An advanced asymmetric supercapacitor electrode material based on Mg(OH)2-Ni3S4 nanocomposite

Abstract

It is imperative to rationally design novel electrode materials for energy storage systems that satisfy the requirements of outstanding specific capacitance, energy density and cycle stability in addition to being safe, efficient and environmentally acceptable. Herein, a bimetallic metal-organic framework derived mixed hydroxide-sulfide Mg(OH)₂-Ni₃S₄ nanocomposite was achieved using a conventional two-step approach. Physiochemical analysis reveals the formation of Mg(OH)₂-Ni₃S₄ nanocomposite with hierarchical porosity and decent surface area. The synergistic effect of Mg²⁺, a non-electroactive metal ion, with the redox-active Ni²⁺ ion provides better electrochemical performance than other Ni₃S₄-based composite electrode materials reported in the literature. Electrochemical analysis shows that the as-synthesized electrode material displays a remarkable specific capacitance of 3316.7 F/g at 1 A/g in 1 M KOH solution. Moreover, the fabricated Mg(OH)₂-Ni₃S₄//AC asymmetric supercapacitor (ASC) device delivers a specific capacitance of 274.7 F/g at 1 A/g. The ASC device also maintains 88.3 % of its initial capacity after 10,000 charge/discharge cycles and reaches a high energy density of 109.1 Wh/kg at a power density of 729.2 W/kg. Additionally, two such devices connected in series can illuminate a red LED for almost 20 min. These findings suggest that Mg(OH)₂-Ni₃S₄ nanocomposite is an attractive choice for use as an active material in the development of ASC devices.