PROTECTION, SIZE FACTORS, AND REACTION DYNAMICS OF COLLOIDAL REDOX CATALYSTS MEDIATING LIGHT-INDUCED HYDROGEN EVOLUTION FROM WATER

Dimethyl viologen (MV2+) is photoreduced to the cation radical in an aqueous solution containing Ru(bpy)32+ as a sensitizer and EDTA as an electron donor. The efficiency of colloidal platinum to mediate hydrogen generation from water via 2MV+ + 2H2O → H2 + 20H- + 2MV2+ is influenced by both the nature of the protective colloid and particle size. A centrifuged, poly (vinyl alcohol) stabilized catalyst having a particle radius of 110 Å showed exceptionally high activity in promoting the above-mentioned reaction. With such a preparation, for the first time, a direct observation was made of the kinetics of MV+interaction with the Pt particles. The reoxidation of MV+, according to eq 1, occurs in only 15 µs at 10-3 M Ptand leads to stoichiometric formation of H2. The quantum yield of H2 formation in such a system was determined as 0.13 ± 10%. © 1979, American Chemical Society. All rights reserved.