; Pan, A.; Cao, G. Template-free synthesis of ultra-large V2O5 nanosheets with exceptional small thickness for high-performance lithium-ion batteries. Nano Energy 2015, 13, 58–66. [Google Scholar] [CrossRef]
  56. Ban, C.; Chernova, N.A.; Whittingham, M.S. Electrospun nano-vanadium pentoxide cathode. Electrochem. Commun. 2009, 11, 522–525. [Google Scholar] [CrossRef]
  57. Yan, B.; Li, X.; Bai, Z.; Li, M.; Dong, L.; Xiong, D.; Li, D. Superior lithium storage performance of hierarchical porous vanadium pentoxide nanofibers for lithium ion battery cathodes. J. Alloy. Compd. 2015, 634, 50–57. [Google Scholar] [CrossRef]
  58. Mai, L.; Xu, L.; Han, C.; Xu, X.; Luo, Y.; Zhao, S.; Zhao, Y. Electrospun ultralong hierarchical vanadium oxide nanowires with high performance for lithium ion batteries. Nano Lett. 2010, 10, 4750–4755. [Google Scholar] [CrossRef] [PubMed]
  59. Li, Z.; Liu, G.; Guo, M.; Ding, L.X.; Wang, S.; Wang, H. Electrospun porous vanadium pentoxide nanotubes as a high-performance cathode material for lithium-ion batteries. Electrochim. Acta 2015, 173, 131–138. [Google Scholar] [CrossRef]
  60. Zhou, H.; Ding, X.; Liu, G.; Jiang, Y.; Yin, Z.; Wang, X. Preparation and Characterization of Ultralong Spinel Lithium Manganese Oxide Nanofiber Cathode via Electrospinning Method. Electrochim. Acta 2015, 152, 274–279. [Google Scholar] [CrossRef]
  61. Yan, B.; Chen, L.; Wang, T.; Xu, J.; Wang, H.; Yang, G. Preparation and characterization of Li3V2(PO4)3 grown on carbon nanofiber as cathode material for lithium-ion batteries. Electrochim. Acta 2015, 176, 1358–1363. [Google Scholar] [CrossRef]
  62. Chen, L.; Yan, B.; Xu, J.; Wang, C.; Chao, Y.; Jiang, X.; Yang, G. Bicontinuous Structure of Li3V2(PO4)3 Clustered via Carbon Nanofiber as High-Performance Cathode Material of Li-ion Batteries. ACS Appl. Mater. Interfaces 2015, 7, 13934–13943. [Google Scholar] [CrossRef] [PubMed]
  63. Arun, N.; Aravindan, V.; Jayaraman, S.; Madhavi, S. Unveiling the Fabrication of “Rocking-Chair” Type 3.2 and 1.2 V Class Cells Using Spinel LiNi0.5Mn1.5O4 as Cathode with Li4Ti5O12. J. Phys. Chem. C 2015, 119, 24332–24336. [Google Scholar] [CrossRef]
  64. Arun, N.; Aravindan, V.; Ling, W.C.; Madhavi, S. Importance of nanostructure for reversible Li-insertion into octahedral sites of LiNi0.5Mn1.5O4 and its application towards aqueous Li-ion chemistry. J. Power Sources 2015, 280, 240–245. [Google Scholar] [CrossRef]
  65. Xu, R.; Zhang, X.; Chamoun, R.; Shui, J.; Li, J.C.M.; Lu, J.; Amine, K.; Belharouak, I. Enhanced rate performance of LiNi0.5Mn1.5O4 fibers synthesized by electrospinning. Nano Energy 2015, 15, 616–624. [Google Scholar] [CrossRef]
  66. Kim, C.; Yang, K.S.; Kojima, M.; Yoshida, K.; Kim, Y.J.; Kim, Y.A.; Endo, M. Fabrication of Electrospinning-Derived Carbon Nanofiber Webs for the Anode Material of Lithium-ion Secondary Batteries. Adv. Funct. Mater. 2006, 16, 2393–2397. [Google Scholar] [CrossRef]
  67. Shi, Z.; Chong, C.; Wang, J.; Wang, C.; Yu, X. Electrospun pitch/polyacrylonitrile composite carbon nanofibers as high performance anodes for lithium-ion batteries. Mater. Lett. 2015, 159, 341–344. [Google Scholar] [CrossRef]
  68. Li, W.; Li, M.; Wang, M.; Zeng, L.; Yu, Y. Electrospinning with partially carbonization in air: Highly porous carbon nanofibers optimized for high-performance flexible lithium-ion batteries. Nano Energy 2015, 13, 693–701. [Google Scholar] [CrossRef]
  69. Lee, B.S.; Yang, H.S.; Jung, H.; Mah, S.K.; Kwon, S.; Park, J.H.; Lee, K.H.; Yu, W.R.; Doo, S.G. Facile method to improve initial reversible capacity of hollow carbon nanofiber anodes. Eur. Polym. J. 2015, 70, 392–399. [Google Scholar] [CrossRef]
  70. Sharma, A.S. Enhanced Electrochemical Performance of Electrospun Ag/Hollow Glassy Carbon Nanofibers as Free-standing Li-ion Battery Anode. Electrochim. Acta 2015, 176, 1266–1271. [Google Scholar]
  71. Li, M.; Zhou, D.; Song, W.L.; Li, X.; Fan, L.Z. Highly stable GeOx@C core-shell fibrous anodes for improved capacity in lithium-ion batteries. J. Mater. Chem. A 2015, 3, 19907–19912. [Google Scholar] [CrossRef]
  72. Im, M.E.; Pham-Cong, D.; Kim, J.Y.; Choi, H.S.; Kim, J.H.; Kim, J.P.; Kim, J.; Jeong, S.Y.; Cho, C.R. Enhanced electrochemical performance of template-free carbon-coated iron (II, III) oxide hollow nanofibers as anode material for lithium-ion batteries. J. Power Sources 2015, 284, 392–399. [Google Scholar] [CrossRef]
  73. An, G.H.; Ahn, H.J. Carbon nanofiber/cobalt oxide nanopyramid core-shell nanowires for high-performance lithium-ion batteries. J. Power Sources 2014, 272, 828–836. [Google Scholar] [CrossRef]
  74. Park, S.H.; Lee, W.J. Hierarchically mesoporous carbon nanofiber/Mn3O4 coaxial nanocables as anodes in lithium ion batteries. J. Power Sources 2015, 281, 301–309. [Google Scholar] [CrossRef]
  75. Mei, L.; Mao, M.; Chou, S.; Liu, H.; Dou, S.; Ng, D.H.L.; Ma, J. Nitrogen-doped carbon nanofibers with effectively encapsulated GeO2 nanocrystals for highly reversible lithium storage. J. Mater. Chem. A 2015, 3, 21699–21705. [Google Scholar] [CrossRef]
  76. Wu, Y.; Zhu, P.; Reddy, M.V.; Chowdari, B.V.; Ramakrishna, S. Maghemite nanoparticles on electrospun CNFs template as prospective lithium-ion battery anode. ACS Appl. Mater. Interfaces 2014, 6, 1951–1958. [Google Scholar] [CrossRef] [PubMed]
  77. Ashuri, M.; He, Q.; Shaw, L.L. Silicon as a potential anode material for Li-ion batteries: Where size, geometry and structure matter. Nanoscale 2016, 8, 74–103. [Google Scholar] [CrossRef] [PubMed]
  78. Wu, J.; Qin, X.; Miao, C.; He, Y.B.; Liang, G.; Zhou, D.; Liu, M.; Han, C.; Li, B.; Kang, F. A honeycomb-cobweb inspired hierarchical core-shell structure design for electrospun silicon/carbon fibers as lithium-ion battery anodes. Carbon 2016, 98, 582–591. [Google Scholar] [CrossRef]
  79. Wang, M.S.; Song, W.L.; Wang, J.; Fan, L.Z. Highly uniform silicon nanoparticle/porous carbon nanofiber hybrids towards free-standing high-performance anodes for lithium-ion batteries. Carbon 2015, 82, 337–345. [Google Scholar] [CrossRef]
  80. Wang, Y.; Wen, X.; Chen, J.; Wang, S. Foamed mesoporous carbon/silicon composite nanofiber anode for lithium ion batteries. J. Power Sources 2015, 281, 285–292. [Google Scholar] [CrossRef]
  81. Chen, Y.; Hu, Y.; Shao, J.; Shen, Z.; Chen, R.; Zhang, X.; He, X.; Song, Y.; Xing, X. Pyrolytic carbon-coated silicon/carbon nanofiber composite anodes for high-performance lithium-ion batteries. J. Power Sources 2015, 298, 130–137. [Google Scholar] [CrossRef]
  82. Zhang, H.; Qin, X.; Wu, J.; He, Y.-B.; Du, H.; Li, B.; Kang, F. Electrospun core-shell silicon/carbon fibers with an internal honeycomb-like conductive carbon framework as an anode for lithium ion batteries. J. Mater. Chem. A 2015, 3, 7112–7120. [Google Scholar] [CrossRef]
  83. Xu, Y.; Zhu, Y.; Han, F.; Luo, C.; Wang, C. 3D Si/C Fiber Paper Electrodes Fabricated Using a Combined Electrospray/Electrospinning Technique for Li-ion Batteries. Adv. Energy Mater. 2015, 5. [Google Scholar] [CrossRef]
  84. Brousse, T.; Crosnier, O.; Devaux, X.; Fragnaud, P.; Paillard, P.; Santos-Peña, J.; Schleich, D. Advanced oxide and metal powders for negative electrodes in lithium-ion batteries. Powder Technol. 2002, 128, 124–130. [Google Scholar] [CrossRef]
  85. Yang, Z.; Meng, Q.; Yan, W.; Lv, J.; Guo, Z.; Yu, X.; Chen, Z.; Guo, T.; Zeng, R. Novel three-dimensional tin/carbon hybrid core/shell architecture with large amount of solid cross-linked micro/nanochannels for lithium ion battery application. Energy 2015, 82, 960–967. [Google Scholar] [CrossRef]
