Nickel Site Modification by High-Valence Doping: Effect of TantalumImpurities on the Alkaline Water Electro-Oxidation by NiO Probedby Operando Raman Spectroscopy

In an effort to support the large-scale implementa-tion of clean hydrogen in industry and society, the electrolyticdecomposition of water is considered a realistically enticingprospect, provided the guarantee of affordable and durable materialcomponents. Within alkaline systems, earth-abundant electro-catalysts could provide both these requirements. However, acontinued exploration of the reactivity and the causes behinddifferent behaviors in performance are necessary to guideoptimization and design. In this paper, Ta-doped NiO thinfilmsare prepared via DC magnetron sputtering (1-2-4 at % Ta) todemonstrate the effect of surface electronic modulation by non-3delements on the catalysis of the oxygen evolution reaction (OER).Material properties of the catalysts are analyzed via Rutherfordbackscattering spectrometry, X-ray diffractometry, photoelectron spectroscopy, and Raman spectroscopy. Ta impurities are shown tobe directly responsible for increasing the valence state of Ni sites and enhancing reaction kinetics, resulting in performanceimprovements of up to 64 mV at 10 mA cm-2relative to pristine NiO. Particularly, we show that by applyingoperandoRamanspectroscopy, Ta enhances the ability to create high-valence Ni in gamma-NiOOH at a lower overpotential compared to the undopedsample. The lowered overpotentials of the OER can thus be attributed to the energetically less hindered advent of the creation of gamma-NiOOH species on the pre-catalyst surface: a phenomenon otherwise unresolved through simple voltammetry