Electrocatalytic CO 2 Reduction with a Ruthenium Catalyst in Solution and on Nanocrystalline TiO 2

A Ru II complex [Ru(PO 3 Et 2 ‐ph‐tpy)(6‐mbpy)(NCCH 3 )] 2+ [PO 3 Et 2 ‐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 CO 2 reduction in both a homogeneous solution and, as a phosphonated derivative, on nanocrystalline‐TiO 2 surfaces. In CH 3 CN, the complex acts as a selective electrocatalyst for reduction of CO 2 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‐TiO 2 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 CO 2 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 TiO 2 after the long‐term electrocatalysis.