The Charge State of Adsorbed H*: A Missing Kinetic Descriptor for Hydrogen Evolution Reaction

The free energy of hydrogen adsorption (Δ G H* ) is widely used as a descriptor for the hydrogen evolution reaction (HER), yet its exclusive focus on thermodynamics may fail to capture reaction kinetics, thereby limiting its predictive power. Here, taking the experimentally debated active sites for HER on the MoS 2 basal plane─sulfur vacancies versus oxygen-substituted sulfur sites─as a model system, we reveal through grand canonical density functional theory (GC-DFT) calculations that the charge state of adsorbed H* (Δ Q H* ) is a key factor governing HER kinetics. Systematic validation across diverse catalysts further confirms the generality of Δ Q H* as a descriptor of HER kinetics. Guided by Δ Q H*, we unveil an H 2 formation pathway on MoS 2 edges that involves dynamic charge switching during H* diffusion, which helps to reconcile theoretical predictions with experimental observations. By integrating Δ Q H* with Δ G H*, we establish an effective dual-descriptor strategy for reliable catalyst screening, which identifies graphene-supported PtC 3 and OsC 4 single-atom catalysts as promising HER candidates. This work introduces Δ Q H* as a missing kinetic descriptor for the HER, providing a robust principle for the rational design of HER catalysts.