Titania-Modified Silver Electrocatalyst for Selective CO2 Reduction to CH3OH and CH4 from DFT Study

Electrochemical reduction of CO2 to produce useful fuels and chemicals is one of the attractive means to reuse CO2. Herein, we constructed a (TiO2)3/Ag(110) model electrocatalyst and examined CO2 reduction pathways. Our results show that the interface between oxide and supporting Ag provides the active sites for CO2 adsorption and activation. These active sites enable the electron transfer to the adsorbed CO2. In this setup, Ag acts as an electron donor, partially reducing the supported (TiO2)3 and supplies the needed electrons to the adsorbed CO2. Once CO2* is formed at the interface, the subsequent hydrogenation steps take place sequentially. Our results further indicate that the dominating pathway to produce CH3OH is via the H2COOH* intermediate following the formation of HCOO*. The formation of H2COOH* with a free energy of 0.47 eV is the potential-limiting step. Furthermore, protonating H2COOH* followed by dehydration to CH3O* and hydrogenation of CH3O* leads to CH4 formation. The COOH* pathway may converge to the same H2COOH* intermediate instead of forming CO*. These results demonstrated the benefit of metal supported metal oxides as electrocatalysts to produce CH3OH or CH4 from electrochemical reduction of CO2.