Enhanced Oxygen Evolution Reaction Activity of Fe-Doped Lithium Nickel-Based Metal Oxide through Modification of Nickel Oxidation State

Abstract

The oxygen evolution reaction (OER) involves the four-electron transfer process of water oxidation to produce oxygen gas and protons. However, this reaction is kinetically sluggish and requires high overpotential compared to hydrogen evolution reaction (HER). Herein, we have fabricated Fe-doped LiNiO2 using electrospray deposition (ESD) technique. With this technique, we can modify the electronic structure of LiNiO2 by controlling amounts of Fe, and the morphology can be controlled with various parameters such as applied voltage, spray rate, and substrate temperature. The synergistic effect of iron doping can modify the electronic structure of the surface Ni ions and increase oxidation state of Ni2+ to Ni3+. Through this oxidation state change, Ni becomes more electrophilic and then adsorbed oxygen in the M – O step, which is considered as rate-determining step in OER, easily reacts with OH ions. In electrochemical analysis, the optimized Fe-doped LiNiO2 showed improved OER performance compared to LiNiO2. The surface chemical compositions of the Fe-doped LiNiO2 electrode were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). From our result, we can improve OER performance and stability with simple control of ESD technique parameters and electronic structure modification by Fe doping.