Binder-free Supercapacitor Electrode Research Articles

Hollow 1D carbon tube core anchored in Co3O4@SnS2 multiple shells for constructing binder-free electrodes of flexible supercapacitors

The design of the core@multi-shell metal sulfide hollow tube is of great importance for various supercapacitor electrodes. Herein, a hollow carbon tube (HCT) core@multi-shell with rich pores is developed for constructing the binder-free flexible electrodes (HCT-x@Co3O4@SnS2). The inner core–shell is derived from the zeolitic imidazole framework (ZIF)-8@ZIF-67 porous carbon tube and is engineered with vertically aligned SnS2 nanosheets. The unique inner core–shell and the outer-shell SnS2 contribute to the excellent characteristics, including abundant pores and channels for the rapid ion transport and storage, high specific surface area, improved electrical conductivity, and additional electroactive sites for the faradaic reaction. Thanks to the synergies between the unique 1D porous hollow structure and the different components, the as-fabricated HCT-2@Co3O4@SnS2 electrode exhibits a high specific capacitance of 439 F/g at 1 A/g. Moreover, the assembled flexible supercapacitor also demonstrates a remarkable energy density of 40.22 Wh kg−1, the corresponding power densities of 750.22 W kg−1, and long cycle life. In addition, no structural deformation and capacitance loss are observed in the bended devices. The developed approach provides a facile structure design route for the flexible binder-free electrode preparation of flexible energy storage applications.

Direct Growth of Binder-Free CNTs on a Nickel Foam Substrate for Highly Efficient Symmetric Supercapacitors.

In the modern civilized world, energy scarcity and associated environmental pollution are the center of focus in the search for reliable energy storage and harvesting devices. The need to develop cheaper and more competent binder-free electrodes for high-performance supercapacitors has attracted considerable research attention. In this study, two different procedures are followed to enhance the growth of carbon nanotubes (CNT-E and CNT-NF) directly coated on a Ni-foam substrate by a well-functioning chemical vapor deposition (CVD) method. Thus, directly grown optimized CNT electrodes are used as electrodes for electrochemical devices. Furthermore, solid-state symmetric supercapacitors are fabricated using CNT-NF//CNT-NF, and fruitful results are obtained with maximum specific capacitance (250.51 F/g), energy density (68.19 Wh/kg), and power density (2799.77 W/kg) at 1 A/g current density. The device exhibited good cyclic stability, with 92.42% capacitive retention and 99.68% Coulombic efficiency at 10 000 cycles, indicating the suitability of the electrodes for practical applications. This study emphasizes the importance of studying the direct growth of binder-free CNT electrodes to understand the actual behavior of electrodes and the proper storage mechanism.

In situ morphological evolution of Ni3S2/MoS2 grow on Ni foam as binder-free electrode for hybrid supercapacitors

In situ morphological evolution of Ni3S2/MoS2 grow on Ni foam as binder-free electrode for hybrid supercapacitors

Construction of thickness-controllable bimetallic sulfides/reduced graphene oxide as a binder-free positive electrode for hybrid supercapacitors.

Devices for electrochemical energy storage with exceptional capacitance and rate performance, outstanding energy density, simple fabrication, long-term stability, and remarkable reversibility have always been in high demand. Herein, a high-performance binder-free electrode (3D NiCuS/rGO) was fabricated as a supercapacitor by a simple electrodeposition process on a Ni foam (NF) surface. The thickness of the deposited materials on the NF surface was adjusted by applying a low cycle number of cyclic voltammetry (5 cycles) which produced a thin layer and thus enabled the easier penetration of electrolytes to promote electron and charge transfer. The NiCuS was anchored by graphene layers producing nicely integrated materials leading to a higher electroconductivity and a larger surface area electrode. The as-fabricated electrode displayed a high specific capacitance (2211.029 F g-1 at 5 mV s-1). The NiCuS/rGO/NF//active carbon device can achieve a stable voltage window of 1.5 V with a highly specific capacitance of 84.3 F g-1 at a current density of 1 A g-1. At a power density of 749 W kg-1, a satisfactory energy density of 26.3 W h kg-1 was achieved, with outstanding coulombic efficiency of 100% and an admirable life span of 96.2% after 10 000 GCD cycles suggesting the significant potential of the as-prepared materials for practical supercapacitors.

