Binder-free Supercapacitor Electrode Research Articles

Ballistic-aggregated Carbon Nanofoam in Target-side of Pulsed Laser Deposition for Energy Storage Applications.

In pulsed laser deposition, along the traditionally exploited deposition on the front-side of the plasma-plume, a coating forms on the surface of the target as well. For reproducibility, this residue is usually cleaned and discarded. Here we instead investigate the target-side coated materials and employ them as a binder-free supercapacitor electrode. The ballistic-aggregated, target-side nanofoam is compact and features a larger fraction of sp2-carbon, higher nitrogen content with higher graphitic-N and lower oxygen content with fewer COOH groups than that of diffusive-aggregated conventional nanofoams. They are highly hydrogenated graphite-like amorphous carbon and superhydrophilic. The resulting symmetric micro-supercapacitor delivers higher volumetric capacitance of 522 mF/cm3 at 100 mV/s and 104% retention after 10000 charge-discharge cycles over conventional nanofoam (215 mF/cm3 and 85% retention) with an areal capacitance of 134 μF/cm2 at 120 Hz and ultrafast frequency response. Utilizing the normally discarded target-side material can therefore enable high performing devices while reducing waste, cost and energy input per usable product. leading towards a greater sustainability on nanomaterials synthesis and deposition techniques.

Ballistic-aggregated Carbon Nanofoam in Target-side of Pulsed Laser Deposition for Energy Storage Applications.

In pulsed laser deposition, along the traditionally exploited deposition on the front-side of the plasma-plume, a coating forms on the surface of the target as well. For reproducibility, this residue is usually cleaned and discarded. Here we instead investigate the target-side coated materials and employ them as a binder-free supercapacitor electrode. The ballistic-aggregated, target-side nanofoam is compact and features a larger fraction of sp2-carbon, higher nitrogen content with higher graphitic-N and lower oxygen content with fewer COOH groups than that of diffusive-aggregated conventional nanofoams. They are highly hydrogenated graphite-like amorphous carbon and superhydrophilic. The resulting symmetric micro-supercapacitor delivers higher volumetric capacitance of 522 mF/cm3 at 100 mV/s and 104% retention after 10000 charge-discharge cycles over conventional nanofoam (215 mF/cm3 and 85% retention) with an areal capacitance of 134 μF/cm2 at 120 Hz and ultrafast frequency response. Utilizing the normally discarded target-side material can therefore enable high performing devices while reducing waste, cost and energy input per usable product. leading towards a greater sustainability on nanomaterials synthesis and deposition techniques.

Hierarchically structured Cu2P2O7 nanoflakes as a binder-free electrodes for high-performance supercapacitors

Metal phosphates-derived materials are emerging as promising candidates for electrode materials in energy storage systems due to their excellent redox properties and high electrical conductivity. In this work, we present a novel study and first report on the fabrication of binder-free electrodes using ultrathin Cu2P2O7 nanoflakes, facilitated through a cost-effective and industrially scalable chemical bath deposition (CBD) technique. These electrodes exhibit a unique surface architecture resembling micro-spherical flower structures, which are directly grown on flexible and conductive nickel foam (NF) substrates. The nanoscale structure of the Cu2P2O7 electrodes is meticulously designed to provide high porosity and an impressive specific surface area, allowing for efficient electrolyte ion infiltration. Consequently, these electrodes exhibit an exceptional specific/areal capacitance value of 1187 F g−1, 1894 mF cm−2 at a scan rate of 5 mA cm−2 and a specific capacity value of 644 C g−1. Notably, when integrated into an aqueous asymmetric supercapacitor (AASC) device, the Cu2P2O7-derived micro-sized flower structure delivers a significant energy density of 39.46 Wh kg−1, a notable specific power of 1.08 kW kg−1, and maintains an exceptional 99 % retention even after 10,000 charge/discharge cycles. This research highlights the potential of transition metal phosphates (TMPOs), specifically Cu2P2O7, as superior electrode materials for supercapacitor applications, offering a scalable and cost-effective approach for enhancing energy storage performance.

