Search Results (21)

Flexible supercapacitors have emerged as pivotal energy storage components in wearable smart electronic systems, owing to their exceptional electrochemical performance. However, the widespread application of flexible supercapacitors in smart electronic devices is significantly hindered by the developmental bottleneck of high-performance anode materials. In this study, a novel electrode composed of surface-modified Fe₂O₃ nanoneedles uniformly coated with a polypyrrole (PPy) film and anchored on Co-MOF-derived N-C nanoflake arrays (PPy/Fe₂O₃/N-C) is designed. This composite electrode, grown in situ on carbon cloth (CC), demonstrated outstanding specific capacity, rate performance, and mechanical flexibility, attributed to its unique hierarchical 3D arrayed structure and the protective PPy layer. The fabricated PPy/Fe₂O₃/N-C@CC (P-FONC) composite electrode exhibited an excellent specific capacitance of 356.6 mF cm⁻² (143 F g⁻¹) at a current density of 2 mA cm⁻². The current density increased to 20 mA cm⁻², and the composite electrode material preserved a specific capacitance of 278 mF cm⁻² (112 F g⁻¹). Furthermore, the assembled quasi-solid-state Mn/Fe asymmetric supercapacitor, configured with P-FONC as the negative electrode and MnO₂/N-C@CC as the positive electrode, demonstrated robust chemical stability and notable mechanical flexibility. This study sheds fresh light on the creation of three-dimensional composite electrode materials for highly efficient, flexible energy storage systems. Full article

A NiCo₂S₄/N-CDs/RGO ternary composite hydrogel was prepared via a one-step hydrothermal method, utilizing lignin-based nitrogen-doped carbon dots as a bridge connecting NiCo₂S₄ and graphene. The specific capacitance of NiCo₂S₄/N-CDs/RGO significantly outperforms that of the GH and NiCo₂S₄/RGO electrodes, achieving 1050 F g⁻¹. The 3D mesh porous hydrogel structure mitigates NiCo₂S₄ nanoparticle aggregation, providing a larger specific surface area for enhanced charge storage. The abundant functional groups of N-CDs interact with Ni (II) and Co (III) cations, favoring NiCo₂S₄ particle synthesis. Additionally, an assembled solid-state asymmetric supercapacitor employing NiCo₂S₄/N-CDs/RGO as the positive electrode exhibited excellent energy density (68.4 Wh kg⁻¹) and cycle stability (82% capacitance retention after 10,000 constant current charge–discharge cycles). Full article

Morphological control of metal-organic frameworks (MOFs) at the micro/nanoscopic scale is critical for optimizing the electrochemical properties of them and their derivatives. In this study, manganese organic phosphate (Mn-MOP) with three distinct two-dimensional (2D) morphologies was synthesized by varying the molar ratio of Mn²⁺ to phenyl phosphonic acid, and one of the morphologies is a unique palm leaf shape. In addition, a series of 2D Mn-MOP derivatives were obtained by calcination in air at different temperatures. Electrochemical studies showed that 2D Mn-MOP derivative calcined at 550 °C and exhibited a superior specific capacitance of 230.9 F g⁻¹ at 0.5 A g⁻¹ in 3 M KOH electrolyte. The aqueous asymmetric supercapacitor and the constructed flexible solid-state device demonstrated excellent rate performance. This performance reveals the promising application of 2D Mn-MOP materials for energy storage. Full article

This study reports the facile synthesis of rationally designed composite materials consisting of nitrogen-doped graphene quantum dots (N-GQDs) and MnCO₃/ZnMn₂O₄ (N/MC/ZM) on Ni foam using a simple hydrothermal method to produce high-performance supercapacitor applications. The N/MC/ZM composite was uniformly synthesized on a Ni foam surface with the hierarchical structure of microparticles and nanosheets, and the uniform deposition of N-GQDs on a MC/ZM surface was observed. The incorporation of N-GQDs with MC/ZM provides good conductivity, charge transfer, and electrolyte diffusion for a better electrochemical performance. The N/MC/ZM composite electrode delivered a high specific capacitance of 960.6 F·g⁻¹ at 1 A·g⁻¹, low internal resistance, and remarkable cycling stability over 10,000 charge–discharge cycles. Additionally, an all-flexible solid-state asymmetric supercapacitor (ASC) device was fabricated using the N/MC/ZM composite electrode. The fabricated ASC device produced a maximum energy density of 58.4 Wh·kg⁻¹ at a power density of 800 W·kg⁻¹ and showed a stable capacitive performance while being bent, with good mechanical stability. These results provide a promising and effective strategy for developing supercapacitor electrodes with a high areal capacitance and high energy density. Full article

