Cu~＋-incorporated TiO_2 overlayer on Cu_2O nanowire photocathodes for enhanced photoelectrochemical conversion of CO_2 to methanol

摘要

In this paper, we report photoelectrochemical(PEC) conversion of carbon dioxide(CO_2) using photocathodes based on Cu_2O nanowires(NWs) overcoated with Cu^+-incorporated crystalline TiO_2(TiO_2–Cu^+ )shell. Cu_2O NW photocathodes show remanent photocurrent of 5.3% after 30 min of PEC reduction of CO_2.After coating Cu_2O with TiO_2–Cu^+ overlayer, the remanent photocurrent is 27.6%, which is an increase by5.2 fold. The charge transfer resistance of Cu_2O/TiO_2–Cu^+ is 0.423 k/cm2, whereas Cu_2O photocathode shows resistivity of 0.781 k/cm2 under irradiation. Mott–Schottky analysis reveals that Cu^+ species embedded in TiO_2 layer is responsible for enhanced adsorption of CO_2 on TiO_2 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 TiO_2–Cu^+ is added to Cu_2O, showing drastic increase from 23.6% by bare Cu_2O photocathodes.