Chemical vapor deposition-grown single-layer graphene-supported nanostructured Co3O4 composite as binder-free electrode for asymmetric supercapacitor and electrochemical detection of caffeic acid

In this study, we developed a monolayer graphene/nanostructured cobalt oxide (MLG/Co3O4) composite for asymmetric supercapacitor and electrochemical sensor applications. The MLG was grown by chemical vapor deposition process and the Co3O4 nanostructures were electrodeposited on the MLG surface. Scanning electron microscopy proved that there were flower-like nanostructured Co3O4 densely electrodeposited on the MLG surface. At a current density of 3 mA cm−2, the MLG/Co3O4 composite produced an areal capacitance of 3.73 F cm−2. After 10,000 cycles, the composite electrode still had 93.6 % of its initial capacitance at 5 mA cm−2. The asymmetric system displayed an areal capacitance of 929 mF cm−2 at 4 mA cm−2 with good cycle stability. The asymmetric electrode produced a specific energy of 51 μWh cm−2 and a specific power of 11.1 mW cm−2. Cyclic voltammetric measurements demonstrated that the composite showed redox peaks at 0.48 eV and 0.09 eV toward the determination of CA. With a sensitivity of 0.13 µA/µM/cm2 and a limit of detection of 0.009 µM, the composite showed CA concentrations, ranging from 0.5 to 480 M. The composite displayed excellent selectivity and the current produced for the interfering compounds was exceedingly low. Using the composite electrode, the spiked CA in red wine and green tea samples recovered remarkably effectively.

Growth of CQD/PPy on cotton cloth as a binder-free high-performance flexible electrode for symmetric supercapacitor

Benefited from the continuous development of nanomaterials, wearable microelectronics with flexible and miniaturized features are booming, and smart textiles are attracting more attentions because of their superior flexibility and perfect safety. The combination of conductive polymers and flexible substrates has created a new field for flexible supercapacitors. Herein, cotton cloth (CC), which is commonly used in daily life, was selected as the flexible substrate and a layer of CQDs was uniformly grown on the CC fibers, and then pyrrole was directly grown on CC by in-situ polymerization under Fe3+ initiation to realize the tight bonding between the conductive polymer and the flexible substrate. The electrochemical properties of the composite electrode could be controlled by changing the amount of CQD. The obtained CC@CQD@PPy electrode has a high specific capacitance (C) of 537.9 F/g at 0.5 A/g. The assembled symmetric CC@CQD@PPy supercapacitor exhibits an excellent energy density (E) of 18.7 Wh/kg at a power density (P) of 125.0 W/kg, and a supreme cycling stability with a capacitance retention of 77.9 % after 10,000 cycles. In addition, the CC@CQD@PPy supercapacitor has excellent flexibility, with almost unchanged electrochemical performance under different bending angles, and the assembled all-solid-state supercapacitor has good electrochemical properties.

Simple and affordable synthesis of a binder-free nickel-zinc sulfide electrode for high-performance supercapacitors

Due to the increasing demand for renewable energy solutions, aqueous energy systems have emerged as promising and sustainable technologies. Nanostructured transition metal sulfides, renowned for their exceptional properties, are prime candidates for electrochemical supercapacitors. In this study, we present the synthesis of nickel-zinc sulfide (Ni-Zn-S) as a binder-free supercapacitor material using the affordable successive ionic layer adsorption and reaction simple technique. The active nanomaterial was directly deposited onto a 3D Ni foam current collector substrate, negating the need for a binder. The synergistic combination of Ni and Zn enhances the electrode capacitance. Various electrochemical techniques were used to evaluate the loaded active material as a binder-free supercapacitor electrode in a 6 M KOH electrolyte. Results indicate pseudocapacitive performance, achieving a high specific capacitance of 400F/g at 0.7 A/g. This material retains 97 % of its capacity, even after 2000 cycles, showcasing exceptional long-term cycling stability. These findings underscore the potential of the Ni-Zn-S electrode for delivering low-cost, high-performance supercapacitors.