Micro/nano-heterostructure with subtle structural design is an effective strategy to reduce the self-aggregation of 2D structure and maintain a large specific surface area to achieve high-performance supercapacitors. Herein, we report a rationally designed micro/nano-heterostructure of complex ternary transition metal oxides (TMOs) by a two-step hydrothermal method. Microflake-assembled island-like CuCo₂O₄ frameworks and secondary inserted units of NiMoO₄ nanosheets endow CuCo₂O₄/NiMoO₄ composites with desired micro/nanostructure features. Three-dimensional architectures constructed from CuCo₂O₄ microflakes offer a robust skeleton to endure structural change during cycling and provide efficient and rapid pathways for ion and electron transport. Two-dimensional NiMoO₄ nanosheets possess numerous active sites and multi-access ion paths. Benefiting from above-mentioned advantages, the CuCo₂O₄/NiMoO₄ heterostructures exhibit superior pseudocapacitive performance with a high specific capacitance of 2350 F/g at 1 A/g as well as an excellent cycling stability of 91.5% over 5000 cycles. A solid-state asymmetric supercapacitor based on the CuCo₂O₄/NiMoO₄ electrode as a positive electrode and activated carbon as a negative electrode achieves a high energy density of 51.7 Wh/kg at a power density of 853.7 W/kg. These results indicate that the hybrid micro/nanostructured TMOs will be promising for high-performance supercapacitors. Full article

MnO₂/nitrogen-containing graphene (x-NGM) composites with varying contents of Mn were used as the electrode materials for flexible asymmetric solid-state supercapacitors. The MnO₂ was a two-phase mixture of γ- and α-MnO₂. The combination of nitrogen-containing graphene and MnO₂ improved reversible Faraday reactions and charge transfer. However, excessive MnO₂ reduced conductivity, hindering ion diffusion and charge transfer. Overloading the electrode with active materials also negatively affected conductivity. Both the mass loading and MnO₂ content were crucial to electrochemical performance. x-NGM composites served as cathode materials, while graphene acted as the anode material. Operating by two charge storage mechanisms enabled a synergistic effect, resulting in better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 exhibited the highest conductivity, efficient charge transfer, and superior capacitive characteristics. It showed a superior specific capacitance of 579 F·g⁻¹, leading to high energy density and power density. Flexible solid-state supercapacitors using x-NGM composites demonstrated good cycle stability, with a high capacitance retention rate of 86.7% after 2000 bending cycles. Full article

Converting biowaste into carbon-based supercapacitor materials provides a new solution for high-performance and environmentally friendly energy storage applications. Herein, the hierarchical PAC/NiCo₂S₄ composite structure was fabricated through the combination of activation and sulfuration treatments. The PAC/NiCo₂S₄ electrode garnered advantages from its hierarchical structure and hollow architecture, resulting in a notable specific capacitance (1217.2 F g⁻¹ at 1.25 A g⁻¹) and superior cycling stability. Moreover, a novel all-solid-state asymmetric supercapacitor (ASC) was successfully constructed, utilizing PAC/NiCo₂S₄ as the cathode and PAC as the anode. The resultant device exhibited exceptionally high energy (49.7 Wh kg⁻¹) and power density (4785.5 W kg⁻¹), indicating the potential of this biomass-derived, hierarchical PAC/NiCo₂S₄ composite structure for employment in high-performance supercapacitors. Full article

A metal–organic framework (MOF) is a highly porous material with abundant redox capacitive sites for intercalation/de-intercalation of charges and, hence, is considered promising for electrode materials in supercapacitors. In addition, dopants can introduce defects and alter the electronic structure of the MOF, which can affect its surface reactivity and electrochemical properties. Herein, we report a copper-doped iron-based MOF (Cu@Fe-MOF/NF) thin film obtained via a simple drop-cast route on a 3D-nickel foam (NF) substrate for the supercapacitor application. The as-deposited Cu@Fe-MOF/NF electrodes exhibit a unique micro-sized bipyramidal structure composited with nanoparticles, revealing a high specific capacitance of 420.54 F g⁻¹ at 3 A g⁻¹ which is twice compared to the nano-cuboidal Fe-MOF/NF (210 F g⁻¹). Furthermore, the asymmetric solid-state (ASSSC) supercapacitor device, derived from the assembly of Cu@Fe-MOF/NFǁrGO/NF electrodes, demonstrates superior performance in terms of energy density (44.20 Wh.kg⁻¹) and electrochemical charge–discharge cycling durability with 88% capacitance retention after 5000 cycles. This work, thus, demonstrates a high potentiality of the Cu@Fe-MOF/NF film electrodes in electrochemical energy-storing devices. Full article