  86. Wang, J.; Song, W.L.; Wang, Z.; Fan, L.Z.; Zhang, Y. Facile Fabrication of Binder-free Metallic Tin Nanoparticle/Carbon Nanofiber Hybrid Electrodes for Lithium-ion Batteries. Electrochim. Acta 2015, 153, 468–475. [Google Scholar] [CrossRef]
  87. Shen, Z.; Hu, Y.; Chen, Y.; Zhang, X.; Wang, K.; Chen, R. Tin nanoparticle-loaded porous carbon nanofiber composite anodes for high current lithium-ion batteries. J. Power Sources 2015, 278, 660–667. [Google Scholar] [CrossRef]
  88. Yu, Y.; Gu, L.; Wang, C.; Dhanabalan, A.; van Aken, P.A.; Maier, J. Encapsulation of Sn@carbon nanoparticles in bamboo-like hollow carbon nanofibers as an anode material in lithium-based batteries. Angew. Chem. 2009, 48, 6485–6489. [Google Scholar] [CrossRef] [PubMed]
  89. Reddy, M.V.; Subba Rao, G.V.; Chowdari, B.V. Metal oxides and oxysalts as anode materials for Li-ion batteries. Chem. Rev. 2013, 113, 5364–5457. [Google Scholar] [CrossRef] [PubMed]
  90. Macak, J.M.; Tsuchiya, H.; Schmuki, P. High-aspect-ratio TiO2 nanotubes by anodization of titanium. Angew. Chem. Int. Ed. 2005, 44, 2100–2102. [Google Scholar] [CrossRef] [PubMed]
  91. Qing, R.; Liu, L.; Bohling, C.; Sigmund, W. Conductivity dependence of lithium diffusivity and electrochemical performance for electrospun TiO2 fibers. J. Power Sources 2015, 274, 667–675. [Google Scholar] [CrossRef]
  92. Cho, J.S.; Hong, Y.J.; Kang, Y.C. Electrochemical properties of fiber-in-tube- and filled-structured TiO2 nanofiber anode materials for lithium-ion batteries. Chemistry 2015, 21, 11082–11087. [Google Scholar] [CrossRef] [PubMed]
  93. Wang, H.; Ma, D.; Huang, X.; Huang, Y.; Zhang, X. General and controllable synthesis strategy of metal oxide/TiO2 hierarchical heterostructures with improved lithium-ion battery performance. Sci. Rep. 2012, 2. [Google Scholar] [CrossRef] [PubMed]
  94. Wang, H.; Wang, G.; Yuan, S.; Ma, D.; Li, Y.; Zhang, Y. Fe3O4-nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures with improved lithium-ion battery performance over wide temperature range. Nano Res. 2015, 8, 1659–1668. [Google Scholar] [CrossRef]
  95. Reddy, M.V.; Jose, R.; Teng, T.H.; Chowdari, B.V.R.; Ramakrishna, S. Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles. Electrochim. Acta 2010, 55, 3109–3117. [Google Scholar] [CrossRef]
  96. Zhu, P.; Wu, Y.; Reddy, M.V.; Sreekumaran Nair, A.; Chowdari, B.V.R.; Ramakrishna, S. Long term cycling studies of electrospun TiO2 nanostructures and their composites with MWCNTs for rechargeable Li-ion batteries. RSC Adv. 2012, 2, 531–537. [Google Scholar] [CrossRef]
  97. Ramakrishna, S.; Le Viet, A.; Reddy, M.; Jose, R.; Chowdari, B. Nanostructured Nb2O5 polymorphs by electrospinning for rechargeable lithium batteries. J. Phys. Chem. C. 2010, 114, 664–671. [Google Scholar]
  98. Reddy, M.V.; Jose, R.; Le Viet, A.; Ozoemena, K.I.; Chowdari, B.V.R.; Ramakrishna, S. Studies on the lithium ion diffusion coefficients of electrospun Nb2O5 nanostructures using galvanostatic intermittent titration and electrochemical impedance spectroscopy. Electrochim. Acta 2014, 128, 198–202. [Google Scholar] [CrossRef]
  99. Le Viet, A.; Reddy, M.V.; Jose, R.; Chowdari, B.V.R.; Ramakrishna, S. Electrochemical properties of bare and Ta-substituted Nb2O5 nanostructures. Electrochim. Acta 2011, 56, 1518–1528. [Google Scholar] [CrossRef]
  100. Jiang, F.; Yin, L.; Yu, Q.; Zhong, C.; Zhang, J. Bacterial cellulose nanofibrous membrane as thermal stable separator for lithium-ion batteries. J. Power Sources 2015, 279, 21–27. [Google Scholar] [CrossRef]
  101. Lee, S.W.; Choi, S.W.; Jo, S.M.; Chin, B.D.; Kim, D.Y.; Lee, K.Y. Electrochemical properties and cycle performance of electrospun poly(vinylidene fluoride)-based fibrous membrane electrolytes for Li-ion polymer battery. J. Power Sources 2006, 163, 41–46. [Google Scholar] [CrossRef]
  102. Gao, K.; Hu, X.; Dai, C.; Yi, T. Crystal structures of electrospun PVdF membranes and its separator application for rechargeable lithium metal cells. Mater. Sci. Eng. B 2006, 131, 100–105. [Google Scholar] [CrossRef]
  103. Choi, S.W.; Kim, J.R.; Ahn, Y.R.; Jo, S.M.; Cairns, E.J. Characterization of electrospun PVdF fiber-based polymer electrolytes. Chem. Mater. 2007, 19, 104–115. [Google Scholar] [CrossRef]
  104. Li, X.; Cheruvally, G.; Kim, J.K.; Choi, J.W.; Ahn, J.H.; Kim, K.W.; Ahn, H.J. Polymer electrolytes based on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) membrane for lithium batteries. J. Power Sources 2007, 167, 491–498. [Google Scholar] [CrossRef]
  105. Huang, F.; Xu, Y.; Peng, B.; Su, Y.; Jiang, F.; Hsieh, Y.L.; Wei, Q. Coaxial Electrospun Cellulose-Core Fluoropolymer-Shell Fibrous Membrane from Recycled Cigarette Filter as Separator for High Performance Lithium-ion Battery. ACS Sustain. Chem. Eng. 2015, 3, 932–940. [Google Scholar] [CrossRef]
  106. Kim, J.K.; Cheruvally, G.; Li, X.; Ahn, J.H.; Kim, K.W.; Ahn, H.J. Preparation and electrochemical characterization of electrospun, microporous membrane-based composite polymer electrolytes for lithium batteries. J. Power Sources 2008, 178, 815–820. [Google Scholar] [CrossRef]
  107. Raghavan, P.; Choi, J.W.; Ahn, J.H.; Cheruvally, G.; Chauhan, G.S.; Ahn, H.J.; Nah, C. Novel electrospun poly(vinylidene fluoride-co-hexafluoropropylene)-in situ SiO2 composite membrane-based polymer electrolyte for lithium batteries. J. Power Sources 2008, 184, 437–443. [Google Scholar] [CrossRef]
  108. Ding, Y.; Zhang, P.; Long, Z.; Jiang, Y.; Xu, F.; Di, W. The ionic conductivity and mechanical property of electrospun P(VdF-HFP)/PMMA membranes for lithium ion batteries. J. Membr. Sci. 2009, 329, 56–59. [Google Scholar] [CrossRef]
  109. Raghavan, P.; Zhao, X.; Shin, C.; Baek, D.H.; Choi, J.W.; Manuel, J.; Heo, M.Y.; Ahn, J.H.; Nah, C. Preparation and electrochemical characterization of polymer electrolytes based on electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/polyacrylonitrile blend/composite membranes for lithium batteries. J. Power Sources 2010, 195, 6088–6094. [Google Scholar] [CrossRef]
  110. Li, W.; Xing, Y.; Wu, Y.; Wang, J.; Chen, L.; Yang, G.; Tang, B. Study the effect of ion-complex on the properties of composite gel polymer electrolyte based on Electrospun PVdF nanofibrous membrane. Electrochim. Acta 2015, 151, 289–296. [Google Scholar] [CrossRef]
  111. Raghavan, P.; Manuel, J.; Zhao, X.; Kim, D.S.; Ahn, J.H.; Nah, C. Preparation and electrochemical characterization of gel polymer electrolyte based on electrospun polyacrylonitrile nonwoven membranes for lithium batteries. J. Power Sources 2011, 196, 6742–6749. [Google Scholar] [CrossRef]
  112. Carol, P.; Ramakrishnan, P.; John, B.; Cheruvally, G. Preparation and characterization of electrospun poly(acrylonitrile) fibrous membrane based gel polymer electrolytes for lithium-ion batteries. J. Power Sources 2011, 196, 10156–10162. [Google Scholar] [CrossRef]
  113. Bi, H.; Sui, G.; Yang, X. Studies on polymer nanofibre membranes with optimized core-shell structure as outstanding performance skeleton materials in gel polymer electrolytes. J. Power Sources 2014, 267, 309–315. [Google Scholar] [CrossRef]
  114. Yanilmaz, M.; Lu, Y.; Li, Y.; Zhang, X. SiO2/polyacrylonitrile membranes via centrifugal spinning as a separator for Li-ion batteries. J. Power Sources 2015, 273, 1114–1119. [Google Scholar] [CrossRef]
