Modulation of a NiFe-Layered Double Hydroxide Electrode Using Zn Doping and Selective Etching Process for High-Performance Oxygen Evolution Reaction

Abstract

In the generation of green hydrogen and oxygen from water, transition metal–based electrode materials have been considered high-performance water-splitting catalysts. In water splitting, the oxygen evolution reaction (OER) is the rate-determining step. To overcome the high overpotential and slow kinetics of OER, the development of effective catalysts to improve electrolysis efficiency is essential. Nickel–iron-layered double hydroxides (NiFe-LDHs) have been recognized for their superior electrochemical performance under alkaline OER conditions and have emerged as promising catalysts owing to their unique structure that enhances electrolyte infiltration and exposes more active sites. However, the unique modulation of the crystalline structure of NiFe-LDHs can further improve OER performance. Accordingly, this study introduces an innovative synthesis approach based on Zn doping and selective Zn etching to increase the ECSA and induce favorable transition-metal oxidation states in NiFe-LDHs, thereby improving OER efficiency. After 6 h of Zn etching (Ni_2.9Zn_0.1Fe-6h), the optimized Ni_2.9Zn_0.1Fe LDH sample demonstrated remarkable electrochemical performance and stability, requiring small overpotentials of 192 and 260 mV at current densities of 10 and 100 mA cm⁻², respectively. Moreover, the Ni_2.9Zn_0.1Fe-6h electrode could maintain its original overpotential (260 mV) at a current density of 100 mA cm⁻² for 250 h. The proposed Zn doping and subsequent partial Zn etching can practically be applied to numerous high-performance transition metal–based electrochemical catalysts.