General solution growth of mesoporous NiCo2O4 nanosheets on various conductive substrates as high-performance electrodes for supercapacitors

Synthesis and Electrochemical Characterization of ZnMoS4 Nanorods on Nickel Foam Substrate for Advanced Hybrid Supercapacitor Applications

A single-step hydrothermal method was utilized to grow ZnMoS4 (ZMS) nanorods uniformly. Initially, [MoS4]2- and Zn2+ ions interacted to create active nucleation centers, which then led to the formation of primary particles. These particles then underwent spontaneous aggregation and self-assembly on the nickel foam (NF) substrate, which served as a superior 3D interconnecting network template. This aggregation occurred nearly perpendicular to the NF and promoted the uniform growth of ZMS nanorods. The nanorods structure ensures efficient and rapid electrolyte accessibility and ion diffusion, resulting in an increased specific capacitance (Cs) of 2,116 Fg1- (846.4 C g-1) at 1 A g-1 and maintaining about 90% of their capacitance after 10,000 cycles of galvanic charge-discharge (GCD). In a hybrid supercapacitor configuration, ZMS@NF//AC@NF achieved a peak specific power of 7.2 kW.kg-1 and a specific energy of 40.3 Wh.kg-1. Remarkably, it preserved 93% of its initial capacitance after more than 20,000 cycles. These findings affirm the potential of binder-free ZMS nanorods as effective positive electrodes in advanced hybrid supercapacitors.

Experimental and computational approach of zirconium and chitosan doped NiCo2O4 nanorods served as dye degrader and bactericidal action

Different concentrations of zirconium with a fixed quantity (4 wt%) of chitosan (CS) doped nickel cobaltite (NiCo2O4) nanorods were synthesized using a co-precipitation approach. This cutting-edge research explores the cooperative effect of Zr-doped CS-NiCo2O4 to degrade the Eriochrome black T (EBT) and investigates potent antibacterial activity against Staphylococcus aureus (S. aureus). Advanced characterization techniques were conducted to analyze structural textures, morphological analysis, and optical characteristics of synthesized materials. XRD pattern unveiled the spinal cubic structure of NiCo2O4, incorporating Zr and CS peak shifted to a lower 2θ value. UV-Vis spectroscopy revealed the absorption range increased with CS and the same trend was observed upon Zr, showing a decrease in bandgap energy (Eg) from 2.55 to 2.4 eV. The optimal photocatalytic efficacy of doped NiCo2O4 within the basic medium was around 96.26 %, and bactericidal efficacy was examined against S. aureus, revealing a remarkable inhibition zone (5.95 mm).

Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo2O4 In Situ Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g-1 (1503.3 C g-1) at 1 A g-1, a superior rate performance of 2335.2 F g-1 at 20 A g-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg-1 at a power density of 800 W kg-1, and the energy density at a peak power density of 20004 W kg-1 still remained at 48.9 Wh kg-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.

Large-Scale Synthesis of High Energy Thermal Battery Cathode Ni0.5Co0.5S2 by a Simple Sintering Technique

With the synergies of multiple elements, bimetallic sulfides exhibit excellent performance as splendid electrode materials and effective catalysts. However, large-scale synthesis of high-performance single-phase multicomponent sulfides has always been a challenge. Based on thermodynamic calculations, the intermediate phases NiS2 and Co3S4 are devoted to the synthesis of single-phase Ni0.5Co0.5S2. Because the reaction from NiS2 and Co3S4 to Ni0.5Co0.5S2 goes through a lower energy, it thermodynamically contributes to achieving a single-phase structure. Thus, single-phase Ni0.5Co0.5S2 can be simply and quickly prepared by two-step sintering and successfully scalable for mass production. This technique can extend to the whole ingredients Ni1-xCoxS2. Ni0.5Co0.5S2 demonstrates excellent thermal stability and good conductivity. It delivers a specific capacity of 671 mAh·g-1 and a specific energy of 1173 Wh·kg-1 when applied to a thermal battery cathode, which are increased by 18.6% and 25.0%, respectively, compared to pristine NiS2 (566 mAh·g-1) and CoS2 (537 mAh·g-1). This work proposes an innovative sintering method, which is applicable for cost-efficient and large-scale synthesis of single-phase multicomponent sulfides.

One-Dimensional Nickel Molybdate Nanostructures with Enhanced Supercapacitor Performance

One-dimensional NiMoO4 nanofibers were successfully prepared by electrospinning and high-temperature calcination. The supercapacitor performance tests were conducted on the prepared materials in a three-electrode system, and it was found that the calcination temperature during the preparation of the fibers seriously affects the final morphology and electrochemical performance of the obtained samples. The sample with a calcination temperature of 500 °C has better performance, its specific capacitance can reach 1947 F g-1, and the retention rate is 82.35% after 3000 cycles of constant current charging-discharging. The improvement of electrochemical performance is primarily on account of the unique one-dimensional nanostructure of the material, which can both enhance the charge transfer efficiency and effectively increase the speed of electrolyte ion diffusion.

