supported by the National Natural Science Foundation of China(21676213,11974276,22078261)；;Natural Science Basic Research Program of Shaanxi(2020JM-422)~~；
1. School of Chemical Engineering/Xi'an Key Laboratory of Special Energy Materials, Northwest University, Xi'an 710069, China;2. School of Physics, Northwest University, Xi'an 710069, China
Abstract:
With rapid industrialization, issues pertaining to the environment and energy have become an alarming concern. Photocatalytic water splitting is considered one of the most promising green technologies capable of resolving these issues, as it can convert solar energy into chemical energy and have a positive impact on the realization of "carbon neutrality". Current research focuses on the development of highly efficient catalysts to improve the photocatalytic H2-production activity. Transition metal phosphides and sulfides are often used as photocatalysts owing to their low H2-evolution overpotential and excellent electrical conductivity. Among them, Ni2P and NiS have generally been used independently during photocatalytic H2 production; however, it is necessary to study the synergistic effect when they are combined as a dual cocatalyst. In this work, we successfully prepared a Ni2P-NiS dual cocatalyst for the first time via a simple hydrothermal method using red phosphorus (RP) and thioacetamide (C2H5NS) as the sources of P and S. Ni2P-NiS was then introduced to the surface of g-C3N4 nanosheets through solvent evaporation to create a Ni2P-NiS/g-C3N4 heterojunction. Furthermore, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible spectrophotometry (UV-Vis), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), linear sweep voltammetry (LSV), Mott-Schottky (M-S), and electrochemical impedance spectroscopy (EIS) were used to reveal the crystal structures, morphologies, element compositions, and photoelectric characteristics of the samples; thus, it was demonstrated that Ni2P-NiS was successfully deposited on the surface of g-C3N4 and that together they exhibited better activity than their monomers. Moreover, the optimized 15% Ni2P-NiS/g-C3N4 composite exhibits a H2 generation rate of 6892.7 μmol·g-1·h-1, which is about 46.1, 7.5 and 4.4 times higher than that of g-C3N4 (150 μmol·g-1·h-1), 15% NiS/g-C3N4 (914.5 μmol·g-1·h-1), and 15% Ni2P/g-C3N4 (1565.9 μmol·g-1·h-1), respectively. In addition, photoelectric performance tests show that Ni2P-NiS/g-C3N4 has a stronger photocurrent intensity, smaller charge-transfer resistance, more positive H2-evolution overpotential, and better charge-separation ability than the individual components (i.e., Ni2P and NiS), suggesting that the coexistence of Ni2P and NiS can further boost the activity of g-C3N4 during H2 evolution compared with their monomers. This is mainly due to the Schottky barrier effect between Ni2P-NiS nanoparticles and g-C3N4 nanosheets, which can greatly promote charge separation and charge transfer at their interface. Additionally, Ni2P-NiS can reduce the H2-evolution overpotential, leading to the increased surface kinetics of H2 evolution. This work offers a promising approach to obtaining a highly active and stable noble-metal-free dual cocatalyst for photocatalytic H2 production.
