Water photolysis by molecular bio-mimetics

The water oxidizing enzyme of photosynthesis is the only catalyst known as doing this reaction in an energetically efficient way (i.e. with a small over-potential). A chemical catalyst that shares this property could greatly improve the efficiency of water electrolysis and photolysis. There is therefore great interest in understanding the mechanism of this enzyme (and enzymes that catalyze the reverse reaction) and in reproducing aspects of its function in artificial systems. A similar interest exists in producing artificial proton-reducing systems to replace platinum as a catalyst in the current electrochemical systems for H2 production. Such new catalysts could also help to improve the efficiency of fuel cells. In addition, bio-inspired photochemical and electrochemical catalysts could well contribute to energy efficient synthesis of other high value chemicals and fuels. The recent improved understanding of the water oxidizing enzyme and of hydrogenases has made research in this area much more realistic than even in the recent past. Improvements in inorganic chemistry, photochemistry and nano-technology all contribute of making research in this area timely. This article presents a brief overview of the current knowledge of the enzyme and some of the artificial systems that it has inspired. (authors)