Tuning parallel manganese dioxide to hollow parallel hydroxyl oxidize iron replicas for high-performance asymmetric supercapacitors

Restricted and epitaxial growth of MnO2-x nano-flowers in/out carbon nanofibers for long-term cycling stability supercapacitor electrodes

Carbon nanofibers (CFs) have been widely applied as electrodes for energy storage devices owing to the features of increased contact area between electrodes and electrolyte, and shortened transmission route of electrons. However, the poor electrochemical activity and severe waste of space hinder their further application as supercapacitors electrodes. In this work, MnO2-x nanoflowers restricted and epitaxial growth in/out carbon nanofibers (MnO2/MnO@CF) were prepared as excellent electrode materials for supercapacitors. With the synergistic effect of uniquely designed structure and the introduction of MnO and MnO2 nanoflowers, the prepared interconnected MnO2/MnO@CF electrodes demonstrated satisfactory electrochemical performance. Furthermore, the MnO2/MnO@CF//activated carbon (AC) asymmetric supercapacitor offered an outstanding long-term cycle stability. Besides, kinetic analysis of MnO2/MnO@CF-90 was conducted and the diffusion-dominated storage mechanism was well-revealed. This concept of "internal and external simultaneous decoration" with different valence states of manganese oxides was proven to improve the electrochemical performance of carbon nanofibers, which could be generalized to the preparation and performance improvement of other fiber-based electrodes.

Shielding Mn3+ Disproportionation with Graphitic Carbon-Interlayered Manganese Oxide Cathodes for Enhanced Aqueous Energy Storage System

Manganese dioxide (MnO2) materials have recently garnered attention as prospective high-capacity cathodes, owing to their theoretical two-electron redox reaction in charge storage processes. However, their practical application in aqueous energy storage systems faces a formidable challenge: the disproportionation of Mn3+ ions, leading to a significant reduction in their capacity. To address this limitation, the study presents a novel graphitic carbon interlayer-engineered manganese oxide (CI-MnOx) characterized by an open structure and abundant defects. This innovative material serves several essential functions for efficient aqueous energy storage. First, a graphitic carbon layer coats the MnOx molecular interlayer, effectively inhibiting Mn3+ disproportionation and substantially enhancing electrode conductivity. Second, the phase variation within MnOx generates numerous crystal defects, vacancies, and active sites, optimizing electron-transfer capability. Third, the flexible carbon layer acts as a buffer, mitigating the volume expansion of MnOx during extended cycling. The synergistic effects of these features result in the CI-MnOx exhibiting an impressive high capacity of 272 mAh g-1 (1224 F g-1) at 0.25 A g-1. Notably, the CI-MnOx demonstrates zero capacity loss after 90 000 cycles (≈3011 h), an uncommon longevity for manganese oxide materials. Spectral characterizations reveal reversible cation intercalation and conversion reactions with multielectron transfer in a LiCl electrolyte.

Advances in Mn-Based MOFs and Their Derivatives for High-Performance Supercapacitor

As the most widely used metal material in supercapacitors, manganese (Mn)-based materials possess the merits of high theoretical capacitance, stable structure as well as environmental friendliness. However, due to poor conductivity and easy accumulation, the practical capacitance of Mn-based materials is far lower than that of theoretical value. Therefore, accurate structural adjustment and controllable strategies are urgently needed to optimize the electrochemical properties of Mn-based materials. Metal-organic frameworks (MOFs) are porous materials with high specific surface area (SSA), tunable pore size, and controllable structure. These features make them attractive as precursors or scaffold for the synthesis of metal-based materials and composites, which are important for electrochemical energy storage applications. Therefore, a timely and comprehensive review on the classification, design, preparation and application of Mn-based MOFs and their derivatives for supercapacitors has been given in this paper. The recent advancement of Mn-based MOFs and their derivatives applied in supercapacitor electrodes are particularly highlighted. Finally, the challenges faced by Mn-MOFs and their derivatives for supercapacitors are summarized, and strategies to further improve their performance are proposed. The aspiration is that this review will serve as a beneficial compass, guiding the logical creation of Mn-based MOFs and their derivatives in the future.

