Morphology Controlled Synthesis of Nickel Cobalt Oxide for Supercapacitor Application with Enhanced Cycling Stability

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.

A hybrid NiCo2O4@NiMoO4 structure for overall water splitting and excellent hybrid energy storage

In this study, a two-step hydrothermal method is used to prepare NiCo2O4@NiMoO4 nanoscale materials for periodic stability supercapacitors. The synthesized product can be directly used as the electrode material of the supercapacitor, and its specific capacitance is 685.7 C g-1. The composite electrode NiCo2O4@NiMoO4 is used as the positive electrode and the hybrid capacitor is assembled. Meanwhile, at the power density of 4050 W kg-1, the energy density is 96.3 W h kg-1, and the capacitance retention is 100% after 10 000 cycles. At the same time, when the composite is used as a catalyst, it exhibits OER overvoltage (300 mV), HER overvoltage (170 mV) and a low battery voltage of 1.65 V at 10 mA cm-2. After 14 hours of long-term use, NiCo2O4@NiMoO4 maintained good stability, indicating that its structure further improved the electrochemical performance, providing a great advantage for the study of low-cost electrode materials for overall water splitting.

3D Hierarchically Mesoporous Zinc-Nickel-Cobalt Ternary Oxide (Zn0.6Ni0.8Co1.6O4) Nanowires for High-Performance Asymmetric Supercapacitors

Increased efforts have been devoted recently to develop high-energy-density supercapacitors (SC) without renouncing their power efficiency. Herein, a hierarchically mesoporous nanostructure of zinc-nickel-cobalt oxide (ZNCO) nanowires (NWs) is constructed by hierarchical aggregation of ZNCO nanoparticles. It is worth noting that cobalt and nickel rich lattice imparts higher charge storage capability by enhanced reversible Faradaic reaction while zinc provides structural stability and higher conductivity. Moreover, particulate nature of ZNCO NWs allows deep diffusion of electrolyte thus enabling reversible charge storage under higher current densities. The as-prepared ZNCO NWs exhibited excellent specific capacitance of 2082.21 F g⁻¹ at the current density of 1 A g⁻¹ with high stability up to 5,000 charge-discharge cycles. Further, the asymmetric SC device was assembled using ZNCO NWs (ZNCO NWs//MWCNTs) which exhibited high energy density of 37.89 Wh kg⁻¹ and excellent capacitance retention up to 88.5% over 1,000 cycles. This work presents ways to construct multi-component high-energy-density materials for next-generation energy storage devices.

Enhanced electrochemical performance of nanoplate nickel cobaltite (NiCo2O4) supercapacitor applications

Well-ordered, unique interconnected nanostructured binary metal oxides with lightweight, free-standing, and highly flexible nickel foam substrate electrodes have attracted tremendous research attention for high performance supercapacitor applications owing to the combination of the improved electrical conductivity and highly efficient electron and ion transport channels. In this study, a unique interconnected nanoplate-like nickel cobaltite (NiCo2O4) nanostructure was synthesized on highly conductive nickel foam and its use as a binder-free material in energy storage applications was assessed. The nanoplate-like NiCo2O4 nanostructure electrode was prepared by a simple chemical bath deposition method under optimized conditions. The NiCo2O4 electrode delivered an outstanding specific capacitance of 2791 F g-1 at a current density of 5 A g-1 in a KOH electrolyte in a three-electrode system as well as outstanding cycling stability with 99.1% retention after 3000 cycles at a current density of 7 A g-1. The as-synthesized NiCo2O4 electrode had a maximum energy density of 63.8 W h kg-1 and exhibited an outstanding high power density of approximately 654 W h kg-1. This paper reports a simple and cost-effective process for the synthesis of flexible high performance devices that may inspire new ideas for energy storage applications.

