Impact of Reaction Environment on Photogenerated Charge Transfer Demonstrated by Sequential Imaging

Most photocatalysis research focuses on understanding the photogenerated charge transfer processes within the solid catalysts themselves. However, these studies often overlook the impact of the reaction environment on photogenerated charge separation and reactions. To address this gap, our study employed a sequential imaging methodology that integrates surface photovoltage microscopy (SPVM), in situ atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM) to track the transfer of photogenerated charges from the space charge region to the reactants at the nanoscale on individual BiVO₄ particles. It identifies the key role that surface charges at the photocatalyst-electrolyte interface play in photogenerated charge transfer. Specifically, we demonstrated that the surface charge generates an additional driving force, which adjusts the interface electric field and reverses the photovoltage of {010} facet from 90 to -25 mV in a neutral electrolyte. This competitive or even larger driving force compels the photogenerated electrons, which are confined within the bulk, to migrate to the surface, ultimately leading to the redistribution of photogenerated charges. Furthermore, our findings uncovered that the difference between the solution pH and the isoelectric point of the facet serves as the origin of the interfacial electric field. Overall, our sequential imaging research fills an important gap in understanding the driving and influencing factors of charge transfer across the solid-liquid interface for photocatalytic reactions in solution. It provides significant insights into clarifying the bottleneck issue of charge separation in photocatalytic reactions.