  115. Jung, H.R.; Ju, D.H.; Lee, W.J.; Zhang, X.; Kotek, R. Electrospun hydrophilic fumed silica/polyacrylonitrile nanofiber-based composite electrolyte membranes. Electrochim. Acta 2009, 54, 3630–3637. [Google Scholar] [CrossRef]
  116. Wang, Q.; Song, W.L.; Fan, L.Z.; Song, Y. Facile fabrication of polyacrylonitrile/alumina composite membranes based on triethylene glycol diacetate-2-propenoic acid butyl ester gel polymer electrolytes for high-voltage lithium-ion batteries. J. Membr. Sci. 2015, 486, 21–28. [Google Scholar] [CrossRef]
  117. Wang, Q.; Song, W.L.; Fan, L.Z.; Shi, Q. Effect of polyacrylonitrile on triethylene glycol diacetate-2-propenoic acid butyl ester gel polymer electrolytes with interpenetrating crosslinked network for flexible lithium ion batteries. J. Power Sources 2015, 295, 139–148. [Google Scholar] [CrossRef]
  118. Zhang, Z.; Sui, G.; Bi, H.; Yang, X. Radiation-crosslinked nanofiber membranes with well-designed core-shell structure for high performance of gel polymer electrolytes. J. Membr. Sci. 2015, 492, 77–87. [Google Scholar] [CrossRef]
  119. Lee, J.H.; Manuel, J.; Choi, H.; Park, W.H.; Ahn, J.H. Partially oxidized polyacrylonitrile nanofibrous membrane as a thermally stable separator for lithium ion batteries. Polymer 2015, 68, 335–343. [Google Scholar] [CrossRef]
  120. Liang, Y.; Ji, L.; Guo, B.; Lin, Z.; Yao, Y.; Li, Y.; Alcoutlabi, M.; Qiu, Y.; Zhang, X. Preparation and electrochemical characterization of ionic-conducting lithium lanthanum titanate oxide/polyacrylonitrile submicron composite fiber-based lithium-ion battery separators. J. Power Sources 2011, 196, 436–441. [Google Scholar] [CrossRef]
  121. Evans, T.; Lee, J.H.; Bhat, V.; Lee, S.H. Electrospun polyacrylonitrile microfiber separators for ionic liquid electrolytes in Li-ion batteries. J. Power Sources 2015, 292, 1–6. [Google Scholar] [CrossRef]
  122. Manthiram, A.; Fu, Y.; Chung, S.H.; Zu, C.; Su, Y.S. Rechargeable Lithium-Sulfur Batteries. Chem. Rev. 2014, 114, 11751–11787. [Google Scholar] [CrossRef] [PubMed]
  123. Wu, F.; Shi, L.; Mu, D.; Xu, H.; Wu, B. A hierarchical carbon fiber/sulfur composite as cathode material for Li-S batteries. Carbon 2015, 86, 146–155. [Google Scholar] [CrossRef]
  124. Song, J.; Yu, Z.; Gordin, M.L.; Wang, D. Advanced Sulfur Cathode Enabled by Highly Crumpled Nitrogen-Doped Graphene Sheets for High-Energy-Density Lithium-Sulfur Batteries. Nano Lett. 2016, 16, 864–870. [Google Scholar] [CrossRef] [PubMed]
  125. Tang, C.; Li, B.Q.; Zhang, Q.; Zhu, L.; Wang, H.F.; Shi, J.L.; Wei, F. CaO-Templated Growth of Hierarchical Porous Graphene for High-Power Lithium-Sulfur Battery Applications. Adv. Funct. Mater. 2016, 26, 577–585. [Google Scholar] [CrossRef]
  126. Ji, L.; Rao, M.; Aloni, S.; Wang, L.; Cairns, E.J.; Zhang, Y. Porous carbon nanofiber-sulfur composite electrodes for lithium/sulfur cells. Energy Environ. Sci. 2011, 4, 5053–5059. [Google Scholar] [CrossRef]
  127. Wang, H.; Zhang, C.; Chen, Z.; Liu, H.K.; Guo, Z. Large-scale synthesis of ordered mesoporous carbon fiber and its application as cathode material for lithium-sulfur batteries. Carbon 2015, 81, 782–787. [Google Scholar] [CrossRef]
  128. Wang, L.; Zhao, Y.; Thomas, M.L.; Byon, H.R. In situ synthesis of bipyramidal sulfur with 3D carbon nanotube framework for lithium-sulfur batteries. Adv. Funct. Mater. 2014, 24, 2248–2252. [Google Scholar] [CrossRef]
  129. Huang, L.; Cheng, J.; Qu, G.; Li, X.; Hu, Y.; Ni, W.; Yuan, D.; Zhang, Y.; Wang, B. Porous carbon nanofibers formed in situ by electrospinning with a volatile solvent additive into an ice water bath for lithium-ulfur batteries. RSC Adv. 2015, 5, 23749–23757. [Google Scholar] [CrossRef]
  130. Lu, J.; Li, L.; Park, J.B.; Sun, Y.K.; Wu, F.; Amine, K. Aprotic and aqueous Li-O2 batteries. Chem. Rev. 2014, 114, 5611–5640. [Google Scholar] [CrossRef] [PubMed]
  131. Kwak, W.J.; Lau, K.C.; Shin, C.D.; Amine, K.; Curtiss, L.A.; Sun, Y.K. A Mo2C/Carbon Nanotube Composite Cathode for Lithium-Oxygen Batteries with High Energy Efficiency and Long Cycle Life. ACS Nano 2015, 9, 4129–4137. [Google Scholar] [CrossRef] [PubMed]
  132. Lee, D.J.; Lee, H.; Kim, Y.J.; Park, J.K.; Kim, H.T. Sustainable Redox Mediation for Lithium-Oxygen Batteries by a Composite Protective Layer on the Lithium-Metal Anode. Adv. Mater. 2016, 28, 857–863. [Google Scholar] [CrossRef] [PubMed]
  133. Luntz, A.C.; McCloskey, B.D. Nonaqueous Li-air batteries: A status report. Chem. Rev. 2014, 114, 11721–11750. [Google Scholar] [CrossRef] [PubMed]
  134. Li, P.; Zhang, J.; Yu, Q.; Qiao, J.; Wang, Z.; Rooney, D.; Sun, W.; Sun, K. One-dimensional porous La0.5Sr0.5CoO2.91 nanotubes as a highly efficient electrocatalyst for rechargeable lithium-oxygen batteries. Electrochim. Acta 2015, 165, 78–84. [Google Scholar] [CrossRef]
  135. Ryu, W.H.; Yoon, T.H.; Song, S.H.; Jeon, S.; Park, Y.J.; Kim, I.D. Bifunctional composite catalysts using Co3O4 nanofibers immobilized on nonoxidized graphene nanoflakes for high-capacity and long-cycle Li-O2 batteries. Nano Lett. 2013, 13, 4190–4197. [Google Scholar] [CrossRef] [PubMed]
  136. Liu, G.; Chen, H.; Xia, L.; Wang, S.; Ding, L.X.; Li, D.; Xiao, K.; Dai, S.; Wang, H. Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3 − x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries. ACS Appl. Mater. Interfaces 2015, 7, 22478–22486. [Google Scholar] [CrossRef] [PubMed]
  137. Song, M.J.; Kim, I.T.; Kim, Y.B.; Shin, M.W. Self-standing, binder-free electrospun Co3O4/carbon nanofiber composites for non-aqueous Li-air batteries. Electrochim. Acta 2015, 182, 289–296. [Google Scholar] [CrossRef]
  138. Xu, S.M.; Zhu, Q.C.; Du, F.H.; Li, X.H.; Wei, X.; Wang, K.X.; Chen, J.S. Co3O4-based binder-free cathodes for lithium-oxygen batteries with improved cycling stability. Dalton Trans. 2015, 44, 8678–8684. [Google Scholar] [CrossRef] [PubMed]
  139. Kim, H.J.; Kim, Y.S.; Seo, M.H.; Choi, S.M.; Cho, J.; Huber, G.W.; Kim, W.B. Highly improved oxygen reduction performance over Pt/C-dispersed nanowire network catalysts. Electrochem. Commun. 2010, 12, 32–35. [Google Scholar] [CrossRef]
  140. Kim, J.M.; Joh, H.I.; Jo, S.M.; Ahn, D.J.; Ha, H.Y.; Hong, S.A.; Kim, S.K. Preparation and characterization of Pt nanowire by electrospinning method for methanol oxidation. Electrochim. Acta 2010, 55, 4827–4835. [Google Scholar] [CrossRef]
  141. Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science 2009, 323, 760–764. [Google Scholar] [CrossRef] [PubMed]
  142. Antolini, E.; Salgado, J.R.; Gonzalez, E.R. The stability of Pt-M (M = first row transition metal) alloy catalysts and its effect on the activity in low temperature fuel cells: A literature review and tests on a Pt-Co catalyst. J. Power Sources 2006, 160, 957–968. [Google Scholar] [CrossRef]
  143. Chang, C.L.; Hsu, C.S.; Huang, J.B.; Hsu, P.H.; Hwang, B.H. Preparation and characterization of SOFC cathodes made of SSC nanofibers. J. Alloy. Compd. 2015, 620, 233–239. [Google Scholar] [CrossRef]
  144. Nabae, Y.; Pointon, K.D.; Irvine, J.T.S. Electrochemical oxidation of solid carbon in hybrid DCFC with solid oxide and molten carbonate binary electrolyte. Energy Environ. Sci. 2008, 1, 148–155. [Google Scholar] [CrossRef]
  145. Kim, H.J.; Kim, Y.S.; Seo, M.H.; Choi, S.M.; Kim, W.B. Pt and PtRh nanowire electrocatalysts for cyclohexane-fueled polymer electrolyte membrane fuel cell. Electrochem. Commun. 2009, 11, 446–449. [Google Scholar] [CrossRef]
