Crystal structure of nickel manganese-layered double hydroxide@cobaltosic oxides on nickel foam towards high-performance supercapacitors

Rational design of the crystal structures of electrode materials is considered as an important strategy to construct high-performance supercapacitors. Herein, the three-dimensional crystal structure NiMn LDH@Co3O4 composites on Ni foam with different feeding Ni/Mn molar ratios were well-designed with hydrothermal, calcination and co-deposition methods, wherein urea hydrolysis supplied the alkali and carbonate ions. The electrochemical properties of the produced electrode materials were analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycling stability tests using 6 M KOH electrolyte. Indeed, the optimal feeding Ni/Mn molar ratio was determined to be 3:1. The resulting electrodes exhibited maximum specific capacitance (607.9 F g(-1) at 0.5 A g(-1)), respectable rate capability and excellent cycling stability with less than 3% loss of capacitance after 1000 cycles, which could be ascribed to the well-designed core-shell architecture and ultrathin nano-sheets structure of LDH. As for practical application, the asymmetric supercapacitor assembled using NiMn LDH@Co3O4 as the positive electrode and activated graphene (AG) as the negative electrode was also evaluated, which demonstrated a high energy density of 26.49 W h kg(-1) at the power density of 350 W kg(-1). The findings suggest that the three-dimensional crystal structure NiMn LDH@ Co3O4 composites have potential application as promising electrode materials for energy storage devices or other applications.