Revealing Enhanced Active Oxygen Formation by Incorporating Chromium into Nickel Hydroxide Nanosheets for Improved Oxygen Evolution Reaction

Nickel-based oxyhydroxides have emerged as promising catalysts for the oxygen evolution reaction (OER) among Earth-abundant metals. While the incorporation of foreign elements is recognized to enhance catalytic activity, the origin of this enhancement is still debated. We synthesize and examine Ni hydroxide nanosheets, both with and without Cr doping, to elucidate the underlying enhancements. Operando UV-vis and Raman spectroscopy are employed to unravel the behavior of the catalysts. The Cr doping facilitates the oxidation of Ni, resulting in the generation of active oxygen species. The enriched active oxygen species improves OER performance through a lattice oxygen-mediated pathway in Fe-free KOH, and further contribute to the creation and increased activity of FeO_<i>x</i>H_<i>y</i> sites in the presence of Fe impurities. This work provides a mechanistic understanding of the performance enhancement in Ni-based catalysts through Cr doping and suggests a strategy for the design of more efficient catalysts in the future.