Kelsey A. Stoerzinger, Wesley T. Hong, Gisele Azimi, Livia Giordano, Yueh-Lin Lee, Ethan J. Crumlin, Michael D. Biegalski, Hendrik Bluhm, Kripa K. Varanasi, and Yang Shao-Horn
Oxides are instrumental to applications such as catalysis, sensing, and wetting, where the reactivity with water can greatly influence their functionalities. We find that the coverage of hydroxyls (*OH) measured at fixed relative humidity trends with the electron-donor (basic) character of wetted perovskite oxide surfaces. Using ambient pressure X‑ray photoelectron spectroscopy, we report that the affinity toward hydroxylation, coincident with strong adsorption energies calculated for dissociated water and hydroxyl groups, leads to strong H bonding that is favorable for wetting while detrimental to catalysis of the oxygen reduction reaction (ORR). Our findings provide novel insights into the coupling between wetting and catalytic activity and suggest that catalyst hydrophobicity should be considered in aqueous oxygen electrocatalysis.