Nanoscale halide perovskites for photocatalytic CO₂ reduction: product selectivity, strategies implemented, and charge-carrier separation

The over-use of fossil fuels leads to a sharp increase in atmospheric concentrations of carbon dioxide (CO₂), which seriously contributes to the energy crisis and climate problems. The direct transformation of CO₂ into high-value chemicals through photocatalysis offers an effective way to mitigate these problems. The key to achieving this goal is to discover a cost-effective, highly efficient, and durable photocatalyst. Due to their straightforward synthesis, high light absorption capacity, rapid exciton production efficiency, and long carrier diffusion length, nanoscale halide perovskites (NHPs) have great potential for solar photocatalysis. However, several crucial problems, like poor long-term stability, low product selectivity, and severe charge recombination, have become bottlenecks in the development of NHP photocatalysts. Therefore, this review aims to summarize the principles of the CO₂ reduction reaction (CO₂RR), the structural features of halide perovskites nanocrystals (NCs) in the system, and the principal approaches to enhancing their photocatalytic activity. Factors that influence the selectivity of CO₂RR final products are also discussed. Moreover, this review pays special attention to the techniques for studying photogenerated carrier transport processes and photocatalytic intermediates, which make a significant contribution to the insight into the reaction mechanism of photocatalytic CO₂ reduction. Finally, the main challenges and prospects for NHP's further development are also presented. This review will offer instructions for the design of NHP photocatalysts to further enhance the photocatalytic performance and product selectivity for CO₂ reduction. It will also offer insights into studying the charge transport process and mechanism for the CO₂ photocatalytic reduction reaction.