Generation of H-2 with liquid-phase adsorption of a thiol (2-mercaptopyridine, RSH) on transition metal surfaces has been confirmed for the first time. This reaction consists of photoinduced reduction of RS adsorbed on the metal to RSH and its re-adsorption during the subsequent dark process. Nearly perfect overcoating of nanometer-sized Ag particles with Pt by photodeposition (Pt-shell/Ag-core/TiO2) remarkably increases the rate of H-2 production, and its reproducibility with cycle time is also much improved. X-ray photoelectron spectroscopy has provided clear evidence for the S-H bond cleavage with adsorption of RSH on Ag and Pt-shell/Ag-core particles loaded on TiO2.