The role of hydroxyl species in the alkaline hydrogen evolution reaction over transition metal surfaces

Abstract

Understanding the activity-determining factors governing the alkaline hydrogen evolution reaction (HER) on transition metal catalysts is indispensable for water electrolysis with renewable energy. However, it remains a critical challenge. Although hydroxyl adsorption has been proposed to influence alkaline HER performance, its exact mechanistic role and quantitative correlations remain elusive. Here, we systematically investigate the alkaline HER on ten transition metal surfaces using density functional theory (DFT), revealing that hydroxyl adsorption critically modulates both pathway selection and reaction energy barrier. However, hydroxyl adsorption energy alone cannot fully explain the anomalous activity of certain catalysts, especially Pt. To address this, we introduce a multi-parameter coupled descriptor (ECS) that integrates electron occupancy (E), adsorption configuration (C), and surface crystallographic (S), enabling a qualitative evaluation of catalytic activity. This descriptor successfully elucidates previously unexplained activity trends and demonstrates a good correlation with over 10 experimental datasets, including those involving single-atom alloy (SAA) catalysts, indicating its robustness beyond pure metals. Our findings provide a descriptor based on the key species of hydroxyl for rational catalyst design and screening, and offer a fundamental framework for advancing the development of high-performance alkaline HER catalysts.