Controlled synthesis of transition metal oxide multi-shell structures andin situstudy of the energy storage mechanism

Multi-shell transition metal oxide hollow spheres show great potential for applications in energy storage because of their unique multilayered hollow structure with large specific surface area, short electron and charge transport paths, and structural stability. In this paper, the controlled synthesis of NiCo2O4, MnCo2O4, NiMn2O4multi-shell layer structures was achieved by using the solvothermal method. As the anode materials for Li-ion batteries, the three multi-shell structures maintained good stability after 650 long cycles in the cyclic charge/discharge test. Thein situtransmisssion electron microscope characterization combined with cyclic voltammetry tests demonstrated that the three anode materials NiCo2O4, MnCo2O4and NiMn2O4have similar charge/discharge transition mechanisms, and the multi-shell structure can effectively buffer the volume expansion and structural collapse during lithium embedding/delithiation to ensure the stability of the electrode structure and cycling performance. The research results can provide effective guidance for the synathesis and charging/discharging mechanism of multi-shell metal oxide lithium-ion battery anode materials.

Recent advances in the development of MXenes/cellulose based composites: A review

Over the past few years, transition metal carbides, nitrides, and carbonitrides, commonly referred to as MXenes have been discovered and utilized quickly in a range of technical fields due to their distinctive and controlled characteristics. MXenes are a new class of two-dimensional (2D) materials that have found extensive use in a variety of fields, including energy storage, catalysis, sensing, biology, and other scientific disciplines. This is because of their exceptional mechanical and structural characteristics, metal electrical conductivity, and other outstanding physical and chemical properties. In this contribution, we review recent cellulose research advances and show that MXene hybrids are effective composites that benefit from cellulose superior water dispersibility and the electrostatic attraction between cellulose and MXene to prevent MXene accumulation and improve the composite's mechanical properties. Electrical, materials, chemical, mechanical, environmental, and biomedical engineering are all fields in which cellulose/MXene composites are used. These properties and applications-based reviews on MXene/cellulose composite, critically analyze the results and accomplishments in these fields and provide context for potential future research initiatives. It examines newly reported applications for cellulose nanocomposites assisted by MXene. To support their development and future applications, perspectives and difficulties are suggested in the conclusion.

Compression-tolerant supercapacitor based on NiCo2O4/Ti3C2Tx MXene/reduced graphene oxide composite aerogel with insights from density functional theory simulations

Compression-tolerant electrodes are critical for developing next-generation wearable energy storage devices. However, most of previous studies on compressible electrodes focus on carbon-based materials, whereas metal-based materials such as spinel metal oxide with faradaic nature have been rarely studied due to their lack of compressibility. Herein, NiCo₂O₄ (NCO) microtubes assembled by ultrathin and mesoporous nanosheets, are deposited on/into Ti₃C₂T_x MXene/reduced graphene oxide aerogel (MGA), an intrinsically compressible host template with high conductivity and specific surface areas. The optimized NCO/MGA-300 sample shows a reversible compressive strain of 60% and a superior durability. Density functional theory (DFT) calculations reveal that the NCO/MGA-300 heterojunction has high electronic conductivity, fast electron transfer ability, and low adsorption energy for OH^- ions. As a result, the NCO/MGA-300 electrode exhibits superb electrochemical performance in terms of its high gravimetric capacitance (1633F g^-1 at 1 A g^-1), rate performance (1492F g^-1 at 10 A g^-1), and remarkable cycling stability of 86.6% after 10,000 charge-discharging cycles. Moreover, an assembled asymmetric supercapacitor based on compressible NCO/MGA-300 shows stable electrochemical performances under different compressive strains (20%. 40% and 60%), or after 100 compression-release cycles. This research finding demonstrates the possibility of metal-based electrode for wearable devices with high energy storage capability and good compressibility.

Novel and flexible asymmetric supercapacitors based on NiCo2O4 nanosheets coated on Al and Cu tapes for wearable devices applications

The binary metal oxides show advantages in energy storage devices. Specifically, nickel cobaltite (NiCo2O4) materials showed promising pseudocapacitive properties, high electrical conductivity and large surface area by virtue of their effective porous structure. NiCo2O4 nanosheets were hydrothermally grown in this work over flexible tapes of Aluminum (Al) and Copper (Cu). A nanosheets structure obtained of NiCo2O4 as confirmed by SEM and AFM images. The measured thickness by 3D profilometer of NiCo2O4 nanosheets based Al framework found to be 4.3 µm compared to 8.4 µm thick of film based-Cu framework. Asymmetric supercapacitor prepared from graphite and NiCo2O4 electrodes separated by filter paper. Acidic aqueous electrolyte of H2SO4 and basic aqueous electrolyte of KOH were employed to verify the cyclic activity and electrochemical reaction of asymmetric prepared supercapacitor devices. The basic KOH electrolyte shows a high stability and better charge transfer/ionic diffusion compared to the acidic H2SO4 electrolyte in particular for NiCo2O4 film-based Cu framework. The energy density and power density values were 0.9 W h kg−1 and 66.45 W kg−1, respectively. The highest specific capacity (in F.g−1) = 10.09 coincides with NiCo2O4/Cu supercapacitor in the basic KOH electrolyte. The charge storage in the supercapacitor system of NiCo2O4 and graphite can be ascribed in the form of Faradic charge transfer and capacitive non-faradic double layer, respectively.