Recent Trends in Supercapacitor Research: Sustainability in Energy and Materials

Supercapacitors (SCs) have emerged as critical components in applications ranging from transport to wearable electronics due to their rapid charge-discharge cycles, high power density, and reliability. This review offers an analysis of recent strides in supercapacitor research, emphasizing pivotal developments in sustainability, electrode materials, electrolytes, and 'smart SCs' designed for modern microelectronics with attributes such as flexibility, stretchability, and biocompatibility. Central to this discourse are two dominant electrode materials: carbon materials (CMs), primarily in electric double layer capacitors (EDLCs), and pseudocapacitive materials, involving oxides/hydroxides, chalcogenides, metal-organic frameworks, conductive polymers and metal nitrides such as MXene. Despite EDLCs' historical use, challenges such as low energy density persist, with heteroatom introduction into the carbon lattice seen as a solution. Concurrently, pseudocapacitive materials dominate recent studies, with efficiency enhancement strategies, such as the creation of hybrids based on different types of materials, surface structural engineering and doping, under exploration. Electrolyte innovation, especially the shift towards gel polymer electrolytes for flexible SCs, and the harmonization of electrode materials with SC designs are highlighted. Emphasis is given to smart SCs with novel attributes such as self-charging, self-healing, biocompatibility, and environmentally conscious designs. In summary, the article underscores the drive in sustainable supercapacitor research to achieve high energy and power density, steering towards SCs that are efficient and versatile and involving bioderived/biocompatible SC materials. This brief review is based on selected recent references, offering depth combined with an accessible overview of the SC landscape.

Anchoring tungsten oxide nanorods on TiO2 nanowires coupled with carbon for efficient lithium-ion storage

Reasonable construction of hierarchical electrode materials is verified as a promising way to improve the electrochemical performance due to the synergistic effect between unique components and constructions. Hence, a hierarchical nanostructure composed of tungsten oxide nanorods anchored on TiO2 nanowires coupled with a carbon layer (TiO2@WOx-C NWs) was synthesized as an electrode material by exploiting the self-assembly function of dopamine and carbonization. The inner one-dimensional TiO2 nanowires served as the stable substrate with WOx anchored on the surface of TiO2 NWs and the tightly coupled carbon nanosheets, which can not only facilitate electron transport but also provide more active sites for electrochemical reactions. As a result, benefitting from the synergistic effects between three functional components and the multi-dimensional hierarchical structures, the as-prepared TiO2@WOx-C NWs displayed excellent lithium storage performance with a specific capacity of 651.4 mA h g-1 after 500 cycles at 1.0 A g-1, which is superior to most Ti-based structures. The enhanced electrochemical performance is mainly attributed to the synergistic effect of the different dimensional structures, the high capacity of tungsten oxide and the surface coating of the conductive carbon material. This work provides a simple and effective approach to designing functional hierarchical structures for energy storage and conversion.

P-N heterojunction NiO/ZnO nanowire based electrode for asymmetric supercapacitor applications

Nickel-based oxides are selected for their inexpensive cost, well-defined redox activity, and flexibility in adjusting nanostructures via optimization of the synthesis process. This communique explores the field of energy storage for hydrothermally synthesized NiO/ZnO nanowires by analysing their capacitive behaviour. The p-type NiO was successfully built onto the well-ordered mesoporous n-type ZnO matrix, resulting in the formation of p-n heterojunction artefacts with porous nanowire architectures. NiO/ZnO nanowire-based electrodes exhibited much higher electrochemical characteristics than bare NiO nanowires. The heterojunction at the interface between the NiO and ZnO nanoparticles, their specific surface area, as well as their combined synergetic influence, are accountable for the high specific capacitance (Cs) of 1135 Fg-1at a scan rate of 5 mV s-1. NiO/ZnO nanowires show an 18% dip in initial capacitance even after 6000 cycles, indicating excellent capacitance retention and low resistance validated by electrochemical impedance spectroscopy. In addition, the specific capacitance, energy and power density of the solid state asymmetric capacitor that was manufactured by employing NiO/ZnO as the positive electrode and activated carbon as the negative electrode were found to be 87 Fg-1, 23 Whkg-1and 614 Wkg-1, respectively. The novel electrode based on NiO/ZnO demonstrates excellent electrochemical characteristics all of which point to its promising application in supercapacitor devices.

