| Excessive use of fossil fuels has caused serious problems such as energy shortages,greenhouse effect and environmental pollution.How to use and produce renewable clean energy has become the focus of attention of researchers from all over the world.As a clean energy with high combustion value and high efficiency,hydrogen energy is an ideal energy source that can fundamentally solve energy and environmental problems.The use of solar energy to decompose water to produce hydrogen is currently one of the most ideal methods for obtaining hydrogen energy.At present,the two main problems faced by photocatalytic decomposition of water to hydrogen production are high cost and low output.Graphite phase carbon nitride(g-C3N4)has great potential as a metal-free low-cost photocatalyst.However,g-C3N4 alone lacks sufficient proton reduction active sites,and there are serious photo-generated electrons and holes on the surface of g-C3N4 during the photocatalytic reaction.These shortcomings greatly limit its photocatalytic hydrogen production activity.This thesis takes g-C3N4 as the research object,designs(Pt/MoP)composite co-catalyst and g-C3N4 assembling to prepare(Pt/MoP)/g-C3N4 composite catalyst for photocatalytic water splitting research.Two-dimensional flake-shaped g-C3N4 and rod-shaped CdS were prepared,and Pt was loaded on the flake-shaped g-C3N4 by immersion H2 reduction to construct a high-performance Pt/g-C3N4 composite catalyst,and then composited with rod-shaped CdS to prepare CdS/(Pt/g-C3N4)ternary catalyst for photocatalytic water splitting research.The specific research content is as follows:(1)The role of the co-catalysts in(Pt/MoP)/g-C3N4 was studied.The(Pt/MoP)composite co-catalyst was prepared by the impregnation H2 reduction method using MoP and the noble metal Pt,and then the(Pt/MoP)/g-C3N4 composite catalyst was prepared by the wet impregnation method with g-C3N4,the optimal hydrogen production of the composite photocatalyst can reach 531.75 μmol/h/g,which is 5.9 times that of MoP/g-C3N4,2.7 times that of 1%Pt/g-C3N4,and 1.9 times that of 3%Pt/g-C3N4.The linear scanning voltammetry curve and electrochemical impedance spectroscopy proved that the precious metal Pt can reduce the hydrogen production overpotential and the interface charge transfer resistance;through the constant current charge and discharge test of the co-catalysts,it is found that MoP has a large capacitance.It has the function of absorbing and storing electrons.(2)The mechanism of the composite co-catalyst(Pt/MoP)was further studied and demonstrated through the surface photovoltage test.Through the steady-state surface photovoltage test,it is found that the photovoltage response intensity of(Pt/MoP)/g-C3N4 is weaker,but the band is the widest,it shows that the large capacitance characteristics of MoP and the existence of Pt particles on the surface of MoP together lead to the uniform distribution of photogenerated electrons;through the transient photovoltage test of different catalysts,it is found that(Pt/MoP)/g-C3N4 has a higher transient photogenerated carrier intensity,and its carrier decay speed is slower.It is further demonstrated(Pt/MoP)mechanism of action.The(Pt/MoP)composite co-catalyst suppresses the recombination of photo-generated carriers while distributing the electrons uniformly.At the same time,the Pt supported on the surface of MoP can catalytically reduce hydrogen to produce hydrogen.This is the main reason for the increased activity of the composite catalyst(Pt/MoP)/g-C3N4.(3)The CdS/(Pt/g-C3N4)ternary composite catalyst for efficient hydrogen production was prepared and its reaction mechanism was studied.Two-dimensional flake-shaped g-C3N4 and rod-shaped CdS were prepared,and Pt was loaded on the surface of flake-shaped g-C3N4 by immersion H2 reduction,and then,the CdS/(Pt/g-C3N4)ternary composite catalyst was prepared by compounding with rod-shaped CdS by ultrasonic method.The photocatalytic activity of the composite catalyst to decompose water for hydrogen production can reach up to 1465.9 mol/h/g,which is 6.9 times that of CdS/g-C3N4,4 times that of Pt/g-C3N4,and 5.3 times that of Pt/CdS.The good morphology of the catalyst was confirmed by TEM and HRTEM tests;the electrochemical characterization analysis found that the electrochemical impedance of the ternary catalyst CdS/(Pt/g-C3N4)was greatly reduced compared with other catalysts,And the slope of the Tafel curve is the lowest,the photocurrent intensity can reach 50A/cm2;the surface photovoltage response of the CdS/(Pt/g-C3N4)composite catalyst is significantly improved and the surface photocurrent response is significantly enhanced,the apparent quantum of CdS/(Pt/g-C3N4)The efficiency can reach 1.5%at 532nm.The compact support of Pt particles on the flake g-C3N4 and the construction of the ternary system improve the separation and transfer efficiency of photogenerated carriers.At the same time,because the two semiconductor catalysts have suitable band gaps and matched energy level positions,The noble metal Pt conducts electrons at the interface of the two catalysts while fully carrying out the proton catalytic reduction reaction to concentrate hydrogen production.The experimental mechanism is further proved by the surface photovoltage and surface photocurrent. |
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