Effect of strontium doping on the electrochemical pseudocapacitance of Y1-xSrxMnO3-δ perovskites

Grid-scale bulk energy storage solutions are needed to utilize the full potential of renewable energy technologies. Pseudocapacitive electrochemical energy storage can play a vital role in developing efficient energy storage solutions. The use of perovskites as anion intercalation-type pseudocapacitor electrodes has received significant attention in recent years. In this study, Sr-doped YMnO₃i.e. Y_1-xSr_xMnO_3-δ perovskite was prepared by the solid-state ceramic route and studied for electrochemical pseudocapacitance in aqueous KOH electrolyte. Microstructures, morphologies, and electrochemical properties of these materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance method. The formation of the mostly cubic phase, with 50% strontium doped YMnO₃ (YSMO-50) provides an equivalent three-dimensional network and superior conductivity due to Mn³⁺-O^2--Mn⁴⁺ hopping conduction. YSMO-50 exhibited low intrinsic resistance, 1.45 Ω cm^-2, and the highest specific capacity, 259.83 F g^-1 at a current density of 1 A g^-1 in 2 M KOH aqueous electrolyte. Redox-mediated interconversion of oxide to hydroxide (M²⁺O^2- + H₂O + e^- ↔ M⁺OH^- + OH^-) in aqueous media is shown to be the reason behind the high capacitance of YSMO-50. The excellent electrochemical performance of YSMOs was attributed to the reversible interconversion of oxide-ion into hydroxide ion coupled with surface redox reaction of Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ occurring during the charge-discharge process. The maximum energy density of 65.13 W h kg^-1 was achieved at a power density of 0.45 kW kg^-1 for an asymmetric mode, in which YSMO serves as a negative electrode and Activated carbon (AC) as a positive electrode in the PVA-KOH gel electrolyte. Our study reveals that the doping of low valence atom (Sr) at the A-site in perovskite manganites (YMnO₃) may be an effective tool to enhance the pseudocapacitive performance of perovskite-based electrodes.

Chemically Synthesized Iron-Oxide-Based Pure Negative Electrode for Solid-State Asymmetric Supercapacitor Devices

Among energy storage devices, supercapacitors have received considerable attention in recent years owing to their high-power density and extended cycle life. Researchers are currently making efforts to improve energy density using different asymmetric cell configurations, which may provide a wider potential window. Many studies have been conducted on positive electrodes for asymmetric supercapacitor devices; however, studies on negative electrodes have been limited. In this study, iron oxides with different morphologies were synthesized at various deposition temperatures using a simple chemical bath deposition method. A nanosphere-like morphology was obtained for α-Fe₂O₃. The obtained specific capacitance (C_s) of α-Fe₂O₃ was 2021 F/g at a current density of 4 A/g. The negative electrode showed an excellent capacitance retention of 96% over 5000 CV cycles. The fabricated asymmetric solid-state supercapacitor device based on α-Fe₂O₃-NF//Co₃O₄-NF exhibited a C_s of 155 F/g and an energy density of 21 Wh/kg at 4 A/g.

Porous spinel-type transition metal oxide nanostructures as emergent electrocatalysts for oxygen reduction reactions

Porous spinel-type transition metal oxide (PS-TMO) nanocatalysts comprising two kinds of metal (denoted as A_xB_3-xO₄, where A, B = Co, Ni, Zn, Mn, Fe, V, Sm, Li, and Zn) have emerged as promising electrocatalysts for oxygen reduction reactions (ORRs) in energy conversion and storage systems (ECSS). This is due to the unique catalytic merits of PS-TMOs (such as p-type conductivity, optical transparency, semiconductivity, multiple valence states of their oxides, and rich active sites) and porous morphologies with great surface area, low density, abundant transportation paths for intermediate species, maximized atom utilization and quick charge mobility. In addition, PS-TMOs nanocatalysts are easily prepared in high yield from Earth-abundant and inexpensive metal precursors that meet sustainability requirements and practical applications. Owing to the continued developments in the rational synthesis of PS-TMOs nanocatalysts for ORRs, it is utterly imperative to provide timely updates and highlight new advances in this research area. This review emphasizes recent research advances in engineering the morphologies and compositions of PS-TMOs nanocatalysts in addition to their mechanisms, to decipher their structure-activity relationships. Also, the ORR mechanisms and fundamentals are discussed, along with the current barriers and future outlook for developing the next generation of PS-TMOs nanocatalysts for large-scale ECSS.

POMCPs with Novel Two Water-Assisted Proton Channels Accommodated by MXenes for Asymmetric Supercapacitors

To develop high-performance supercapacitors, the negative electrode is at present viewed as one of the most challenging tasks for obtaining the next-generation of energy storage devices. Therefore, in this study, a polyoxometalate-based coordination polymer [Zn(itmb)₃ H₂ O][H₂ SiW₁₂ O₄₀ ]·5H₂ O (1) is designed and prepared by a simple hydrothermal method for constructing a high-capacity negative electrode. Polymer 1 has two water-assisted proton channels, which are conducive to enhancing the electrical conductivity and storage capacity. Then, MXene Ti₃ C₂ T_x is chosen to accommodate coordination polymer 1 as the interlayer spacers to improve the conductivity and cycling stability of 1, while preventing the restacking of MXene. Expectedly, the produced composite electrode 1@Ti₃ C₂ T_x shows an excellent specific capacitance (1480.1 F g^-1 at 5 A g^-1 ) and high rate performance (a capacity retention of 71.5% from 5 to 20 A g^-1 ). Consequently, an asymmetric supercapacitor device is fabricated using 1@Ti₃ C₂ T_x as the negative electrode and celtuce leaves-derived carbon paper as the positive electrode, which demonstrates ultrahigh energy density of 32.2 Wh kg^-1 , and power density 2397.5 W kg^-1 , respectively. In addition, the ability to illuminate a red light-emitting diode for several minutes validates its feasibility for practical application.

