Surface hydroxide accelerates acidic hydrogen oxidation kinetics

Mechanistic understanding of hydrogen oxidation reaction (HOR) kinetics is crucial for developing high-performance fuel cell anode catalysts. Adsorbed hydroxide (OH_ad) significantly impacts HOR kinetics in alkaline conditions by directly participating as a reactant, but its impact in acidic conditions is overlooked due to its instability on metal surfaces and inability to be replenished. Here, we demonstrate that OH_ad can be stably anchored on Ru, Pd, and Rh surfaces in the HOR potential region through pre-electrooxidation treatment, significantly promoting their acidic HOR kinetics. In-situ spectroscopies and ab initio molecular dynamics simulation verify that OH_ad persists on pre-oxidized metal surfaces and alters the water orientation from ‘H-down’ to ‘O-down’ within the electric double layer. This change shortens the distance between adsorbed hydrogen (H_ad) and interfacial water and promotes the formation of the interfacial hydrogen-bond network, thereby weakening the apparent hydrogen binding energy and reducing H_ad desorption energy barriers from the catalyst surface to bulk electrolyte, enhancing acidic HOR kinetics. Inspired by the fundamental understandings, a Ru-RuO_x(OH)_y catalyst is synthesized, achieving a 41-fold enhancement in HOR mass activity compared with Ru/C. The Ru-RuO_x(OH)_y illustrates comparable performance to Pt in practical proton-exchange membrane fuel cell (PEMFC) applications and superior voltage reversal tolerance during start-up/shut-down processes, enabling the development of a totally Pt-free PEMFC.