Structure-designed synthesis of hierarchical NiCo2O4@NiO composites for high-performance supercapacitors

Recent Development on Transition Metal Oxides-Based Core-Shell Structures for Boosted Energy Density Supercapacitors

In recent years, nanomaterials exploration and synthesis have played a crucial role in advancing energy storage research, particularly in supercapacitor development. Researchers have diversified materials, including metal oxides, chalcogenides, and composites, as well as carbon materials, to enhance energy and power density. Balancing energy density with electrochemical stability remains challenging, driving intensified efforts in advancing electrode materials. This review focuses on recent progress in designing and synthesizing core-shell materials tailored for supercapacitors. The core-shell architecture offers advantages such as increased surface area, redox active sites, electrical conductivity, ion diffusion kinetics, specific capacitance, and cyclability. The review explores the impact of core and shell materials, specifically transition metal oxides (TMOs), on supercapacitor electrochemical behavior. Metal oxide choices, such as cobalt oxide as a preferred core and manganese oxide as a shell, are discussed. The review also highlights characterization techniques for assessing structural, morphological, and electrochemical properties of core-shell materials. Overall, it provides a comprehensive overview of ongoing TMOs-based core-shell material research for supercapacitors, showcasing their potential to enhance energy storage for applications ranging from gadgets to electric vehicles. The review outlines existing challenges and future opportunities in evolving TMOs-based core-shell materials for supercapacitor advancements, holding promise for high-efficiency energy storage devices.

Hydrothermal Synthesis of a Cellular NiO Film on Carbon Paper as a Promising Way to Obtain a Hierarchically Organized Electrode for a Flexible Supercapacitor

The formation of a cellular hierarchically organized NiO film on a carbon paper substrate under hydrothermal conditions using triethanolamine as a base has been studied. The thermal behavior of the carbon paper substrate with the applied semi-product shell was studied using synchronous thermal analysis (TGA/DSC) and it was demonstrated that such modification of the material surface leads to a noticeable increase in its thermal stability. Using scanning electron microscopy (SEM), it was shown that the NiO film grown on the carbon fiber surface is characterized by a complex cellular morphology, organized by partially layered individual nanosheets of about 4-5 nm thickness and lateral dimensions up to 1-2 μm, some edges and folds of which are located vertically relative to the carbon fiber surface. The surface of the obtained material was also examined using atomic force microscopy (AFM), and the electronic work function of the oxide shell surface was evaluated using the Kelvin probe force microscopy (KPFM) method. The electrochemical parameters of the obtained flexible NiO/CP electrode were analyzed: the dependence of the specific capacitance on the current density was determined and the stability of the material during cycling was studied, which showed that the proposed approach is promising for manufacturing hierarchically organized electrodes for flexible supercapacitors.

Nanostructured mixed transition metal oxide spinels for supercapacitor applications

There have been numerous applications of supercapacitors in day-to-day life. Along with batteries and fuel cells, supercapacitors play an essential role in supplementary electrochemical energy storage technologies. They are used as power sources in portable electronics, automobiles, power backup, medical equipment, etc. Among various working electrode materials explored for supercapacitors, nanostructured transition metal oxides containing mixed metals are highly specific and special, because of their stability, variable oxidation states of the constituted metal ions, possibility to tune the mixed metal combinations, and existence of new battery types and extrinsic pseudocapacitance. This review presents the key features and recent developments in the direction of synthesis and electrochemical energy storage behavior of some of the recent morphology-oriented transition metal oxide and mixed transition metal oxide nanoparticles. We also targeted the studies on a few of the recently developed flexible and bendable supercapacitor devices based on these mixed transition metal oxides.

ZIF-67 Derived Co2VO4 Hollow Nanocubes for High Performance Asymmetric Supercapacitors

In this work, a new type of Co₂VO₄ hollow nanocube (CoVO-HNC) was synthesized through an ion exchange process using ZIF-67 nanocubes as a template. The hollow nanocubic structure of the CoVO-HNC provides an abundance of redox sites and shortens the ion/electron diffusion path. As the electrode material of supercapacitors, the specific capacitance of CoVO-HNC is 427.64 F g⁻¹ at 1.0 A g⁻¹. Furthermore, an asymmetric supercapacitor (ASC) was assembled using CoVO-HNC and activated carbon (AC) as electrodes. The ASC device attains an energy density of 25.28 Wh kg⁻¹ at a high-power density of 801.24 W kg⁻¹, with 78% capacitance retention after 10,000 cycles at 10 A g⁻¹.

