fig4

Figure 4. Constrained AIMD profiles for Volmer water dissociation. (A and B) Free-energy profiles near the barrier on (A) Au(111) and (B) Pt(111) without cations and with one Li⁺, Na⁺, or K⁺ ion. (C and D) Surface-normal distance of the reacting oxygen from (C) Au(111) and (D) Pt(111) over the displayed CV window. The CV is d(O-H) - d(M-H), with M denoting the target surface metal atom. Gray, red, blue, and green curves denote cation-free, Li⁺, Na⁺, and K⁺ conditions, respectively. Insets in (A and B) show local hydroxide environments under cation-free conditions (upper inset in (A); lower inset in (B)) and with K⁺ (lower inset in (A); upper inset in (B)), rendered using VESTA 3.5.8.^[53]. Full profiles are given in Supplementary Figure 5. Supplementary Table 1 lists all eight barrier estimates. Trajectory snapshots are provided for Pt(111) and Au(111) in Supplementary Figures 6 and 7, respectively.