The need for renewable sources of energy tracks with increases in both population and the standard of living. Currently, the great majority of energy consumed by humans derives from the combustion of fossil fuels that results in increasing atmospheric CO2 levels. Solar fuel energy could be an alternative green source of energy. The reaction in eq 1 produces H2, an environmentally clean fuel. This reaction is thermodynamically unfavorable, but the required energy can be provided by sunlight. The required electrochemical potential (voltage) can be provided by a solar (e.g. photovoltaic) cell. Despite substantial progress, an highly effective anodic electrocatalyst to reduce overpotentials for water oxidation to oxygen has not been developed. In contrast, the reaction to produce hydrogen proceeds with almost no overpotential on platinized cathodes. Recently, we reported that the carbon free complexes, Rb8K2[{Ru4O4(OH)2(H2O)4}("SiW10O36)2] (1) and Na10[Co4(H2O)2(PW9O34)2] (2) [1"2], catalyze homogeneous water oxidation at pH 7-9 very efficiently. In this work we attempted to immobilize these homogeneous catalysts on the surface of different electrodes and to use these modified electrodes as the anode in water electrolysis. We employed two different immobilization approaches. First, complex 1 (as a TBA salt) was adsorbed on carbon nanotubes and the resulting material was cast on different electrodes (glassy carbon, graphite, carbon papers, etc) by a procedure similar to that reported by Toma et al [3]. Under minimally optimized conditions, H2 and O2 were formed with high yields in 2:1 ratio at overpotentials of less than 0.6 V.