PPy-PdO modified MXene for flexible binder-free electrodes for asymmetric supercapacitors: Insights from experimental and DFT investigations

Binder-free, flexible electrodes of V2C MXene, V2C-PPy, and V2C-PPy-PdO (a ternary composite of vanadium carbide, polypyrrole, and palladium oxide) were fabricated using a simplified, one-step electrodeposition method. A comprehensive assessment has subsequently been conducted on the microstructural and electrochemical attributes of these electrode materials when utilized in supercapacitors with a 1 M H2SO4 electrolyte. Notably, an impressive specific capacitance of 487F g−1 is achieved for V2C-PPy-PdO ternary composite at 1 A/g. This exceptional performance is due to the considerable active surface area and inherent structural stability of the host material. These factors significantly enhanced the electrochemical reaction kinetics and cyclic reversibility. Furthermore, the V2C-PPy-PdO composite demonstrated a notable specific capacitance of 250F g−1 when integrated into an asymmetric coin cell configuration alongside activated porous carbon under a current density of 1 A/g. Remarkably, it maintained an outstanding capacitance retention of 92 % across 10,000 charge–discharge cycles. Our experimental discoveries were additionally substantiated through the Density Functional Theory calculations, which unveiled that the inclusion of PdO within the V2C-PPy-PdO composite led to an augmentation of electronic states near the Fermi level. This increase in electronic states ultimately improved the quantum capacitance, rendering the V2C-PPy-PdO composite a highly promising candidate for supercapacitor applications.

Bimetallic NiCo2Se4/Fe2CoSe4 chrysanthemum flowers assembled by nanosheets: An efficient electrode material for hybrid supercapacitor applications

Transition metal selenides have excellent promise for high-performance electrode materials owing to their great electrical conductivity and theoretical capacity. Unfortunately, the electrochemical performance of single-metal selenides is undesirable because of their low energy density and poor cyclic stability, and one practical approach is to introduce heteroatoms to create bimetallic selenides. Herein, a novel bimetallic NiCo2Se4/Fe2CoSe4 chrysanthemum flower assembled by nanosheets on NiF was synthesized via a hydrothermal process as a binder-free electrode for a hybrid supercapacitor. Because of the presence of plentiful redox active sites, unique architecture with large surface area and mesoporous channels, desirable electrical conductivity, and synergistic effect of Ni, Co, and Fe, the bimetallic NiCo2Se4/Fe2CoSe4 electrode material shows significantly increased electrochemical performance. Interestingly, the bimetallic NiCo2Se4/Fe2CoSe4 electrode material shows an outstanding specific capacity of 323.66 mAhg−1 (1175.97 Cg−1) at 1 Ag−1, retaining 91.08% of the initial capacity at 20 Ag−1, with long-lasting cyclic stability of 91.08% after 10,000 GCD cycles at 20 Ag−1. A binder-free bimetallic NiCo2Se4/Fe2CoSe4 @NiF electrode's outstanding electrochemical efficiency can be related to the existence of two bimetallic selenides, and beneficial interaction, which yields quick charge transfer reactions. Moreover, the NiCo2Se4/Fe2CoSe4@NiF//AC@NiF hybrid supercapacitor by bimetallic NiCo2Se4/Fe2CoSe4@NiF (positive electrode) and activated carbon (AC@NiF, negative electrode) displayed specific energy which is 51.83 Whkg−1 at 749.83 Wkg−1 and 34.2 Whkg−1 at 14996.34 Wkg−1 at 20 Ag−1 and superior stability of 92.33% after 10,000 GCD cycles. This research provides some insight into the design of an electrode material with a flower-like decorated with nanosheets morphology for hybrid supercapacitors.