Constructing nickel sulfide @ nickel boride hybrid nanosheet arrays with crystalline/amorphous interfaces for supercapacitors

Designing a heterostructure with unique morphology and nanoarchitecture is regarded as an efficient strategy to achieve high-energy-density supercapacitors (SCs). Herein, a rational nickel sulfide @ nickel boride (Ni9S8@Ni2B) heterostructure is in situ synthesized on carbon cloth (CC) substrate via a simple electrodepositon strategy followed by a chemical reduction method. The three-dimensional hierarchically porous Ni9S8@Ni2B nanosheet arrays, consisting of crystalline Ni9S8 nanosheets and amorphous Ni2B nanosheets, can expose ample electroactive centers, shorten ion diffusion distance, and buffer volume changes during charging/discharging process. More importantly, the generation of crystalline/amorphous interfaces in the Ni9S8@Ni2B composite modulates its electrical structure and improves electrical conductivity. Owing to the synergy of Ni9S8 and Ni2B, the as-synthesized Ni9S8@Ni2B electrode acquires a specific capacity of 901.2C g-1 at 1 A g-1, a sound rate capability (68.3% at 20 A g-1), along with good cycling performance (79.7% capacity retention over 5000 cycles). Additionally, the assembled Ni9S8@Ni2B//porous carbon asymmetric supercapacitor (ASC) exhibits a cell voltage of 1.6 V and a maximum energy density of 59.7 Wh kg-1 at 805.2 W kg-1. These findings might offer a simple and innovative approach to fabricate advanced electrode materials for high-performance energy storage systems.

Polyphosphazene-derived carbon modified nanowires for high-performance electrochemical energy storage

Two one-dimensional nanowires, Fe3O4and MnO2nanowires, were modified with polyphosphazene-derived carbon (PZSC) usingin situpolymerization and high-temperature calcination methods. PZSC coated with MnO2nanowire (MnO2/PZSCNW) was designed as the positive electrode, while PZSC coated with Fe3O4nanowire (Fe3O4/PZSCNW) was designed as the negative electrode. Both MnO2/PZSCNW (+) and Fe3O4/PZSCNW (-) exhibit much larger specific capacities than the corresponding MnO2and Fe3O4nanowires, reaching 75.5 mAh g-1and 75.9 mAh g-1, respectively. The maximum specific capacity, power and energy density of MnO2/PZSCNW (+)//Fe3O4/PZSCNW (-) in alkaline electrolyte are up to 63.2 mAh g-1, 429.6 W kg-1and 53.7 Wh kg-1, respectively. After 10 000 cycles, the cell maintains 100% capacity. The experimental results indicate that the polyphosphazene-derived carbon coating can significantly improve the electrochemical performance, providing a feasible solution for constructing high-performance supercapacitors.

