Search Results (72)

The escalating demand for high-performance energy storage devices has driven extensive research into flexible electrode materials for supercapacitors. Integrating structured carbon nanomaterials with flexible substrates to construct binder-free electrode architectures represents a promising strategy for improving supercapacitor capacitance and rate capability. However, achieving stable, binder-free integration of structure-controlled nanostructured carbon materials with flexible substrates remains a critical challenge. In this study, we report a direct synthesis approach for one-dimensional (1D) carbon nanofibers (CNFs) on commercial flexible carbon fabric (CF) via chemical vapor deposition (CVD). The resulting CNFs exhibit two typical average diameters—approximately 25 nm and 50 nm—depending on the growth temperature, with both displaying highly graphitized structures. Electrochemical characterization of the CNFs/CF composites in 1 M H₂SO₄ electrolyte revealed typical electric double-layer capacitor (EDLC) behavior. Notably, the 25 nm-CNFs/CF electrode achieves a high specific capacitance of 87.5 F/g, significantly outperforming the 50 nm-CNFs/CF electrode, which reaches 50.2 F/g. Compared with previously reported carbon nanotube CNTs/CF electrodes, the 25 nm-CNFs/CF electrode exhibits superior capacitance and lower resistance. Full article

Activated carbons derived from coconut coir dust were synthesized via a two-step process combining carbonization and steam activation for application as electrode materials in supercapacitors. The influence of carbonization temperature (500–700 °C) on the morphological, structural, textural, and electrochemical properties of the resulting activated carbons was systematically investigated. Increasing the carbonization temperature led to a progressive collapse of the cellular structure and formation of a more compact and thermally stable carbon matrix, while the overall morphology remained largely unchanged after steam activation. The steam-activated carbon prepared from the carbonized sample at 700 °C (SA-CCD-7) exhibited the highest specific surface area (889 m² g⁻¹) and a well-developed hierarchical micro–mesoporous structure. Structural analyses confirmed the amorphous nature and an increase in structural disorder after activation, consistent with the enhanced pore development. Electrochemical measurements in 6 M KOH using a three-electrode system revealed that the SA-CCD-7 displayed a typical electric double-layer capacitor (EDLC) behavior, delivering the highest specific capacitance of 86 F g⁻¹ at 1 A g⁻¹ and retaining 81% of its initial capacitance at 20 A g⁻¹, demonstrating excellent rate capability. The symmetric coin-cell supercapacitor device assembled with SA-CCD-7 as the electrodes achieved an energy density of 0.9–1.2 Wh kg⁻¹ and a power density of 50–2500 W kg⁻¹, along with remarkable cycling stability over 10,000 cycles with negligible capacitance loss. These findings highlight steam activation of coconut coir dust as a simple, scalable, and eco-friendly approach for producing biomass-derived carbon electrodes for sustainable energy storage applications. Full article

The increasing demand for high-performance energy storage devices has stimulated interest in advanced electrolyte materials. Among them, ionic liquids ($\mathrm{I}\mathrm{L}\mathrm{s}$) stand out for their thermal stability, wide electrochemical windows, and good ionic conductivity. When doped into polymeric matrices, these ionic liquids form hybrid polymeric electrolytes that synergize the benefits of both liquid and solid electrolytes. This study explores a polymeric electrolyte based on polyethylene oxide ($\mathrm{P}\mathrm{E}\mathrm{O}$) doped with tributylmethylphosphonium iodide $\left(\mathrm{T}\mathrm{M}\mathrm{P}\mathrm{I}\right)$ and ammonium iodide ($\mathrm{N}{\mathrm{H}}_4\mathrm{I}$), focusing on its synthesis, structural and electrical properties, and performance in energy storage devices such as dye-sensitized solar cells and supercapacitors. Strategies to improve its ionic conductivity, mechanical and chemical stability, and electrode compatibility are also discussed, along with future directions in this field. Full article

This study successfully demonstrates the synthesis of foxtail millet carbon-activated (FMCA) materials using a two-step carbonization process from foxtail millet husk (FMH). The pre-carbonized biomass-derived millet husk was chemically activated with KOH at 500 °C and subsequently carbonized in an inert argon atmosphere at 800 °C in a tubular furnace. XRD analysis revealed a diffraction peak at 2θ = 23.67°, corresponding to the (002) plane, indicating the presence of graphitic structures. The Raman analysis of FMCA materials showed an intensity ratio (I_G/I_D) of 1.13, signifying enhanced graphitic ordering and structural stability. The as-prepared FMC and FMCA electrode materials demonstrate efficient charge storage electrochemical symmetric devices. Electrochemical analysis revealed the charge–discharge curves and a specific capacitance of Csp (FMC//FMC) 55.47 F/g and (FMCA//FMCA) 82.94 F/g at 0.5 A/g. Additionally, the FMCA//FMCA symmetric device exhibits superior performance with a higher capacity retention of 94.89% over 5000 cycles. The results confirm the suitability of FMCA for energy storage applications, particularly in electrochemical double-layer capacitors (EDLCs), making it a promising material for next-generation supercapacitors. Full article

