Coverage Effects on Hydrogen Evolution across Metals, Oxides, MXenes, and Dichalcogenides

Hydrogen adsorption thermodynamics at realistic surface coverages play an important role in determining electrocatalyst activity for the hydrogen evolution reaction. However, most first-principles studies assess H binding in the dilute limit, implicitly neglecting lateral adsorbate interactions that can become important under operating conditions. We report a systematic density functional theory investigation of coverage-dependent H adsorption on representative hydrogen evolution reaction materials spanning different classes: the noble metal Pt(111), the oxide α-Ir₂O₃(0001), the oxygen-terminated MXene Mo₂CO₂, and the two-dimensional semiconductor 1H-MoS₂. We control effective coverage by varying the surface supercell size, allowing a consistent comparison of lateral H-H interactions across low-dimensional, oxide, and metallic systems. Coverage effects are strongly material-dependent. Hydrogen adsorption on Pt(111) rapidly converges as the surface area increases due to efficient metallic screening. In contrast, Mo₂CO₂ shows pronounced coverage sensitivity, with lateral interactions modifying adsorption energetics and Gibbs free energies. α-Ir₂O₃(0001) and 1H-MoS₂ show clear depolarization effects, reflected in coverage-dependent changes in work function and electronic structure. These results show that H coverage is an essential variable for evaluating hydrogen evolution descriptors and highlight the limitations of dilute-limit approximations. The present results, therefore, establish a basis for incorporating coverage effects into theoretical assessments of hydrogen evolution catalysts across diverse material classes.