Binder free supercapacitor electrodes by hydrothermal deposition of thermally reduced graphite oxide on Nickel foam: Characterization and electrochemical performance

Thermally reduced graphite oxide (TRGO) samples were hydrothermally deposited (120 °C, 12 h) on nickel foam current collector without any binder. TRGO of different reduction levels were synthesized through the thermal reduction of graphite oxide at 100 and 200 °C. The binding affinity of the oxygen functional groups enabled the binder free deposition. We could achieve specific capacitance Csp of 524F/g (at 1 A/g) for Ni/TRGO200 and 136F/g (at 1 A/g) for Ni/TRGO100 electrodes. These values are significantly larger than those till reported for binder free reduced graphite oxide electrodes. The capacitive retention of Ni/TRGO100 is 82.5 % and for Ni/TRGO200 it is 81.5 % over 1000 charge discharge cycles. Coulombic efficiency reaches 99 % and 100 % respectively for Ni/TRGO100 and Ni/TRGO200. Detailed analysis of the electrochemical storage mechanism is also reported.

In Situ Growth of MnO2 Nanosheets on a Graphite Flake as an Effective Binder-Free Electrode for High-Performance Supercapacitors.

In this work, manganese dioxide (MnO2) nanosheets in situ loaded on a high-purity graphite flake (GF) were prepared by one-step hydrothermal deposition. It was found that the specific capacitance value of a single MnO2/GF electrode was 882 F/g at a current density of 1.0 A/g in a KOH electrolyte, and the specific capacitance retention of the MnO2/GF electrode can reach about 90.1% after 5000 charge-discharge cycles at a current density of 10 A/g. Furthermore, a MnO2/GF∥MnO2/GF symmetric supercapacitor device was fabricated with two pieces of MnO2/GF electrodes and ordinary filter paper with a 1 M KOH/PVA gel electrolyte as a separator. The single symmetric device displayed a high energy density of 64.2 Wh/kg at a power density of 400 W/kg within an applied voltage of 1.6 V, and this value was superior to those of previously reported MnO2-based systems. A tandem device consisting of a five-series tandem device (the applied voltage of a single device was 0.7 V) and a three-series tandem device (the applied voltage of a single device was 1.6 V) was prepared to drive a red light-emitting diode (LED). These findings open up application prospects for MnO2-based composite electrode materials for high-performance supercapacitors.

Sulfidation of ZIF-Derived Core-Shell NiCo LDH/Ni MOF Heterostructure toward Supercapacitor Electrodes with Enhanced Performance

Developing electrodes in a reasonable structure is essential to boost the performance of supercapacitors. Self-supporting heterostructures enriched active sites are promising as binder-free electrodes for supercapacitors. Here, core-shell layered double hydroxide (LDH)/Metal organic frame (MOF) heterostructure was directly grown on carbon cloth (CC) substrate derived from L-Co ZIF NWAs. Subsequently, the composite was treated with a sulfidation process to optimize its electrical conductivity. Thanks to its unique network structure, it facilitates active site exposure and efficient charge transfer, together with the synergetic effect between NiCo double hydroxide and Ni MOF nanosheets. This hybrid electrode possesses an excellent specific capacity (1200 F g−1 at 1 A g−1) and stable cycle performance with 86% capacity maintained after 4000 cycles, indicating its potential superiority for use in high-efficiency electrochemical capacitors.