Attention to electrochemical energy storage (EES) devices continues to grow as the demand increases for energy storage systems in the storage and transmission of renewable energy. The expanded market requirement for mobile electronics devices and flexible electronic devices also calls for efficient energy suppliers. EES devices applying pseudocapacitive materials and generated pseudocapacitive storage are gaining increasing focus because they are capable of overcoming the capacity limitations of electrical double-layer capacitors (EDLCs) and offsetting the rate performance of batteries. The pseudocapacitive storage mechanism generally occurs on the surface or near the surface of the electrode materials, which could avoid the slow ion diffusion process. Developing materials with beneficial nanostructures and optimized phases supporting pseudocapacitive storage would efficiently improve the energy density and charging rate for EES devices, such as batteries and flexible supercapacitors. This review offers a detailed assessment of pseudocapacitance, including classification, working mechanisms, analysis methods, promotion routes and advanced applications. The future challenges facing the effective utilization of pseudocapacitive mechanisms in upcoming energy storage devices are also discussed. Full article

Carbon nanomaterials-based electric double-layer capacitors (EDLCs) are reliable and appealing energy-storage systems offering high power density and long cycling stability. However, these energy storage devices are plagued with critical shortcomings, such as low specific capacitance, inefficient physical/chemical activation process, and self-discharge of electrode materials, hindering their future application. In this work, we use a self-activation process, an environmentally benign and low-cost process, to produce high-performance activated carbon (AC). Novel activated carbon from pecan shells (PS) was successfully synthesized through a single-step self-activation process, which combines the carbonization and activation processes. The as-synthesized pecan shell-derived activated carbon (PSAC) provides a high-porosity, low-resistance, and ordered pore structure with a specific pore volume of 0.744 cm³/g and BET surface area of 1554 m²/g. The supercapacitors fabricated from PSAC demonstrate a specific capacitance of 269 F/g at 2 A/g, excellent cycling stability over 15,000 cycles, and energy and power density of 37.4 Wh/kg and of 2.1 kW/kg, respectively. It is believed that the high-efficiency PSAC synthesized from the novel self-activation method could provide a practical route to environmentally friendly and easily scalable supercapacitors. Full article

Among electrochemical energy storage (EES) technologies, rechargeable batteries (RBs) and supercapacitors (SCs) are the two most desired candidates for powering a range of electrical and electronic devices. The RB operates on Faradaic processes, whereas the underlying mechanisms of SCs vary, as non-Faradaic in electrical double-layer capacitors (EDLCs), Faradaic at the surface of the electrodes in pseudo-capacitors (PCs), and a combination of both non-Faradaic and Faradaic in hybrid supercapacitors (HSCs). EDLCs offer high power density but low energy density. HSCs take advantage of the Faradaic process without compromising their capacitive nature. Unlike batteries, supercapacitors provide high power density and numerous charge–discharge cycles; however, their energy density lags that of batteries. Supercapatteries, a generic term that refers to hybrid EES devices that combine the merits of EDLCs and RBs, have emerged, bridging the gap between SCs and RBs. There are numerous articles and reviews on EES, and many of those articles have emphasized various aspects of HSCs and supercapatteries. However, there are no recent reviews that dealt with supercapatteries in general. Here, we review recently published critically selected articles on supercapatteries. The review discusses different EES devices and how supercapatteries are different from others. Also discussed are properties, design strategies, and future perspectives on supercapatteries. Full article

The investigated starch biopolymer membrane was found to be a sustainable alternative to currently reported and used separators due to its properties, which were evaluated using physicochemical characterization. The molecular dynamics of the biomembrane were analyzed using low-field nuclear magnetic resonance (LF NMR) as well as Raman and infrared spectroscopy, which proved that the chemical composition of the obtained membrane did not degrade during microwave-assisted polymerization. Easily and cheaply prepared through microwave-assisted polymerization, the starch membrane was successfully used as a biodegradable membrane separating the positive and negative electrodes in electric double-layer capacitors (EDLCs). The obtained results for the electrochemical characterization via cyclic voltammetry (CV), galvanostatic charge with potential limitation (GCPL), and electrochemical impedance spectroscopy (EIS) show a capacitance of 30 F g⁻¹ and a resistance of 2 Ohms; moreover, the longevity of the EDLC during electrochemical floating exceeded more than 200 h or a cyclic ability of 50,000 cycles. Furthermore, due to the flexibility of the membrane, it can be easily used in novel, flexible energy storage systems. This proves that this novel biomembrane can be a significant step toward ecologically friendly energy storage devices and could be considered a cheaper alternative to currently used materials, which cannot easily biodegrade over time in comparison to biopolymers. Full article

