Dataset of the article "Unriddling the role of alkali metal cations and Pt-surface hydroxide in alkaline hydrogen evolution reaction" accepted in Nature Catalysis. The optimized geometries (in VASP format) and full 100-ps AIMD trajectories (in xyz format) of Pt(111)/water interface with alkali metal cations (Li+, Na+, K+) and with or without surface *OH.