Oxygen Vacancy‐Mediated 3D/2D Hydrange‐Type Bismuth Oxides with 1D Bi ₂ Se ₃ Nanowires Confined via a Mild Selenization Strategy to Trigger Dual Built‐in Electric Fields for Accelerated Energy Conversion

Abstract Modulating electronic states near the Fermi energy level to facilitate electron transport and optimize the electronic structure of the active site remains a challenge for the development of high‐performance electrocatalysts. In this study, 1D Bi ₂ Se ₃ nanowires and oxygen vacancy‐mediated 3D hydrange‐type BiO _2‐x (BO) are confined on ultrathin 2D Bi ₂ MoO ₆ (BMO) nanosheets via a mild selenization strategy. This precise modulation constructs BS/BO/BMO heterojunction catalyst with a 1D/3D/2D hierarchical structure and triggers dual built‐in electric fields (BIEFs) with bidirectional electron flow within the catalyst. The mechanism of BIEFs is systematically elucidated in the electron transport process using in situ Kelvin probe force microscopy (KPFM) and density functional theory (DFT). The stacking of dual BIEFs and oxygen vacancies not only increased the effective active sites but also promoted charge transfer and proton diffusion between the electrodes and electrolyte. At a current density of 10 mA cm ⁻² , the HER overpotential of the BS/BO/BMO catalyst is only 93.9 mV, and the energy conversion efficiency of the photovoltaic device assembled with BS/BO/BMO attained 8.87%. The study presents an optimized strategy for the synthesis of multidimensional heterojunction catalysts with dual BIEFs, providing important insights for advancing catalyst design in various electrochemical applications.