Charge separation via asymmetric illumination in photocatalytic Cu 2 O particles

Solar-driven photocatalytic reactions provide a potential route to sustainable fuels. These processes rely on the effective separation of photogenerated charges, and therefore understanding and exploring the driving force for charge separation is key to improving the photocatalytic performance. Here, using surface photovoltage microscopy, we demonstrate that the photogenerated charges can be separated effectively in a high-symmetry Cu 2 O photocatalyst particle by asymmetric light irradiation. The holes and electrons are transferred to the illuminated and shadow regions, respectively, of a single photocatalytic particle. Quantitative results show that the intrinsic difference between electron and hole mobilities enables a diffusion-controlled charge separation process, which is stronger than that caused by conventional built-in electric fields (40 mV versus 10 mV). Based on the findings, we assemble spatially separated redox co-catalysts on a single photocatalytic particle and, in doing so, enhance the performance for a model photocatalytic reaction by 300%. These findings highlight the driving force caused by charge mobility differences and the use of asymmetric light illumination for charge separation in photocatalysis.