Unification of DAQ-rGO-PEDOT as binder-free ternary nanocomposite electrode for high performance solid-state symmetrical supercapacitor

A high energy density hybrid supercapacitor has been developed from highly π-conjugated 1,4-diaminioanthraquinone covalently bonded to reduced graphene oxide (DAQ:rGO). The drop casting of DAQ:rGO suspension onto nanostructured PEDOT matrixes has enhanced the microstructure/orderliness, higher homogeneity as confirmed by Raman, FE-SEM and HRTEM studies. The high gravimetric capacitance (622.4 F g−1 at 1 A g−1) emerges from extensively porous matrix of nanostructured PEDOT and low band gap of DAQ:rGO evident from a voltage window of -0.2 to 0.8 V facilitating the redox activity of DAQ. In addition, solid-state symmetric supercapacitor based on ternary electrode with free standing PVA-H2SO4 gel electrolyte possesses specific capacitance of 492.5 F g−1 at 1.5 A g−1 with exceptional energy density (68.39 W h kg−1) and excellent cyclic stability (retaining 100% capacitance after 10,000 cycles. The ability of the four devices to illuminate the LED for 120 s manifests utility of the nanocomposite for future microelectronics.

Exploring the potential of simultaneous nanoarchitectonics and utilization of Co-MOFs electrode as well as powder for aqueous supercapacitors

The current study emphasized a leaf-like architecture of Co-MOFs electrodes on a stainless-steel mesh substrate (Co-MOFs/SSM) and Co-MOFs powder for supercapacitors (SCs), with a particular emphasis on utilizing the residual product as an electrode material instead of discarding it. Additionally, the investigation explored the impact of using a binder and binder-free electrode for SCs. The Co-MOFs powder (R-Co-MOFs) was obtained from the residual material left after synthesizing Co-MOFs/SSM using the reaction-diffusion framework method. The structural and compositional analysis confirmed the formation of both Co-MOFs/SSM and R-Co-MOFs. The morphological studies revealed an interconnected and non-interconnected leaf-like architecture for Co-MOFs/SSM and R-Co-MOFs respectively. R-Co-MOFs were screen printed on a stainless-steel mesh substrate (R-Co-MOFs/SSM) and used as an electrode material for SCs. The Co-MOFs/SSM and R-Co-MOFs/SSM exhibited maximum specific capacitance (Cs) of 534 and 269 F/g at 5 mV/s respectively. Moreover, Co-MOFs/SSM and R-Co-MOFs/SSM exhibited retention rates of 62 % and 99 % after 5000th cycles, respectively. Likewise, the symmetric aqueous device, Co-MOFs/FSS//Co-MOFs/FSS achieved a maximum Cs of 85 F/g at 10 mV/s which surpassed the value of 34 F/g for R-Co-MOFs/SSM//R-Co-MOFs/SSM. It also showed higher energy density and power density values of 19.31 Wh/kg and 1333 W/kg at 4 mA compared to R-Co-MOFs/SSM//R-Co-MOFs/SSM, respectively. The Co-MOFs/SSM//Co-MOFs/SSM and R-Co-MOFs/SSM//R-Co-MOFs/SSM revealed retention rates of 72 % and 98 % after 3000th cycles respectively. This investigation provides valuable insights to researchers regarding the sustainable synthesis and utilization of Co-MOFs electrodes and powder for SCs.

Electrodeposited ultra-thin FeCo2O4 nanosheets on nickel foam as binder-free electrodes for high-performance supercapacitors

The cobalt-based spinel oxides MCo2O4(M = Ni, Mn, Cu, Fe, etc.) have garnered significant attention due to their potential applications in energy storage. In this study, ultra-thin FeCo2O4 nanosheets have been synthesized through a facile electrodeposition method and used as binder-free electrodes for high-performance supercapacitors. The results indicate that the FeCo2O4 nanosheet (FCS) electrode obtained through 5 min of electrodeposition using ferrous salt (FeSO4) as the precursor has a more abundant pore structure and exhibits the best electrochemical performance. The specific capacitance of the FeCo2O4 nanosheets electrode reaches 679 F g−1 at a current density of 1 A g−1, and it retains 92.9 % of its initial capacitance after undergoing 5000 cycles. In addition, the assembled FeCo2O4 nanosheet (FCS)//activated carbon (AC) asymmetric supercapacitor shows a high energy density of 62.5 Wh kg−1 at 750 W kg−1 and with a capacitance retention of 91.3 % after 5000 cycles. Furthermore, the electrodeposition method utilized in the synthesis of the FeCo2O4 nanosheets is cost-effective, environmentally friendly, and can be employed to fabricate other MCo2O4 materials with superior electrochemical properties.

