Internal Electric Field Enhancement by the I‐Rich Surface of Highly Crystallized BiOI Nanosheets for Boosted Photocatalytic Degradation of Phenol

Although the internal electric field (IEF) of bismuth oxyiodide (BiOI) is acknowledged as a potent driving force for efficient charge separation, enhancing the intensity of IEF remains a challenge. Herein, highly crystalline BiOI nanosheets with I‐rich surface are employed to intensify IEF and direct the charge migration. In comparison to I‐poor BiOI nanosheets, which possess Bi−O layer termination and I‐defects, the I‐rich BiOI demonstrates 62.5‐fold improvement in IEF intensity to its well‐developed high crystalline structure, and its IEF direction is reversed by the surface I‐rich layers. This intensified IEF of I‐rich BiOI induces numerous holes (h + ) to migrate to the surface of primary exposed (001) facets and electrons (e − ) to the lateral facets efficiently, resulting in efficient charge separation spatially. Additionally, the surface accumulates h + and superoxide radicals and acts in synergy to enhance the photodegradation of phenol. The photocatalytic activity of the I‐rich BiOI is found to be approximately fivefold and threefold higher than that of I‐poor BiOI under full spectra and visible light, respectively. Herein, the manipulation of IEF through surface and bulk structure regulation of BiOI for efficient charge separation is discussed, expecting to rationally improve photocatalytic performances.