Highly Efficient and Durable Electrocatalysis by a Molecular Catalyst with Long Alkoxyl Chains Immobilized on a Carbon Electrode for Water Oxidation

A dinuclear Ru complex, proximal, proximal -[Ru 2 L(C 8 Otpy) 2 (OH)(OH 2 )] 3+ (C 8 Otpy = 4′-octyloxy-2,2’; 6′,2″-terpyridine) ( 1 ) with long alkoxyl chains, was synthesized to be immobilized on a carbon paper (CP) electrode via hydrophobic interactions between the long alkoxyl chains and the CP surface. The 1 /CP electrode demonstrated efficient electrocatalytic water oxidation with a low overpotential (η onset ) of 0.26 V (based on the onset potential for water oxidation) in an aqueous medium at pH 7.0, which is compared advantageously with those of hitherto-reported molecular anodes for water oxidation. The active species of Ru III Ru III (μ-OO) with a μ-OO bridge was involved in water oxidation at 0.95 V versus Ag/AgCl. As the applied potential increased to 1.40 V, water oxidation was promoted by participation of the more active species of Ru III Ru IV (μ-OO), and very durable electrocatalysis was gained for more than 35 h without elution of 1 into the electrolyte solution. The introduced long alkoxyl chains act as a dual role of the linker of 1 on the CP surface and decrease the η value. Theoretical investigation provides insights into the O–O bond formation mechanism and the activity difference between Ru III Ru III (μ-OO) and Ru III Ru IV (μ-OO) for electrocatalytic water oxidation.