Sodium alginate-based gel electrodes without binder for high-performance supercapacitors

Binder use results in an expansion of the dead volume of the active material and a decline in the active sites, which will lead to a decrease in the electrochemical activity of the electrode. Therefore, the construction of electrode materials without the binder has been the research focus. Here, a novel ternary composite gel electrode without the binder (reduced graphene oxide/sodium alginate/copper cobalt sulfide, rGSC) were designed using a convenient hydrothermal method. Benefiting from the dual-network structure of rGS via the hydrogen bonding between rGO and sodium alginate not only better encapsulates CuCo2S4 with high pseudo-capacitance, but also simplifies the electron transfer path, and reduces the electron transfer resistance, which leads to a remarkable enhanced electrochemical performance. The rGSC electrode exhibits a specific capacitance of up to 1600.25 F g-1 when the scan rate is 10 mV s-1. The asymmetric supercapacitor was constructed with rGSC and activated carbon as the positive and negative electrode in a 6 M KOH electrolyte. It has a large specific capacitance and high energy/power density (10.7 Wh kg-1/1329.1 W kg-1). This work proposes a promising strategy for designing gel electrodes for higher energy density and larger capacitance without the binder.

Nanostructured conversion-type anode materials of metal-organic framework-derived spinel XMn2O4 (X = Zn, Co, Cu, Ni) to boost lithium storage

Bimetallic spinel transition metal oxides play a major part in actualizing eco-friendly electrochemical energy storage systems (ESSs). However, structural precariousness and low electrochemical capacitance restrict their actual implementation in lithium-ion batteries (LIBs). To address these demerits, the sacrificial template approach has been considered as a prospective way to strengthen electrochemical stability and rate performance. Herein, metal-organic frameworks (MOFs) derived XMn₂O₄-BDC (H₂BDC = 1,4-dicarboxybenzene, X = Zn, Co, Cu, Ni) are prepared by a hydrothermal approach in order to discover the effects of various metal cations on the electrochemical performance. Among them, ZnMn₂O₄-BDC displays best electrochemical properties (1321.5 mAh g^-1 at the current density of 0.1 A g^-1 after 300 cycles) and high efficiency with accelerated Li⁺ diffusivity. Density functional theory (DFT) calculations confirm the ZnMn₂O₄ possesses the weakest adsorption energy on Li⁺ with a minimized value of -0.92 eV. In comparison with other XMn₂O₄ through traditional fabrication method, MOF-derived XMn₂O₄-BDC possesses a higher number of Li⁺ transport channels and better electric conductivity. This tactic provides a feasible and effective method for preparing bimetallic transition metal oxides and enhances energy storage applications.

Na superionic conductor-type compounds as protective layers for dendrites-free aqueous Zn-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) have attracted much attention owing to their safety, high energy density and environmental friendliness. However, dendrite formation and corrosive reactions on Zn anode surface limit the development of ARZIBs. Here, Ga3+-doped NaV2(PO4)3 with Na superionic conductor (NASICON) structure [NVP-Ga(x), x = 0, 0.25, 0.5, 0.75] have been exploited as the high-efficiency artificial layer to stabilize Zn anode. The optimal NVP-Ga(0.5) layer can homogenize ion flux and promote uniform deposition of zinc, the dendrite growth and the parasitic reactions can be greatly inhibited. The symmetric cell based on this unique protection layer can stably operate over 1,300 h at 0.5 mA cm-2 with 0.5 mAh cm-2. Benefitting from the high-performance Zn metal anode, the full batteries paired with MnO2 cathode deliver a high discharge capacity of 106 mAh/g with the capacity retention rate of 85 % after 8,000 cycles. This work provides an advanced strategy to stabilize Zn anode for the industrialization of ARZIBs in the near future.

Microwave Absorption of α-Fe2O3@diatomite Composites

A neoteric round sieve diatomite (De) decorated with sea-urchin-like alpha-type iron trioxide (α-Fe₂O₃) synthetics was prepared by the hydrothermal method and further calcination. The results of the electromagnetic (EM) parameters of α-Fe₂O₃-decorated De (α-Fe₂O₃@D) showed that the minimum reflection loss (RL_min) of α-Fe₂O₃@D could reach -54.2 dB at 11.52 GHz and the matched absorber thickness was 3 mm. The frequency bandwidth corresponding to the microwave RL value below -20 dB was up to 8.24 GHz (9.76-18 GHz). This indicates that α-Fe₂O₃@D composite can be a lightweight and stable material; because of the low density of De (1.9-2.3 g/cm³), the density of α-Fe₂O₃@D composite material is lower than that of α-Fe₂O₃ (5.18 g/cm³). We found that the combination of the magnetic loss of sea-urchin-like α-Fe₂O₃ and the dielectric loss of De has the most dominant role in electromagnetic wave absorption and loss. We focused on comparing the absorbing properties before and after the formation of sea-urchin-like α-Fe₂O₃ and explain in detail the effects of the structure and crystal shape of this novel composite on the absorbing properties.

