The oxygen evolution reaction (OER) currently limits the production of low-cost hydrogen from water. Transition metal (TM) oxides show promising activities toward OER, and outcompete benchmark Ru and Ir electrocatalysts in alkaline electrolyte. Here, we investigate the "boosting" effect of Fe-doping in electrodeposited Ni, Co, and Mn oxide catalysts. Fe-doping has been shown to impact the adsorption energies of the OER intermediates, and electronic and physical properties such as the Ni2+/Ni3+ redox process and conductivity. Here, we explore how Fe influence the metal-oxygen (M-O) covalency using operando soft X-ray absorption spectroscopy (XAS). Based on the intensity of the O K pre-edge peak around 528 eV, we find that Fe lowers the covalency, which is correlated to a higher activity. The pre-peak feature has been linked to anionic redox, which involves extracting charge from lattice oxygens. We employ surface enhanced Raman spectroscopy (SERS) to extract further information on the “active oxygen” species, visible as a band centered around 1050 cm-1, and correlated to the anionic redox process. We find strongest signal of active oxygen in the pure Ni catalyst, and that Fe suppresses these species. O16/O18 isotope exchange confirms a low degree of lattice oxygen exchange during OER in all catalysts. Surprisingly, largest exchange is found in the non-catalytic state, and Fe-dopants suppress lattice exchange. Our studies show that both anionic redox and lattice oxygen paticipation is minimal in catalysts with high OER activity, especially in Fe-doped catalysts. These findings shine new light onto the catalytic mechanism in TM electrocatalysts and challenge the current understanding of active oxygen species in water oxidation.

The boosting effect of Fe in water oxidation electrocatalysts investigated using operando spectroscopy

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