  146. Li, M.; Han, G.; Yang, B. Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats. Electrochem. Commun. 2008, 10, 880–883. [Google Scholar] [CrossRef]
  147. Kim, Y.S.; Nam, S.H.; Shim, H.S.; Ahn, H.J.; Anand, M.; Kim, W.B. Electrospun bimetallic nanowires of PtRh and PtRu with compositional variation for methanol electrooxidation. Electrochem. Commun. 2008, 10, 1016–1019. [Google Scholar] [CrossRef]
  148. Shui, J.L.; Chen, C.; Li, J.C.M. Evolution of Nanoporous Pt-Fe Alloy Nanowires by Dealloying and their Catalytic Property for Oxygen Reduction Reaction. Adv. Funct. Mater. 2011, 21, 3357–3362. [Google Scholar] [CrossRef]
  149. Higgins, D.C.; Wang, R.; Hoque, M.A.; Zamani, P.; Abureden, S.; Chen, Z. Morphology and composition controlled platinum-cobalt alloy nanowires prepared by electrospinning as oxygen reduction catalyst. Nano Energy 2014, 10, 135–143. [Google Scholar] [CrossRef]
  150. Ghouri, Z.K.; Barakat, N.A.; Kim, H.Y. Influence of copper content on the electrocatalytic activity toward methanol oxidation of CoxCuy alloy nanoparticles-decorated CNFs. Sci. Rep. 2015, 5. [Google Scholar] [CrossRef] [PubMed]
  151. Wang, S.; Dai, C.; Li, J.; Zhao, L.; Ren, Z.; Ren, Y.; Qiu, Y.; Yu, J. The effect of different nitrogen sources on the electrocatalytic properties of nitrogen-doped electrospun carbon nanofibers for the oxygen reduction reaction. Int. J. Hydrog. Energy 2015, 40, 4673–4682. [Google Scholar] [CrossRef]
  152. Liu, D.; Zhang, X.; Sun, Z.; You, T. Free-standing nitrogen-doped carbon nanofiber films as highly efficient electrocatalysts for oxygen reduction. Nanoscale 2013, 5, 9528–9531. [Google Scholar] [CrossRef] [PubMed]
  153. Qiu, Y.; Yu, J.; Shi, T.; Zhou, X.; Bai, X.; Huang, J.Y. Nitrogen-doped ultrathin carbon nanofibers derived from electrospinning: Large-scale production, unique structure, and application as electrocatalysts for oxygen reduction. J. Power Sources 2011, 196, 9862–9867. [Google Scholar] [CrossRef]
  154. Lai, C.; Kolla, P.; Zhao, Y.; Fong, H.; Smirnova, A.L. Lignin-derived electrospun carbon nanofiber mats with supercritically deposited Ag nanoparticles for oxygen reduction reaction in alkaline fuel cells. Electrochim. Acta 2014, 130, 431–438. [Google Scholar] [CrossRef]
  155. Thamer, B.M.; El-Newehy, M.H.; Al-Deyab, S.S.; Abdelkareem, M.A.; Kim, H.Y.; Barakat, N.A.M. Cobalt-incorporated, nitrogen-doped carbon nanofibers as effective non-precious catalyst for methanol electrooxidation in alkaline medium. Appl. Catal. A Gen. 2015, 498, 230–240. [Google Scholar] [CrossRef]
  156. Zhao, W.; Yuan, P.; She, X.; Xia, Y.; Komarneni, S.; Xi, K.; Che, Y.; Yao, X.; Yang, D. Sustainable seaweed-based one-dimensional (1D) nanofibers as high-performance electrocatalysts for fuel cells. J. Mater. Chem. A 2015, 3, 14188–14194. [Google Scholar] [CrossRef]
  157. McClure, J.P.; Jiang, R.; Chu, D.; Fedkiw, P.S. Oxygen electroreduction on Fe or Co-containing carbon fibers. Carbon 2014, 79, 457–469. [Google Scholar] [CrossRef]
  158. Uhm, S.; Jeong, B.; Lee, J. A facile route for preparation of non-noble CNF cathode catalysts in alkaline ethanol fuel cells. Electrochim. Acta 2011, 56, 9186–9190. [Google Scholar] [CrossRef]
  159. Yousef, A.; Brooks, R.M.; El-Halwany, M.; Abdelkareem, M.A.; Khamaj, J.A.; EL-Newehy, M.H.; Barakat, N.A.; Kim, H.Y. Fabrication of Electrical Conductive NiCu-Carbon Nanocomposite for Direct Ethanol Fuel Cells. Int. J. Electrochem. Sci. 2015, 10, 7025–7032. [Google Scholar]
  160. Yin, J.; Qiu, Y.; Yu, J. Onion-like graphitic nanoshell structured Fe-N/C nanofibers derived from electrospinning for oxygen reduction reaction in acid media. Electrochem. Commun. 2013, 30, 1–4. [Google Scholar] [CrossRef]
  161. Yan, X.; Liu, K.; Wang, X.; Wang, T.; Luo, J.; Zhu, J. Optimized electrospinning synthesis of iron-nitrogen-carbon nanofibers for high electrocatalysis of oxygen reduction in alkaline medium. Nanotechnology 2015, 26. [Google Scholar] [CrossRef] [PubMed]
  162. Barakat, N.A.M.; Motlak, M.; Kim, B.S.; El-Deen, A.G.; Al-Deyab, S.S.; Hamza, A.M. Carbon nanofibers doped by NixCo1 − x alloy nanoparticles as effective and stable non precious electrocatalyst for methanol oxidation in alkaline media. J. Mol. Catal. A Chem. 2014, 394, 177–187. [Google Scholar] [CrossRef]
  163. Tolba, G.M.K.; Barakat, N.A.M.; Bastaweesy, A.M.; Ashour, E.A.; Abdelmoez, W.; El-Newehy, M.H.; Al-Deyab, S.S.; Kim, H.Y. Hierarchical TiO2/ZnO Nanostructure as Novel Non-precious Electrocatalyst for Ethanol Electrooxidation. J. Mater. Sci. Technol. 2015, 31, 97–105. [Google Scholar] [CrossRef]
  164. Suryamas, A.B.; Anilkumar, G.M.; Sago, S.; Ogi, T.; Okuyama, K. Electrospun Pt/SnO2 nanofibers as an excellent electrocatalysts for hydrogen oxidation reaction with ORR-blocking characteristic. Catal. Commun. 2013, 33, 11–14. [Google Scholar] [CrossRef]
  165. Cavaliere, S.; Subianto, S.; Savych, I.; Tillard, M.; Jones, D.J.; Rozière, J. Dopant-Driven Nanostructured Loose-Tube SnO2 Architectures: Alternative Electrocatalyst Supports for Proton Exchange Membrane Fuel Cells. J. Phys. Chem. C 2013, 117, 18298–18307. [Google Scholar] [CrossRef]
  166. Savych, I.; Subianto, S.; Nabil, Y.; Cavaliere, S.; Jones, D.; Roziere, J. Negligible degradation upon in situ voltage cycling of a PEMFC using an electrospun niobium-doped tin oxide supported Pt cathode. Phys. Chem. Chem. Phys. 2015, 17, 16970–16976. [Google Scholar] [CrossRef] [PubMed]
  167. Zheng, Y.; Chen, H.; Dai, Y.; Zhang, N.; Zhao, W.; Wang, S.; Lou, Y.; Li, Y.; Sun, Y. Preparation and characterization of Pt/TiO2 nanofibers catalysts for methanol electro-oxidation. Electrochim. Acta 2015, 178, 74–79. [Google Scholar] [CrossRef]
  168. Savych, I.; Bernard d’Arbigny, J.; Subianto, S.; Cavaliere, S.; Jones, D.J.; Rozière, J. On the effect of non-carbon nanostructured supports on the stability of Pt nanoparticles during voltage cycling: A study of TiO2 nanofibres. J. Power Sources 2014, 257, 147–155. [Google Scholar] [CrossRef]
  169. Park, J.; Wycisk, R.; Pintauro, P.; Yarlagadda, V.; Van Nguyen, T. Electrospun Nafion®/Polyphenylsulfone Composite Membranes for Regenerative Hydrogen Bromine Fuel Cells. Materials 2016, 9. [Google Scholar] [CrossRef]
  170. Kim, T.-E.; Juon, S.M.; Park, J.H.; Shul, Y.-G.; Cho, K.Y. Silicon carbide fiber-reinforced composite membrane for high-temperature and low-humidity polymer exchange membrane fuel cells. Int. J. Hydrog. Energy 2014, 39, 16474–16485. [Google Scholar] [CrossRef]
  171. Wang, R.; Higgins, D.C.; Lee, D.U.; Prabhudev, S.; Hassan, F.M.; Chabot, V.; Lui, G.; Jiang, G.; Choi, J.Y.; Rasenthiram, L.; et al. Biomimetic design of monolithic fuel cell electrodes with hierarchical structures. Nano Energy 2016, 20, 57–67. [Google Scholar] [CrossRef]
  172. Liu, W.; Wang, S.; Xiao, M.; Han, D.; Meng, Y. A proton exchange membrane fabricated from a chemically heterogeneous nonwoven with sandwich structure by the program-controlled co-electrospinning process. Chem. Commun. 2012, 48, 3415–3417. [Google Scholar] [CrossRef] [PubMed]
  173. Dong, B.; Gwee, L.; Salas-dela Cruz, D.; Winey, K.I.; Elabd, Y.A. Super proton conductive high-purity nafion nanofibers. Nano Lett. 2010, 10, 3785–3790. [Google Scholar] [CrossRef] [PubMed]
  174. Mollá, S.; Compañ, V.; Gimenez, E.; Blazquez, A.; Urdanpilleta, I. Novel ultrathin composite membranes of Nafion/PVA for PEMFCs. Int. J. Hydrog. Energy 2011, 36, 9886–9895. [Google Scholar] [CrossRef]
