Atomic-scale regulation of photogenerated electrons remains a central challenge in reductive photocatalysis because highly reductive electrons are intrinsically prone to rapid recombination and spatial delocalization. Although crystal-facet engineering and defect modulation have independently improved photocatalytic performance, their synergistic coupling in governing electron accumulation and carrier kinetics remains poorly understood. Here, we report a facet-defect coupling strategy that enables spatially confined electron accumulation in ZnIn2S4 through preferential exposure of high-index {102} facets. Density functional theory calculations reveal that the {102} facets simultaneously have a more negative conduction band minimum and intrinsically lower sulfur vacancy formation energy than conventional {110} facets, thereby coupling enhanced reduction thermodynamics with spontaneous defect generation. Guided by these predictions, an ethanol-glycerol-mediated solvothermal strategy was developed to stabilize the high-energy {102} facets via surface-energy regulation. Combined crystallographic, spectroscopic, and ultrafast transient absorption analyses demonstrate that the facet-induced sulfur vacancies act as long-lived electron-trapping centers, promoting electron localization, suppressing charge recombination, and prolonging carrier lifetime. As a result, the engineered ZnIn2S4 exhibits substantially enhanced catalytic activity across representative multielectron transformations, including H2O2 photosynthesis, H2 evolution, Cr(VI)/U(VI) reduction, and perfluoroalkyl substance defluorination. This work establishes facet-defect coupling as a general strategy for regulating electron accumulation and carrier behavior to advance reductive photocatalysis at the atomic scale.
