Unravelling Facet-Dependent Carrier Transport and Charge Anisotropy in Micron-Scale BiVO4 Crystals

Understanding carrier transport in semiconductor materials is essential to improving the efficiency of future solar energy conversion devices. Despite significant effort, the influence of anisotropic carrier transport and facet-dependent electron transfer kinetics remains poorly understood for many relevant photocatalyst materials. Here, we investigate these effects in well-defined, micron-scale monoclinic BiVO4 particles by mapping photoelectrochemical reactions using scanning electrochemical cell microscopy (SECCM), revealing pronounced heterogeneities in charge transport across different crystallographic facets. SECCM mapping reveals that {110} facets exhibit higher photocurrents compared to {010} and {111} facets, indicating preferential charge transfer in this system. Similar results were obtained with both inner sphere and outer sphere redox couples, demonstrating that photoelectrochemical reactions at BiVO4 are intrinsically facet dependent due to anisotropic carrier transport. Carrier Generation-Tip Collection SECCM imaging further shows that the in-plane transport length of photogenerated electrons (Lxy = 3.3 μm) is twice that of photogenerated holes (Lxy = 1.6 μm), suggesting asymmetrical carrier mobility within the BiVO4 lattice. These results provide important insights into the fundamental mechanisms governing photocatalytic performance in BiVO4 and offer guidance for the design of improved photocatalyst materials for solar energy conversion.