Catalysis for H + reduction by polypyridyl platinum complexes (e.g., bis(2,2 ' -bipyridine) platinum(II) nitrate (Pt(bpy) 2 2 + ) and chloro(2,2 ' :6 ' ,2 ' ' -terpyridine) platinum(II) chloride (Pt(terpy)Cl + )) dispersed in a Nafion membrane was studied by using a polymer-modified electrode system. These Pt complexes incorporated in the polymer membrane worked as active catalyst for H + reduction to produce H 2 . The cathodic current due to the H + reduction increased with reaction time indicating that the electrocatalytic reaction does not take place by a simple catalysis of the original Pt complex. The valence state of the Pt complexes after the reduction was investigated by both UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) showing the presence Pt 0 species. Photochemical H 2 formation was investigated in a photochemical H + reduction system composed of Pt(bpy) 2 2 + (or Pt(terpy)Cl + ), Ru(bpy) 3 2 + sensitizer, methyl viologen (MV 2 + ) acceptor, and sacrificial donor (EDTA). An induction period for the H 2 evolution was observed, which was ascribed to the formation of active Pt species by MV . + reductant produced by the photochemical reaction. It was concluded that in both the two systems the Pt complexes at first change to active species (zero-valent Pt), and then work as the H + reduction catalyst.