2D nanoporous Ni(OH)2 film as an electrode material for high-performance energy storage devices

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique. The nanostructured Ni(OH)₂ film was flexible and translucent, and could be directly compressed on a current collector. Owing to the uniform well-defined morphology and stable structure, the Ni(OH)₂ film binder-free electrode displayed a high specific capacity, exceptional rate capability, and admirable cycle life. The specific capacitance was 453.6 mA h g⁻¹ (1633 F g⁻¹) at 0.5 A g⁻¹. The assembled Ni(OH)₂//activated carbon (AC) asymmetric supercapacitor (ASC) device had an energy density of 58.7 W h kg⁻¹ at a power density of 400 W kg⁻¹. These prominent electrochemical properties of Ni(OH)₂ were attributed to the high electrical conductivity, high surface area, and unique porous architecture. Free tailoring, binder-free, and direct pressing were the most significant achievements of the Ni(OH)₂ film in the development of high-performance energy storage devices.

A two-dimensional (2D) nanoporous Ni(OH)₂ film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique.

Nickel Cobalt Thiospinel Nanoparticles as Hydrodesulfurization Catalysts: Importance of Cation Position, Structural Stability, and Sulfur Vacancy

First-row transition metal-based thiospinels are prepared via a one-pot versatile strategy and for the first time investigated as hydrodesulfurization (HDS) catalysts. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis confirm that these thiospinels consist of agglomerated nanoparticles (NPs) and contain multivalent metal cations. Among the sulfides synthesized at 230 °C, NiCo₂S₄ presents the highest thiophene conversion. This high intrinsic activity is found to be correlated with the normal spinel structure with Ni cations located on the tetrahedral sites and Co cations on the octahedral sites. However, the spent NiCo₂S₄ NPs experience phase transformation because of the relatively low synthetic temperature. Accordingly, six NiCo₂S₄ samples are prepared in the temperature range of 180-350 °C, and their HDS activity increases monotonically with the synthetic temperature, which is attributed to the higher structural stability and more surface sulfur vacancy of the NiCo₂S₄ NPs prepared at higher temperatures. Notably, the NiCo₂S₄ NPs synthesized at 350 °C exhibit a much higher thiophene conversation of 62.9% than the classic MoS₂ catalyst (39.3%) as well as excellent reusability. Our study suggests that the NiCo₂S₄ thiospinels with high activity and stability can represent a new promising class of industrial HDS catalysts.

Flowery nickel–cobalt hydroxide via a solid–liquid sulphur ion grafting route and its application in hybrid supercapacitive storage

In our research, a two-step solid–liquid route was employed to fabricate flowery nickel–cobalt hydroxide with sulphur ion grafting (Ni1Co2–S). The utilization of NaOH/agar and Na₂S/agar could efficiently retard the release rates of OH⁻ or S²⁻ ions at the solid–liquid interface due to strong bonding between agar hydrogel and these anions. Ni1Co2–S generally displays ultrathin flowery micro-frame, ultrathin internal nanosheets and expanded pore size. Besides, the introduction of suitable sulphide species into nickel–cobalt hydroxide could improve its conductivity due to the lower band gap of Ni–Co sulphide. The supercapacitive electrode Ni1Co2–S presented capacitance of 1317.8 F g⁻¹ (at 1 A g⁻¹) and suitable rate performance (77.9% at 10 A g⁻¹ and 59.3% at 20 A g⁻¹). Furthermore, a hybrid supercapacitor (HSC) was developed utilizing positive Ni1Co2–S and negative activated carbon electrodes. As expected, the HSC device exhibited excellent specific capacitance (117.1 F g⁻¹ at 1 A g⁻¹), considerable energy densities (46.7 W h kg⁻¹ at 0.845 kW kg⁻¹ and 27.5 W h kg⁻¹ even at 9 kW kg⁻¹) and suitable cycling performance, which further illuminated the high energy storage capacity of Ni1Co2–S.

The Ni1Co2–S material fabricated via a solid–liquid route achieves high-performance supercapacitive storage.

Application of nickel cobalt oxide nanoflakes for electrochemical sensing of estriol in milk

In this work, a nickel cobalt oxide (Ni/Co oxide) nanoflake based electrochemical sensor for the fast determination of estriol in milk is presented for the first time.