Hydrothermal Synthesis of Binder-Free Metallic NiCo2O4 Nano-Needles Supported on Carbon Cloth as an Advanced Electrode for Supercapacitor Applications

It is of great significance to design electrochemical energy conversion and storage materials with excellent performance to fulfill the growing energy demand. Bimetallic cobalt/nickel-based electrode materials exhibit excellent electrical conductivity compared to mono oxides. However, their potential as electrode materials for high-performance supercapacitors (SCs) is limited because of their poor cycling stability and high-capacity fading. This work demonstrates the synthesis of binder-free bimetallic NiCo₂O₄ nano-needles supported on CC (NCO@CC) via a facile and scalable hydrothermal process. Excellent electrical conductivity and interconnected nanostructure of NCO@CC nano-needles provide the fast transfer of electrons with numerous channels for ion diffusion. Owing to such features, the binder-free NCO@CC electrode for SC discloses excellent specific capacitance (1476 Fg⁻¹ at 1.5 Ag⁻¹) with 94.25% capacitance retention even after 5000 cycles. From these outstanding electrochemical performances, it can be inferred that NCO@CC nano-needle array-structured electrodes may be potential candidates for SC applications.

High-performance freestanding supercapacitor electrode based on polypyrrole coated nickel cobalt sulfide nanostructures

In the present work, we report the successful fabrication of dandelion-like Nickel-Cobalt Sulfide@Polypyrrole microspheres through the hydrothermal method and its possible application as a binder-free electrode in supercapacitors. This electrode exhibited low charge transfer resistance with a remarkable specific capacitance of 2554.9 F g^-1 at 2.54 A g^-1, in addition to considerable cycle life stability. Also, an asymmetric device was prepared using NiCo₂S₄@PPy/NF as positive and rGO/NF as negative electrodes. This asymmetric supercapacitor exhibited a specific capacitance of 98.9 F g^-1 at 1.84 A g^-1 and delivered an energy density of 35.17 Wh kg^-1 at a power density of 1472 W kg^-1. Such a remarkable performance can be originated from the synergy effect of NiCo₂S₄ and PPy and the direct deposition of the composite on the current collector. Our findings suggest the dandelion-like NiCo₂S₄@PPy as a promising material for making high-performance supercapacitors.

Self-Supported Transition Metal-Based Nanoarrays for Efficient Energy Storage

Rechargeable batteries and supercapacitors are currently considered as promising electrochemical energy storage (EES) systems to address the energy and environment issues. Self-supported transition metal (Ni, Co, Mn, Mo, Cu, V)-based materials are promising electrodes for EES devices, which offer highly efficient charge transfer kinetics. This review summarizes the latest development of transition metal-based materials with self-supported structures for EES systems. Special focus has been taken on the synthetic methods, the selection of substrates, architectures and chemical compositions of different self-supported nanoarrays in energy storage systems. Finally, the challenges and opportunities of these materials for future development in this field are briefly discussed. We believe that the advancement in self-supported electrode materials would pave the way towards next-generation EES.

Fabrication of an ultra-stable composite electrode material of La2O3/Co3O4/graphene on nickel foam for high-performance supercapacitors

A three-dimensional lily-like structure was constructed by the novel combination of La2O3, Co3O4, and graphene on nickel foam (LCGN) through hydrothermal synthesis and thermal annealing.

Thioacetamide-induced Ce2O2S nanostructures with tunable morphology for supercapacitors in wide pH range

Here, Rare-earth metal oxysulfide Ce₂O₂S nanostructures with tunable morphology are successfully grown on carbon cloth (CC) for supercapacitors (SCs) via a facile hydrothermal process followed by pyrolysis treatment for the first time. The feeding amount of sulfur source thioacetamide (TAA) plays an important role in the formation of Ce₂O₂S nanostructures with tunable morphology. Adjusting TAA feeding amount from 0.5 to 1.0, 1.5, and 2.0 g, the morphology of the resulted Ce₂O₂S nanostructure can change from pine bark-like agglomerated nanoparticles to fan-shaped nanosheets with edged branches, cuttlefish-like nanostructure with long terminal whiskers and polygon prism with spikes. Among them, Ce₂O₂S/CC-1.0 g TAA nanostructure with largest specific surface area and abundant mesopores exhibits a high specific capacitance of 670, 321.5 or 588.3 mF cm^-2 at 1 mA cm^-2 in an acid, neutral or alkaline electrolyte, respectively. Moreover, Ce₂O₂S/CC-1.0 g TAA electrode delivers excellent cycling stability with high capacitance retention of 93% after 5000 cycles in alkaline electrolyte. Our findings present a new strategy to fabricate rare-earth metal oxysulfide Ce₂O₂S nanostructures with controllable morphology and systematically reveal their electrochemical performance for SCs, moreover, provide new perspectives for boosting the preparation and application of metal oxysulfides in energy storage.

