Ab initio modelling of photocatalytic CO2 reduction reactions over Cu/TiO2 semiconductors including the electronic excitation effects

Photocatalysis is a promising method for reducing CO2 in an environmentally friendly way. Despite extensive experimental studies, theoretical studies lag behind and often resort to describing catalysts in the excited state, while the reaction mechanism is mostly studied at the ground level. We theoretically calculate a full reaction mechanism of CO2 reduction to CO in the excited state for five surfaces: Cu(111), anatase(110), rutile(101) and Cu/anatase, Cu/rutile using the ΔSCF approach. We show that excited states considerably lower activation barriers, making it necessary in describing the experimental performance. The density functional theory calculations in the excited state are used to construct a microkinetic model, which is used to predict the performance of each catalytic surface. We show that Cu(111) is photocatalytically inactive, TiO2 is only active in the UV range and catalyzes water splitting. Only Cu/rutile is active for CO2 reduction to CO, while Cu/anatase produces more H2.