Type-II heterojunction photocathode for CO₂ reduction and light-assisted metal-CO₂ batteries

Light-assisted metal-CO2 batteries have attracted extensive attention. It is highly desirable to develop a photocathodic catalyst to simultaneously facilitate the activation and transformation of CO2 and maintain long-term operational stability. Here, for the first time we report a one-dimensional Fe2O3/Cu2O type-II heterojunction nanowire photocathode for light-assisted metal-CO2 batteries. With this new photocathode, a Li-CO2 battery can achieve an ultralow voltage gap of 0.19 V and a superior round-trip efficiency of 88% after 260 cycles under irradiation of full sunlight (AM 1.5 G). This cycling performance is the highest level ever reported (<= 100 cycles) in the field of light-assisted metal-CO2 batteries so far. The impressive performance can be attributed to the built-in electric field across the Fe2O3/Cu2O type-II heterojunction featuring desired catalytic capability for both CO2 reduction/evolution kinetics and (photo)electrochemical reversibility. The Fe2O3/Cu2O type-II heterojunction photocathode also shows potential application in flexible energy storage devices.