Development of Three-Dimensional Nickel-Cobalt Oxide Nanoflowers for Superior Photocatalytic Degradation of Food Colorant Dyes: Catalyst Properties and Reaction Kinetic Study

In this work, we present three-dimensional flower-like nickel-cobalt oxide (F-NCO) nanosheets developed in a facile, eco-friendly hydrothermal route to apply as photocatalysts for food colorant Allura Red AC dye removal under light illumination. Using Brunauer-Emmett-Teller analysis, it was found that the F-NCO nanosheets displayed a surface area of ∼53.65 m²/g and a Barrett-Joyner-Halenda pore size of ∼14 nm, which was also confirmed by the calculated crystallite size of ∼15 nm using powder X-ray diffraction (XRD) analysis. From Williamson-Hall analysis of XRD spectra, F-NCO nanosheets revealed a crystal-lattice strain of ∼3.42 × 10^-3 and a dislocation density of ∼4.397 × 10¹⁵ lines/m² in the crystal structure. Transmission electron microscopy analysis revealed that F-NCO nanosheets accumulated to form flower-like nanostructures of <100 nm length with a d-spacing of ∼2.6 Å, which is attributed to the (311) crystallographic plane (α = γ = β = 90°, a = b = c = 8.110 Å, JCPDS No. 00-020-0781) of the cubic phase. The F-NCO nanosheets exhibited an excellent photocatalytic efficiency of ∼94.75% in ∼10 min with sodium borohydride under UV light. The Langmuir-Hinshelwood model determined pseudo-first-order reaction kinetics of dye degradation using the ln[AtA0]versus time plot. The kinetic study produced a first-order rate constant (k) of ∼0.219 min^-1, resulting in ∼3.16 min half-life (t_1/2) for the F-NCO-catalyzed degradation reaction. Thus outstanding photocatalytic performance of F-NCO nanosheets would display their huge potential for organic-pollutant removal from water with exceptional recyclability for wide research applications in the future.

Energy storage properties of hydrothermally processed ultrathin 2D binder-free ZnCo2O4nanosheets

High energy-density supercapacitors (SCs) with long operating life, cost-effective, and competitive cycling performance is attracted great research attention to competing in the requirements of the modern age. However, despite these benefits, SC hampers inadequate rate-capability and structural deterioration, which primarily affects its commercialization. Herein, ultra-thin two-dimensional (2D) ZnCo₂O₄nanosheets arein situanchored on the conductive surface of nickel foam (denoted as ZCO@NF) by hydrothermal process. The binder-free ZCO@NF is employed as an electrode for SCs and shows impressive charge storage properties. ZCO@NF electrode exhibited a high capacitance of 1250 (750) and 733 F g^-1(440 C g^-1) at 2.5 and 20 A g^-1, respectively, demonstrating the outstanding rate-capability of 58.6% even at 8 times larger current density. Furthermore, the ZCO@NF electrode exhibits admirable capacitance retention of 96.5% after 10 000 cycles. This impressive performance of the ZCO@NF electrode is attributed to the high surface area which gives a short distance for ion/electron transfer, a high conductivity with extensive electroactive cities, and strong structural stability. The binder-free approach provides a strong relationship between the current collector and the active material, which turns into improved electrochemical operation as an electrode material for SCs.

Biomimetic and bioinspired surface topographies as a green strategy for combating biofouling: a review

Biofouling refers to the adverse attachment and colonization of fouling organisms, including macromolecules, bacteria, and sessile invertebrates, on the surfaces of materials submerged in aquatic environments. Almost all structures working in watery surroundings, from marine infrastructures to healthcare facilities, are affected by this sticky problem, resulting in massive direct and indirect economic loss and enormous cost every year in protective maintenance and remedial cleaning. Traditional approaches to preventing marine biofouling primarily rely on the application of biocide-contained paints, which certainly impose adverse effects on the ocean environment and marine ecology. Biomimicry offers an efficient shortcut to developing environmentally friendly antifouling techniques and has yielded encouraging and promising results. The antifouling strategies learned from nature can be broadly classified into two categories according to the nature of the cues applied for biofouling control. One is the chemical antifouling techniques, which are dedicated to extracting the effective antifoulant compounds from marine organisms and synthesizing chemicals mimicking natural antifoulants. In contrast, the physical biomimetic (BM) antifouling practices focus on the emulation and optimization of the physical cues such as micro and nanoscale surface topographies learned from naturally occurring surfaces for better antifouling efficacy. In this review, a synopsis of the techniques for manufacturing the BM and bioinspired (BI) antifouling surface topographies is introduced, followed by the bioassay to assess the antifouling performance of the structured surfaces. Then, the BM and BI surface topographies that were reported to possess enhanced antifouling competence are introduced, followed by a summary of theoretical modeling. The whole paper is concluded by summarizing the studies' deficiencies so far and outlooking the research directions in the future.

An enhancement on supercapacitor properties of porous CoO nanowire arrays by microwave-assisted regulation of the precursor

A microwave-assisted hydrothermal approach with a follow up thermal treatment was employed to prepare 1D porous CoO nanowires, which is constructed by numerous high crystallinity nanoparticles. A significant change in crystal structure of the precursor were observed, as position shift and absence of some diffraction peaks, which was induced by the microwave-assistance during hydrothermal process. Moreover, the precursor's purity was also effectively improved. As a result, the as-synthesized CoO annealed from the microwave-assisted precursor exhibited a morphology and phase structure significantly different from that of without microwave involvement. Benefiting from the 'microwave effect', the microwave-assisted as-fabricated porous CoO nanowires showed an enhanced specific capacitance (728.8 versus 503.7 F g^-1 at 1 A g^-1 ), strengthened rate performance (70.0% versus 53.2% maintenance at 15 A g^-1), reduced charge transfer resistance (1.06 Ω versus 2.39 Ω), enlarged window voltage (0.85 versus 0.7 V) and enhanced cycle performance (82.3% versus 76.5% retention after 5000 cycles at 15 A g^-1), compared with that of sample without microwave assistance. In addition, the corresponding electrochemical properties are also higher than those reported CoO sample prepared by solvothermal method. In conclusion, this work provides a practical way for enhancing electrochemical properties of supercapacitor materials through adjusting the precursor by microwave assistance into hydrothermal process.

