Characterization of NiFe oxyhydroxide electrocatalysts by integrated electronic structure calculations and spectroelectrochemistry

Significance The conversion of water to oxygen and hydrogen molecules is essential for a variety of renewable energy technologies. Nickel–iron (NiFe) oxyhydroxide is an important, earth-abundant electrocatalyst for the oxygen evolution reaction. A combined experimental and computational study of pure Ni oxyhydroxide and mixed NiFe oxyhydroxide thin films elucidates the chemistry governing their different electrochemical and optical properties. The Ni and Fe oxidation states in each system are assigned as a function of applied potential based on quantum-mechanical calculations, cyclic voltammetry, and UV-visible spectroscopy. In the more catalytically active NiFe system, oxidation to Fe 4+ coincides with the onset of oxygen evolution. Synergy between experiment and theory provides a detailed, atomistic understanding of this robust catalyst.