Optimized 3D interconnected foam-like NiO@rGO composite as a binder-free electrode for high-performance asymmetric supercapacitor

Bonding of transition metal oxides and highly conductive carbon materials to exploit the synergistic effect of both materials has been proven to be an efficient means to develop high-capacity electrode materials. A unique interconnected foam-like NiO@rGO structure was constructed by loading the NiO nanoparticles onto rGO frameworks as a binder-free supercapacitor electrode via three steps including hydrothermal reaction, electrodeposition and heating treatment. The morphology and crystallinity were tuned by controlling the electrodeposition time and heating temperature, and the electrochemical properties of the NiO@rGO composites were systematically investigated. The optimized NiO@rGO-250 composite showed excellent electrochemical properties (1399 F g−1 at 1 A g−1) and superior cycling stability. Furthermore, an asymmetric supercapacitor using NiO@rGO and active carbon as two electrodes achieved a high specific energy of 40.4 Wh k g−1 at a specific power of 750 W k g−1.

Unidirectional growth of polyaniline on 3D CoO nanowires for aqueous asymmetric supercapacitors

Metal oxide-based binary nanohybrids are a new class of binder-free supercapacitor electrodes. This paper reports the enhanced electrochemical performance of polyaniline (PANI)/CoO nanowires grown on Ni foam for use in aqueous asymmetric supercapacitors (SCs). Several synthetic parameters were optimized for the unidirectional growth of PANI on CoO nanowires. The rationally designed core-shell structured electrode exhibited a high specific capacity of 1113C g−1 (specific capacitance of 2473 F g−1) at a current density of 3 A g−1 and good cycling stability of 86.3 % over 10,000 charge/discharge cycles in a 1 M KOH electrolyte through a substantial synergistic contribution from each component. In addition, an aqueous asymmetric supercapacitor based on these PANI/CoO nanowire arrays exhibited a high specific energy of 35.8 Wh kg−1 and high cycling stability (89.1 % after 5000 cycles). Two aqueous asymmetric supercapacitors connected in series could light up 19 red light-emitting diodes (LEDs). Therefore, this electrode can be considered a superior candidate for the next-generation SC electrodes.

Constructing metal organic framework derived manganese cobalt layered double hydroxide nanosheets on Ni foam as cost-effective binder-free electrodes of high-performance supercapacitors

A vital aspect of energy storage devices is the development of novel materials with excellent electrical conductivity and rational structures. In combination with alkaline electrolytes, the manganese-cobalt layered double hydroxide (MnCo-LDH) cathode material has long been recognized as a highly desirable cathode material. Nevertheless, the synthesis of MnCo-LDH is time-consuming and required high temperatures. Therefore, it is important to find simple routes for the synthesis of MnCo-LDH. Herein, we propose a synthesis of metal organic framework (MOF)-derived MnCo-LDH nanosheets on conductive nickel foam (NF) for the supercapacitor (SC) application. The CoMOF decorated NF was fabricated by simple precipitation method, and then it was converted to MnCo-LDH by etching process at 80 °C for 5 min (MnCo-LDH/80 °C). The MOF-derived MnCo-LDH/80 °C electrode provides large accessible regions for electrolytes, low charge transfer resistance, and rich electroactive sites. Therefore, the MnCo-LDH/80 °C electrode demonstrates preferable energy storage property with a high areal capacitance of 2.62 F/cm2 at 20 mV/s. In this study, an asymmetric supercapacitor (ASC) is constructed using MnCo-LDH/80 °C and activated carbon (AC) on NF as the positive and negative electrodes, respectively. The optimized MnCo-LDH//AC device provides the maximum energy of 0.116 mWh/cm2 at the maximum power density of 2.49 mW/cm2. Added to that, the ASC has excellent cyclic stability with 78% as the capacitance retention and Coulombic efficiency of 94.3% after 5000 charge-discharge cycles.