Novel design of Sulfur-doped nickel cobalt layered double hydroxide and polypyrrole nanotube composites from zeolitic imidazolate Framework-67 as efficient active material of battery supercapacitor hybrids

Nickel and cobalt layered double hydroxide (NiCo-LDH) has large specific surface area and interlayer spacing, multiple redox states and high ion-exchange capability, but poor electrical conductivity, severe agglomerations and structural defect restrict energy storage ability of NiCo-LDH as active materiel of battery supercapacitor hybrids (BSH). In this study, it is the first time to design sulfur-doped NiCo-LDH and polypyrrole nanotubes composites (NiCo-LDH-S/PNTs) from zeolitic imidazolate framework-67 (ZIF-67) as the efficient active material of BSH using electrospinning and hydrothermal processes. Effects of sulfur doping amounts are investigated. The one-dimensional hollow polypyrrole decorated with NiCo-LDH-S sheets with high aspect ratio provides straight charge-transfer routes and abundant contacts with electrolyte. The highest specific capacitance (C_F) of 1936.3 F/g (specific capacity of 322.8 mAh/g) is achieved for the NiCo-LDH-S/PNTs with sulfur doping amount of 7% at 10 mV/s. The BSH comprising graphene LDH negative electrode and NiCo-LDH-S/PNTs positive electrode shows the maximum energy density of 16.28 Wh/kg at 650 W/kg. The C_F retention of 74% and Coulombic efficiency of 90% are also achieved after 8000 charge/discharge cycles.

Multi-step electrodeposited Ni-Co-P@LDH nanocomposites for high-performance interdigital asymmetric micro-supercapacitors

The development of high-performance electrode materials and the rational design of asymmetric structures are the two main keys to fabricating micro-supercapacitors (MSCs) with high energy density. Transition metal compounds, especially nickel-cobalt phosphides and hydroxides, are promising electrode materials with excellent pseudo-capacitance. However, they are rarely used in fabricating asymmetric MSCs (AMSCs) due to the limitations of the preparation method. In this work, we constructed hierarchical Ni-Co-P@LDH nanocomposites with outstanding mass specific capacitance (1980 F g^-1 at 1 A g^-1) via a multi-step electrodeposition method, which is employed with FeOOH to fabricate an interdigital AMSC device (Ni-Co-P@LDHs//PVA-KOH//FeOOH). The as-prepared device exhibits a high working voltage (1.4 V), a large specific capacitance (24.0 mF cm^-2 at 0.14 mA cm^-2), a high energy density (6.54 μW h cm^-2 at a power density of 100 μW cm^-2) and good cycling stability (86.5% of capacitance retention after 5000 cycles). This work may provide novel methods for the synthesis of high-performance nickel-cobalt composite materials and their potential applications in interdigital AMSC devices.

