Unique synergistic effects of ZIF-9(Co)-derived cobalt phosphide and CeVO4 heterojunction for efficient hydrogen evolution

Abstract

The photocatalytic decomposition of water to produce hydrogen is an important process, through which solar energy can be converted to chemical energy. Non-precious metal phosphides have quietly attracted attention as an emerging inexpensive photocatalyst. In this study, we reported that a CoP/CeVO4 hybrid photocatalyst exhibited high hydrogen evolution efficiency owing to EY (eosin Y) sensitization under visible light irradiation for the first time, and the amount of generated hydrogen reached 444.6 μmol in 5 h. The CoP/CeVO4 nanohybrids were synthesized by a simple chemical precipitation method. The coupling of CoP and CeVO4 with ZIF-9 as a precursor could be completed in one step. The CeVO4 particles were firmly attached to the surface of the CoP particles to form a “small point” to “big point” heterojunction. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, EDX, and transmission electron microscopy showed the formation of CoP and CeVO4 nanoparticles and the structure of the composite. Based on a detailed analysis of the Mott-Schottky plot, the UV-vis diffuse reflectance spectra, photocurrent-time (it) curve, Tafel curve, Nyquist curve (EIS), linear volt-ampere curve (LSV), and steady-state fluorescence spectra were studied. The time-resolved photoluminescence measurements indicated that the reason for the high-efficiency hydrogen evolution of CoP/CeVO4 was that the bands of CoP and CeVO4 were bent due to the existence of the Schottky barrier, and a heterojunction was formed between CoP and CeVO4, which generated an internal electric field and accelerated the charge transfer. In addition, the synergistic effect between CoP and CeVO4 provided a new hydrogen-evolution activity center for each of them. The improved carrier separation efficiency and the decrease in the photo-generated recombination rate led to the excellent photocatalytic hydrogen-evolution activity of the CoP/CeVO4 composite catalyst. This work provides a new strategy for modulating the electronic structure and carrier behavior of transition metal phosphide photocatalysts.