Cu+-incorporated TiO2 overlayer on Cu2O nanowire photocathodes for enhanced photoelectrochemical conversion of CO2 to methanol

In this paper, we report photoelectrochemical (PEC) conversion of carbon dioxide (CO2) using photocathodes based on Cu2O nanowires (NWs) overcoated with Cu+-incorporated crystalline TiO2 (TiO2Cu+) shell. Cu2O NW photocathodes show remanent photocurrent of 5.3% after 30 min of PEC reduction of CO2. After coating Cu2O with TiO2Cu+ overlayer, the remanent photocurrent is 27.6%, which is an increase by 5.2 fold. The charge transfer resistance of Cu2O/TiO2Cu+ is 0.423 kΩ/cm2, whereas Cu2O photocathode shows resistivity of 0.781 kΩ/cm2 under irradiation. Mott–Schottky analysis reveals that Cu+ species embedded in TiO2 layer is responsible for enhanced adsorption of CO2 on TiO2 surface, as evidenced by the decrease of capacitance in the Helmholtz layer. On account of these electrochemical and electronic effects by the Cu+ species, the Faradaic efficiency (FE) of photocathodes reaches as high as 56.5% when TiO2Cu+ is added to Cu2O, showing drastic increase from 23.6% by bare Cu2O photocathodes.