Achieving Ultrahigh Capacity with Self-Assembled Ni(OH)2 Nanosheet-Decorated Hierarchical Flower-like MnCo2O4.5 Nanoneedles as Advanced Electrodes of Battery-Supercapacitor Hybrid Devices

Microwave-Assisted Doping Engineering Construction of Spinel-Structured Nonstoichiometric Manganese Cobaltite with Mixed 1D/2D Morphology for Supercapacitor Application

High-performance electrode materials are fundamental to improving supercapacitor performance, serving as key factors in developing devices with high energy density, high power density, and excellent cyclic stability. Non-stoichiometric spinels with phase deficiencies can achieve electrochemical performance that surpasses that of stoichiometric materials, owing to their unique structural characteristics. In this study, we used a microwave-assisted method to synthesize a high-performance non-stoichiometric spinel material with phase deficiencies, Mn0.5Co2.5O4, which displayed a wide potential window (1.13 V in a traditional aqueous three-electrode system) and high specific capacitance (716.9 F g-1 at 1 A g-1). More critically, through microwave-assisted doping engineering, nickel was successfully doped into the phase-deficient Mn0.5Co2.5O4, resulting in a spinel material, Ni-Mn0.5Co2.5O4, with significant lattice defects and a mixed 1D/2D morphology. The doping of nickel effectively promoted the high-state conversion of manganese valence states within the manganese cobaltite material, substantially increasing the quantity of highly active Co3+ ions. These changes led to an increase in the density of reactive sites, effectively promoting synergistic interactions, thereby significantly enhancing the material's conductivity and energy storage performance. The specific capacitance of Ni-Mn0.5Co2.5O4 reached 1180.6 F g-1 at 1 A g-1, a 64.7% improvement over the original Mn0.5Co2.5O4; at a high current density of 10 A g-1, the capacitance increased by 14.3%. Notably, the charge transfer resistance was reduced by a factor of 41.6. After 5000 cycles of testing, the capacity retention stood at 79.2%. This work reveals the effectiveness of microwave-assisted doping engineering in constructing high-performance non-stoichiometric spinel-type bimetallic oxide materials, offering advanced strategies for the development of high-performance electrode materials.

g-C3N4 modified flower-like CuCo2O4 array on nickel foam without binder for high-performance supercapacitors

This study investigates the impact of integrating g-C3N4 into CuCo2O4 electrodes on electrochemical performance working as binder-free electrodes. Flower-like CuCo2O4 nanostructures on nickel foam are decorated with few-layer g-C3N4 using a secondary hydrothermal process. The hierarchical g-C3N4/CuCo2O4 nanoflower electrode demonstrates a specific capacity of 247.5 mA h g-1 at a current density of 1 A g-1, while maintaining a capacity of 87.0 mA h g-1 at a heightened current density of 5 A g-1. Notably, this electrode exhibited remarkable durability, retaining 98% of its capacity after 1000 cycles. The g-C3N4/CuCo2O4 heterostructure shows promise for high-performance energy storage devices.

Two birds with one stone: facile fabrication of an iron-cobalt bimetallic sulfide nanosheet-assembled nanosphere for efficient energy storage and hydrogen evolution

Transition metal sulfides are widely regarded as the most promising electrode materials for supercapacitors. Herein, we utilized a straightforward electrodeposition method to prepare an iron-cobalt bimetallic sulfide nanosheet-assembled nanosphere on nickel foam (FeCo2S4/NF). The synergistic effect between bimetals and the unique three-dimensional structure significantly improved its capacitive performance. As a result, it demonstrated a remarkable specific capacitance, brilliant long-term stability and acceptable rate capability. Moreover, FeCo2S4/NF and active carbon (AC) were used to assemble an asymmetric supercapacitor (ASC), and FeCo2S4//AC displays a maximum energy density of 29.4 W h kg-1 at 800 W kg-1. Moreover, when adopted as an electrocatalyst for the hydrogen evolution reaction (HER), FeCo2S4/NF exhibited excellent catalytic properties (η10 = 165 mV). Our research provides a valuable insight into the multidisciplinary integration of high-performance energy materials.

