Recent Advances in Heterogeneous Photocatalytic CO2 Conversion to Solar Fuels

As a promising approach to achieving two objectives with one strategy, photocatalytic CO2 conversion for C1/C2 "solar fuels" production can provide a package solution to the current global warming and growing energy demand by using inexhaustible solar energy and increasing atmospheric CO2. Although numerous efforts have been made to enhance the CO2 conversion efficiency through developing photocatalysts and CO2 reduction systems in recent years, some challenges still remain in improving the activity and selectivity of the CO2 photoreduction reactions. This review gives an overview of fundamental aspects and recent research advances of heterogeneous photocatalytic CO2 conversion systems in the last 3 years, and the catalysts are categorized as one-step excitation semiconductor systems, one-step excitation photosensitized semiconductor systems, and two-step excitation hybrid systems such as semiconductor heterojunction and Z-scheme systems. Also, some suggestions are given for further confirming that the carbon-containing "solar fuels" are derived from CO2 rather than from the possible carbonaceous impurities in the photocatalytic system, because most of the papers cited in this review have not demonstrated that CO2 is the actual carbon source for photoreduction through (CO2)-C-13 labeling or other techniques. Lastly, a short perspective on the challenges and new directions in this field is proposed, which would be of great interest for the further improvements of activity and selectivity of the CO2 reduction reactions.