In this study, poly(m-aminophenol) (PmAP) has been investigated as a multi-functional conductive supercapacitor binder to replace the conventional non-conductive binder, namely, poly(vinylene difluoride) (PVDF). The kye benefits of using PmAP are that it is easily soluble in common organic solvent and has good film-forming properties, and also its chemical functionalities can be involved in pseudocapacitive reactions to boost the capacitance performance of the electrode. A new ternary nanocomposite film based on vanadium pentoxide (V₂O₅), amino-functionalized graphene (amino-FG) and PmAP was fabricated via hydrothermal growth of V₂O₅ nanoparticles on graphene surfaces and then blending with PmAP/DMSO and solution casting. The electrochemical performances of V₂O₅/amino-FG/PmAP nanocomposite were evaluated in two different electrolytes, such as KCl and Li₂SO₄, and compared with those of V₂O₅/amino-FG nanocomposite with PVDF binder. The cyclic voltametric (CV) results of the V₂O₅/amino-FG/PmAP nanocomposite exhibited strong pseudocapacitive responses from the V₂O₅ and PmAP phases, while the faradaic redox reactions on the V₂O₅/amino-FG/PVDF electrode were suppressed by the inferior conductivity of the PVDF. The V₂O₅/amino-FG/PmAP electrode delivered a 5-fold greater specific capacitance than the V₂O₅/amino-FG/PVDF electrode. Solid-state asymmetric supercapacitors (ASCs) were assembled with V₂O₅/amino-FG/PmAP film as a positive electrode, and their electrochemical properties were examined in both KCl and Li₂SO₄ electrolytes. Although the KCl electrolyte-based ASC has greater specific capacitance, the Li₂SO₄ electrolyte-based ASC delivers a higher energy density of 51.6 Wh/kg and superior cycling stability. Full article

In this study, a flexible all-solid-state asymmetric supercapacitor (FASC) device has been successfully fabricated via full recycling of heated tobacco waste (HTW). Tobacco leaves and cellulose acetate tubes have been successfully carbonized (HTW-C) and mixed with metal oxides (MnO₂ and Fe₃O₄) to obtain highly active materials for supercapacitors. Moreover, poly(lactic acid) (PLA) filters have been successfully dissolved in an organic solvent and mixed with the as-prepared active materials using a simple paste mixing method. In addition, flexible MnO₂- and Fe₃O₄-mixed HTW-C/PLA electrodes (C-MnO₂/PLA and C-Fe₃O₄/PLA) have been successfully fabricated using the drop-casting method. The as-synthesized flexible C-MnO₂/PLA and C-Fe₃O₄/PLA electrodes have exhibited excellent electrical conductivity of 378 and 660 μS cm⁻¹, and high specific capacitance of 34.8 and 47.9 mF cm⁻² at 1 mA cm⁻², respectively. A practical FASC device (C-MnO₂/PLA//C-Fe₃O₄/PLA) has been assembled by employing the C-MnO₂/PLA as the positive electrode and C-Fe₃O₄/PLA as the negative electrode. The as-prepared FASC device showed a remarkable capacitance of 5.80 mF cm⁻² at 1 mA cm⁻². Additionally, the FASC device manifests stable electrochemical performance under harsh bending conditions, verifying the superb flexibility and sustainability of the device. To the best of our knowledge, this is the first study to report complete recycling of heated tobacco waste to prepare the practical FASC devices. With excellent electrochemical performance, the experiments described in this study successfully demonstrate the possibility of recycling new types of biomass in the future. Full article

In this study, an asymmetric supercapacitor (ASSC) device is assembled by the deposition and annealing of silver-doped mixed metal oxides on reduced graphene oxide (rGO)/Ni foam and activated carbon (AC) on Ni foam as positive and negative electrodes, respectively. The best performing Ag:MnCoNiO active material is synthesized on rGO/Ni foam using chronopotentiometry combined with heat treatment. The XRD study clearly confirms the crystalline nature of the electrode with MnCo₂O₄ and MnNi₂O₄ phases. FT-IR and XPS studies revealed the formation of Ag:MnCoNiO/rGO on Ni foam. SEM images show a thin-film layer of fabricated material on the surface of rGO/Ni foam. The supercapacitor properties were tested in two- and three-electrode configurations, with cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) experiments in a 6 M KOH aqueous electrolyte. In the three-electrode configuration, reversible faradic reactions can be observed in a potential range of 0.0 and +0.6 V vs. Hg/HgSO₄. In the two-electrode device configuration, the system exhibits a maximum energy density of 45.5 Wh kg⁻¹ and provides a maximum power density of 4.5 kW kg⁻¹. The results showed that the doping of Ag in a MnCoNiO electrode shows promising properties, achieved by a very simple fabrication process. The results showcase the synergistic effects achieved by mixed multiple-component metal oxides, leading to improved supercapacitive properties. Full article