Modern Developments for Textile-Based Supercapacitors

Smart textiles are transforming the future of wearable technology, and due to that, there has been a great deal of new research looking for alternative energy storage. Supercapacitors offer high discharge rates, flexibility, and long life cycles and can be integrated fully into a textile. Optimization of these new systems includes utilizing electrically conductive materials, employing successful electrostatic charge and/or faradaic responses, and fabricating a textile-based energy storage system without disrupting comfort, washability, and life cycle. This paper examines recent developments in fabrication methods and materials used to create textile supercapacitors and what challenges still remain.

Nickel Cobaltite: A Positive Electrode Material for Hybrid Supercapacitors

The increased demand of energy due to the recent technological advances in diverse fields such as portable electronics and electric vehicles is often hindered by the poor capability of energy-storage systems. Although supercapacitors (SCs) exhibit higher power density than state-of-the art batteries, their insufficient energy density remains a major challenge. An emerging concept of hybrid supercapacitors (HSCs) with the combination of one capacitive and one battery electrode in a single cell holds a great promise to deliver high energy density without sacrificing power density and cycling stability. This Minireview elaborates the recent advances of use of nickel cobaltite (NiCo₂ O₄ ) as a potential positive electrode (battery-like) for HSCs. A brief introduction on the structural benefits and charge storage mechanisms of NiCo₂ O₄ was provided. It further shed a light on composites of NiCo₂ O₄ with different materials like carbon, polymers, metal oxides, and others, which altogether helps in increasing the electrochemical performance of HSCs. Finally, the key scientific challenges and perspectives on building high-performance HSCs for future-generation applications were reviewed.

Hierarchical coral-like MnCo2O4.5@Co-Ni LDH composites on Ni foam as promising electrodes for high-performance supercapacitor

Transition metal oxides are generally designed as hybrid nanostructures with high performance for supercapacitors by enjoying the advantages of various electroactive materials. In this paper, a convenient and efficient route had been proposed to prepare hierarchical coral-like MnCo₂O_4.5@Co-Ni LDH composites on Ni foam, in which MnCo₂O_4.5nanowires were enlaced with ultrathin Co-Ni layered double hydroxides nanosheets to achieve high capacity electrodes for supercapacitors. Due to the synergistic effect of shell Co-Ni LDH and core MnCo₂O_4.5, the outstanding electrochemical performance in three-electrode configuration was triggered (high area capacitance of 5.08 F cm^-2at 3 mA cm^-2and excellent rate capability of maintaining 61.69% at 20 mA cm^-2), which is superior to those of MnCo₂O_4.5, Co-Ni LDH and other metal oxides based composites reported. Meanwhile, the as-prepared hierarchical MnCo₂O_4.5@Co-Ni LDH electrode delivered improved electrical conductivity than that of pristine MnCo₂O_4.5. Furthermore, the as-constructed asymmetric supercapacitor using MnCo₂O_4.5@Co-Ni LDH as positive and activated carbon as negative electrode presented a rather high energy density of 220μWh cm^-2at 2400μW cm^-2and extraordinary cycling durability with the 100.0% capacitance retention over 8000 cycles at 20 mA cm^-2, demonstrating the best electrochemical performance compared to other asymmetric supercapacitors using metal oxides based composites as positive electrode material. It can be expected that the obtained MnCo₂O_4.5@Co-Ni LDH could be used as the high performance and cost-effective electrode in supercapacitors.

