Electrocatalytic and Solar-Driven CO2 Reduction to CO with a Molecular Manganese Catalyst Immobilized on Mesoporous TiO2.

Electrocatalytic CO2 reduction to CO was achieved with a novel Mn complex, fac-[MnBr(4,4'-bis(phosphonic acid)-2,2'-bipyridine)(CO)3 ] (MnP), immobilized on a mesoporous TiO2 electrode. A benchmark turnover number of 112±17 was attained with these TiO2 |MnP electrodes after 2 h electrolysis. Post-catalysis IR spectroscopy demonstrated that the molecular structure of the MnP catalyst was retained. UV/vis spectroscopy confirmed that an active Mn-Mn dimer was formed during catalysis on the TiO2 electrode, showing the dynamic formation of a catalytically active dimer on an electrode surface. Finally, we combined the light-protected TiO2 |MnP cathode with a CdS-sensitized photoanode to enable solar-light-driven CO2 reduction with the light-sensitive MnP catalyst.