Durian shell waste was used to fabricate activated carbon (AC) using a hydrothermal process and three-dimensional (3-D) ball milling. Reduced graphene oxide (rGO) was composited with activated durian shell carbon (DC) to enhance the electrochemical properties for fabricating a supercapacitor (SC) device. Scanning electron microscopic (SEM) examination of the AC from hydrothermally processed durian shell carbon (AC–HDC) and AC–HDC that was 3D ball milled for 15 min (rGO/AC–HDC–3D15M) showed compacted and uniformly distributed particles with good porosity. The rGO/AC–HDC–3D15M sample exhibited high specific surface area (SSA) using the Brunauer–Emmett–Teller (BET) methodology, 2311 m²/g, and an average pore size of 1.88 nm. Electrochemical results showed that the rGO/AC–HDC–3D15M sample had the highest specific capacitance (Cs) of 545.78 F/g, power density (Pd) of 260.834 W/kg and energy density (Ed) of 60.834 Wh/kg. A coin cell SC device using an rGO/AC–HDC3D15M electrode with a 3M KOH electrolyte exhibited a high Cs of 65.585 F/g with a high energy density of 5.123 W h/kg and power density of 47.286 W/kg. Thus, the novelty of this manuscript is that (1) the structure of the rGO/AC–HDC–3D15M composite could promote fast ionic and electronic migration during charging and discharging and (2) a rGO/AC–HDC–3D15M composite, which showed electric double-layer capacitor (EDLC) could produce a positive synergistic effect for efficient electrochemical reactions. Moreover, the high surface area of the rGO/AC–HDC–3D15M composite may mitigate the volume expansion of electrodes during cycling. Thus, this work shows that an rGO/AC–HDC–3D15M composite prepared using a hydrothermal process with 3-D ball milling can show enhanced electrochemical performance for the fabrication of an EDLC supercapacitor device. Full article

The urgent need for efficient energy storage devices (supercapacitors and batteries) has attracted ample interest from scientists and researchers in developing materials with excellent electrochemical properties. Electrode material based on carbon, transition metal oxides, and conducting polymers (CPs) has been used. Among these materials, carbon has gained wide attention in Electrochemical double-layer capacitors (EDLC) due to its variable morphology of pores and structural properties as well as its remarkable electrical and mechanical properties. In this context, the present review article summarizes the history of supercapacitors and the basic function of these devices, the type of carbon electrode materials, and the different strategies to improve the performance of these devices. In addition, we present different approaches to studying the charging mechanism of these devices through different electrochemical techniques existing in the literature, since a deeper understanding of the interfacial charge storage mechanisms is also crucial in the elaboration and performance of the electrode material. We make a comparison of the different techniques and present their advantages and challenges. Taking these advances into account, we consider that the coupling between two methods/techniques provides a better understanding of the charge storage mechanisms in energy storage devices. Full article

The presented work discusses in detail the preparation of a cheap and environmentally friendly biopolymer membrane from isinglass and its physicochemical characterisation. One of the possible uses of the obtained membrane can be as a separator between electrodes in novel green electrochemical devices as in, for example, electric double-layer capacitors (EDLCs). The functionality of the mentioned membrane was investigated and demonstrated by classical electrochemical techniques such as cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), and electrochemical impedance spectroscopy (EIS). The obtained values of capacitance (approximately 30 F g⁻¹) and resistance (approximately. 3 Ohms), as well as the longevity of the EDLC during electrochemical floating at a voltage of 1.6 V (more than 200 h), show that the proposed biopolymer membrane could be an interesting alternative among the more environmentally friendly energy storage devices, while additionally it could be more economically justified. Full article

An ionic liquid (IL) 1-ethyl, 2-methyl imidazolium thiocyanate incorporated biopolymer system is reported in this communication for applications in dual energy devices, i.e., electric double-layer capacitors (EDLCs) and dye-sensitized solar cells (DSSCs). The solution caste method has been used to synthesize ionic-liquid-incorporated biopolymer electrolyte films. The IL mixed biopolymer electrolytes achieve high ionic conductivity up to the order of 10⁻³ S/cm with good thermal stability above 250 °C. Electrical, structural, and optical studies of these IL-doped biopolymer electrolyte films are presented in detail. The performance of EDLCs was evaluated using low-frequency electrochemical impedance spectroscopy, cyclic voltammetry, and constant current charge–discharge, while that of DSSCs was assessed using J–V characteristics. The EDLC cells exhibited a high specific capacitance of 200 F/gram, while DSSCs delivered 1.53% efficiency under sun conditions. Full article