In–situ synthesis of MnO dispersed carbon nanofibers as binder-free electrodes for high-performance supercapacitors

Manganese oxides have attracted great interest as promising pseudocapacitive materials due to its low cost, variable oxidation states, and high theoretical capacitance. In this work, we report the in-situ synthesis of MnO-dispersed carbon nanofibers (CNFs) using electrospinning and a unique two-step carbonization technique. While the single-step carbonization resulted in mixed MnxOy forms, however, by employing a suitable and optimized two-step carbonization, we were able to obtain CNFs assimilated with MnO nanoparticles (MnO-CNFs). The synthesized MnO-CNF electrodes achieved a high specific capacitance of 246 F g−1 at 0.5 A g−1 in a three-electrode system. A symmetric supercapacitor device assembled with these electrodes exhibited remarkable electrochemical performance with a maximum power density of 5000 W kg−1, maximum energy density of 14 W h kg−1, and an excellent cycling stability (97.5% retention after 10,000 cycles). The exceptional electrochemical performance of MnO-CNFs makes them promising electrode materials for practical energy storage applications.

Unveiling the surface dominated capacitive properties in flexible ternary polyaniline/NiFe2O4/reduced graphene oxide nanocomposites hydrogel electrode for supercapacitor applications

The 3D ternary nanocomposites hydrogel have been effectively fabricated on carbon cloth using a two-step synthesis approach. Nickel ferrite nanoparticles (NiFe2O4) prepared by template method have been dispersed onto/within rGO nanosheets leading to the formation of NiFe2O4/rGO (NFG) nanocomposites. Afterward, polyaniline hydrogel has been polymerized on NFG nanosheets to prepare ternary polyaniline/NiFe2O4/rGO hydrogel (PNFG) nanocomposites on carbon cloth that can be further utilized as a binder-free supercapacitor electrode. The resulting 3D ternary nanocomposites hydrogel achieved maximum specific capacitance of 1134.28 F/g at a current density of 1 A/g and 76.46 % of capacitive retention at 10 A/g. The supercapacitor electrode exhibited outstanding rate capability and superior cyclic stability up to 5000 successive cycles. In addition, the symmetric supercapacitor cell delivered 0.61 kW/kg of specific power and 19.29 Wh/kg of specific energy. The excellent electrochemical characteristics of PNFG is ascribed to its well-designed 3D microstructure and the synergistic effect created by the capacitive mechanism due to electric double layer capacitance (EDLC) and pseudocapacitance (surface redox reactions) as well as diffusion-controlled mechanism (faradaic redox reactions). It has been revealed that the overall electrode reaction is dominated by surface-controlled processes, with a small contribution from diffusion-controlled faradaic processes.

The hybrid structure of nanoflower-like CoxMnyNizO4 nanoparticles embedded biomass-lignin carbon nanofibers as free-standing and binder-free electrodes for high performance supercapacitors

We introduced the concept of a novel hybrid faradaic structure as a mechanism to improve the performance of biomass-derived carbon-based supercapacitors (SCs). Organic-inorganic hybrid composition, nanostructures, porosity, surface area and active redox reactions were carefully designed. We reported the facile, cost-effective and environmentally friendly fabrication of pure lignin carbon nanofibers (LCNFs) incorporated with flower-like, multi-metal and intrinsically capacitive ([email protected]2) nanoparticles in a flexible and binder-free electrode for SCs by the electrospinning technique using various electrolytes (1 M Na2SO4, 0.5 M KI and 1 M Na2SO4 +0.5 M KI). Mechanically robust LCNFs were used as a free-standing electrode and characterized for electrochemical performance using a two-electrode system in a Swagelok cell. Specific capacitance of the LCNFs in 1 M Na2SO4 electrolyte (current density 0.1 A/g) of 129 F/g increased to 200 F/g when adding 1 % manganese oxide nanoparticles that introduced intrinsic capacitance into the nanofibers. This value further increased to 303 F/g by adding 1 % Ni-Co to the manganese oxide. The nanoflower morphology significantly increased the surface area via micro and mesopore modification on carbonization and via macropore expansion on activation. After applying a mixed electrolyte (1 M Na2SO4 + 0.5 M KI), the capacitance reached 400 F/g and remained stable up to 1000 GDC cycles. Using the same composite nanofibers, 1,021 F/g was achieved using 0.5 M KI as an electrolyte. However, the latter system appeared unstable beyond 200 GDC cycles, suggesting that it can be applied as a disposable fast-charge supercapacitor. In the presence of a chemically-stable, highly-porous and partially-conductive carbon matrix, we concluded that interplay between the multi-metal oxides and electrolytes increased oxidation numbers, thereby boosting the faradaic reaction and enhancing electronic conductivity.