Electrochemical Performance of MnO2/Graphene Flower-like Microspheres Prepared by Thermally-Exfoliated Graphite

To enhance the electrochemical performance of MnO₂/graphene composite, herein, thermally-exfoliated graphite (TE-G) is adopted as a raw material, and a hydrothermal reaction is conducted to achieve the exfoliation of TE-G and the loading of MnO₂ nanosheets. Through optimizing the TE-G/KMnO₄ ratio in the redox reaction between carbon and KMnO₄, flower-like MnO₂/G microspheres (MnO₂/G-10) are obtained with 83.2% MnO₂ and 16.8% residual graphene. Meanwhile, corresponding MnO₂/rGO composites are prepared by using rGO as raw materials. Serving as a working electrode in a three-electrode system, MnO₂/G-10 composite displays a specific capacitance of 500 F g⁻¹ at 1 A g⁻¹, outstanding rate performance, and capacitance retention of 85.3% for 5,000 cycles. The performance is much better than that of optimized MnO₂/rGO composite. We ascribe this to the high carbon fraction in TE-G resulting in a high fraction of MnO₂ in composite, and the oxygen-containing groups in rGO reduce the resulting MnO₂ fraction in the composite. The superior electrochemical performance of MnO₂/G-10 is dependent on the hierarchical porous structure constructed by MnO₂ nanosheet arrays and the residual graphene layer in the composite. In addition, a supercapacitor assembled by TE-G negative electrode and MnO₂/G positive electrode also exhibits superior performance. In consideration of the low cost of raw materials, the MnO₂/G composite exhibits great application potential in the field of supercapacitors.

Recent Advancements in Electrochemical Deposition of Metal-Based Electrode Materials for Electrochemical Supercapacitors

The demand for energy storage devices with high energy and power densities has increased tremendously in this rapidly growing world. Conventional capacitors, fuel cells, and lithium-ion batteries have been used as energy storage devices for the long term. However, supercapacitors are one of the most promising energy storage devices because of their high specific capacitance, high power density, and longer cycle life. Recent research has focused on synthesizing transition-metal oxides/hydroxides, carbon materials, and conducting polymers as supercapacitor electrode materials. The performance of supercapacitors can be improved by altering electrolytes, electrode materials, current collectors, experimental temperatures, and film thickness. Thousands of papers on supercapacitors have already been published, reflecting the significance and elucidating how much demanding such energy storage devices for this fast-growing generation. This review aims to illustrate the electrode materials loaded on various conductive substrates by electrochemical deposition employed for supercapacitors to provide broad knowledge on synthetic pathways, which will pave the way for future research. We also discussed the basic parameters involved in supercapacitor studies and the advantages of the electrochemical deposition techniques through literature analysis. Finally, future trends and directions on exploring metals/metal composites toward designing and constructing viable, high-class, and even newly featured flexible energy storage materials, electrodes, and systems are presented.

Carbon spheres decorated-graphene oxide framework as an excellent active material for redox flow battery and supercapacitors

Composite of dextrose-derived oxygen-rich carbon spheres and graphene oxide, synthesised using a cost-effective and easy hydrothermal process, was used as an active material in two of the trending and promising energy storage devices. The surface morphology and properties of the composite were studied using scanning electron microscope, X-ray diffractometer, energy dispersive X-ray analysis, elemental mapping and Raman spectra. To analyse the electrochemical behaviour of the material, several electrochemical techniques such as cyclic voltammetry (CV), chronopotentiometry, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation study were used. The reversibility of Fe²⁺/Fe³⁺ redox species and resistance offered by electrolyte towards the modified electrode were studied using CV, EIS and Tafel studies. Further evaluation of efficacy of the active material towards the iron redox flow battery (IRFB) of 132 cm² area was analysed by performing charge discharge studies at varied current densities. Substantial increase in the electrochemical performance of the IRFB with a coulombic efficiency (CE) 93% along with the good life cycle stability up to 25 cycles was observed. The composite was also used as a superior electrode material for supercapacitor application resulting in significant enhancement in the electrochemical performance with specific capacitance of 610 F g^-1 and CE of 83% with 93% retention up to 1600 cycles.

