Hollow and hybrid nanomaterials are excellent electrocatalysts on account of their novel electrocatalytic properties compared with homogeneous solid nanostructures. In this report, NiSe-Ni3Se2 hybrid nanostructure with morphology of hollow hexagonal nanodisk was synthesized in situ on graphene. A series of NiSe-Ni3Se2/RGO with different phase constitutions and nanostructures were obtained by controlling the durations of solvothermal treatment. Because of their unique hollow and hybrid structure, NiSe-Ni3Se2/RGO hollow nanodisks exhibited higher electrocatalytic performance than NiSe/RGO and solid NiSe-Ni3Se2/RGO nanostructure for reducing I3(-) as counter cell (CE) of dye-sensitized solar cells (DSSCs). Additionally, NiSe-Ni3Se2/RGO hollow nanodisks achieved much lower charge transfer resistance (Rct = 0.68 Ω) and higher power conversion efficiency (PCE) (7.87%) than those of Pt (Rct = 1.41 Ω, PCE = 7.28%).

electronic structure, charge transfer, and separation efficiency ultimately result in distinct catalytic abilities. [3,4] The photocatalytic performance of single-crystalline Ag 3 PO 4 with only (110) facets exhibited much higher activities than Ag 3 PO 4 with (100) facets because the surface energy of (110) facets (1.31 J m −2 ) is higher than that of (100) facets (1.12 J m −2 ). [5] Furthermore, it was easily to form oxygen vacancies on the (110) facets of Ag 3 PO 4 than on the (110) facets and the abundant catalytically active sites enhance the photocatalytic activity. [5] Thus, crystal facet engineering was usually identified as a versatile strategy to prepare highly active photocatalysts by tuning crystal growth process. [6,7] Moreover, introducing oxygen defects could further improve the photocatalytic performance of photocatalysts with the high reactivity dominant exposed facets. Xue et al. reported that ZnO-6, added by 6 mmol zinc powder, exhibited excellent gas response and selectivity, which ascribed to the exposed (0001) crystal facet and the formation of abundant electron donor aroused by zinc interstitial and oxygen vacancy surface defects. [8] The introduction of vacancy/defect is efficient and promi sing to Engineer photocatalysts with the enhanced photocatalytic efficiency. [9] The change of electronic structures of catalysts with vacancy/defect improved their catalytic activity greatly. [9,10] The V Bi ″′V O •• V Bi ″′ vacancy enhanced the solar-driven photocatalytic activity of ultrathin BiOCl nanosheets significantly. [11] BiPO 4−x with high-content oxygen vacancies exhibited excellent photocatalytic performance because the surface oxygen vacancies broadened its the valence band and narrowed its bandgap compared to that of pure BiPO 4 . [12] Because of their high surface to volume ratio, nanomaterials generate much more vacancies inevitably. [13] Therefore, the exposed atoms on the facet surface of ultrathin 2D nanosheet materials are easy to escape and form vacancies and then improved its catalytic efficiency. [11,14,15] Bismuth oxyhalides (BiOX, X = Cl, Br, and I) are a class of ternary compounds and their photocatalytic potential makes them promising layered semiconductor photocatalysts. [16][17][18][19][20] Among layered BiOX materials, BiOI has narrow bandgap (about 1.7-1.9 eV), and therefore high absorption coefficient under visible light. [21] In addition, as a V-VI-VII ternary compound with a layer structure characterized by [Bi 2 O 2 ] 2+ slabs interleaved by halogen atoms, BiOI favors charge separationThe increasing application of exposed high energy facet is an effective strategy to improve the photocatalytic performance of photocatalysts because the vacancies are beneficial to photocatalytic reaction. Vacancy dominates numerous distinct properties of semiconductor materials and thus plays a conclusive role in the photocatalysis applications. In this work, two kinds of BiOI nanomaterials with different vacancies are synthesized via a facile solvothermal method. The positron annihilat...

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Vacancy engineering is an effective strategy to enhance solar‐driven photocatalytic performance of semiconductors. It is highly desirable to improve the photocatalytic performance of composite nanomaterials by the introduction of vacancies, but the role of vacancies and the heterostructure in the photocatalytic process is elusive to the composite nanomaterials. Herein, the introduction of I vacancies can significantly enhance the photocatalytic activity of Bi2O3–BiOI composite nanosheets in a synergistic manner. The excellent photocatalytic performance of the Bi2O3–BiOI composites is attributed to the combination of Bi2O3 and BiOI and the existence of I vacancies in Bi2O3–BiOI composites. Specifically, density functional theory calculation shows that the existence of I vacancies would create a new electric states vacancy band below the conduction band of BiOI and thus can reduce the bandgap of BiOI nanosheets. This greatly facilitates the scavenging of the photogenerated electron on the surface of BiOI by Bi2O3, therefore, enhancing the overall photocatalytic activity of the composites. The enhanced photocatalytic efficiency is demonstrated by the degradation of tetracycline (TC), which reaches 96% after 180 min and by the high total organic carbon (TOC) removal (89% after 10 h visible light irradiation). This study provides a novel approach for the design of high‐performance composite catalysts.

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