  175. Ballengee, J.B.; Pintauro, P.N. Morphological Control of Electrospun Nafion Nanofiber Mats. J. Electrochem. Soc. 2011, 158, B568–B572. [Google Scholar] [CrossRef]
  176. Li, X.; Hao, X.; Xu, D.; Zhang, G.; Zhong, S.; Na, H.; Wang, D. Fabrication of sulfonated poly(ether ether ketone ketone) membranes with high proton conductivity. J. Membr. Sci. 2006, 281, 1–6. [Google Scholar] [CrossRef]
  177. Park, J.W.; Wycisk, R.; Pintauro, P.N. Nafion/PVdF nanofiber composite membranes for regenerative hydrogen/bromine fuel cells. J. Membr. Sci. 2015, 490, 103–112. [Google Scholar] [CrossRef]
  178. Maneeratana, V.; Bass, J.D.; Azaïs, T.; Patissier, A.; Vallé, K.; Maréchal, M.; Gebel, G.; Laberty-Robert, C.; Sanchez, C. Fractal inorganic-organic interfaces in hybrid membranes for efficient proton transport. Adv. Functi. Mater. 2013, 23, 2872–2880. [Google Scholar] [CrossRef]
  179. Ketpang, K.; Lee, K.; Shanmugam, S. Facile synthesis of porous metal oxide nanotubes and modified nafion composite membranes for polymer electrolyte fuel cells operated under low relative humidity. ACS Appl. Mater. Interfaces 2014, 6, 16734–16744. [Google Scholar] [CrossRef] [PubMed]
  180. Chen, J.Z.; Wang, C.; Hsu, C.C.; Cheng, I.C. Ultrafast synthesis of carbon-nanotube counter electrodes for dye-sensitized solar cells using an atmospheric-pressure plasma jet. Carbon 2016, 98, 34–40. [Google Scholar] [CrossRef]
  181. Mokurala, K.; Mallick, S.; Bhargava, P. Alternative quaternary chalcopyrite sulfides (Cu2FeSnS4 and Cu2CoSnS4) as electrocatalyst materials for counter electrodes in dye-sensitized solar cells. J. Power Sources 2016, 305, 134–143. [Google Scholar] [CrossRef]
  182. Sugathan, V.; John, E.; Sudhakar, K. Recent improvements in dye sensitized solar cells: A review. Renew. Sustain. Energy Rev. 2015, 52, 54–64. [Google Scholar] [CrossRef]
  183. Le Viet, A.; Jose, R.; Reddy, M.; Chowdari, B.; Ramakrishna, S. Nb2O5 photoelectrodes for dye-sensitized solar cells: Choice of the polymorph. J. Phys. Chem. C 2010, 114, 21795–21800. [Google Scholar] [CrossRef]
  184. Kumar, A.; Jose, R.; Fujihara, K.; Wang, J.; Ramakrishna, S. Structural and optical properties of electrospun TiO2 nanofibers. Chem. Mater. 2007, 19, 6536–6542. [Google Scholar] [CrossRef]
  185. Mali, S.S.; Shim, C.S.; Kim, H.; Patil, J.V.; Ahn, D.H.; Patil, P.S.; Hong, C.K. Evaluation of various diameters of titanium oxide nanofibers for efficient dye sensitized solar cells synthesized by electrospinning technique: A systematic study and their application. Electrochim. Acta 2015, 166, 356–366. [Google Scholar] [CrossRef]
  186. Zhang, W.; Zhu, R.; Ke, L.; Liu, X.; Liu, B.; Ramakrishna, S. Anatase mesoporous TiO2 nanofibers with high surface area for solid-state dye-sensitized solar cells. Small 2010, 6, 2176–2182. [Google Scholar] [CrossRef] [PubMed]
  187. Yang, L.; Leung, W.W. Application of a bilayer TiO2 nanofiber photoanode for optimization of dye-sensitized solar cells. Adv. Mater. 2011, 23, 4559–4562. [Google Scholar] [CrossRef] [PubMed]
  188. Yang, W.G.; Wan, F.R.; Chen, Q.W.; Li, J.J.; Xu, D.S. Controlling synthesis of well-crystallized mesoporous TiO2 microspheres with ultrahigh surface area for high-performance dye-sensitized solar cells. J. Mater. Chem. 2010, 20, 2870–2876. [Google Scholar] [CrossRef]
  189. Hwang, S.H.; Kim, C.; Song, H.; Son, S.; Jang, J. Designed architecture of multiscale porous TiO2 nanofibers for dye-sensitized solar cells photoanode. ACS Appl. Mater. Interfaces 2012, 4, 5287–5292. [Google Scholar] [CrossRef] [PubMed]
  190. Hieu, N.T.; Baik, S.J.; Chung, O.H.; Park, J.S. Fabrication and characterization of electrospun carbon nanotubes/titanium dioxide nanofibers used in anodes of dye-sensitized solar cells. Synth. Met. 2014, 193, 125–131. [Google Scholar] [CrossRef]
  191. Li, Y.; Lee, D.K.; Kim, J.Y.; Kim, B.; Park, N.G.; Kim, K.; Shin, J.H.; Choi, I.S.; Ko, M.J. Highly durable and flexible dye-sensitized solar cells fabricated on plastic substrates: PVdF-nanofiber-reinforced TiO2 photoelectrodes. Energy Environ. Sci. 2012, 5, 8950–8957. [Google Scholar] [CrossRef]
  192. Li, F.; Wang, G.; Jiao, Y.; Li, J.; Xie, S. Efficiency enhancement of ZnO-based dye-sensitized solar cell by hollow TiO2 nanofibers. J. Alloy. Compd. 2014, 611, 19–23. [Google Scholar] [CrossRef]
  193. Aboagye, A.; Elbohy, H.; Kelkar, A.D.; Qiao, Q.; Zai, J.; Qian, X.; Zhang, L. Electrospun carbon nanofibers with surface-attached platinum nanoparticles as cost-effective and efficient counter electrode for dye-sensitized solar cells. Nano Energy 2015, 11, 550–556. [Google Scholar] [CrossRef]
  194. Sookhakian, M.; Ridwan, N.; Zalnezhad, E.; Yoon, G.; Azarang, M.; Mahmoudian, M.; Alias, Y. Layer-by-Layer Electrodeposited Reduced Graphene Oxide-Copper Nanopolyhedra Films as Efficient Platinum-Free Counter Electrodes in High Efficiency Dye-Sensitized Solar Cells. J. Electrochem. Soc. 2016, 163, 154–159. [Google Scholar] [CrossRef]
  195. Joshi, P.; Zhang, L.; Chen, Q.; Galipeau, D.; Fong, H.; Qiao, Q. Electrospun carbon nanofibers as low-cost counter electrode for dye-sensitized solar cells. ACS Appl. Mater. Interfaces 2010, 2, 3572–3577. [Google Scholar] [CrossRef] [PubMed]
  196. Park, S.H.; Jung, H.R.; Lee, W.J. Hollow activated carbon nanofibers prepared by electrospinning as counter electrodes for dye-sensitized solar cells. Electrochim. Acta 2013, 102, 423–428. [Google Scholar] [CrossRef]
  197. Park, S.H.; Kim, B.K.; Lee, W.J. Electrospun activated carbon nanofibers with hollow core/highly mesoporous shell structure as counter electrodes for dye-sensitized solar cells. J. Power Sources 2013, 239, 122–127. [Google Scholar] [CrossRef]
  198. Mohamed, I.M.A.; Motlak, M.; Akhtar, M.S.; Yasin, A.S.; El-Newehy, M.H.; Al-Deyab, S.S.; Barakat, N.A.M. Synthesis, characterization and performance as a Counter Electrode for dye-sensitized solar cells of CoCr-decorated carbon nanofibers. Ceram. Int. 2016, 42, 146–153. [Google Scholar] [CrossRef]
  199. Motlak, M.; Barakat, N.A.M.; Akhtar, M.S.; Hamza, A.M.; Kim, B.S.; Kim, C.S.; Khalil, K.A.; Almajid, A.A. High performance of NiCo nanoparticles-doped carbon nanofibers as counter electrode for dye-sensitized solar cells. Electrochim. Acta 2015, 160, 1–6. [Google Scholar] [CrossRef]
  200. Barakat, N.A.M.; Shaheer Akhtar, M.; Yousef, A.; El-Newehy, M.; Kim, H.Y. Pd-Co-doped carbon nanofibers with photoactivity as effective counter electrodes for DSSCs. Chem. Eng. J. 2012, 211–212, 9–15. [Google Scholar]
  201. Yousef, A.; Akhtar, M.S.; Barakat, N.A.M.; Motlak, M.; Yang, O.B.; Kim, H.Y. Effective NiCu NPs-doped carbon nanofibers as counter electrodes for dye-sensitized solar cells. Electrochim. Acta 2013, 102, 142–148. [Google Scholar] [CrossRef]
  202. Saranya, K.; Subramania, A.; Sivasankar, N. Influence of earth-abundant bimetallic (Fe-Ni) nanoparticle-embedded CNFs as a low-cost counter electrode material for dye-sensitized solar cells. RSC Adv. 2015, 5, 43611–43619. [Google Scholar] [CrossRef]
  203. Saranya, K.; Subramania, A.; Sivasankar, N.; Mallick, S. Electrospun TiC embedded CNFs as a low cost platinum-free counter electrode for dye-sensitized solar cell. Mater. Res. Bull. 2016, 75, 83–90. [Google Scholar] [CrossRef]
  204. Jeong, I.; Lee, J.; Vincent Joseph, K.L.; Lee, H.I.; Kim, J.K.; Yoon, S.; Lee, J. Low-cost electrospun WC/C composite nanofiber as a powerful platinum-free counter electrode for dye sensitized solar cell. Nano Energy 2014, 9, 392–400. [Google Scholar] [CrossRef]