Ni–Mo–O@Ni–P nanowires as binder-free electrodes for aqueous asymmetric supercapacitors with high specific capacity and excellent stability

Ni–Mo–O@Ni–P nanowires as binder-free electrodes for aqueous asymmetric supercapacitors with high specific capacity and excellent stability

Binder-free vertical graphene nanosheets templated NiO petals for high-performance supercapacitor applications

Transition metal oxide and carbon-based hybrid nanostructures with high charge capacity and rate capabilities are emerging as promising electrodes for commercial supercapacitor devices. Herein, we report the fabrication of binder-free supercapacitor electrodes of vertical graphene nanosheets (VGN) templated NiO petals. The NiO petals are grown under different background O2 pressure, deposition temperature, and the number of laser shots using pulsed laser deposition (PLD). The morphology, microstructure, and stoichiometry of the NiO petals are greatly influenced by the background O2 pressure and deposition temperature. The increase in deposition temperature has been found to increase the particle size, whereas the number of laser shots affected the morphology and stoichiometry. Further, the VGN templated growth facilitates the NiO to possess a high surface area and, in turn, results in ∼2.5 times higher areal capacitance than the NiO directly grown on carbon paper substrate without VGN. In the present study, the VGN templated NiO petals exhibited areal capacitance as high as 175 mF/cm2 @ 0.1 V/s. The high areal capacitance is correlated with morphology, microstructure, particle size, and mass loading. An asymmetric coin cell device fabricated using NiO/VGN hybrid and oxygenated VGN electrodes exhibited energy and power densities of 0.4 μWh/cm2 and 102 μW/cm2, respectively. Further, LED lighting using the coin cell reveals the potential utilization of NiO/VGN hybrid electrodes for commercial applications.

Stable polyaniline/sodium alginate/graphene oxide composite hydrogels as binder-free supercapacitor electrodes

Stable polyaniline/sodium alginate/graphene oxide composite hydrogels as binder-free supercapacitor electrodes

Facile Synthesis of NiCo2O4 Nanowire Arrays/Few-Layered Ti3C2-MXene Composite as Binder-Free Electrode for High-Performance Supercapacitors.

Herein, a 3D hierarchical structure is constructed by growing NiCo2O4 nanowires on few-layer Ti3C2 nanosheets using Ni foam (NF) as substrate via simple vacuum filtration and solvothermal treatment. Ti3C2 nanosheets are directly anchored on NF surface without binders or surfactants, and NiCo2O4 nanowires composed of about 15 nm nanoparticles uniformly grow on Ti3C2/NF skeleton, which can provide abundant active sites and ion diffusion pathways for enhancing electrochemical performance. Benefiting from the unique structure feature and the synergistic effects of active materials, NiCo2O4/Ti3C2 exhibits a high specific capacitance of 2468 F g−1 at a current density of 0.5 A g−1 and a good rate performance. Based on this, an asymmetric supercapacitor (ASC) based on NiCo2O4/Ti3C2 as positive electrode and activated carbon (AC)/NF as negative electrode is assembled. The ASC achieves a high specific capacitance of 253 F g−1 at 1 A g−1 along with 91.5% retention over 10,000 cycles at 15 A g−1. Furthermore, the ACS presents an outstanding energy density of 90 Wh kg−1 at the power density of 2880 W kg−1. This work provides promising guidance for the fabrication of binder-free, free-standing and hierarchical composites for energy storage application.

