Electrocatalytic CO2 Reduction with a Ruthenium Catalyst in Solution and on Nanocrystalline TiO2.

A RuII complex [Ru(PO3 Et2 -ph-tpy)(6-mbpy)(NCCH3 )]2+ [PO3 Et2 -ph-tpy=diethyl(4-[(2,2':6',2''-terpyridin)-4'-yl]phenyl)phosphonate; 6-mbpy=6-methyl-2,2'-bipyridine] is explored as a molecular catalyst for electrocatalytic CO2 reduction in both a homogeneous solution and, as a phosphonated derivative, on nanocrystalline-TiO2 surfaces. In CH3 CN, the complex acts as a selective electrocatalyst for reduction of CO2 to CO at a low overpotential of 340 mV but with a limited turnover number (TON). An enhancement in reactivity was observed by immobilizing the phosphonated derivative of the catalyst on a nanocrystalline-TiO2 electrode surface, with the catalyst surface protected by a thin overlayer of NiO. The surface-functionalized electrode was characterized by X-ray photoelectron and diffuse reflectance spectroscopies (XPS and DRS). Electrocatalytic reduction of CO2 to CO occurred at -1.65 V versus Fc+/0 with a TON of 237 per catalyst site during 4 h of electrocatalysis. Post-catalysis XPS measurements reveal that the molecular structure of the catalyst is retained on TiO2 after the long-term electrocatalysis.