Importance of Nickel Oxide Lattice Defects for Efficient\nOxygen Evolution Reaction

Abstract

Nickel oxide/hydroxides\n[NiO_<i>x</i>(OH)_<i>y</i>] are considered to be promising materials\nto replace noble metals for the oxygen evolution reaction in alkaline\nmedia. While several studies showed that iron impurities promote the\nactivity of nickel-based catalysts, the effects of intrinsic nickel\ndefects and the underlying mechanism remain unknown. In this work,\nX-ray photoelectron spectroscopy is combined with surface-enhanced\nRaman scattering to understand the reactivity of NiO_<i>x</i> thin films, which were prepared at different temperatures\nand thus varied in their chemical composition and crystalline order.\nRaman spectroscopy was used to follow the characteristic oxidation\nof nickel species from Ni^II(OH)₂ to Ni^IIIOOH and Ni^IVOO^– under electrochemical\nconditions. A stronger oxide-to-hydroxide conversion, consistent with\nthe post-electrochemistry study, was associated with the presence\nof initial Ni^III impurities and oxygen vacancies and appears\nbeneficial for the electrocatalytic activity.