Fig. 6: The Reaction mechanism.

a DFT-calculated free energy diagrams for S1, S4 and S6. b The optimized atomic structure models of adsorbed *H showed along different directions on S1(100) surface, (c) S4(001) surface and (d) S6(100) surface. (Red and white balls inside represent O and H atoms). e Potential-resolved in situ FT-IR spectra for S1, S4 and S6.