Structure-engineering of core-shell ZnCo2O4@NiO composites for high-performance asymmetric supercapacitors

The implementation of a structure-designed strategy to construct hierarchical architectures of multicomponent metal oxide-based electrode materials for energy storage devices is in the limelight. Herein, we report NiO nanoflakes impregnated on ZnCo2O4 nanorod arrays as ZnCo2O4@NiO core-shell structures on a flexible stainless-steel mesh substrate, fabricated by a simple, cost-effective and environmentally friendly reflux condensation method. The core-shell structure of ZnCo2O4@NiO is used as an electrode material in a supercapacitor as it provides a high specific surface area (134.79 m2 g-1) offering high electroactive sites for a redox reaction, reduces the electron and ion diffusion path, and promotes an efficient contact between the electroactive material and electrolyte. The binder-free ZnCo2O4@NiO electrode delivers a high specific capacitance of 882 F g-1 at 4 mA cm-2 current density and exhibits remarkable cycling stability (∼85% initial capacitance retention after 5000 charge-discharge cycles at 10 mA cm-2). The asymmetric supercapacitor device ZnCo2O4@NiO//rGO delivered a maximum energy density of 46.66 W h kg-1 at a power density of 800 W kg-1. The device exhibited 90.20% capacitance retention after 4000 cycles. These results indicate that the ZnCo2O4@NiO architecture electrode is a promising functional material for energy storage devices.

Hierarchical CuCo2O4@CoS-Cu/Co-MOF core-shell nanoflower derived from copper/cobalt bimetallic metal-organic frameworks for supercapacitors

Rational design of composite materials with unique core-shell nanoflower structures is an important strategy for improving the electrochemical properties of supercapacitors such as capacitance and cycle stability. Herein, a two-step electrodeposition technique is used to orderly synthesize CuCo₂O₄ and CoS on Ni foam coated with Cu/Co bimetal metal organic framework (Cu/Co-MOF) to fabricate a hierarchical core-shell nanoflower material (CuCo₂O₄@CoS-Cu/Co-MOF). This unique structure can increase the electrochemically active site of the composite, promoting the Faradaic redox reaction and enhancing its electrochemical properties. CuCo₂O₄@CoS-Cu/Co-MOF shows a prominent specific capacitance of 3150 F g^-1 at 1 A g^-1, marvelous rate performance of 81.82% (2577.3 F g^-1 at 30 A g^-1) and long cycle life (maintaining 96.74% after 10,000 cycles). What is more, the assembled CuCo₂O₄@CoS-Cu/Co-MOF//CNTs device has an energy density of 73.19 Wh kg^-1 when the power density is 849.94 W kg^-1. It has unexpected application prospects.

Controllable synthesis of ZIF-derived NixCo3-xO4 nanotube array hierarchical structures based on self-assembly for high-performance hybrid alkaline batteries

In this study, a novel NixCo3-xO4 nanotube array hierarchical structure derived from zeolitic imidazolate frameworks (ZIFs) is grown on Ni foam (NixCo3-xO4 NAHS/Ni foam) using the template-assisted and self-assembly approach for a high-performance hybrid energy storage device in alkaline solution. The material characteristics of the resultant samples were characterized by XPS, XRD, ICP, SEM, TEM and BET. Due to the unique hollow structure with a large specific surface area and the exposure of large active sites originating from ZIFs, the optimal NixCo3-xO4 NAHS/Ni foam exhibits substantially enhanced electrochemical properties. The NixCo3-xO4 NAHS/Ni foam directly acts as an electrode, which provides an excellent specific capacity of 290.48 mA h g-1 at 1 A g-1. Subsequently, the corresponding hybrid alkaline batteries that consist of NixCo3-xO4 NAHS/Ni foam and carbon materials display a highly satisfactory specific capacity of 54.94 mA h g-1 at 1 A g-1, a satisfactory long-term stability of 85.47% after 2000 cycles, a maximum energy density of 43.95 W h kg-1 and a power density of 8000 W kg-1. This work combines the design of the electronic structure with the optimization of composition, and provides a reference for the application of hybrid rechargeable alkaline batteries (RABs).

Construction of hierarchical Co9S8@NiO synergistic microstructure for high-performance asymmetric supercapacitor

Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co₉S₈ structure and NiO nanosheets (Co₉S₈@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co₉S₈@NiO electrode materials exhibit a superior specific capacitance of 1627 F g^-1 at a current density of 1 A g^-1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg^-1 at a power density of 749.8 W Kg^-1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.