Among energy storage devices, supercapacitors have received considerable attention in recent years owing to their high-power density and extended cycle life. Researchers are currently making efforts to improve energy density using different asymmetric cell configurations, which may provide a wider potential window. Many studies have been conducted on positive electrodes for asymmetric supercapacitor devices; however, studies on negative electrodes have been limited. In this study, iron oxides with different morphologies were synthesized at various deposition temperatures using a simple chemical bath deposition method. A nanosphere-like morphology was obtained for α-Fe₂O₃. The obtained specific capacitance (C_s) of α-Fe₂O₃ was 2021 F/g at a current density of 4 A/g. The negative electrode showed an excellent capacitance retention of 96% over 5000 CV cycles. The fabricated asymmetric solid-state supercapacitor device based on α-Fe₂O₃-NF//Co₃O₄-NF exhibited a C_s of 155 F/g and an energy density of 21 Wh/kg at 4 A/g. Full article

To overcome the issues related to supercapacitor (SC) electrodes, such as high cost, low specific capacitance (C_s), low energy density (ED), requirements for expensive binder, etc., binderless electrodes are highly desirable. Here, a new ternary nanohybrid is presented as a binder-free SC electrode based on Ni₃S₂, CoMoS₄, and MnO₂. A facile two-step hydrothermal route, followed by a short thermal annealing process, is developed to grow amorphous polyhedral structured CoMoS₄ and further wrap MnO₂ nanowires on Ni foam. This rationally designed binder-free electrode exhibited the highest C_s of 2021 F g⁻¹ (specific capacity of 883.8 C g⁻¹ or 245.5 mAh g⁻¹) at a current density of 1 A g⁻¹ in 1 M KOH electrolyte with a highly porous surface morphology. This electrode material exhibited excellent cycling stability (90% capacitance retention after 4000 cycles) due to the synergistic contribution of individual components and advanced surface properties. Furthermore, an aqueous binder-free asymmetric SC based on this ternary composite exhibited an ED of 20.7 Wh kg⁻¹, whereas a solid-state asymmetric SC achieved an ED of 13.8 Wh kg⁻¹. This nanohybrid can be considered a promising binder-free electrode for both aqueous and solid-state asymmetric SCs with these remarkable electrochemical properties. Full article

To reach high energy density and excellent cycle stability, an asymmetric supercapacitor device combining a high-power electric double-layer capacitor (EDLC) anode and high energy density battery-type cathode has been designed and fabricated. A binder-free strategy was used to prepare cathode by coating graphene (G) on Ni foam (Ni), then electrodepositing MnO₂, followed by calcination process. The potentiodynamic (PD) electrodeposition cycles of MnO₂ onto graphene significantly impact the electrochemical properties. Benefiting from the hierarchical structure and binder-free process of the designed 75 C/G/Ni hybrid cathode, potentiostatic (PS) electrodeposition followed by PD electrodeposition for 75 cycles demonstrates a high specific capacitance of 691 F g⁻¹ at 2 A g⁻¹. The enhanced capacitive performance can be attributed to the synergistic effect between MnO₂ nanosheets and graphene, in which graphene can serve as ideal support matrix and conductive channels. Furthermore, an asymmetric supercapacitor was fabricated with 75 C/G/Ni and (G + AC)/Ni as the cathode and anode, respectively, and a carboxymethyl cellulose–potassium hydroxide (CMC-KOH) gel electrolyte. The 75 C/G/Ni//(G + AC)/Ni asymmetric supercapacitor (ASC) exhibits a maximum energy density of 43 kW kg⁻¹ at a power density of 302 W kg⁻¹ with a potential window of 1.6 V and maintains good cycling stability of 88% capacitance retention at 2 A g⁻¹ (over 5000 cycles). Four solid-state asymmetric supercapacitors stack connected in series display an effective 5.0 V working potential to increase the voltage and output energy as a device. The device was charged using a 18,650 Li battery with a voltage of +3.8 V for 30 s and discharged six white LEDs for 20 min. The facile fabrication and remarkable capacitive performance of the MnO₂/G/Ni hybrid make it a promising electrode candidate in electrochemical energy conversion/storage devices. Full article

Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m² g⁻¹) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g⁻¹ at 0.5 A g⁻¹), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO₂/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g⁻¹ at 0.2 A g⁻¹ under a wide potential operation window of 0–1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg⁻¹ at a power density of 180 W kg⁻¹ and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future. Full article