Activity analysis of mononuclear ruthenium ammine complex dispersed in a polymer membrane as an electrochemical water oxidation catalyst

The activity of an electrochemical water oxidation catalyst based on pentaamminechlororuthenium(III) ([Ru(NH3)(5)Cl](2+)) complex incorporated in an electrode-coated Nafion membrane was investigated. The complex worked as an active electrochemical catalyst, and an optimum concentration for the turnover number (TN) of the catalyst in the O-2 evolution was exhibited. The TN increased with the concentration at low concentrations, which was ascribed either to charge transfer between the catalysts or to cooperative catalysis by the complex. The TN decrease at high concentrations was ascribed to bimolecular decomposition of the catalyst. The catalyst activity (TN) was analyzed in terms of a charge transfer distance between the catalysts (r(0)/nm), a cooperative catalysis distance by the complex (r(co)/nm), and a critical decomposition distance of the catalyst (r(d)/nm) based on intermolecular distance distribution. It was suggested that the activity was controlled mainly by r(co) and r(d), and the values r(co) = 1.26 nm and r(d) = 0.82 nm were obtained. (C) 1999 Elsevier Science B.V. All rights reserved.