Influence of Crystallographic Structure and Metal Vacancies on the Oxygen Evolution Reaction Performance of Ni‐based Layered Hydroxides**

Abstract

Nickel-based layered hydroxides (LHs) are a family of efficientelectrocatalysts for the alkaline oxygen evolution reaction (OER).Nevertheless, fundamental aspects such as the influence of thecrystalline structure and the role of lattice distortion of thecatalytic sites remain poorly understood and typically muddled.Herein, we carried out a comprehensive investigation on ɑ-LH, β-LHand layered double hydroxide (LDH) phases by means of structural,spectroscopical, in-silico and electrochemical studies, whichsuggest the key aspect exerted by Ni-vacancies in the ɑ-LHstructure. Density functional theory (DFT) calculations and X-rayabsorption spectroscopy (XAS) confirm that the presence ofNi-vacancies produces acute distortions of the electroactive Ni sites(reflected as the shortening of the Ni−O distances and changes inthe O−Ni−O angles), triggering the appearance of Ni localisedelectronic states on the Fermi level, reducing the Egap, andconsequently, increasing the reactivity of the electroactive sites inthe ɑ-LH structure. Furthermore, post-mortem Raman and XASmeasurements unveil its transformation into a highly reactiveoxyhydroxide-like phase that remains stable under ambient conditions.Hence, this work pinpoints the critical role of the crystallinestructure as well as the electronic properties of LH structures ontheir inherent electrochemical reactivity towards OER catalysis. Weenvision Ni-based ɑ-LH as a perfect platform for hosting trivalentcations, closing the gap toward the next generation of benchmarkefficient earth-abundant electrocatalysts