Carbon Nanotube Based Robust and Flexible Solid-State Supercapacitor

All solid-state flexible electrochemical double-layer capacitors (EDLCs) are crucial for providing energy options in a variety of applications, ranging from wearable electronics to bendable micro/nanotechnology. Here, we report on the development of robust EDLCs using aligned multiwalled carbon nanotubes (MWCNTs) grown directly on thin metal foils embedded in a poly(vinyl alcohol)/phosphoric acid (PVA/H₃PO₄) polymer gel. The thin metal substrate holding the aligned MWCNT assembly provides mechanical robustness and the PVA/H₃PO₄ polymer gel, functioning both as the electrolyte as well as the separator, provides sufficient structural flexibility, without any loss of charge storage capacity under flexed conditions. The performance stability of these devices was verified by testing them under straight and bent formations. A high value of the areal specific capacitance (C_SP) of ∼14.5 mF cm^-2 with an energy density of ∼1 μW h cm^-2 can be obtained in these devices. These values are significantly higher (in some cases, orders of magnitude) than several graphene as well as single-walled nanotube-based EDLC's utilizing similar electrolytes. We further show that these devices can withstand multiple (∼2500) mechanical bending cycles, without losing their energy storage capacities and are functional within the temperature range of 20 to 70 °C. Several strategies for enhancing the capacitive charge storage, such as physically stacking (in parallel) individual devices, or postproduction thermal annealing of electrodes, are also demonstrated. These findings demonstrated in this article provide tremendous impetus toward the realization of robust, stackable, and flexible all solid-state supercapacitors.

Core-shell shaped Ni2CoHCF@PPy microspheres from prussian blue analogues for high performance asymmetric supercapacitors

Recently, prussian blue analogues (PBAs), as the most classical class of metal-organic frameworks, have been widely studied by scientists. Nevertheless, the inferior conductivity of PBAs restricts the application in supercapacitors. In this work, nickel cobalt hexacyanoferrate (Ni₂CoHCF) had been produced via a simple co-precipitation approach and coated with polypyrrole on its surface. The conductivity of PBAs was improved by the polypyrrole coating. The Ni₂CoHCF@PPy-400 microspheres were demonstrated to the outstanding specific capacity of 82 mAh g^-1at 1 A g^-1. After 3000 cycles, the Ni₂CoHCF@PPy-400 microspheres had a long cycle life and 86% specific capacity retention rate at 5 A g^-1. Additionally, it was coupled with activated carbon to build high performance asymmetric supercapacitor (Ni₂CoHCF@PPy-400//AC), which displayed a high energy density of 21.7 Wh kg^-1at the power density of 888 W kg^-1and good cycle stability after 5000 cycles (a capacity retention rate of 85.2%). What is more, the results reveal that the Ni₂CoHCF@PPy-400 microspheresare a prospective candidate for exceptional energy storage devices.

Standing and Lying Ni(OH)2 Nanosheets on Multilayer Graphene for High-Performance Supercapacitors

For conventional synthesis of Ni(OH)₂/graphene hybrids, oxygen-containing functional groups should be firstly introduced on graphene to serve as active sites for the anchoring of Ni(OH)₂. In this work, a method for growing Ni(OH)₂ nanosheets on multilayer graphene (MLG) with molecular connection is developed which does not need any pre-activation treatments. Moreover, Ni(OH)₂ nanosheets can be controlled to stand or lie on the surface of MLG. The prepared hybrids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The growth processes are suggested according to their morphologies at different growth stages. The enhanced electrochemical performances as supercapacitor electrode materials were confirmed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. Ni(OH)₂ nanosheets standing and lying on MLG show specific capacities of 204.4 mAh g⁻¹ and 131.7 mAh g⁻¹, respectively, at 1 A g⁻¹ based on the total mass of the hybrids and 81.5% and 92.8% capacity retention at a high current density of 10 A g⁻¹, respectively. Hybrid supercapacitors with as-prepared hybrids as cathodes and activated carbon as anode were fabricated and tested.

Structural evolution and sulfuration of nickel cobalt hydroxides from 2D to 1D on 3D diatomite for supercapacitors

Transition metal nickel–cobalt hydroxides are widely used as electrode materials for supercapacitors due to their intriguing active component properties.

One-step synthesis of Ni(OH)2/MWCNT nanocomposites for constructing a nonenzymatic hydroquinone/O2 fuel cell

In this work, a H-type hydroquinone/O2 fuel cell was assembled and shows high energy density in neutral phosphate buffer solution at moderate temperature. The anodic material, Ni(OH)2/MWCNTs, was synthesized by a one-step hydrothermal synthesis method to oxidize hydroquinone. The cathode material, Pt/MWCNTs, was obtained by an electrodeposition method, and shows great oxygen reduction reaction (ORR) activity. The properties and the morphology of Ni(OH)2/MWCNT nanocomposites were characterized by TEM, XPS, EDS-mapping and electrochemical methods, like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that Ni(OH)2/MWCNTs can effectively oxidize hydroquinone and play a dominant role in enhancing the fuel cell performance. The nonenzymatic fuel cell possesses a high power density of 0.24 mW cm-2 at a cell potential of 0.49 V.