Fabrication of a High-Performance Hybrid Supercapacitor Based on Hydrothermally Synthesized Highly Stable Cobalt Manganese Phosphate Thin Films

In the present study, cobalt manganese phosphate (H-CMP-series) thin films with different compositions of Co/Mn are prepared on stainless steel (SS) substrate via a facile hydrothermal method and employed as binder-free cathode electrodes in a hybrid supercapacitor. The XRD study reveals a monoclinic crystal structure, and the FE-SEM analysis confirmed that H-CMP-series samples displayed a nano/microarchitecture (microflowers to nanoflakes) on the surface of SS substrate with excess available surfaces and unique sizes. Interestingly, the synergy between cobalt and manganese species in the cobalt manganese phosphate thin film electrode demonstrates a maximum specific capacitance of 571 F g^-1 at a 2.2 A g^-1 current density in 1 M KOH. Besides, the nano/microstructured cobalt manganese phosphate was able to maintain capacitance retention of 88% over 8000 charge-discharge cycles. More importantly, the aqueous/all-solid-state asymmetric supercapacitor manufactured with the cobalt manganese phosphate thin film as the cathode and reduced graphene oxide (rGO) as the anode displays a high operating potential window of 1.6 V. The aqueous asymmetric device exhibited a maximum specific capacitance of 128 F g^-1 at a current density of 1 A g^-1 with an energy density of 45.7 Wh kg^-1 and a power density of 1.65 kW kg^-1. In addition, the all-solid-state asymmetric supercapacitor device provides a high specific capacitance of 37 F g^-1 at 1 A g^-1 with 13.3 Wh kg^-1 energy density and 1.64 kW kg^-1 power density in a polymer gel (PVA-KOH) electrolyte. The long cyclic life of both devices (87 and 84%, respectively, after 6000 cycles) and practical demonstration of the solid-state device (lighting of a LED lamp) suggest another alternative choice for cathode materials to develop stable energy storage devices with high energy density. Furthermore, the aforementioned study paves the way to investigate phosphate-based materials as a new class of materials for supercapacitor applicability.

Superhydrophilic Ni-based Multicomponent Nanorod-Confined-Nanoflake Array Electrode Achieves Waste-Battery-Driven Hydrogen Evolution and Hydrazine Oxidation

The low thermodynamic potential (-0.33 V) and safe by-product of N₂ /H₂ O, make utilizing hydrazine oxidation reaction (HzOR) to replace thermodynamically-unfavorable and kinetically-sluggish oxygen evolution reaction a promising tactic for energy-efficient hydrogen production. However, the complexity of bifunctionality increases difficulties for effective material design, thus hindering the large-scale hydrogen generation. Herein, we present the rationally designed synthesis of superhydrophilic Ni-based multicomponent arrays (Ni NCNAs) composed of 1D nanorod-confined-nanoflakes (2D), which only needs -26 mV of working potential and 47 mV of overpotential to reach 10 mA cm^-2 for HzOR and HER, respectively. Impressively, this Ni NCNA electrode exhibits the top-level bifunctional activity for overall hydrazine splitting (OHzS) with an ultralow voltage of 23 mV at 10 mA cm^-2 and a record-high current density of 892 mA cm^-2 at just 0.485 V, also achieves the high-speed hydrogen yield driven by a waste AAA battery for OHzS.

Palladium Particles Modified by Mixed-Frequency Square-Wave Potential Treatment to Enhance Electrocatalytic Performance for Formic Acid Oxidation

Palladium catalysts have attracted widespread attention as advanced electrocatalysts for the formic acid oxidation (FAO) due to their excellent electrocatalytic activity and relatively high abundance. At present, electrodeposition methods have been widely developed to prepare small-sized and highly-dispersed Pd electrocatalysts. However, the customary use of surfactants would introduce heterogeneous impurities, which requires complicated removal processes. In this work, we reported a two-step electrochemical method that employed square-wave potential treatment (SWPT) to modify electrodeposited Pd particles without the use of capping agents. Under the SWPT with a mixed frequency, Pd particles show significantly reduced size and more dispersed distribution, exhibiting a high mass activity of 1.43 A mg−1 toward FAO, which is 4.6 times higher than the counterpart of commercial Pd/C. The increase in electrocatalytic activity of FAO is attributed to the highly developed surface of palladium particles uniformly distributed over the support surface.

