Three-dimensional ternary NixCuyZnz(CO3)(OH)2 electrodes for supercapacitors: electrochemical properties and applications.

ABSTRACT

Transition metal-based binary and ternary compound arrays were directly grown on a porous Ni foam substrate using a facile one-step hydrothermal method. Transition metals are considered ideal electrode materials for faradaic capacitors because they exhibit a wide range of oxidation states enabling effective redox charge transfer. Furthermore, compounds in which two or more transition metals react can help increase the number of active sites for charge-discharge reactions and provide more valence changes for improved charge transfer. In this work, we fabricated ternary electrodes with Ni, Cu, and Zn ions, exhibiting a larger surface area and higher entropy than those made with binary compounds. The NixCuyZnz-based ternary electrode had a shorter diffusion path for the electrolyte ions owing to its larger surface area. Ternary compounds can increase the entropy of the electrode because of the reaction between atoms of different sizes, bringing about a synergistic effect for high characteristic electrochemical values. The optimized NixCuyZnz(CO3)(OH)2 compound showed a maximum specific capacity of 344 mA h g-1 at a current density of 3 A g-1, which was remarkably higher than that of the binary electrode, and a cycling stability of 84.9% after 5000 cycles. An asymmetric supercapacitor produced with this compound as the positive electrode and graphene as the negative electrode exhibited a high energy density of 36.2 W h kg-1 at a power density of 103.1 W kg-1 and a current density of 2 A g-1. The asymmetric supercapacitor fabricated using the NixCuyZnz(CO3)(OH)2 compound as the positive electrode exhibited excellent electrical properties when used in an illuminated LED device.