Catalyst design for photocatalytic CO2 reduction: recent advances, challenges, and future perspectives

The photoreduction of CO2 is a growingly interesting research topic due to the intriguing possibility of producing solar fuels from a concerning pollutant. TiO2 photocatalysts were the first materials used for this application, but since then, various strategies have been developed to optimise the catalytic performance and operating conditions to obtain competitive yield. This review presents the findings of the last decade of research on different semiconductors, TiO2 and g-C3N4 and their composites. The main features of the reaction and its key issues are first overviewed, focusing on the effect of different reaction conditions on the performance and recalling the mechanism of the reaction. The strategies developed to overcome the challenges of this demanding reaction are described in the following paragraphs, including the use of dopants or co-catalysts, heterojunctions between different semiconductors and the use of electron transfer mediators. Finally, some unifying concepts are summarised, suggesting the calculation of the stored energy amount and the relative efficiency to allow a safer comparison between literature data collected under widely variable conditions and leading to different products.