Electrodeposited coral-like bimetallic NiCo-MOFs on Ni foam as binder-free electrodes for high performance all solid-state asymmetric supercapacitors

The rational design of electrode materials is greatly significant for improving the performance of the supercapacitor. In this work, high mass loading coral-like bimetallic nickel/cobalt-based metal-organic frameworks are in-situ constructed on cobalt-modified nickel foam (NiCo-MOFs/NF) via a facile cathodic electrodeposition process as binder-free electrodes for supercapacitors. Such electrodes with optimized Ni/Co molar ratios, high specific surface area and unique hierarchical structure with open channels provide abundant reaction active sites and fast ion transfer kinetics, and the three-dimensional porous Ni foam (NF) offers successive pathways for fast electron transportation. As a result, an ultrahigh areal specific capacitance of over 9300 mF cm−2 with a high-capacity retention of over 87% is achieved at 10 mA cm−2. And the NiCo-MOFs/NF with Ni/Co molar ratio of 1:3 presents a favorable stability of retaining its 73% original specific capacitance after a long-term cycling of 10,000 cycles. Moreover, the assembled all solid-state asymmetric supercapacitors (ASSCs) device performs an energy density of 617.2 mWh cm−2 at a power density of 7506.9 mW cm−2.

Controllable synthesis of MnSe2/Co0.85Se nanosheets as a binder-free electrode for high-performance asymmetric supercapacitors

With the increasingly serious environmental pollution and depletion of natural resources, it is necessary to develop efficient and environmentally friendly energy storage equipments to alleviate the problem of resource shortage. In this study, a novel MnSe2/Co0.85Se (MCSe) electrode was successfully prepared using a simple, green and environmentally friendly electrodeposition method. The MCSe electrode exhibited good electrochemical performance, and possesses a high specific capacity (Cs) of 1380C/g at a current density (CD) of 1 A/g. An asymmetric supercapacitor (ASC) assembled using a positive electrode (the MCSe electrode) and a negative electrode (active carbon (AC) electrode) delivered a high specific energy density (Es) of 49.63 Wh/kg at a specific power density (Ps) of 750 W/kg. Hence, this study provides a new approach for designing metal selenides for energy storage and conversion.

Electrodeposition Synthesis of Coral-like MnCo Selenide Binder-Free Electrodes for Aqueous Asymmetric Supercapacitors.

Bimetallic selenide compounds show great potential as supercapacitor electrode materials in energy storage and conversion applications. In this work, a coral-like MnCo selenide was grown on nickel foam using a facile electrodeposition method to prepare binder-free supercapacitor electrodes. The heating temperature was varied to tune the morphology and crystal phase of these electrodes. Excellent electrochemical performance was achieved due to the unique coral-like, dendritic- dispersed structure and a bimetallic synergistic effect, including high specific capacitance (509 C g-1 at 1 A g-1) and outstanding cycling stability (94.3% capacity retention after 5000 cycles). Furthermore, an asymmetric supercapacitor assembled with MnCo selenide as the anode and active carbon as the cathode achieved a high specific energy of 46.2 Wh kg-1 at 800 W kg-1. The work demonstrates that the prepared coral-like MnCo selenide is a highly promising energy storage material.