Synthesis of the cathode and anode materials from discarded surgical masks for high-performance asymmetric supercapacitors

Advanced carbon-based electrode materials derived from wastes are essential to high-performance supercapacitors due to their abundance and sustainability. In this work, we fabricate novel cathodes and anodes based on discarded surgicalmask-derived carbon (DSM-C). Discarded surgicalmasks are good candidates for carbon-based electrode materials due to their unique fibrous structure and simple composition compared to conventional biomass sources. Benefiting from the excellent electrical conductivity of DSM-C and abundant redox reactions from nickel oxide (NiO), the electrochemical performances of NiO/DSM-C composites have been greatly improved. Specifically, the DSM-C and NiO/DSM-C electrodes show high specific capacitances of 240 F g^-1 and 496 F g^-1 at 1 A g^-1 respectively, and excellent rate capability. Moreover,asymmetric supercapacitors (ASCs) are assembled using DSM-C and NiO/DSM-C as anodes and cathodes, respectively. They deliver a high energy density of 57 Wh kg^-1 at a power density of 702 W kg^-1, accompanied by superior cycling stability (98.5% capacitance retention after 10,000 cycles). This work shows prospective applications of DSM-C as an electrode material for energy storage systems.

Beyond hierarchical mixed nickel-cobalt hydroxide and ferric oxide formation onto the green carbons for energy storage applications

To attain superior energy density concurrently with high power density, high-performance supercapacitors have been developed. Herein an innovative strategy has been adopted to fabricate unique binder-free electrodes composed of a unique porous structure of binary metal carbonate hydroxide nanomace-decorated hydrothermal porous carbon spheres (PCSs). Hierarchical nickel-cobalt carbonate hydroxide (NiCOCH) nanomaces, directly grown on PCSs, are used as positive electrodes for supercapacitors fabrication. Furthermore, Fe₂O₃@PCS composites, having benefits of highly reversible redox reaction in the negative potential window and highly porous structure, are employed as the negative electrode in the fabrication of the asymmetric supercapacitors (ASCs). The assembled NiCoCH@PCS// Fe₂O₃@PCS asymmetric devices with a wide electrochemical potential window not only have the merit of high energy and power densities but also receive benefits from remarkable cycle stability. These encouraging outcomes that are mutually beneficial, make these fabricated ASCs significantly ideal for high-performance electronics.

Enhanced faradic activity by construction of p-n junction within reduced graphene oxide@cobalt nickel sulfide@nickle cobalt layered double hydroxide composite electrode for charge storage in hybrid supercapacitor

The intrinsic faradic reactivity is the uppermost factor determining the charge storage capability of battery material, the construction of p-n junction composing of different faradic components is a rational tactics to enhance the faradic activity. Herein, a reduced graphene oxide@cobalt nickle sulfide@nickle cobalt layered double hydroxide composite (rGO@CoNi₂S₄@NiCo LDH) with p-n junction structure is designed by deposition of n-type nickle cobalt layered double hydroxide (NiCo LDH) around p-type reduced graphene oxide@cobalt nickle sulfide (rGO@CoNi₂S₄), the charge redistribution across the p-n junction enables enhanced faradic activities of both components and further the overall charge storage capacity of the resultant rGO@CoNi₂S₄@NiCo LDH battery electrode. As expected, the rGO@CoNi₂S₄@NiCo LDH electrode can deliver high specific capacity (C_s, 1310 ± 26 C g^-1 at 1 A g^-1) and good cycleability (77% C_s maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the rGO@CoNi₂S₄@NiCo LDH p-n junction battery electrode exports high energy density (E_cell, 57.4 Wh kg^-1 at 323 W kg^-1) and good durability, showing the prospect of faradic p-n junction composite in battery typed energy storage.

Marigold micro-flower like NiCo2O4 grown on flexible stainless-steel mesh as an electrode for supercapacitors

Nanostructured NiCo₂O₄ is a promising material for energy storage systems. Herein, we report the binder-free deposition of porous marigold micro-flower like NiCo₂O₄ (PNCO) on the flexible stainless-steel mesh (FSSM) as (PNCO@FSSM) electrode by simple chemical bath deposition. The SEM and EDS analysis revealed the marigold micro-flowers like morphology of NiCo₂O₄ and its elemental composition. The porous nature of the electrode is supported by the BET surface area (100.47 m² g⁻¹) and BJH pore size diameter (∼1.8 nm) analysis. This PNCO@FSSM electrode demonstrated a specific capacitance of 530 F g⁻¹ at a high current density of 6 mA cm⁻² and revealed 90.5% retention of specific capacitance after 3000 cycles. The asymmetric supercapacitor device NiCo₂O₄//rGO within a voltage window of 1.4 V delivered a maximum energy density of 41.66 W h kg⁻¹ at a power density of 3000 W kg⁻¹. The cyclic stability study of this device revealed 73.33% capacitance retention after 2000 cycles. These results indicate that the porous NiCo₂O₄ micro-flowers electrode is a promising functional material for the energy storage device.