Two-for-one strategy: Three-dimensional porous Fe-doped Co3O4 cathode and N-doped carbon anode derived from a single bimetallic metal-organic framework for enhanced hybrid supercapacitor

"Two-for-one" strategy is an effective method to construct two kinds of materials from a single precursor owing to the simplicity of fabricating procedure and reduction of manufacturing cost. However, such a strategy has seldom been utilized to produce both battery-type and capacitive electrodes of a hybrid supercapacitor (HSC) device. Here, we adopt the "two-for-one" strategy to fabricate three-dimensional (3D) porous iron-doped (Fe-doped) Co₃O₄ and nitrogen-doped (N-doped) carbon via a single bimetallic metal-organic framework, FeCo-ZIF-67. Fe-doped amounts and carbonization temperature are used to adjust their individual electrochemical behaviors. The optimal 3D porous Fe-doped Co₃O₄ and N-doped carbon possess a high capacitance of 767.9 and 277C g^-1 at 1 A g^-1, respectively. Charge storage mechanism of Fe-doped Co₃O₄ is further investigated via analysis of capacitive and diffusion-controlled contribution. A Fe-doped Co₃O₄//N-doped carbon HSC device achieves desirable specific energy (37 Wh kg^-1) and power (750 Wkg^-1), and satisfied cycling stability (90% retention after 4000 cycles). A light-emitting diode (LED) is successfully light by the HSC device, suggesting its potential application in the field of green energy conversion and storage devices.

Textile-based supercapacitors for flexible and wearable electronic applications

Electronic textiles have garnered significant attention as smart technology for next-generation wearable electronic devices. The existing power sources lack compatibility with wearable devices due to their limited flexibility, high cost, and environment unfriendliness. In this work, we demonstrate bamboo fabric as a sustainable substrate for developing supercapacitor devices which can easily integrate to wearable electronics. The work demonstrates a replicable printing process wherein different metal oxide inks are directly printed over bamboo fabric substrates. The MnO₂–NiCo₂O₄ is used as a positive electrode, rGO as a negative electrode, and LiCl/PVA gel as a solid-state electrolyte over the bamboo fabrics for the development of battery-supercapacitor hybrid device. The textile-based MnO₂–NiCo₂O₄//rGO asymmetric supercapacitor displays excellent electrochemical performance with an overall high areal capacitance of 2.12 F/cm² (1,766 F/g) at a current density of 2 mA/cm², the excellent energy density of 37.8 mW/cm³, a maximum power density of 2,678.4 mW/cm³ and good cycle life. Notably, the supercapacitor maintains its electrochemical performance under different mechanical deformation conditions, demonstrating its excellent flexibility and high mechanical strength. The proposed strategy is beneficial for the development of sustainable electronic textiles for wearable electronic applications.

Fabrication and Electrochemical Performance of PVA/CNT/PANI Flexible Films as Electrodes for Supercapacitors

The flexible and rechargeable energy storage device with excellent performance is highly desired due to the demands of portable and wearable devices. Herein, by integrating the bendability and stretchability of Polyvinyl alcohol (PVA), pseudocapacitance of Polyaniline (PANI), and the charge transport ability of carbon nanotubes (CNTs), PVA/CNT/PANI flexible film was fabricated as supercapacitor electrodes with excellent electrochemical performance and flexibility. Full-solid supercapacitor is prepared based on PVA/H₂SO₄ gel electrolyte and as-prepared film electrodes. The device achieves an areal capacitance of 196.5 mF cm^-2 with high cycling stability. The flexible properties of PVA, the conductivity of CNT, and the pseudo-capacitance of PANI contribute to the superior performance. Present work develops a facile and effective way for preparing flexible electrode materials. In present work, we fabricated PVA/CNT/PANI flexible film as supercapacitor electrodes with excellent electrochemical performance and flexibility.

