Microscopic charge pumping and macroscopic transport channels: A dual-engineering strategy for high-efficiency...

Photoelectrocatalytic performance of bismuth oxyiodide (BiOI) is fundamentally limited by severe charge recombination and sluggish carrier transport. Herein, we propose a dual-engineering strategy that synergistically integrates atomic-scale composition tuning with microstructure control to break through these bottlenecks. This dual-engineering strategy, combining microscopic composition regulation and macroscopic morphology optimization, is the core innovation of this work. A series of phase-pure BiOI_1-xBr_x solid solutions are first constructed via hydrothermal synthesis. Among them, BiOI_0.5Br_0.5 exhibits an optimized bandgap (∼2.19 eV) and, more importantly, a pronounced microscopic built-in electric field induced by the Br/I electronegativity difference, which acts as an internal "charge pump" to drive efficient electron-hole separation. Furthermore, by precisely regulating the concentration of the surfactant PVP, we achieve tailored morphological evolution from nanoparticles to thin nanosheets, and finally to three-dimensional hierarchical nanoflowers (NF). The 3D hierarchical structure constructs macroscopic charge transport channels, which effectively shortens the migration path of photogenerated carriers. The NF-BiOI_0.5Br_0.5 architecture delivers outstanding photoelectrocatalytic activity, with a photocurrent density of 0.60 mA·cm^-2 at 1.23 V vs. RHE, a peak apparent photon-to-current efficiency of 0.18%, and the lowest charge-transfer resistance. Mechanism analysis reveals that the remarkable performance arises from the synergistic coupling between the built-in electric field enabled by compositional engineering and the shortened transport paths coupled with abundant surface sites enabled by morphological engineering. The synergistic effect of microscopic charge pumping and macroscopic charge transport is proposed in BiOI-based photoelectrocatalysts, which demonstrates a multiscale regulation paradigm, from atomic disorder to nano-architecture, providing a generalizable design route for high-performance semiconductor photoelectrocatalysts.