Operando Imaging of Polaron-Mediated Charge Transfer across the Electric Double Layer of BiVO 4

Unraveling the interfacial dynamics of photogenerated charges at active sites is fundamental to advancing photocatalysis and related solar energy conversion systems. However, direct observation of the charge behavior within the electric double layer (EDL) under working conditions remains a major challenge. Here, we investigate nanoscale charge dynamics on a single BiVO₄ particle model system by directly visualizing light-induced charge distribution within the EDL using a combination of spatially and temporally resolved techniques. Our findings reveal that oxygen vacancies stabilize the coexistence of localized electrons and holes, efficiently driving photocatalytic oxidation and reduction reactions between adjacent atoms. Moreover, defect-induced small polaron formation is shown to suppress ultrafast exciton recombination, extending hole lifetimes to 32 ms from subnanoseconds. Simultaneously, photogenerated electrons are effectively extracted by Fe³⁺ at the interface, overriding the influence of the net internal electric field and preventing their migration into the bulk. This study elucidates a synergistic mechanism involving reaction-driven electron transport and defect-assisted small-polaron-mediated oxygen evolution. This mechanism challenges the traditional mean-field electrostatic model of interfacial charge transport and highlights the critical role of localized charges for understanding how catalytic reactions reshape charge flow at solid-liquid interfaces. Our findings open avenues for the rational design of defect-engineered photocatalysts and operando-responsive materials in solar-to-chemical energy conversion.