Reorganizing the Pt Surface Water Structure for Highly Efficient Alkaline Hydrogen Oxidation Reaction

Abstract

The hydrogen oxidation reaction (HOR) in alkaline electrolytes exhibits markedly slower kinetics than that in acidic electrolytes. This poses a critical challenge for alkaline exchange membrane fuel cells (AEMFCs). The slower kinetics in alkaline electrolytes is often attributed to the more sluggish Volmer step (hydrogen desorption). It has been shown that the alkaline HOR activity on the Pt surface can be considerably enhanced by the presence of oxophilic transition metals (TMs) and surface-adsorbed hydroxyl groups on TMs (TM–OH_ad), although the exact role of TM–OH_ad remains a topic of active debates. Herein, using single-atom Rh-tailored Pt nanowires as a model system, we demonstrate that hydroxyl groups adsorbed on the Rh sites (Rh–OH_ad) can profoundly reorganize the Pt surface water structure to deliver a record-setting alkaline HOR performance. In situ surface characterizations, together with theoretical studies, reveal that surface Rh–OH_ad could promote the oxygen-down water (H₂O_↓) that favors more hydrogen bond with Pt surface adsorbed hydrogen (H₂O_↓···H_ad-Pt) than the hydrogen-down water (OH_2↓). The H₂O_↓ further serves as the bridge to facilitate the formation of an energetically favorable six-membered-ring transition structure with neighboring Pt–H_ad and Rh–OH_ad, thus reducing the Volmer step activation energy and boosting HOR kinetics.