  205. Zakeeruddin, S.M.; Graetzel, M. Solvent-Free Ionic Liquid Electrolytes for Mesoscopic Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2009, 19, 2187–2202. [Google Scholar] [CrossRef]
  206. Park, J.Y.; Lee, J.W.; Park, K.H.; Kim, T.Y.; Yim, S.H.; Zhao, X.G.; Gu, H.B.; Jin, E.M. Dye-sensitized solar cells based on electrospun poly(vinylidenefluoride-co-hexafluoropropylene) nanofibers. Polym. Bull. 2013, 70, 507–515. [Google Scholar] [CrossRef]
  207. Snaith, H.J.; Schmidt-Mende, L. Advances in Liquid-Electrolyte and Solid-State Dye-Sensitized Solar Cells. Adv. Mater. 2007, 19, 3187–3200. [Google Scholar] [CrossRef]
  208. Kim, J.U.; Park, S.H.; Choi, H.J.; Lee, W.K.; Lee, J.K.; Kim, M.R. Effect of electrolyte in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers on dye-sensitized solar cells. Sol. Energy Mater. Sol. Cells 2009, 93, 803–807. [Google Scholar] [CrossRef]
  209. Vijayakumar, E.; Subramania, A.; Fei, Z.; Dyson, P.J. Effect of 1-butyl-3-methylimidazolium iodide containing electrospun poly(vinylidene fluoride-co-hexafluoropropylene) membrane electrolyte on the photovoltaic performance of dye-sensitized solar cells. J. Appl. Polym. Sci. 2015, 132. [Google Scholar] [CrossRef]
  210. Park, S.H.; Won, D.H.; Choi, H.J.; Hwang, W.P.; Jang, S.I.; Kim, J.H.; Jeong, S.H.; Kim, J.U.; Lee, J.K.; Kim, M.R. Dye-sensitized solar cells based on electrospun polymer blends as electrolytes. Sol. Energy Mater. Sol. Cells 2011, 95, 296–300. [Google Scholar] [CrossRef]
  211. Vijayakumar, E.; Subramania, A.; Fei, Z.; Dyson, P.J. High-performance dye-sensitized solar cell based on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/cobalt sulfide nanocomposite membrane electrolyte. RSC Adv. 2015, 5, 52026–52032. [Google Scholar] [CrossRef]
  212. Zhao, X.G.; Jin, E.M.; Park, J.Y.; Gu, H.B. Hybrid polymer electrolyte composite with SiO2 nanofiber filler for solid-state dye-sensitized solar cells. Compos. Sci. Technol. 2014, 103, 100–105. [Google Scholar] [CrossRef]
  213. Sethupathy, M.; Pandey, P.; Manisankar, P. Evaluation of photovoltaic efficiency of dye-sensitized solar cells fabricated with electrospun PVdF-PAN-Fe2O3 composite membrane. J. Appl. Polym. Sci. 2014, 131. [Google Scholar] [CrossRef]
  214. Sethupathy, M.; Ravichandran, S.; Manisankar, P. Preparation of PVdF-PAN-V2O5 hybrid composite membrane by electrospinning and fabrication of dye-sensitized solar cells. Int. J. Electrochem. Sci. 2014, 9, 3166–3180. [Google Scholar]
  215. Fan, Z.; Yan, J.; Wei, T.; Zhi, L.; Ning, G.; Li, T.; Wei, F. Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density. Adv. Funct. Mater. 2011, 21, 2366–2375. [Google Scholar] [CrossRef]
  216. Wang, G.; Zhang, L.; Zhang, J. A review of electrode materials for electrochemical supercapacitors. Chem. Soc. Rev. 2012, 41, 797–828. [Google Scholar] [CrossRef] [PubMed]
  217. Chen, S.; Zhu, J.; Wu, X.; Han, Q.; Wang, X. Graphene oxide-MnO2 nanocomposites for supercapacitors. ACS Nano 2010, 4, 2822–2830. [Google Scholar] [CrossRef] [PubMed]
  218. Huang, Y.; Liang, J.; Chen, Y. An overview of the applications of graphene-based materials in supercapacitors. Small 2012, 8, 1805–1834. [Google Scholar] [CrossRef] [PubMed]
  219. Ma, C.; Song, Y.; Shi, J.; Zhang, D.; Zhong, M.; Guo, Q.; Liu, L. Phenolic-based carbon nanofiber webs prepared by electrospinning for supercapacitors. Mater. Lett. 2012, 76, 211–214. [Google Scholar] [CrossRef]
  220. Lawrence, D.W.; Tran, C.; Mallajoysula, A.T.; Doorn, S.K.; Mohite, A.; Gupta, G.; Kalra, V. High-energy density nanofiber-based solid-state supercapacitors. J. Mater. Chem. A 2016, 4, 160–166. [Google Scholar] [CrossRef]
  221. Kim, B.H.; Yang, K.S.; Kim, Y.A.; Kim, Y.J.; An, B.; Oshida, K. Solvent-induced porosity control of carbon nanofiber webs for supercapacitor. J. Power Sources 2011, 196, 10496–10501. [Google Scholar] [CrossRef]
  222. Le, T.; Yang, Y.; Huang, Z.; Kang, F. Preparation of microporous carbon nanofibers from polyimide by using polyvinyl pyrrolidone as template and their capacitive performance. J. Power Sources 2015, 278, 683–692. [Google Scholar] [CrossRef]
  223. Ma, C.; Song, Y.; Shi, J.; Zhang, D.; Zhai, X.; Zhong, M.; Guo, Q.; Liu, L. Preparation and one-step activation of microporous carbon nanofibers for use as supercapacitor electrodes. Carbon 2013, 51, 290–300. [Google Scholar] [CrossRef]
  224. Tai, Z.; Yan, X.; Lang, J.; Xue, Q. Enhancement of capacitance performance of flexible carbon nanofiber paper by adding graphene nanosheets. J. Power Sources 2012, 199, 373–378. [Google Scholar] [CrossRef]
  225. Wang, T.; Song, D.; Zhao, H.; Chen, J.; Zhao, C.; Chen, L.; Chen, W.; Zhou, J.; Xie, E. Facilitated transport channels in carbon nanotube/carbon nanofiber hierarchical composites decorated with manganese dioxide for flexible supercapacitors. J. Power Sources 2015, 274, 709–717. [Google Scholar] [CrossRef]
  226. Zhou, Z.; Wu, X.F. Graphene-beaded carbon nanofibers for use in supercapacitor electrodes: Synthesis and electrochemical characterization. J. Power Sources 2013, 222, 410–416. [Google Scholar] [CrossRef]
  227. Tian, X.; Zhao, N.; Song, Y.; Wang, K.; Xu, D.; Li, X.; Guo, Q.; Liu, L. Synthesis of nitrogen-doped electrospun carbon nanofibers with superior performance as efficient supercapacitor electrodes in alkaline solution. Electrochim. Acta 2015, 185, 40–51. [Google Scholar] [CrossRef]
  228. Mu, J.; Chen, B.; Guo, Z.; Zhang, M.; Zhang, Z.; Zhang, P.; Shao, C.; Liu, Y. Highly dispersed Fe3O4 nanosheets on one-dimensional carbon nanofibers: Synthesis, formation mechanism, and electrochemical performance as supercapacitor electrode materials. Nanoscale 2011, 3, 5034–5040. [Google Scholar] [CrossRef]
  229. Abouali, S.; Garakani, M.A.; Zhang, B.; Xu, Z.L.; Heidari, E.K.; Huang, J.Q.; Huang, J.; Kim, J.K. Electrospun Carbon Nanofibers with in Situ Encapsulated Co3O4 Nanoparticles as Electrodes for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 13503–13511. [Google Scholar] [CrossRef] [PubMed]
  230. Ghouri, Z.K.; Barakat, N.; Alam, A.M.; Park, M.; Han, T.H.; Kim, H.Y. Facile synthesis of Fe/CeO2-doped CNFs and their capacitance behavior. Int. J. Electrochem. Sci. 2015, 10, 2064–2071. [Google Scholar]
  231. Zhi, M.; Manivannan, A.; Meng, F.; Wu, N. Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors. J. Power Sources 2012, 208, 345–353. [Google Scholar] [CrossRef]
  232. Wang, J.G.; Yang, Y.; Huang, Z.H.; Kang, F. Coaxial carbon nanofibers/MnO2 nanocomposites as freestanding electrodes for high-performance electrochemical capacitors. Electrochim. Acta 2011, 56, 9240–9247. [Google Scholar] [CrossRef]
  233. Zhao, X.; Du, Y.; Li, Y.; Zhang, Q. Encapsulation of manganese oxides nanocrystals in electrospun carbon nanofibers as free-standing electrode for supercapacitors. Ceram. Int. 2015, 41, 7402–7410. [Google Scholar] [CrossRef]
  234. Wu, Y.; Balakrishna, R.; Reddy, M.V.; Nair, A.S.; Chowdari, B.V.R.; Ramakrishna, S. Functional properties of electrospun NiO/RuO2 composite carbon nanofibers. J. Alloy. Compd. 2012, 517, 69–74. [Google Scholar] [CrossRef]
  235. Yang, K.S.; Kim, B.H. Highly conductive, porous RuO2/activated carbon nanofiber composites containing graphene for electrochemical capacitor electrodes. Electrochim. Acta 2015, 186, 337–344. [Google Scholar] [CrossRef]
  236. Kim, C.H.; Kim, B.H. Zinc oxide/activated carbon nanofiber composites for high-performance supercapacitor electrodes. J. Power Sources 2015, 274, 512–520. [Google Scholar] [CrossRef]
