Preparation of\n3D/2D ZnIn<sub>2</sub>S<sub>4</sub>/Porphyrin(Cu)-COF Type II Heterojunction:\nAn In-Depth Insight into\nInterfacial Charge Transfer for Efficient Light-to-Hydrogen Conversion

Semiconductor heterojunctions could accelerate carrier\nseparation\nand transfer for improving light-to-hydrogen (LTH) conversion efficiency.\nHowever, the lack of tight and efficient interfacial charge cross\nin three-dimensional semiconductor-based heterojunctions limits their\npractical application and the relevant profound understanding of the\ninterfacial charge delivery. In this work, porphyrin (Cu)-based COF\nwith a highly conjugated structure was deposited onto three-dimensional\n(3D) ZnIn<sub>2</sub>S<sub>4</sub> by a facile solvothermal method\nto prepare a 3D/2D ZnIn<sub>2</sub>S<sub>4</sub>@CuP–Ph COF\nheterojunction. The content-optimized ZnIn<sub>2</sub>S<sub>4</sub>@CuP–Ph COF composite showed an excellent LTH conversion rate\nof up to 2667.94 μmol g<sup>–1</sup> h<sup>–1</sup>, about 13.5 times higher than that of pristine ZnIn<sub>2</sub>S<sub>4</sub>. The significantly meliorated photocatalytic performance\nis attributed to the synergistically functioning contributors, that\nis, the fast interfacial charge transfer and the augmented light capturing\ncapability after integration. Also, the work function results by DFT\ncalculation reveals that the electrons of CuP–Ph COF (Φ\n= 4.41 eV) transfer from the interface electron delivery channels\nof the two components to ZIS (Φ = 7.03 eV) until the Fermi level\nof the two components reaches equilibrium. This moment, the work function\nof ZnIn<sub>2</sub>S<sub>4</sub>@CuP–Ph COF (Φ = 6.50\neV) lies between the two components, and an electron accumulation\nregion is formed on the side of ZIS. Additionally, the free-energy\nbarriers of hydrogen evolution dominated by ZnIn<sub>2</sub>S<sub>4</sub>@CuP–Ph COF (0.0955 eV) is much lower than that of\nZnIn<sub>2</sub>S<sub>4</sub> (0.1256 eV). This study possesses certain\nguiding significance for the design of organic–inorganic heterojunction\nphotocatalysts for efficient LTH conversion.