Smartly tailored Co(OH)2-Ni(OH)2 heterostucture on nickel foam as binder-free electrode for high-energy hybrid capacitors

Concave Ni(OH)2 Nanocube Synthesis and Its Application in High-Performance Hybrid Capacitors

The controlled synthesis of hollow structure transition metal compounds has long been a very interesting and significant research topic in the energy storage and conversion fields. Herein, an ultrasound-assisted chemical etching strategy is proposed for fabricating concave Ni(OH)2 nanocubes. The morphology and composition evolution of the concave Ni(OH)2 nanocubes suggest a possible formation mechanism. The as-synthesized Ni(OH)2 nanostructures used as supercapacitor electrode materials exhibit high specific capacitance (1624 F g-1 at 2 A g-1) and excellent cycling stability (77% retention after 4000 cycles) due to their large specific surface area and open pathway. In addition, the corresponding hybrid capacitor (Ni(OH)2//graphene) demonstrates high energy density (42.9 Wh kg-1 at a power density of 800 W kg-1) and long cycle life (78% retention after 4000 cycles at 5 A g-1). This work offers a simple and economic approach for obtaining concave Ni(OH)2 nanocubes for energy storage and conversion.

Metal–organic framework induced hybrid NiCo2S4/PPy structures with unique interface features for high performance flexible energy storage devices

In this work, we report hybrid-structure NiCo2S4/PPy nanosheets through hydrothermal synthesis and electrodeposition methods. Meanwhile, the NiCo2S4/PPy-110 samples exhibit a high specific capacitance of 983 C g−1 at 1 A g−1 and excellent stability.

Hydrothermal temperature-driven evolution of morphology and electrocatalytic properties of hierarchical nanostructured CoFe-LDHs as highly efficient electrocatalysts for oxygen evolution reactions

The development of economical and efficient oxygen evolution reaction (OER) catalysts plays an important part in electrochemical water oxidation, and it has been known that the electrocatalytic performance of these materials is closely related to their micromorphology at micro/nanometer scales. Herein, we report a unique hierarchical nanosheet-nanowire structure of a CoFe layered double hydroxide (LDH) electrocatalyst directly grown on conductive nickel foam (NF) by optimizing the hydrothermal temperature of the reaction. The hydrothermal temperature is decisive in driving the formation of the wire-in-sheet morphology of CoFe-LDH, while the hydrothermal time has almost no effect on the morphology of the electrocatalyst. The possible mechanism of the morphological evolution has been proposed. The wire-in-sheet nanoarray of CoFe-LDH provides a higher number of active sites, more intricate transmission networks and improved electronic conductivity, resulting in enhanced electrocatalytic performance. Consequently, the resultant CoFe-LDH exhibits superior OER performance: a low overpotential of 242 mV at 100 mA cm^-2 (η = 242 mV@100 mA cm^-2), with an exceedingly small Tafel slope of 41 mV dec^-1, as well as an ultra-long durability (97 h) in 1 M KOH electrolyte. Therefore, the design of a unique hierarchical nanostructure by tuning the reaction conditions may open up a new avenue for high-performance OER electrocatalysts.

Constructing nickel cobaltate @nickel-manganese layered double hydroxide hybrid composite on carbon cloth for high-performance flexible supercapacitors

Flexible supercapacitors have received considerable interest owing to their potential application in wearable electronics. Designing subtle hybridization of active materials and constructing smart electrode architectures are effective strategies for developing high-performance flexible supercapacitors. Herein, a hierarchically hybrid electrode is engineered by integrating nanoneedle-like structural NiCo₂O₄ and NiMn layered double hydroxide (NiMn-LDH) composite on highly conductive carbon cloth (CC). This architecture can endow abundant active sites, rapid electron collection pathways and efficient ion transport channels. The resultant hybrid electrode delivers high areal capacitance of 4010.4 mF cm^-2, excellent cyclic stability and good rate performance. Furthermore, by pairing with an activated carbon (AC)/CC anode, a flexible solid-state asymmetric supercapacitor (ASC) is assembled, which exhibits the high areal energy/power density of 0.78 mWh cm^-2/40.4 mW cm^-2 and superior capacitive stability at bending deformation. Meanwhile, the assembled ASC possesses outstanding cycling stability with 97.7% capacitance retention after 10,000 cycles. This work presents the effects of rational design of hybrid electrode with high electrochemical properties and flexibility, holding great potential for flexible energy storages.

