Charge Separation in Photocatalysts: Mechanisms, Physical Parameters, and Design Principles

Photocatalytic fuel production has gathered increasing attention due to its potential for large-scale deployment, but the quantum yield of existing photocatalysts remains limited mainly by the inefficient separation of photogenerated charge carriers. In addition, the charge-separation principle of photocatalysts differs from that of photoelectrodes or photoelectrocatalysts. Therefore, comparing the charge-separation principles among all the materials and systems reported under the classification of “photocatalysts” is desirable. We have identified three types of charge-separation modes based on their driving forces: asymmetric energetics, asymmetric kinetics, and their hybrid. Based on this renewed categorization for photocatalysts, we elucidate, analyze, and compare the charge-separation strategies employed in the reported photocatalyst systems. Furthermore, physical parameters and the respective performance limitation relevant to all types of photocatalysts have been summarized, and recent advances and challenges have been outlined. Our framework and discussions aim to provide instructions for pursuing an efficient photocatalyst.