In-Situ Synthesis of Heterostructured Carbon-Coated Co/MnO Nanowire Arrays for High-Performance Anodes in Asymmetric Supercapacitors

Structural design is often investigated to decrease the electron transfer depletion in/on the pseudocapacitive electrode for excellent capacitance performance. However, a simple way to improve the internal and external electron transfer efficiency is still challenging. In this work, we prepared a novel structure composed of cobalt (Co) nanoparticles (NPs) embedded MnO nanowires (NWs) with an N-doped carbon (NC) coating on carbon cloth (CC) by in situ thermal treatment of polydopamine (PDA) coated MnCo₂O_4.5 NWs in an inert atmosphere. The PDA coating was carbonized into the NC shell and simultaneously reduced the MnCo₂O_4.5 to Co NPs and MnO NWs, which greatly improve the surface and internal electron transfer ability on/in MnO boding well supercapacitive properties. The hybrid electrode shows a high specific capacitance of 747 F g⁻¹ at 1 A g⁻¹ and good cycling stability with 93% capacitance retention after 5,000 cycles at 10 A g⁻¹. By coupling with vanadium nitride with an N-doped carbon coating (VN@NC) negative electrode, the asymmetric supercapacitor delivers a high energy density of 48.15 Wh kg⁻¹ for a power density of 0.96 kW kg⁻¹ as well as outstanding cycling performance with 82% retention after 2000 cycles at 10 A g⁻¹. The electrode design and synthesis suggests large potential in the production of high-performance energy storage devices.

High performance flexible hybrid supercapacitors based on nickel hydroxide deposited on copper oxide supported by copper foam for a sunlight-powered rechargeable energy storage system

Herein, an integrated system combining solar cells with a hybrid supercapacitor for operating a homemade windmill device was assembled, achieving energy conversion, storage and utilization. As a candidate for positive electrode of hybrid supercapacitor devices, battery-like Ni(OH)₂@CuO@Cu binder-free electrode was fabricated by a two-step process at ambient temperature. CuO@Cu was prepared by chemical oxidation method to act as the supporting electrode for electrochemical deposition of Ni(OH)₂. Various deposition times (30, 50, 90, 150 and 200 s) were investigated to optimize the energy storage characteristics of the resulting Ni(OH)₂@CuO@Cu electrode materials. Among all the samples, Ni(OH)₂@CuO@Cu-150 exhibited the largest areal capacity of 7063 mC cm^-2 at 20 mA cm^-2, and was therefore chosen as the positive electrode in a hybrid supercapacitor device. Using N-doped reduced graphene oxide on nickel foam (N-rGO/NF) as the negative electrode, a hybrid supercapacitor was assembled. It displayed good flexibility, cycling stability and high areal energy density of 130.4 μWh cm^-2 at a power density of 1.6 mW cm^-2. Two hybrid supercapacitor devices were connected in series to successfully lighten up a red LED for 12 min 39 s, while three devices assembled in series were able to successfully power a three-digit digital display for 1 min 28 s. Interestingly, the hybrid supercapacitor device, charged by solar cells, further operated a homemade windmill device for 59 s, achieving sunlight-powered integration system. All of the findings suggested the practical application potential of the hybrid supercapacitor based on Ni(OH)₂@CuO@Cu composite as energy storage device.

Selenium-rich nickel cobalt bimetallic selenides with core-shell architecture enable superior hybrid energy storage devices

The continuous exploration of advanced electrode materials is of remarkable significance to revolutionize next-generation high-performance energy storage devices towards a green future. Benefiting from their electrochemically active sites and abundant redox centers, bimetallic selenides with desirable nanostructures recently have emerged as promising electrode alternatives for battery-supercapacitor hybrid (BSH) devices which demonstrate enormous potential in bridging the gap between electrochemical properties with high power densities (supercapacitors) and energy densities (batteries). Herein, employing the hydrothermal approach with solid Ni-Co spheres as precursors followed by the selenization process, selenide-rich bimetallic selenide spheres with a core-shell nanostructure were rationally designed and synthesized for use as the cathode electrode in superior BSH devices. The as-obtained (NiCo)₉Se₈/(NiCo)_0.85Se (Ni-Co-Se) exhibits a high specific capacity of 164.44 mA h g^-1 at a current density of 1 A g^-1 with 85.72% capacity retention even after 5000 cycles at a current density of as high as 8 A g^-1, suggesting its great promise in practical applications for BSH devices. By integrating activated carbon as the anode with the as-obtained bimetallic selenides as the cathode, an alkaline aqueous BSH device is fabricated and delivers a high energy density of 37.54 W h kg^-1 at a high power density of 842.7 W kg^-1. It is found that the excellent electrochemical performances can be ascribed to facile ion and electron transport pathways, high electrical conductivity and reliable structural robustness of the prepared selenides. Moreover, the synthetic strategy presented in this paper opens up an avenue to guide the synthesis of various anion doped bimetallic compounds towards high-performance energy conversion and storage devices.

