Electronic structure modification induced electrochemical performance enhancement of bi-functional multi-metal hydroxide

Herein, multi-metal hydroxide exhibiting enhanced electrochemical performance for supercapacitor and oxygen evolution reaction (OER) applications is presented experimentally and theoretically. This is achieved via electronic structure modification through metal doping, including Mn, Fe, and Mg, into NiCo hydroxide. Both X-ray photoelectron spectroscopy and density functional theory calculation are used to examine the electronic structure modification. We show that the electrochemical performance improves with elevating metal, giving the hydroxide having 5 cations, i.e., high entropy hydroxide (HEOH), the best one. The Co²⁺ and Ni²⁺ dominates the capacitance, the phase stability accounts for the cycle stability, and the charge transfer resistance controls the rate retention in the supercapacitor. The obtained HEOH exhibits excellent specific capacity of 2,476 mC cm⁻² at 2 mA cm⁻², remarkable rate retention of 73% at 10 mA cm⁻², and outstanding cycle stability of 116% after 2,000 cycles. Supercapattery cell consisting of HEOH//Fe₃O₄/activated carbon clothes is shown to have a high energy density of 0.2 mWh cm⁻² at power density of 0.8 mW cm⁻² with excellent long-term durability. The HEOH also shows OER overpotential of 240 and 361 mV at high current densities of 100 and 1,500 mA cm⁻², respectively, and stability up to 100-h, outperforming the benchmark catalyst.