  237. Kim, B.H.; Kim, C.H.; Yang, K.S.; Rahy, A.; Yang, D.J. Electrospun vanadium pentoxide/carbon nanofiber composites for supercapacitor electrodes. Electrochim. Acta 2012, 83, 335–340. [Google Scholar] [CrossRef]
  238. Hyun, T.S.; Tuller, H.L.; Youn, D.Y.; Kim, H.G.; Kim, I.D. Facile synthesis and electrochemical properties of RuO2 nanofibers with ionically conducting hydrous layer. J. Mater. Chem. 2010, 20, 9172–9179. [Google Scholar] [CrossRef]
  239. Bhagwan, J.; Sahoo, A.; Yadav, K.L.; Sharma, Y. Porous, One dimensional and High Aspect Ratio Mn3O4 Nanofibers: Fabrication and Optimization for Enhanced Supercapacitive Properties. Electrochim. Acta 2015, 174, 992–1001. [Google Scholar] [CrossRef]
  240. Ren, B.; Fan, M.; Liu, Q.; Wang, J.; Song, D.; Bai, X. Hollow NiO nanofibers modified by citric acid and the performances as supercapacitor electrode. Electrochim. Acta 2013, 92, 197–204. [Google Scholar] [CrossRef]
  241. Binitha, G.; Soumya, M.S.; Madhavan, A.A.; Praveen, P.; Balakrishnan, A.; Subramanian, K.R.V.; Reddy, M.V.; Nair, S.V.; Nair, A.S.; Sivakumar, N. Electrospun α-Fe2O3 nanostructures for supercapacitor applications. J. Mater. Chem. A 2013, 1, 11698–11704. [Google Scholar] [CrossRef]
  242. Zhou, G.; Zhu, J.; Chen, Y.; Mei, L.; Duan, X.; Zhang, G.; Chen, L.; Wang, T.; Lu, B. Simple method for the preparation of highly porous ZnCo2O4 nanotubes with enhanced electrochemical property for supercapacitor. Electrochim. Acta 2014, 123, 450–455. [Google Scholar] [CrossRef]
  243. Cao, Y.; Lin, B.; Sun, Y.; Yang, H.; Zhang, X. Synthesis, structure and electrochemical properties of lanthanum manganese nanofibers doped with Sr and Cu. J. Alloy. Compd. 2015, 638, 204–213. [Google Scholar] [CrossRef]
  244. Cao, Y.; Lin, B.; Sun, Y.; Yang, H.; Zhang, X. Symmetric/Asymmetric Supercapacitor Based on the Perovskite-type Lanthanum Cobaltate Nanofibers with Sr-substitution. Electrochim. Acta 2015, 178, 398–406. [Google Scholar] [CrossRef]
  245. Cao, Y.; Lin, B.; Sun, Y.; Yang, H.; Zhang, X. Sr-doped Lanthanum Nickelate Nanofibers for High Energy Density Supercapacitors. Electrochim. Acta 2015, 174, 41–50. [Google Scholar] [CrossRef]
Figure 1. Schematic diagram of an electrospinning set-up.
Figure 1. Schematic diagram of an electrospinning set-up.
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Figure 2. Schematics of: (a) Li-ion batteries; (b) lithium-sulfur batteries; (c) lithium-oxygen batteries.
Figure 2. Schematics of: (a) Li-ion batteries; (b) lithium-sulfur batteries; (c) lithium-oxygen batteries.
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Figure 3. Model image of the triaxial nanowire with a vapor-grown carbon fiber (VGCF) core column and the two layer shells: an outer shell of amorphous carbon and an inner composite shell of LiFePO4 and amorphous carbon. Reproduced with permission from [53]. Copyright American Physical Society, 2010.
Figure 3. Model image of the triaxial nanowire with a vapor-grown carbon fiber (VGCF) core column and the two layer shells: an outer shell of amorphous carbon and an inner composite shell of LiFePO4 and amorphous carbon. Reproduced with permission from [53]. Copyright American Physical Society, 2010.
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Figure 4. Schematics of the structural design of the core-shell silicon/carbon fiber (Si/po-C@C) composite fiber: (a) structural formation and change of Si/po-C@C during heat treatment and cycling process, respectively; (b) three-dimensional (3D) sketch of the overall structure. (SEI: solid-electrolyte interphase). Reproduced with permission from [82]. Copyright Royal Society of Chemistry, 2015.
Figure 4. Schematics of the structural design of the core-shell silicon/carbon fiber (Si/po-C@C) composite fiber: (a) structural formation and change of Si/po-C@C during heat treatment and cycling process, respectively; (b) three-dimensional (3D) sketch of the overall structure. (SEI: solid-electrolyte interphase). Reproduced with permission from [82]. Copyright Royal Society of Chemistry, 2015.
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Figure 5. Photographs of the electrospun/sprayed flexible paper electrode (a) before and (b) after carbonization with 72 wt % Si; SEM images of the 3D Si/C fiber paper electrode: (ce) top view and (f) cross-section. Reproduced with permission from [83]. Copyright Wiley, 2014.
Figure 5. Photographs of the electrospun/sprayed flexible paper electrode (a) before and (b) after carbonization with 72 wt % Si; SEM images of the 3D Si/C fiber paper electrode: (ce) top view and (f) cross-section. Reproduced with permission from [83]. Copyright Wiley, 2014.
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Scheme 1. Preparation of Sn@carbon nanoparticles encapsulated in hollow carbon nanofibers. Reproduced with permission from [88]. Copyright Wiley, 2009.
Scheme 1. Preparation of Sn@carbon nanoparticles encapsulated in hollow carbon nanofibers. Reproduced with permission from [88]. Copyright Wiley, 2009.
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Scheme 2. Formation mechanism of the TiO2 nanofiber with a fiber-in-tube nanostructure from the tributyltin (TBT)-poly(vinylpyrrolidone) (PVP) composite nanofiber. Reproduced with permission from [92]. Copyright Wiley, 2015.
Scheme 2. Formation mechanism of the TiO2 nanofiber with a fiber-in-tube nanostructure from the tributyltin (TBT)-poly(vinylpyrrolidone) (PVP) composite nanofiber. Reproduced with permission from [92]. Copyright Wiley, 2015.
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Scheme 3. Schematic illustration of the typical preparation procedure for the Co3O4-based binder-free (CCTN) electrode. Reproduced with permission from [138]. Copyright Royal Society of Chemistry, 2015.
Scheme 3. Schematic illustration of the typical preparation procedure for the Co3O4-based binder-free (CCTN) electrode. Reproduced with permission from [138]. Copyright Royal Society of Chemistry, 2015.
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Figure 6. (a) TEM micrographs of microtomed sections of 5 at. % Nb-SnO2 loose tubes obtained using 8.5 w/v % SnCl2. Inset: close-up of the cross-section of a loose-tube fiber. (b) Loose tubes of niobium-doped SnO2 (8.5 w/v % SnCl2 and 5 at. % Nb) prepared using heating rates of 1, 5 and 10 °C/min during calcination. Reproduced with permission from [165]. Copyright American Chemical Society, 2013.
Figure 6. (a) TEM micrographs of microtomed sections of 5 at. % Nb-SnO2 loose tubes obtained using 8.5 w/v % SnCl2. Inset: close-up of the cross-section of a loose-tube fiber. (b) Loose tubes of niobium-doped SnO2 (8.5 w/v % SnCl2 and 5 at. % Nb) prepared using heating rates of 1, 5 and 10 °C/min during calcination. Reproduced with permission from [165]. Copyright American Chemical Society, 2013.
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Figure 7. Schematic diagram of the fabrication procedure and SEM images of the bilayer TiO2 nanofiber photoanode (BNF: bigger-diameter nanofiber; SNF: smaller-diameter nanofiber). Reproduced with permission from [187]. Copyright Wiley, 2011.
Figure 7. Schematic diagram of the fabrication procedure and SEM images of the bilayer TiO2 nanofiber photoanode (BNF: bigger-diameter nanofiber; SNF: smaller-diameter nanofiber). Reproduced with permission from [187]. Copyright Wiley, 2011.
