Enhanced photo-electrochemical reduction of CO2 into methanol at CuInS2/CuFeO2 thin-film photocathodes with synergistic catalysis of oxygen vacancy and S–O bond

The low reaction rate and poor selectivity to target products have largely limited the application of photo-electrochemical CO2 reduction. Herein we introduce oxygen vacancy (Vo) and S–O bond into CuInS2/CuFeO2 (CIS/CFO) composite thin-film catalysts by tuning the composition of precursor solution during the electrodeposition process. Vo causes the formation of unique S–O bond at CIS/CFO interface. Vo improves the visible-light absorption performance and enhances *CO adsorption on catalyst surface. S–O bond improves Vo stability, increases the carrier lifetime, and reduces the energy barrier. When polyvinyl alcohol concentration in the precursor solution is 12 mg mL−1, the resulted 12CIS/CFO-Vo-SO thin-film photocathode provides methanol yield of 0.31 mM at −0.700 V (vs saturated calomel electrode) within 1 h, which is twice of that at CIS/CFO thin-film photocathode, and Faradaic efficiency as high as 90 %. This synergistic catalysis strategy provides an innovative route for improving the photo-electrochemical performance of catalysts.