Study on photoelectrochemical CO2 reduction over Cu2O

Cu2O is an attractive photocathode for CO2 reduction reaction (CO2RR). The instability of Cu2O usually makes it present as a part of composite or multilayer in CO2RR. The systematic study of pure Cu2O for CO2RR is quite rare, resulting in the elusiveness of the origin for the activity and selectivity of CO2RR under different conditions. Herein, exploration of the factors that influence the product distribution and Faradic efficiency of CO2RR using pure Cu2O is carried out, like Cu2O structure and electrolyte composition. Persistent Cu+ is found to be key for selective CO2RR, especially favoring the formation of C2 product (CH3COOH). The Cu2O film thickness, local pH, and the electrolyte cations are revealed to influence the amount of surface Cu+. The number of H+ and dissolved CO2 affected by electrolytes also account for the disparity of CO2RR results. Therefore, by considering both the CO2RR and the dynamic change of Cu2O, this work has provided a compositional descriptor to link the structure of Cu2O and the CO2RR property, which can be useful for future development of Cu2O-based catalysts.