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Figure 8. Photocurrent density-voltage (J-V) curves for the DSSC containing (a) 0.5 M 1-butyl-3-methylimidazolium iodide (BMImI)-LE and (b) 0.5 M BMImI-esPME. Reproduced with permission from [209]. Copyright Wiley, 2015.
Figure 8. Photocurrent density-voltage (J-V) curves for the DSSC containing (a) 0.5 M 1-butyl-3-methylimidazolium iodide (BMImI)-LE and (b) 0.5 M BMImI-esPME. Reproduced with permission from [209]. Copyright Wiley, 2015.
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Table 1. Electrospun cathode materials for Li-ion batteries (LIBs) and the corresponding electrochemical performance. DC: Discharge capacity.
Table 1. Electrospun cathode materials for Li-ion batteries (LIBs) and the corresponding electrochemical performance. DC: Discharge capacity.
MaterialDiameter/μmStructureDC (after Cycle Number)/mAh·g−1RateReference
LiCoO20.5–2fiber123 (20)20 mA/g[41]
LiCoO2–MgO1–2core-shell fiber163 (40)20 mA/g[42]
LiNi0.5Co0.2Mn0.3O20.3particle160 (5)20 mA/g[45]
LiNi1/3Co1/3Mn1/3O20.1–0.8nanofiber116 (30)85 mA/g[46]
Li1.2Mn0.54Ni0.13Co0.13O2/CNFsnanofiber176.7 (100)1 C[47]
Li1.2Ni0.17Co0.17Mn0.5O20.1–0.5nanofiber141–205 (20)14.2 mA/g[48]
LiFePO4/Cfiber131–145 (0.1)[51]
LiFePO4/CNT/C0.168nanofiber169 (average)0.05 C[52]
LiFePO4/CNT/Ccore-shell fiber[53]
V2O50.2–0.5nanofiber240 (25)0.1 mA/cm2[56]
V2O50.2–0.4hierarchical porous nanofiber133.9 (100)800 mA/g[57]
V2O50.1–0.2hierarchical nanowire201 (30)30 mA/g[58]
V2O50.3–0.5porous nanotube130.5 (50)0.2 C[59]
LiMn2O40.17porous network146 (1)0.1 C[60]
Li3V2(PO4)3/CNF0.3nanofiber102 (1000)20 C[61]
Li3V2(PO4)3/CNF0.18–0.43nanofiber118.9 (1000)20 C[62]
LiNi0.5Mn1.5O4<0.2nanofiber138 (1)50 mA/g[63]
LiNi0.5Mn1.5O40.05–0.25nanofiber120 (50)0.01 mA/cm[64]
LiNi0.5Mn1.5O40.05–0.1nanofiber300 (1)27 mA/g[65]
Table 2. Electrospun anode materials for LIBs and the corresponding electrochemical performance.
Table 2. Electrospun anode materials for LIBs and the corresponding electrochemical performance.
MaterialDiameter/μmStructureDC (after Cycle Number)/mAh·g−1RateReference
Carbon0.2–0.3nanofiber350100 mA/g[66]
Carbon0.3–0.4nanofiber255 (200)0.2 A/g[67]
Carbon0.1–0.2porous nanofiber1780 (40)50 mA/g[68]
Carbon0.9–1.2hollow nanofiber900.6 (1)100 mA/g[69]
Ag/C~0.3hollow nanofiber600.15 (100)50 mA/g[70]
GeOx@C1core-shell875 (400)160 mA/g[71]
Co3O4/CNF0.8–1.2core-shell nanowire795 (50)100 mA/g[73]
Mn3O4/CNF0.5–1hierarchically mesoporous760 (50)100 mA/g[74]
N/GeO2-CNFs0.075nanofiber1031 (200)100 mA/g[75]
Si/C2–5hollow fiber725 (40)0.2 A/g[78]
Si/C0.6–0.8porous nanofiber870 (100)0.1 A/g[79]
Si/Chollow fiber1045 (20)100 mA/g[80]
Si/C0.186nanofiber1215.2 (50)600 mA/g[81]
Si/C~2core-shell603 (300)0.5 A/g[82]
Si/C~0.2Fiber paper1267 (100)500 mA/g[83]
Sn/C0.1–0.18core-shell546.7 (100)40 mA/g[85]
Sn/C~0.2porous nanofiber774 (200)0.8 A/g[87]
Sn/C0.15–0.25Hollow nanofiber737 (200)0.5 C[88]
TiO2~0.119nanofiber176.7 (100)0.1 C[91]
TiO2~0.5fiber-in-tube177 (1000)200 mA/g[92]
Co3O4/TiO2~0.3hierarchical602.7 (480)200 mA/g[93]
Table 3. Electrospun separators for LIBs and the corresponding electrochemical performance. PVdF: poly(vinylidene fluoride); HFP: hexafluoropropylene; TEGDA-BA: triethylene glycol diacetate-2-propenoic acid butyl ester; PEO: polyethylene oxide; LLTO: lithium lanthanum titanate oxide.
Table 3. Electrospun separators for LIBs and the corresponding electrochemical performance. PVdF: poly(vinylidene fluoride); HFP: hexafluoropropylene; TEGDA-BA: triethylene glycol diacetate-2-propenoic acid butyl ester; PEO: polyethylene oxide; LLTO: lithium lanthanum titanate oxide.
MaterialDiameter/μmConductivity/mS·cm1 (T/°C)DC (after-1st)/mAh·g1 (Rate/C)Anodic Stability Voltage/V (vs. Li/Li+)Reference
PVdF1–1.651.0 (25)4.5[103]
PVdF-HFP11.0 (20)136–142 (0.1)4.5[104]
PVdF-HFP0.512–0.7106.16 (20)138–184 (0.2)5.0[105]
PVdF-HFP/SiO22–54.3 (25)139–170 (0.1)[106]
PVdF-HEP/SiO21–28.06 (20)153–170 (0.1)>4.5[107]
PVdF-HEP/PMMA0.200–0.3502.0 (25)133.5–145 (0.1)[108]
PVdF-HEP/PAN0.320–0.4901.0 (25)131–145 (0.1)>4.6[109]
PVdF/SiO2-PAALi0.7503.5 (25)151–156.5 (0.1)5.05[110]
PAN0.3502.14 (25)135–150 (0.1)>4.7[111]
PAN0.880–1.2601.7 (20)108–113 (0.5)[112]
PAN-PMMA0.2–1.05.1 (-)127–135 (0.1)5.2[113]
PAN/SiO20.8–1.42.8–3.6 (-)−163(0.2)4.75[114]
PAN/SiO20.100–0.30011 (-)127–139 (0.5)5.0[115]
PAN/Al2O3-TEGDA-BA3–52.35 (25)240.4 (0.1)>4.5[116]
PAN-TEGDA-BA0.1825.9 (25)127–163.6 (0.1)>5.0[117]
PAN-PEO0.250–0.3305.36 (-)134 (0.1)[118]
PAN-LLTO0.2501.95 (25)148–162 (0.2)5.0[121]
Table 4. Photovoltaic performance parameters of dye-sensitized solar cells (DSSCs) with electrospun fibers. FF: fill factor = Vmax × Jmax/Voc × Jsc.
Table 4. Photovoltaic performance parameters of dye-sensitized solar cells (DSSCs) with electrospun fibers. FF: fill factor = Vmax × Jmax/Voc × Jsc.
MaterialDiameter/nmVoc/VJsc/mA·cm2FF (%)η (%)Reference
CNF+Pt NPs2500.8312.66–13.3365.6–68.87–8[193]
CNF2500.7612.6575.5[195]
H-ACNF190/2700.7314.5626.58[196]
Meso-HACNF200/3600.73/0.7415.4/15.364/617.21/6.91[197]
CNF+Co Cr NPs0.6858.784543.27[198]
CNF+Co Ni NPs0.7411.12544.47[199]
CNF+Co Pd NPs1509.80.705362.5[200]
CNF+Cu Ni NPs0.707.67653.5[201]
CNF+Fe Ni NPs2300.7210.1654.7[202]
CNF/TiC280–3000.73/0.72/0.729.29/9.71/9.5662/64/634.2/4.5/4.3[204]
Table 5. Photovoltaic performance of the DSSCs based on electrospun fibers.
Table 5. Photovoltaic performance of the DSSCs based on electrospun fibers.
MaterialVoc/VJsc/mA·cm2FF (%)η (%)Reference
PVdF-HFP0.7512.3575.21[208]
PVdF-HFP0.78/0.76/0.775.759/6.028/5.37866.18/68.05/66.272.98//3.13/2.75[206]
BMImI-esPME0.7113.10696.42[209]
PVdF-HFP/PS0.7611.8665.75[210]
PVdF-HFP/CoS0.7314.42707.34[211]
PEO-PVdF-HFP-SiO20.58/0.60/0.5913.37/13.63/13.1860.24/59.54/59.674.68/4.85/4.66[212]
PVdF-PAN-Fe2O30.7710.4624.9[213]
PVdF-PAN-V2O50.7813.8727.75[214]

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Sun, G.; Sun, L.; Xie, H.; Liu, J. Electrospinning of Nanofibers for Energy Applications. Nanomaterials 2016, 6, 129. https://doi.org/10.3390/nano6070129

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Sun G, Sun L, Xie H, Liu J. Electrospinning of Nanofibers for Energy Applications. Nanomaterials. 2016; 6(7):129. https://doi.org/10.3390/nano6070129

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Sun, Guiru, Liqun Sun, Haiming Xie, and Jia Liu. 2016. "Electrospinning of Nanofibers for Energy Applications" Nanomaterials 6, no. 7: 129. https://doi.org/10.3390/nano6070129

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