Binder-free polypyrrole/fluorinated graphene nanocomposite hydrogel as a novel electrode material for highly efficient supercapacitors

Nowadays, many scientific communities and researchers are disparate towards the development of new and advanced energy storage/conversion devices to fulfill the increasing energy demands. Supercapacitors have considered as attractive energy storage devices because of their tremendous features. But their low conductivity creates a barrier to their practical applications, which is a consequence of the presence of binder in the formation of electrode material. Herein, a binder-free flexible supercapacitor electrode based on polypyrrole/fluorinated graphene (PFG) nanocomposite hydrogel on carbon cloth has been designed using in-situ oxidative polymerization. The resultant composite hydrogel possessed excellent electrochemical performance with a high specific capacitance of 1372 F/g in 1 M H2SO4 at a current density of 0.5 A/g. The maximum specific energy and specific power were estimated to be 20.13 Wh/kg and 176 W/kg, respectively. The outstanding electrochemical performance may be attributed to the combined effect of polypyrrole, fluorinated graphene as well as porous morphology of hydrogel. The resultant flexible and binder-free supercapacitor electrode with outstanding electrochemical performance will play a significant role in the field of wearable electronics, touch screens, electronic papers and roll up displays.

Spinel NiCo2O4 nanowires synthesized on Ni foam as innovative binder-free supercapacitor electrodes

Well-organized, independent nanoscale binary metal oxides exhibit high electrical conductivity and good ion transportability. In this study, a nickel-cobalt oxide (NiCo2O4) nanoparticle electrode was synthesized on Ni foam with a large surface area. Such a composite material is valuable as a binder-free and excellent current-carrying electrode material. Hence, it is particularly attractive for high-performance energy storage systems. NiCo2O4 nanowires were fabricated via a simple chemical bath deposition process. Consequently, the NiCo2O4 electrodes exhibited a remarkable specific capacity of 342.5 mA h g−1 at the current density of 3 A g−1 and cycling stability of 80.7%, which was maintained following 10,000 long-cycles at 5 A g−1. In addition, an asymmetric supercapacitor (NiCo2O4//graphite) device comprising of NiCo2O4 as a positive electrode and graphite as a negative electrode was fabricated. The NiCo2O4//graphite asymmetric supercapacitor has the highest energy density of 45.8 W h kg−1, and an excellent power density of approximately 5689 W h kg−1. Furthermore, NiCo2O4//graphite device delivered sufficient capacitive power to enlighten a red LED indicator. The excellent electrochemical performance of the asymmetric supercapacitor device can be attributed to the high specific surface area of the cathode electrode material and its enriched redox kinetics. This paper presents an easy and environmentally-friendly procedure for fabricating a compound electrode material for an asymmetric supercapacitor. It is expected that this novel high-performance electrode can stimulate new directions in the development of efficient energy storage.

Hierarchical grass-like NiCo2O4 nanowires grown on nickel foam as a binder-free supercapacitor electrode

Hierarchical interconnected grass-like NiCo2O4 nanowires are successfully developed on conducting nickel foam as a binder-less supercapacitor electrode. The hydrothermally synthesized electrode delivered a gravimetric specific capacitance of 361 Fg−1 and a high rate capability of 84 % at a high current density of 5Ag−1. An enhancement in the cycling behavior with excellent capacitance retention of 105 % is achieved after 2000 continuous charge–discharge cycles. The remarkable performance could be ascribed to the porous hierarchical grass-like morphology of NiCo2O4 and the 3D interlinked scaffold of conducting nickel foam. The novel grass-like NiCo2O4/Ni can be considered a promising electrode for supercapacitor application.

Electrophoretic deposition of Ti3C2Tx MXene nanosheet N-carbon cloth as binder-free supercapacitor electrode material

