Evolution of Alkaline Hydrogen Oxidation Reaction Mechanisms and Design of Pt-Based Catalysts from Adsorption Descriptors to Interfacial Microenvironment Engineering

Abstract

The hydrogen oxidation reaction (HOR) is the key anodic reaction in anion exchange membrane fuel cells (AEMFCs), yet its kinetics remain markedly sluggish in alkaline media even on platinum (Pt) surfaces. This anomalous pH dependence indicates that alkaline HOR cannot be adequately explained by a single adsorption descriptor. To account for its rate-limiting origin, extensive efforts have invoked hydrogen binding energy (HBE), the bifunctional mechanism, the potential of zero free charge and potential of zero total charge (PZFC/PZTC), interfacial water, and cation effects. Rather than representing mutually isolated mechanisms, these perspectives describe different levels of the alkaline HOR reaction interface. Alkaline HOR is therefore more appropriately understood as an interfacial conversion process governed by coupled constraints across multiple interfacial layers. In this review, we first revisit how the mechanistic understanding of alkaline HOR has evolved from surface adsorption thermodynamics to the real working interface. We then reorganize the design logic of Pt-based catalysts around four interrelated classes of interfacial variables, namely the thermodynamic boundary of H* on Pt, the OH-related cooperative region adjacent to Pt, the near-surface charge state and interfacial water structure under reaction potentials, and the outer ionic, hydration, and mass-transport boundaries. Finally, we discuss several key challenges facing the field, including the dynamic operando interface, interfacial descriptors and mechanistic criteria, the integration of operando characterization with multiscale simulation, and the formation and retention of favorable interfacial conditions at the device scale. Overall, alkaline HOR research is shifting from active-site optimization toward working-interface organization. This transition provides a new analytical framework for the design of Pt-based AEMFC anodic catalysts and may also offer broader insight into multilayer constraints in electrocatalytic interfacial reactions.