Novel NiMgOH-rGO-Based Nanostructured Hybrids for Electrochemical Energy Storage Supercapacitor Applications: Effect of Reducing Agents

This paper describes the synthesis and characterization of NiMgOH-rGO nanocomposites made using a chemical co-precipitation technique with various reducing agents (e.g., NaOH and NH4OH) and reduced graphene oxide at 0.5, 1, and 1.5 percent by weight. UV-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, a particle size analyzer, and cyclic voltammetry were used to characterize the composite materials. The formation of the NiMgOH-rGO nanocomposite with crystallite sizes in the range of 10–40 nm was inferred by X-ray diffraction patterns of materials, which suggested interlayers of Ni(OH)2 and Mg(OH)2. The interactions between the molecules were detected using Fourier-transform infrared spectroscopy, while optical properties were studied using UV-visible spectroscopy. A uniform average particle size distribution in the range of 1–100 nm was confirmed by the particle size analyzer. Using cyclic voltammetry and galvanostatic charge/discharge measurements in a 6 M KOH solution, the electrochemical execution of NiMgOH-rGO nanocomposites was investigated. At a 1 A/g current density, the NiMgOH-rGO nanocomposites prepared with NH4OH as a reducing agent had a higher specific capacitance of 1977 F/g. The electrochemical studies confirmed that combining rGO with NiMgOH increased conductivity.

Facile fabrication of core-shell structured Ni(OH)2/Ni(PO3)2 composite via one-step electrodeposition for high performance asymmetric supercapacitor

Metal metaphosphates, particularly those with core-shell structure, have showed extraordinary potential in energy storage field due to their superior chemical and physical properties. However, the core-shell metal metaphosphates with high energy density in supercapacitor application is rarely reported. Here, the core-shell structured Ni(OH)₂/Ni(PO₃)₂ (NNP) hybrid electrode were prepared by one-step electrodeposition, which exhibits a superior specific capacitance of 1477 F g^-1 at a current density of 1 A g^-1. Furthermore, an aqueous asymmetric supercapacitor (ASC) based on NNP hybrid composite as cathode and reduced graphene oxide (rGO) as anode is assembled successfully to deliver a prominent energy density of 67 Wh kg^-1 at 775 W kg^-1 and splendid stability with capacitance retention of 81% after 8000 cycles. The outstanding electrochemical capabilities are attributed to the porous nanoflake and hierarchical core-shell structure of NNP hybrid composite, which can accelerate ion diffusion and charge transfer in redox reaction. These results indicate that nanohybrid NNP material has promise to be an advanced energy storage material.

A High-Energy-Density Hybrid Supercapacitor with P-Ni(OH)2 @Co(OH)2 Core-Shell Heterostructure and Fe2 O3 Nanoneedle Arrays as Advanced Integrated Electrodes

Transition metal hydro/oxides (TMH/Os) are treated as the most promising alternative supercapacitor electrodes thanks to their high theoretical capacitance due to the various oxidation states and abundant cheap resources of TMH/Os. However, the poor conductivity and logy reaction kinetics of TMH/Os severely restrict their practical application. Herein, hierarchical core-shell P-Ni(OH)₂ @Co(OH)₂ micro/nanostructures are in situ grown on conductive Ni foam (P-Ni(OH)₂ @Co(OH)₂ /NF) through a facile stepwise hydrothermal process. The unique heterostructure composed of P-Ni(OH)₂ rods and Co(OH)₂ nanoflakes boost the charge transportation and provide abundant active sites when used as the intergrated cathode for supercapacitors. It delivers an ultrahigh areal specific capacitance of 4.4 C cm^-2 at 1 mA cm^-2 and the capacitance can maintain 91% after 10 000 cycles, showing an ultralong cycle life. Additionally, a hybrid supercapacitor composed with P-Ni(OH)₂ @Co(OH)₂ /NF cathode and Fe₂ O₃ /CC anode shows a wider voltage window of 1.6 V, a remarkable energy density of 0.21 mWh cm^-2 at the power density of 0.8 mW cm^-2 , and outstanding cycling stability with about 81% capacitance retention after 5000 cycles. This innovative study not only supplies a newfashioned electronic apparatus with high-energy density and cycling stability but offers a fresh reference and enlightenment for synthesizing advanced integrated electrodes for high-performance hybrid supercapacitors.