Nanostrucutured MnO2-TiN nanotube arrays for advanced supercapacitor electrode material

The capacitance of MnO2 supercapacitors (SCs) is not high as expected due to its low conductivity of MnO2. The synergistic effects of MnO2 with high theoretical specific capacitance and TiN with high theoretical conductivity can extremely enhance the electrochemical performance of the MnO2-TiN electrode material. In this work, we synthesized different nanostructured and crystalline-structured MnO2 modified TiN nanotube arrays electrode materials by hydrothermal method and explained the formation mechanism of different nanostructured and crystalline-structured MnO2. The influences of MnO2 nanostructures and crystalline-structures on the electrochemical performance has been contrasted and discussed. The specific capacitance of δ-MnO2 nanosheets-TiN nanotube arrays can reach 689.88 F g-1, the highest value among these samples TN-MO-SS, TN-MO-S, TN-MO-SR, TN-MO-RS, and TN-MO-R. The reason is explained based on MnO2 nanostructure and crystalline-structure and electron/ion transport properties. The specific capacitance retention rates are 97.2% and 82.4% of initial capacitance after 100 and 500 cycles, respectively, indicating an excellent charging-discharging cycle stability.

Facile synthesis of a 2D multilayer core–shell MnO2@LDH@MMT composite with a nanoflower shape for electromagnetic wave absorption

Manganese dioxide@NiFe layered double hydroxide@montmorillonite (MNFM) with a nanoflower-like two-dimensional layered core–shell construction has been successfully synthesized by a two-step hydrothermal method.

Capacitive performance of electrochemically deposited Co/Ni oxides/hydroxides on polythiophene-coated carbon-cloth

Cobalt, nickel, and their mixed hydroxides were electrochemically deposited on polythiophene-coated carbon-cloth substrate to develop new pseudo-capacitive electrodes for energy storage devices. Thiophene was electro-polymerized on carbon-cloth by the potentiodynamic method in acetonitrile containing 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ionic-liquid as supporting electrolyte. The scanning-electron-microscopy images imply that flower-like Co(OH)2 microstructures deposited on bamboo-like polythiophene coatings on carbon-fibers but they are covered by net curtain like thin Ni(OH)2 layer. The Co-Ni layered-double-hydroxide deposited from their equimolar sulfate solutions is composed of large aggregates. The electron-dispersive-spectrum exhibits that Co/Ni ratio equals unity in the layered-double-hydroxide. The capacitances of Co, Ni, and Co-Ni hydroxide-coated PTh electrodes are 100, 569, and 221 F/g at 5 mA/cm2 in 1 M KOH solution, respectively. Their corresponding oxides obtained by calcination at 450 °C in de-aerated medium possess higher capacitance up to 911, 643, and 696 F/g at 2 A/cm2. The shape of cyclic-voltammetry and galvanostatic-charge-discharge curves, as well as the Nyquist plots derived from electrochemical-impedance-spectroscopy measurements, reveal that hydroxide coatings on the polythiophene-coated carbon-cloth are more promising electrode materials for supercapacitor applications. The mixed hydroxide-coated electrode shows good cyclic stability of 100% after 400 cycles at 5 mA/cm2.

A multidimensional rational design of nickel-iron sulfide and carbon nanotubes on diatomite via synergistic modulation strategy for supercapacitors

Based on their characteristics, transition metal layered double hydroxides have been of great scientific interest for their use in supercapacitors. Up until now, severe aggregation and low intrinsic conductivity have been the major hurdles for their application. In this work, nickel-iron sulfide nanosheets (NiFeSx) and carbon nanotubes (CNTs) were synthesized on diatomite using chemical vapor deposition and a two-step hydrothermal method to overcome these challenges. Synthesis of this composite successfully exploits the synergistic effect of multicomponent materials to improve the electrochemical performance. Diatomite is selected as a substrate to provide preferable surroundings for the uniform dispersion of nanomaterial on its surface, which enlarges the active sites that come in contact with the electrolytes, significantly improving the electrochemical properties. Combined with high conductivity and a synchronous sulfurization effect, the NiFeSx@CNTs@MnS@Diatomite electrode delivered a high specific capacitance of 552F g^-1 at a current density of 1 A g^-1, a good rate capability of 68.4% retention at 10 A g^-1, and superior cycling stability of 89.8% capacitance retention after 5000 cycles at 5 A g^-1. Furthermore, an asymmetric supercapacitor assembled via NiFeSx@CNTs@MnS@Diatomite and graphene delivered a maximum energy density of 28.9 Wh kg^-1 and a maximum power density of 9375 W kg^-1 at a potential of 1.5 V. This research lays the groundwork for ideal material preparation as well as a rational design for the electrode material, including property enhancement of diatomite-based material for use in supercapacitors.