Three-dimensional nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels as binder-free electrodes for symmetric supercapacitors

Herein, nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels (N-GQDs/rGOs) were prepared via a hydrothermal approach from graphene oxide (GO) aqueous solution. During the preparation of the samples, ammonia water was used as reducing agent, pH regulator and nitrogen dopant, and graphene quantum dots (GQDs) were used as spacer between graphene sheets. Benefiting from their three-dimensional porous structures, large specific surface area, large number of heteroatom functional groups (N, O) on the surface, and the synergistic effect between GQDs and graphene sheets, the synthesized samples exhibit excellent electrochemical performance. Particularly, the N-GQDs/rGO-20 sample based binder-free symmetric supercapacitor show a high specific capacitance of 277.8 F g−1 at 0.3 A g−1, and this value can still maintain at 220.9 F g−1 even at 10 A g−1 in 6 M KOH electrolyte. Moreover, the capacitance retention rate of the symmetric supercapacitor can reach 92.7% after 10,000 cycles at 10 A g−1, indicating its excellent cycle stability.

Direct growth of AC@NiCo2S4 composite on nickel foam as binder-free electrodes for supercapacitors

In this study, folded nanotubes were directly grown on Ni foam by two-step hydrothermal method to form activated carbon (AC) and NiCo2S4 composite material with a unique structure like nano-urchin. In addition, the morphology and structure can be controlled by the time of hydrothermal reaction. The resulting samples were characterized by means of XRD, XPS, EDS and SEM. The electrochemical test results show that compared with the 6 h and 24 h hydrothermal composites, the 12 h hydrothermal composites (AC@NiCo2S4–2) form a complete folded nanotube structure, provide a large number of reactive sites, and show better electrochemical properties. And compared with the capacitance of NiCo2S4 (456.14 C g−1), the AC@NiCo2S4–2 exhibited a high specific capacitance of 653.9 C g−1 at a current density of 1 A g−1. In addition, after combination with AC, AC@NiCo2S4 has better electrochemical performance and cycle stability, the capacitance retention rate at 10 A g−1 is 62.84 % of 1 A g−1, and can still maintain 84.96 % of the initial capacitance after 3000 cycles. Moreover, the fabricated hybrid supercapacitor (HSC) based on AC@NiCo2S4–2 and AC electrodes achieved a high energy density of 29.75 Wh kg−1 at the power density of 700 W kg−1 and still maintain the energy density of 16.86 Wh kg−1 at the high power density of 7000 W kg−1.

The Morphology-Controllable Synthesis of Ni–Co–O Nanosheets on a 3D Porous Ni Template as a Binder-Free Electrode for a Solid-State Symmetric Supercapacitor

In this work, a porous Ni template (Ni–Co–O@3D Ni) with Ni–Co oxide nanosheets (Ni–Co–O)@3D was synthesized by incorporating Ni–Co oxide nanosheets within a 3D porous Ni template as a binder-free electrode for a supercapacitor. The 3D Ni template was synthesized with hydrogen bubble templates that possessed different applied voltages that marked differences in terms of physicochemical properties, as well as factors that affect the subsequent growth of Ni–Co–O nanosheets. Then, Ni and Co metal ion sources were introduced to produce the morphology adjustment of Ni–Co–O@3D Ni with a multiple hierarchical architecture with a hydrothermal process. Field emission scanning electron microscopy (FESEM), X-ray absorption spectroscopy (XAS), and an electrochemical analysis were employed to investigate the morphological, structural, and electrochemical characteristics. FESEM and XAS results evidenced that Ni–Co–O@3D Ni consists of a 3D, well-designed hierarchical interconnected network, and the local electronic structure change has a great influence on the capacitive performance. The electrochemical results of Ni–Co–O@3D Ni displayed an excellent electrochemical performance due to the synergistic effect of Ni and Co on Ni–Co–O@3D Ni, which possessed multiple oxidation states to enable various reversible Faradaic redox reactions. Remarkably, the solid-state symmetric supercapacitor fabricated with Ni–Co–O@3D Ni exhibited excellent capacitive behaviour at a wide operating voltage window and cycling performance. Also, the as-assembled solid-state symmetric supercapacitor (two devices in series) can successfully illuminate a desired parallel pattern consisting of 36 red LED lights, demonstrating its practical application as a supercapacitor.