Importance of Nickel Oxide Lattice Defects for Efficient Oxygen Evolution Reaction
Hannes Radinger, Paula Connor, Sven Tengeler, Robert W. Stark, Wolfram Jaegermann, Bernhard Kaiser
Abstract
Nickel oxide/hydroxides [NiOx(OH)y] are considered to be promising materials to replace noble metals for the oxygen evolution reaction in alkaline media. While several studies showed that iron impurities promote the activity of nickel-based catalysts, the effects of intrinsic nickel defects and the underlying mechanism remain unknown. In this work, X-ray photoelectron spectroscopy is combined with surface-enhanced Raman scattering to understand the reactivity of NiOx thin films, which were prepared at different temperatures and thus varied in their chemical composition and crystalline order. Raman spectroscopy was used to follow the characteristic oxidation of nickel species from NiII(OH)2 to NiIIIOOH and NiIVOO– under electrochemical conditions. A stronger oxide-to-hydroxide conversion, consistent with the post-electrochemistry study, was associated with the presence of initial NiIII impurities and oxygen vacancies and appears beneficial for the electrocatalytic activity.