A new Ru complex was synthesized to investigate electrocatalytic water oxidation on a mesoporous ITO electrode using multi-potential-step chronocoulospectrometry.

investigation of electrocatalytic water oxidation by a mononuclear ruthenium complex in a homogeneous solution, Journal of Photochemistry and Photobiology A: Chemistry http://dx.2 Highlight • Electrocatalytic water oxidation was studied by Potential-step chronocoulospectrometry. • [Ru(EtOtpy)(bpy)OH 2 ] 2+ can work for electrocatalytic water oxidation under weakly acidic conditions. • The rate-determining step for the electrocatalysis is oxidation of Ru IV =O to Ru V =O species. Abstract Electrochemical water oxidation by [Ru(EtOtpy)(bpy)OH 2 ] 2+ (1) (EtOtpy = 4'-ethoxy-2,2':6'2''-terpyridine, bpy = 2,2'-bipydidine) was investigated in a homogeneous solution under weakly acidic conditions (pH = 5.3). The cyclic voltammogram of a 1 aqueous solution showed that successive proton-coupled electron transfer reactions of Ru II -OH 2 / Ru III -OH and Ru III -OH / Ru IV =O redox pairs and high anodic current above 1.1 V vs SCE. Electrocatalytic water oxidation was corroborated by the bulk electrolysis at 1.5 V; the significant amount of O 2 was evolved compared with the blank during the electrolysis. Potential-step chronocoulospectrometry (PSCCS) from 0.0 V to 1.52 V vs SCE was conducted to observe the change of 1 in solution during the electrocatalysis. The in situ UV visible spectral change showed oxidation of 1 (Ru II -OH 2 ) to Ru III -OH and to further oxidation of Ru III -OH to Ru IV =O, and that the Ru IV =O species mainly exists in a steady state after 200 s in the electrocatalysis. The in situ UV visible spectral change in a reverse potential step from 1.52 V to 0.22 V vs SCE exhibited that Ru II -OH 2 completely recovers by 2 electron re-reduction process from the steady state in the electrocatalysis. The observation of Ru IV =O in a steady state suggests that a rate determining step in the catalytic cycle is oxidation of Ru IV =O to Ru V =O rather than the O-O bonding formation by nucleophilic attack of water to Ru V =O in the 3 electrocatalysis in a homogeneous solution.