High-performance nanostructured bio-based carbon electrodes for energy storage applications

Polyacrylonitrile (PAN)-based carbon precursor is a well-established and researched material for electrodes in energy storage applications due to its good physical properties and excellent electrochemical performance. However, in the fight of preserving the environment and pioneering renewable energy sources, environmentally sustainable carbon precursors with superior electrochemical performance are needed. Therefore, bio-based materials are excellent candidates to replace PAN as a carbon precursor. Depending on the design requirement (e.g. carbon morphology, doping level, specific surface area, pore size and volume, and electrochemical performance), the appropriate selection of carbon precursors can be made from a variety of biomass and biowaste materials. This review provides a summary and discussion on the preparation and characterization of the emerging and recent bio-based carbon precursors that can be used as electrodes in energy storage applications. The review is outlined based on the morphology of nanostructures and the precursor's type. Furthermore, the review discusses and summarizes the excellent electrochemical performance of these recent carbon precursors in storage energy applications. Finally, a summary and outlook are also given. All this together portrays the promising role of bio-based carbon electrodes in energy storage applications.

Effect of the Anionic Counterpart: Molybdate vs. Tungstate in Energy Storage for Pseudo-Capacitor Applications

Nickel-based bimetallic oxides (BMOs) have shown significant potential in battery-type electrodes for pseudo-capacitors given their ability to facilitate redox reactions. In this work, two bimetallic oxides, NiMoO4 and NiWO4, were synthesized using a wet chemical route. The structure and electrochemical properties of the pseudo-capacitor cathode materials were characterized. NiMoO4 showed superior charge storage performance in comparison to NiWO4, exhibiting a discharge capacitance of 124 and 77 F.g-1, respectively. NiMoO4, moreover, demonstrates better capacity retention after 1000 cycles with 87.14% compared to 82.22% for NiWO4. The lower electrochemical performance of the latter was identified to result from the redox behavior during cycling. NiWO4 reacts in the alkaline solution and forms a passivation layer composed of WO3 on the electrode, while in contrast, the redox behavior of NiMoO4 is fully reversible.

Improved chemical precipitation prepared rapidly NiCo2S4 with high specific capacitance for supercapacitors

In this work, rapid chemical precipitation assisted annealing method is used to prepare flower-like NiCo₂S₄. And the flower-like structure after polyethylene glycol (PEG) modification yields an excellent specific capacitance (2198.9 F g^-1 at 1 A g^-1). And an asymmetric supercapacitor assembled with NiCo₂S₄ (PEG-modified) and activated carbon (AC) shows an energy density of 38.2 Wh kg^-1 at 400 W kg^-1, and outstanding stability (80% remained after 3000 cycles at 5 A g^-1). Benefited by a larger specific surface area and suitable pore size of the aggregate structure, the specific capacitance of prepared NiCo₂S₄ is increased by about 2 times. This uncomplicated preparation method is proved to be suitable for NiCo₂S₄ with a high specific capacitance of supercapacitors.

In situ microwave-assisted solvothermal synthesis via morphological transformation of ZnCo2O4 3D nanoflowers and nanopetals to 1D nanowires for hybrid supercapacitors

Over recent decades, the conversion of energy and its storage have been in the lime light due to the depletion of fossil resources. The electrochemical energy storage devices like supercapacitors and batteries, and their materials and fabrication methods have been extensively evaluated, which is the best solution for the energy crisis. Herein, zinc cobaltite (ZnCo2O4; ZCO) nanostructures grown on nickel (Ni) foam by microwave-assisted solvothermal fabrication for hybrid supercapacitors are reported. Two different structures/samples, ZCO-15/Ni (nanoflowers) and ZCO-30/Ni (nanowires), were obtained by simply adjusting the reaction time. The electrochemical and physicochemical properties of the as-prepared samples were systematically determined. Particularly, ZCO-15/Ni exhibits excellent structural stability due to its dual morphologies: nanoflowers and nanopetals, and exhibits a large electroactive surface area (25.61 m2 g-1), pore diameter (48.38 nm), and robust adhesion to Ni foam, enabling ion and electron transport. ZCO-15/Ni foam electrode delivers an excellent specific capacity of 650.27 C g-1 at 0.5 A g-1 and admirable cyclic performance of 91% capacitance retention after 5000 cycles compared to ZCO-30/Ni electrode. The excellent electrochemical performance of ZCO makes them promising electrode materials for batteries, hybrid supercapacitors, and other alternative energy storage applications.

Artificial Heterointerfaces Achieve Delicate Reaction Kinetics towards Hydrogen Evolution and Hydrazine Oxidation Catalysis

Electrochemical water splitting for H₂ production is limited by the sluggish anode oxygen evolution reaction (OER), thus using hydrazine oxidation reaction (HzOR) to replace OER has received great attention. Here we report the hierarchical porous nanosheet arrays with abundant Ni₃ N-Co₃ N heterointerfaces on Ni foam with superior hydrogen evolution reaction (HER) and HzOR activity, realizing working potentials of -43 and -88 mV for 10 mA cm^-2 , respectively, and achieving an industry-level 1000 mA cm^-2 at 200 mV for HzOR. The two-electrode overall hydrazine splitting (OHzS) electrolyzer requires the cell voltages of 0.071 and 0.76 V for 10 and 400 mA cm^-2 , respectively. The H₂ production powered by a direct hydrazine fuel cell (DHzFC) and a commercial solar cell are investigated to inspire future practical applications. DFT calculations decipher that heterointerfaces simultaneously optimize the hydrogen adsorption free energy (ΔG_H* ) and promote the hydrazine dehydrogenation kinetics. This work provides a rationale for advanced bifunctional electrocatalysts, and propels the practical energy-saving H₂ generation techniques.

Electrodeposition of hybrid nanosheet-structured NiCo2O4 on carbon fiber paper as a non-noble electrocatalyst for efficient electrooxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Hybrid nanosheet-structured NiCo₂O₄ on CFP as a self-supporting electrode for electrochemical oxidation of HMF to FDCA.

