Decoupling the HOR enhancement on PtRu: Dynamically matching interfacial water to reaction coordinates

Platinum-ruthenium alloys (PtRu) represent state-of-the-art alkaline hydrogen oxidation reaction (HOR) catalysts, yet the atomic-scale origin of their superiority over pure Pt remains incompletely understood. Here, we employ density functional theory calculations, ab initio molecular dynamics simulations, and microkinetic modeling on Pt(111) and PtRu(111) surfaces to systematically investigate the key factors, including active sites distribution, species adsorption, and solvent reorganization, that affect the HOR activity and decouple their contributions. The results reveal that while the moderate hydrogen binding energy and improved hydroxyl (OH) species adsorption both contribute to the enhanced activity, the dominant factor is the substantial reduction in solvent reorganization energy on the PtRu(111). This is facilitated by the spatial separation of active sites: Pt atoms preferentially stabilize adsorbed hydrogen, while Ru atoms strongly bind OH and interfacial water molecules. This configuration increases the probability of hydrogen interacting with OH/water and enhances the fraction of “H-up” water molecules, forming a well-organized hydrogen bond network within the electric double layer. The dynamically compatible interfacial water structure and HOR coordination promote H desorption and proton transfer in the Volmer step, thereby accelerating the HOR kinetics. The PtRu(111)-alkali interface demonstrates superior hydrogen oxidation activity owing to reduced solvent reorganization energy, enabled by the synergistic matching of reaction coordinates, favorable water orientation, and an optimized hydrogen bond network.