Binder-free marigold micro-flower like NiCo₂O₄ deposited on FSSM as electrode in ASC device (NiCo₂O₄//rGO) is a promising functional material for energy storage device.

High-performance supercapacitor electrode based on naphthoquinone-appended dopamine neurotransmitter as an efficient energy storage material

NQ-DP based organic material was successfuly synthesized and employed as an efficient pseudocapacitor material.

Superior lithium-storage properties derived from a g-C3N4-embedded honeycomb-shaped meso@mesoporous carbon nanofiber anode loaded with Fe2O3 for Li-ion batteries

In this work, a honeycomb-shaped meso@mesoporous carbon nanofiber material incorporating homogeneously dispersed ultra-fine Fe2O3 nanoparticles (denoted as Fe2O3@g-C3N4@H-MMCN) is synthesised through a pyrolysis process. The honeycomb-shaped configuration of the meso@mesoporous carbon nanofiber material derived from a natural bio-carbon source (crab shell) acts as a support for an anode material for Li-ion batteries. Graphitic carbon nitride (g-C3N4) is produced via the one-step pyrolysis of urea at high temperature under an N2 atmosphere without the assistance of additives. The resulting favorable electrochemical performance, with superior rate capabilities (1067 mA h g-1 at 1000 mA g-1), a remarkable specific capacity (1510 mA h g-1 at 100 mA g-1), and steady cycling performance (782.9 mA h g-1 after 500 cycles at 2000 mA g-1), benefitted from the advantages of both the host material and the Fe2O3 nanoparticles, which play an important role due to their ultra-fine particle size of 5 nm. The excellent cycle life and high capacity demonstrate that this strategy of strong synergistic effects represents a new pathway for pursuing high-electrochemical-performance materials for lithium-ion batteries.

Hierarchical copper cobalt sulfide nanobelt arrays for high performance asymmetric supercapacitors

Rational construction of the morphology of the positive and negative electrodes to assemble a high performance asymmetric supercapacitor.

One-step phosphating synthesis of CoP nanosheet arrays combined with Ni2P as a high-performance electrode for supercapacitors

A transition metal phosphide is an excellent candidate for supercapacitors due to its superior electrical conductivity and high theoretical capacity. In addition, compared with traditional 3D nano-materials, 2D nanosheets possess a greater specific surface area and shorter electron transport distance. In this study, a reasonable approach is proposed for the synthesis of ZIF-67 nanosheets on nickel foam with subsequent phosphorization by chemical vapor deposition (CVD) to obtain flake-like CoP combined with Ni2P (NCP/NF), in which nickel foam serves as the current collector as well as the resource of Ni to form Ni2P. Benefiting from the nanosheet array of CoP, the NCP/NF can improve the capacity of Ni2P from 0.57 C cm-2 to 1.43 C cm-2 at 1 mA cm-2. Furthermore, the NPC/NF/reduced graphene oxide (RGO) asymmetric supercapacitor (ASC) shows an energy density of 26.9 μW h cm-2 at a power density of 0.896 mW cm-2, and excellent cycling performance with a capacity retention of 93.75% after 5000 cycles at 10 mA cm-2.

Construction of ultra-stable trinickel disulphide (Ni3S2)/polyaniline (PANI) electrodes based on carbon fibers for high performance flexible asymmetric supercapacitors

Highly flexible supercapacitors (SCs) have attracted significant attention in modern electronics. However, it has been found that flexible, metal sulfide-based electrodes usually suffer from corrosion, instability and low conductivity, which significantly limits their large scale application. Herein, we report on an electrode comprised of highly stable, free-standing carbon fiber/trinickel disulphide covered with polyaniline (CF/Ni₃S₂@PANI). This electrode was prepared and then employed in a high-performance of flexible asymmetric SCs (FASC). The coating layer of polyaniline served as both a protector and conducting shell for the Ni₃S₂ due to the nature of the highly stable N-Ni bonds that formed between the polyaniline and Ni₃S₂. In addition, the lightweight carbon fiber support served as both a current collector and flexible support. The prepared CF/Ni₃S₂@PANI electrode exhibited a significantly enhanced specific capacity (715.3 F·g^-1 at 1 A·g^-1) compared with the carbon fiber/Ni₃S₂ electrode (318 F·g^-1 at 1 A·g^-1). More importantly, the assembled FASC device delivered an impressive energy density of 35.7 Wh·kg^-1 at a power density of 850 W·kg^-1. The FASC device benefited from the interconnected flexible microstructure and the stable bond bridges, so that it could be bent into various angles without noticeably impairing its performance. This effective protective strategy may further inspire the design and manufacture of metallic oxide or sulfide electrode with ultrahigh-stability interbond bridges for high-performance flexible supercapacitors.

