Origin of Catalytic Effect in the Reduction of CO₂ at Nanostructured TiO₂ Films

Electrocatalytic activity of nanostructured TiO2 films toward the reduction of CO2 is probed by depositing a nanostructured film on a glassy carbon electrode. The one-electron reduction of CO2 in acetonitrile seen at an onset potential of −0.95 V (vs NHE) is significantly lower than the one observed with a glassy carbon electrode. The electrocatalytic role of TiO2 is elucidated through spectroelectrochemistry and product analysis. Ti3+ species formed when the TiO2 film is subjected to negative potentials have been identified as active reduction sites. Binding of CO2 to catalytically active Ti3+ followed by the electron transfer facilitates the initial one-electron reduction process. Methanol was the primary product when the reduction was carried out in wet acetonitrile.