Design and assembly of a high stability asymmetric supercapacitor based on pseudocapacitive zinc–nickel sulfide nanosheets and fast ion-transport carbon nanosheets

A novel asymmetric supercapacitor is designed and assembled based on flower-like zinc–nickel sulfides (Zn–Ni–S) positive electrode and pitaya mesocarps-based carbon nanosheets (PMCN) negative electrode, which exhibits an excellent electrochemical performance.

NiCo2O4 arrays with a tailored morphology as hole transport layers of perovskite solar cells

Inorganic p-type semiconductors have broadly served as hole transport materials (HTLs) in perovskite solar cells (PSCs) in recent years. Among them, NiCo2O4 with its excellent conductivity and hole mobility is the emerging candidate for HTLs and is attracting increasing attention. Here, we employ a simple hydrothermal method to fabricate high-quality mesoporous NiCo2O4 films as HTLs of PSCs. The study finds that the morphology of NiCo2O4 can be regulated from nanosheets (NSs) to nanowires (NWs) as the hydrothermal reaction time increases, and the morphology of NiCo2O4 significantly affects the device performance. Specially, the device with NWs achieves a best efficiency of 11.58%, ascribed to the fact that such a one dimension material could provide a straight path for hole extraction/transport. And benefiting from the mesoporous structures of NiCo2O4 films, all the devices exhibited a very repeatable and desirable long-term stability. Overall, this work develops alternative NiCo2O4 nanostructure-based HTLs and opens up new opportunities in fabricating PSCs.

An efficient and stable coral-like CoFeS2 for wearable flexible all-solid-state asymmetric supercapacitor applications

CoFeS2 was synthesized by an organic solvothermal method as a positive electrode for flexible asymmetric supercapacitors, which showed high specific capacitance and good stability.

Morphological Modulation of Conducting Polymer Nanocomposites with Nickel Cobaltite/Reduced Graphene Oxide and Their Subtle Effects on the Capacitive Behaviors

This work reports on the urchin-like architecture-based nickel cobaltite (NiCo₂O₄)/reduced graphene oxide (rGO)/conducting polymer [polyaniline (PANI) or polypyrrole (PPy)] nanocomposites prepared through a hydrothermal synthesis procedure, followed by in situ polymerization techniques. Subsequently, these materials are subjected to electrochemical investigation to search for promising electrode materials for energy storage applications. Interestingly, the morphology of NiCo₂O₄ varies upon the addition of rGO as well as nitrogen-doped rGO (N-rGO). When it is composite with rGO, it forms an urchin-like architecture, and with N-rGO, it forms nanoparticle structures having a diameter of 90 ± 10 nm. Further, these nanostructures are intricately coated by conducting polymers (such as PANI and PPy) as evidenced from the field emission scanning electron microscopy and high-resolution transmission electron microscopy observations, and the overall shape does not alter after the modification. All composites are investigated thoroughly by Fourier transform infrared, Raman, X-ray powder diffraction, and X-ray photoelectron spectroscopies to confer the formation and presence of polymers. The NiCo₂O₄/rGO/PPy nanocomposites exhibit an excellent specific capacitance of 1547 ± 5 F/g at a current density of 0.5 A/g, a better energy density of 34.37 ± 0.11 W h/kg at 0.5 A/g, a notable power density of 99.98 ± 0.31 W/kg at 0.5 A/g, and retains its 94 ± 1% specific capacitance after 5000 charge-discharge cycles. The uniform coating over the urchin-like architecture by conducting polymers constructs a typical morphology, and possibly, it is the key factor behind gaining such superior electrochemical behavior owing to (a) the enhancement of surface area and (b) the combination of double-layer capacitive and pseudocapacitive properties. Furthermore, a symmetric flexible supercapacitor device made of NiCo₂O₄/rGO/PPy nanocomposites provides superior electrochemical behavior.

Ultra-long cycle life and binder-free manganese-cobalt oxide supercapacitor electrodes through photonic nanostructuring

We report a novel photonic processing technique as a next-generation cost-effective technique to instantaneously synthesize nanostructured manganese-cobalt mixed oxide reduced graphitic oxide (Mn-Co-rGO) for supercapacitor electrodes in energy storage applications. The active material was prepared directly on highly conductive Pt-Si substrate, eliminating the need for a binder. Surface morphological analysis showed that the as-prepared electrodes have a highly porous and resilient nanostructure that facilitates the ion/electron movement during faradaic redox reactions and buffers the volume changes during charge-discharge processes, leading to the improved structural integrity of the electrode. The presence of distinct redox peaks, due to faradaic redox reactions, at all scan rates in the cyclic voltammetry (CV) curves and non-linear nature of the charge-discharge curves suggest the pseudocapacitive charge storage mechanism of the electrode. The electrochemical stability and the life cycle were examined by carrying out galvanostatic charge-discharge (GCD) measurements at 0.40 mA cm^-2 constant areal current density for 80 000 cycles, and the electrode showed 95% specific capacitance retention, exhibiting excellent electrochemical stability and an ultra-long cycle life. Such remarkable electrochemical performance could be attributed to the enhanced conductivity of the electrode, the synergistic effect of metal ions with rGO, and the highly porous morphology, which provides large specific surface area for electrode/electrolyte interaction and facilitates the ion transfer.