Electrochemical capacitors operating in an aqueous electrolyte solution have become ever-more popular in recent years, mainly because they are cheap and ecofriendly. Additionally, aqueous electrolytes have a higher ionic conductivity than organic electrolytes and ionic liquids. These materials can exist in the form of a liquid or a solid (hydrogel). The latter form is a very promising alternative to liquid electrolytes because it is solid, which prevents electrolyte leakage. In our work, hydrogel polymer electrolytes (HPEs) were obtained via photopolymerization of a mixture of acrylic oligomer Exothane 108 with methacrylic acid (MAA) in ethanol, which was later replaced by electrolytes (1 M Na₂SO₄). Through the conducted research, the effects of the monomers ratio and the organic solvent concentration (ethanol) on the mechanical properties (tensile test), electrolyte sorption, and ionic conductivity were examined. Finally, hydrogel polymer electrolytes with high ionic conductivity (σ = 26.5 mS∙cm⁻¹) and sufficient mechanical stability (σ_max = 0.25 MPa, ε_max = 20%) were tested using an AC/AC electrochemical double layer capacitor (EDLC). The electrochemical properties of the devices were investigated via cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. The obtained results show the application potential of the obtained HPE in EDLC. Full article

Herein, unique three-dimensional (3D) hierarchically structured carbon nanofiber (CNF)/metal oxide/conducting polymer composite materials were successfully synthesized by combinations of various experimental methods. Firstly, base CNFs were synthesized by carbonization of electrospun PAN/PVP fibers to attain electric double-layer capacitor (EDLC) characteristics. To further enhance the capacitance, tin oxide (SnO₂) and iron oxide (Fe₂O₃) were coated onto the CNFs via facile hydrothermal treatment. Finally, polypyrrole (PPy) was introduced as the outermost layer by a dispersion polymerization method under static condition to obtain 3D-structured CNF/SnO₂/PPy and CNF/Fe₂O₃/PPy materials. With each synthesis step, the morphology and dimension of materials were transformed, which also added the benign characteristic for supercapacitor application. For the practical application, as-synthesized CNF/SnO₂/PPy and CNF/Fe₂O₃/PPy were applied as active materials for supercapacitor electrodes, and superb specific capacitances of 508.1 and 426.8 F g⁻¹ (at 1 A g⁻¹) were obtained (three-electrode system). Furthermore, an asymmetric supercapacitor (ASC) device was assembled using CNF/SnO₂/PPy as the positive electrode and CNF/Fe₂O₃/PPy as the negative electrode. The resulting CNF/SnO₂/PPy//CNF/Fe₂O₃/PPy device exhibited excellent specific capacitance of 101.2 F g⁻¹ (at 1 A g⁻¹). Notably, the ASC device displayed a long-term cyclability (at 2000 cycles) with a retention rate of 81.1%, compared to a CNF/SnO₂//CNF/Fe₂O₃ device of 70.3% without an outermost PPy layer. By introducing the outermost PPy layer, metal oxide detachment from CNFs were prevented to facilitate long-term cyclability of electrodes. Accordingly, this study provides an effective method for manufacturing a high-performance and stable supercapacitor by utilizing unique 3D hierarchical materials, comprised of CNF, metal oxide, and conducting polymer. Full article

The search for biocompatible and renewable materials for the next generation of energy devices has led to increasing interest in using biopolymers as a matrix component for the development of electric double-layer capacitors (EDLCs). However, using biopolymers as host matrices presents limitations in performance and scalability. At the same time, ionic liquids (ILs) have shown exceptional properties as non-aqueous electrolytes. This review intends to highlight the progress in integrating ILs and biopolymers for EDLC. While ILs have been used as solvents to process biopolymers and electrolyte materials, biopolymers have been utilized to provide novel chemistries of electrolyte materials via one of the following scenarios: (1) acting as host polymeric matrices for IL-support, (2) performing as polymeric fillers, and (3) serving as backbone polymer substrates for synthetic polymer grafting. Each of these scenarios is discussed in detail and supported with several examples. The use of biopolymers as electrode materials is another topic covered in this review, where biopolymers are used as a source of carbon or as a flexible support for conductive materials. This review also highlights current challenges in materials development, including improvements in robustness and conductivity, and proper dispersion and compatibility of biopolymeric and synthetic polymeric matrices for proper interface bonding. Full article