Study On Photocatalytic Hydrogen Evolution Performance Of Transition Metal Phosphides/Cadmium Sulfide

Energy shortage and environmental pollution are the two major social problems,which can be solved by developing renewable clean energy to replace traditional fossil fuels,and hydrogen（H₂）is regarded as an excellent alternative due to its high energy density and pollution-free advantages.For photocatalytic water splitting,active charge carriers are excited in semiconductors by solar light to drive water splitting,possessing the advantages of solar energy driving and environmental friendliness.Cadmium sulfide（CdS）is a good visible light photocatalyst,but it also suffers from serious carrier recombination and photocorrosion,so how to improve its catalytic performance is still an urgent task.At present,precious metal platinum（Pt）is the most popular co-catalyst,but the scarce output and high price hinder its large-scale application,so to develop an inexpensive and excellent catalytic transition metal phosphide is of great significance.Based on the above considerations,in this thesis we focus on the optimization of CdS morphology and transition metal phosphide loading to improve photocatalytic performance and stability of CdS photocatalysts.The main contents of our thesis are as follows:In chapter 1,the following six aspects are mainly discussed,including photocatalytic hydrogen production mechanism,cadmium sulfide photocatalyst,transition metal phosphides,research progress of transition metal and its phosphide/cadmium sulfide in photocatalytic hydrogen production and the main research contents.In chapter 2,Synthesis of 2D-2D heterostructured CdS-CoP photocatalysts for efficient visible light H₂ evolution.CdS nanosheets were synthesized by the hydrothermal method,and CoP nanosheets were synthesized by hydrothermal-oxidation-phosphodation process.Then 2D-2D CdS-CoP photocatalysts were formed by ultrasonically mixing their solution.Their morphology,chemical valence and heterostructure were estimated by transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,fluorescence spectrometer（PL）and so on.Using ethanol as hole sacrificial agent,the catalytic hydrogen production performance of CdS-CoP under visible light excitation was measured,and the effect of CoP loading amount on its hydrogen production activity was also studied.The photocatalytic activity enhancement mechanism of CoP on CdS was evaluated by comparing their photoluminescence spectra,electrochemical impedance spectroscopy,and transient photocurrent spectra of CdS-CoP and CdS.In chapter 3,Controllable photodeposition of nickel phosphide（NiP_x）cocatalysts on cadmium sulfide nanosheets for enhanced photocatalytic hydrogen evolution performance.CdS nanosheets were prepared by hydrothermal method,followed by in-situ loading nickel phosphide nanoparticles on their surface by photochemical reduction method,and NiP_x loading amounts could be adjusted just by the photodeposition time.The synthesized CdS-NiP_x was characterized by scanning electron microscopy（SEM）,X-ray diffraction spectrum（XRD）,fluorescence spectrometer and so on.Using ethanol as a hole sacrificial agent,the visible light catalytic performance of CdS-NiP_x was measured,and the effect of photoreduction time on the photocatalytic hydrogen production activity of CdS was studied.The enhancement mechanism of NiP_x on their photocatalytic activity was estimated by comparing the photoluminescence spectra,electrochemical impedance spectra and transient photocurrent spectra of CdS-NiP_x and CdS.In chapter 4,photodeposition of Cobalt-nickel cocatalysts on cadmium sulfide/carbon nitride composites for efficient H₂ evolution under visible light irradiation.CdS nanosheets were synthesized by the hydrothermal method.Carbon nitride nanosheets were prepared by two-step oxidation method.Then,CdS/C₃N₄composite was synthesized by the electrostatic adsorption method,followed by in-situ loading cobalt-nickel nanoparticles on their surface by photochemical reduction method.Their morphology was confirmed by transmission electron microscopy.Considering the photocorrosion of cadmium sulfide,sodium sulfide and sodium sulfite were used as sacrificial agents,and the catalytic hydrog en production performance of CdS/C₃N₄-Co Ni under visible light excitation was measured and the enhancement mechanism of its photocatalytic activity was further evaluated.