Despite the existing advances of Ti3C2Tx MXene as supercapacitor electrode material, its capacitance can be further enhanced through the composite strategy. In this work, the nitrogen-doped superhydrophilic carbon cloth (ENCC) was firstly prepared by N-doping of carbon cloth (CC), and then Ti3C2Tx MXene nanosheets were electrophoretically deposited to yield the binder-free Ti3C2Tx(EPD)/ENCC as supercapacitor electrode material. As a result, the composite electrode exhibited an area-specific capacitance of 2080.1 mF·cm−2 at 1 mA·cm−2 current density. The analysis implied that the varying Ti valence states provided certain psedocapacitance to the capacitance of the as-prepared electrode, though the main contribution was still dominantly from the electric double layer capacitance (EDLC). Further, the assembled symmetric supercapacitor yielded a wide voltage window of 1.8 V, and a good cyclic stability with 91% capacitance retention after 10,000 charge/discharge cycles at 20 mA·cm−2. Overall, the employed composite strategy enabled the good dispersion of the MXene flakes on the surface of the flexible substrate. Meanwhile, the large number of functional groups (-OH, -F, etc.) on the surface of Ti3C2Tx MXene interacted with the carbon layer through hydrogen bonding effects, which endows it as an ideal electrode for electrochemical capacitors.

Binder-Free MnO2/MWCNT/Al Electrodes for Supercapacitors.

Recently, significant progress has been made in the performance of supercapacitors through the development of composite electrodes that combine various charge storage mechanisms. A new method for preparing composite binder-free MnO2/MWCNT/Al electrodes for supercapacitors is proposed. The method is based on the original technique of direct growth of layers of multi-walled carbon nanotubes (MWCNTs) on aluminum foil by the catalytic pyrolysis of ethanol vapor. Binder-free MnO2/MWCNT/Al electrodes for electrochemical supercapacitors were obtained by simply treating MWCNT/Al samples with an aqueous solution of KMnO4 under mild conditions. The optimal conditions for the preparation of MnO2/MWCNT/Al electrodes were found. The treatment of MWCNT/Al samples in a 1% KMnO4 aqueous solution for 40 min increased the specific capacitance of the active material of the samples by a factor of 3, up to 100–120 F/g. At the same time, excellent adhesion and electrical contact of the working material to the aluminum substrate were maintained. The properties of the MnO2/MWCNT/Al samples were studied by electron probe microanalysis (EPMA), Raman spectroscopy, cyclic voltammetry (CV), and impedance spectroscopy. Excellent charge/discharge characteristics of composite electrodes were demonstrated. The obtained MnO2/MWCNT/Al electrodes maintained excellent stability to multiple charge-discharge cycles. After 60,000 CVs, the capacitance loss was less than 20%. Thus, this work opens up new possibilities for using the MWCNT/Al material obtained by direct deposition of carbon nanotubes on aluminum foil for the fabrication of composite binder-free electrodes of supercapacitors.

Three-dimensional core-shell niobium-metal organic framework@carbon nanofiber mat as a binder-free positive electrode for asymmetric supercapacitor

The metal-organic-frameworks (MOFs) have attracted considerable attention as potential electrode materials for energy storage devices. In the present work, niobium(pyridine-2,6-dicarboxylic acid) MOFs (Nb(PDCA)MOFs) are grown on the surface of electrospun porous carbon nanofiber (CNF) via in-situ solvothermal process. As prepared Nb(PDCA)MOF@CNF hybrid mats were characterized and used as working electrode for supercapacitor applications. To find out ideal electrolyte, the electrochemical characteristics of the Nb(PDCA)MOF@CNF electrode were investigated in different electrolytes such as 3 KOH and 1 M LiCl. The hybrid electrode delivered greater specific capacitance in KOH electrolyte, i.e., 1248.8 F/g at 0.5 A/g, compared to LiCl electrolyte (816.8 F/g), while it has a more stable cycling performance in LiCl electrolyte. The asymmetric supercapacitors (ASCs) were constructed with the as-prepared binder-free Nb(PDCA)MOF@CNF mat as a cathode and the CNF as an anode and investigated their electrochemical properties in both the electrolytes. The higher specific capacitance was achieved for the KOH electrolyte-based ASC. However, the LiCl electrolyte-based ASC delivered superior energy density (64.24 Wh kg−1) and greater cycling stability (98.3 % after 4000 cycles) compared to ASC in KOH electrolyte. The ionic conductivity, chemical nature, and hydrated ionic radius of the electrolyte were found to be important factors to the electrochemical performance of the ASC device.