Supercapattery electrode materials by Design: Plasma-induced defect engineering of bimetallic oxyphosphides for energy storage

Although transition metal hydroxides are promising candidates as advanced supercapattery materials, they suffer from poor electrical conductivity. In this regard, previous studies have typically analyzed separately the impacts of defect engineering at the atomic level and the conversion of hydroxides to phosphides on conductivity and the overall electrochemical performance. Meanwhile, this paper uniquely studies the aforementioned methodologies simultaneously inside an all-in-one simple plasma treatment for nickel cobalt carbonate hydroxide, examines the effect of altering the nickel-to-cobalt ratio in the binder-free defect-engineered bimetallic Ni-Co system, and estimates the respective quantum capacitance. Results show that the concurrent defect-engineering and phosphidation of nickel cobalt carbonate hydroxide boost the amount of effective redox and adsorption sites and increase the conductivity and the operating potential window. The electrodes exhibit ultra-high-capacity of 1462 C g^-1, which is among the highest reported for a nickel-cobalt phosphide/phosphate system. Besides, a hybrid supercapacitor device was fabricated that can deliver an energy density of 48 Wh kg^-1 at a power density of 800 W kg^-1, along with an outstanding cycling performance, using the best performing electrode as the positive electrode and graphene hydrogel as the negative electrode. These results outperform most Ni-Co-based materials, demonstrating that plasma-assisted defect-engineered Ni-Co-P/PO_x is a promising material for use to assemble efficient energy storage devices.

Engineering triangular bimetallic metal-organic-frameworks derived hierarchical zinc-nickel-cobalt oxide nanosheet arrays@reduced graphene oxide-Ni foam as a binder-free electrode for ultra-high rate performance supercapacitors and methanol electro-oxidation

The rigorous fabrication of electrode materials using upper-ranked porous precursor especially metal organic frameworks (MOFs) are challenging but appealing task to procure electrochemical energy storage and conversion system with altitudinous performance. Herein, we replenish the rational construction of atypical electrode of hollow Zn-Ni-Co-oxide (ZNCO) nanosheet arrays onto rGO garnished Ni foam (rGO/NF) via two step solution based method. Firstly, 2D Zn-Co-MOFs derived nanoleave arrays are prepared by co-precipitation method. Next, hollow and porous ZNCO nanostructure from 2D solid nanoleave arrays are achieved by ion-exchange and etching process conjoined with post annealing treatment. The as-fabricated hierarchical ZNCO nanosheet arrays offer large numbers of electroactive sites with short ion-diffusion pathways, reflecting the outstanding electrochemical performance in-terms of excellent specific capacity (267 mAh g^-1) ultra-high rate capability (83.82% at 50 A/g) and long-term cycling life (~90.16%) in three electrode configuration for supercapacitor (SCs). Moreover, the hollow and porous ZNCO nanostructure responds as immensely active and substantial electrocatalyst for methanol oxidation with lowest onset potential of 0.27 V. To demonstrate the practicability, hybrid supercapacitor (HSC) device is constructed using ZNCO@rGO-NF nanostructure as positive and rGO decorated MOF derived porous carbon (rGO-MDPC) as negative electrode. The as-assembled ZNCO//rGO-MDPC ASC device delivers higher energy density of 61.25 Wh kg^-1 at the power density of 750 W kg^-1 with long-term cyclic stability (<6% to its initial specific capacity value) after 6000 cycles.