Interface engineering of Co3O4 nanowire arrays with ultrafine NiO nanowires for high-performance rechargeable alkaline batteries

Interface engineering multi-component core-shell nanostructures with highly efficient and reversible faradaic reactions for energy conversion storage devices is still a challenge. Here, Co₃O₄ nanowires@NiO ultrafine nanowires on Ni foam were well fabricated via coating the NiO ultrafine nanowires on porous Co₃O₄ nanowire arrays. The combination of structural and compositional advantages endows the Co₃O₄@NiO core-shell composites with excellent electrochemical performance, such as a favorable specific capacity of 0.71 mA h cm^-2 at 3 mA cm^-2, excellent rate capability and 85% retention rate up to 10,000 cycles. Rechargeable alkaline batteries with the Co₃O₄@NiO core-shell composites and AC as cathode and anode, respectively, had a high specific capacity of 0.51 mA h cm^-2 and stable cycling ability (81% retention after 5000 cycles). The hierarchical core-shell heterostructure electrode exhibits excellent electrochemical performance, making it a very promising material for next-generation energy storage device applications.

3D hierarchical porous nitrogen-doped carbon/Ni@NiO nanocomposites self-templated by cross-linked polyacrylamide gel for high performance supercapacitor electrode

Three-dimensional nitrogen-doped carbon network incorporated with nickel@nickel oxide core-shell nanoparticles composite (3D NC/Ni@NiO) has been facilely prepared, self-templated by the cross-linked polyacrylamide aerogel precursor containing NiCl₂. Characterizations reveal that the Ni@NiO nanoparticles distribute homogeneously in the 3D nitrogen-doped carbon matrix and the composite is of hierarchical porous structure. When used as supercapacitor electrode in a three-electrode system, the 3D NC/Ni@NiO exhibits enhanced electrical conductivity and excellent electrochemical performance, presenting a high specific capacitance (389F g^-1 at 5 mV s^-1), good rate capability (276 F g^-1 at 100 mV s^-1) and outstanding cycling performance (with the capacitance retention of 70.2% after 5000 charge-discharge cycles). This is due to the synergistic effects of conductive metallic nickel, pseudocapacitive nickel oxide as well as in situ nitrogen doping of carbon network. Moreover, an asymmetric supercapacitor (ASC) was fabricated with NC/Ni@NiO as positive electrode and active carbon as negative electrode. The ASC device exhibits a maximum energy density of 19.4 W h kg^-1 at a power density of 700 W kg^-1 and shows good cycling stability (73.8% capacity retention after 3000 cycles), indicating that it has great promise for practical energy storage and conversion application.

Hierarchical core-shell electrode with NiWO4 nanoparticles wrapped MnCo2O4 nanowire arrays on Ni foam for high-performance asymmetric supercapacitors

Rational construction of MnCo₂O₄-based core-shell nanomaterials with distinctive and desirable architectures possesses great potential in the advanced electrode material of high-performance supercapacitors. Here, a new class of hierarchical core-shell nanowire arrays (NWAs) with a shell of NiWO₄ nanoparticles and a core of MnCo₂O₄ nanowires is reported, which can significantly improve the electrochemical energy storage properties of supercapacitors. The unique core-shell structure endows the MnCo₂O₄@NiWO₄ NWAs electrode with a high areal specific capacitance of 5.09 F cm^-2 at a current density of 1 mA cm^-2 and a superior cyclic retention of 96% after 5000 charge-discharge cycles, which are more preferable than those of MnCo₂O₄ NWAs electrode. More importantly, an aqueous electrochemical energy storage device (core-shell MnCo₂O₄@NiWO₄ NWAs as the positive electrode and active carbon as the negative electrode, MnCo₂O₄@NiWO₄//AC ASC) was assembled and shows a high energy density of 0.23 mWh cm^-2 at a power density of 2.66 mW cm^-2, and 0.09 mWh cm^-2 at 16.00 mW cm^-2, indicating hopeful potential for practical applications. This work highlights the significance of NiWO₄ as a shell for hierarchical core-shell nanostructures, which can further improve the electron transport characteristic of the electrode material, thereby achieving performance breakthroughs in energy storage devices.