CuO nanorods grown vertically on graphene nanosheets as a battery-type material for high-performance supercapacitor electrodes

This work reports the preparation and characterization of the CuO nanorods grown vertically on graphene nanosheets, denoted as CuO/rGO@NF. Graphene is deposited by electrostatic attraction showing the morphology of folded nanosheets, which improves the electrical conductivity of the electrode, while CuO is modified by filtered cathodic vacuum arc technology and subsequent electrochemical oxidation presenting the morphology of nanorods, which increases the contact area of active sites and shortens the ion and electronic diffusion path. The results show that the CuO/rGO@NF electrode deliver an ultrahigh specific capacity (2.51 C cm⁻² at 2 mA cm⁻²), remarkable rate performance (64.6%) and improved conductivity. A symmetrical supercapacitor is assembled by two identical electrodes, presenting the maximum energy density of 38.35 W h kg⁻¹ at a power density of 187.5 W kg⁻¹. Therefore, the CuO/rGO@NF electrode can be used as a prospective electrode for energy storage devices. In addition, the whole electrode preparation process is short in time, safe and environmentally friendly, which provides a new idea for the preparation of other electrode materials.

The CuO/rGO@NF electrode is prepared by a simple and time-saving method, which has ultrahigh area capacity and excellent rate performance.

Construction of hierarchical cobalt-molybdenum selenide hollow nanospheres architectures for high performance battery-supercapacitor hybrid devices

Transition metal selenides have aroused widespread attention as a class of emerging electrode materials for high-performance supercapacitors attributed to their featured with high theoretical capacitance and low electronegativity. Nevertheless, their practical applications are seriously restricted by the large volume expansion during high-rate charge/discharge. It is imperative to reasonably construct tunable composition and attractive architectures for electrode materials at nanoscale to mitigate the issues. Herein, hierarchical cobalt-molybdenum selenide (denoted as CoSe₂/MoSe₂-3-1) hollow nanospheres architectures are purposefully prepared via an efficient gas bubble-templated method combined with post-annealing process. Benefiting from the rationally hierarchical hollow structures and maximized utilization ratio of active materials, the novel bimetallic selenides acquire superior electrochemical performance with high specific capacity (211.97 mA h g^-1 at 1 A g^-1) and remarkable cycling stability (94.2% capacity retention over 2000 cycles at 3 A g^-1). Significantly, the assembled CoSe₂/MoSe₂-3-1//activated carbon (AC) battery-supercapacitor hybrid (BSH) device renders a high energy density up to 51.84 W h kg^-1 at a power density of 799.2 W kg^-1 and preeminent cycling stability with 93.4% retention over 10,000 cycles. The present work provides an effective and rational design route to engineer advanced bimetallic selenides with hierarchical hollow structures for electrochemical energy storage and conversion.

Construction of a MnCo2O4@NiyMx (S and P) crosslinked network for efficient electrocatalytic water splitting

Using MnCo₂O₄@Ni₃S₂ as a bifunctional water splitting catalyst, an overpotential of ∼370 mV is obtained at a very low cell voltage of 1.60 V with a current density of 10 mA cm⁻² in 1.0 M KOH.

Construction of ZnCo2S4@Ni(OH)2 core–shell nanostructures for asymmetric supercapacitors with high energy densities

ZnCo₂S₄ nanoneedle clusters are uniformly grown as a core on foamed nickel and then are coated with Ni(OH)₂ nanosheets as shell layers.