Improved Hydrogen Production with Tetramethyl‐and Hexamethylviologen as Electron‐Transfer Agents in the System H2O‐Ru(bpy)2+3‐edta‐Pt

Abstract

AbstractThe 1,1′,2,2′‐tetramethyl‐4,4′‐bipyridinium and the 1,1′,2,2′,6,6′‐hexamethyl‐4,4′‐bipyridinium dications have been compared with methylviologen as electron‐transfer agents in the photoreduction of water by the title system at pH 5.0 and 7.0. Rates of formation and yields of hydrogen, turnover numbers of viologens, and rates of decay of viologen radicals have been measured at different concentrations of platinum and in the presence of glutathione. The results suggest that improved performance by tetramethyl‐ and hexamethylviologen in the production of hydrogen is related to higher rates in the hydrogen‐producing step and to increased stability towards platinum‐induced side reactions, such as catalytic hydrogenation. These side reactions can be largely suppressed by addition of glutathione to give improved yields and rates of formation of hydrogen and increased turnover numbers for the viologens.