Insights into CO2 activation and charge transfer in photocatalytic reduction of CO2 on pure and metal single atom modified TiO2 surfaces

Large amounts of CO2 emissions associated with expanded fossil fuel consumption have caused global warming and energy crisis. The photocatalytic reduction of CO2 is one of the most promising ways to solve these problems. However, some basic issues in CO2 photocatalytic reduction over pure and modified TiO2 surfaces, such as the transfer of photogenerated electrons, CO2 adsorption configuration with excess electrons, the mechanism of CO2 activation, still lack in-depth investigation and analysis. In this work, using density functional theory (DFT) calculations, we systematically calculated the transfer of photogenerated electrons, workfunction, CO2 adsorption energy, charge density difference, density of states (DOS), and CO2 dissociation energy barrier on different pure and metal single atom modified TiO2 surfaces. Based on these results, we further analyzed the effect of photogenerated electrons and metal single atoms on CO2 adsorption and activation, and identified the different behavior of photogenerated electrons on pure and metal single atom modified TiO2 surfaces. Finally, a synergetic effect of photogenerated electrons and loaded metal atoms is proposed, which is crucial in understanding CO2 photocatalytic reduction and designing efficient new photocatalytic materials.