Preparation Of MoS₂/CdS-based Composite And Photoelectrocatalytic Hydrogen Evolution Performance

The shortage of energy and environmental issues are the two majorproblems that constrain the development of human society.Many countries have successively engaged in the research of new pollution-free energy which can successfully replace the traditional fossil fuels.Hydrogen energy is recognized as an ideal energy among many new energies due to its high energy density,abundant reserves,clean and pollution-free.Since the Japanese scientists Fujishima and Honda carried the photocatalytic decomposition of hydrogen in the TiO₂ electrode in 1972,more and more new semiconductor catalytic materials have been used in photoelectrocatalytic decomposition of water for hydrogen evolution reaction.Among the photoelectrocatalytic materials,CdS has attracted extensive attention due to its suitable forbidden band gap,good light response range and light absorption capability.But CdS also has the problems of photo-corrosion and the rapid recombination of photogenerated charge carriers.In view of the above problems,a common method is to load cocatalyst on the surface of CdS in order to improve its catalytic performance.Two-dimensional layered transition metal sulfides?TMDs?have attracted extensive attention due to the unique structure,good optical,electrical and catalytic properties.Among them,MoS₂ has become a research hotspot for its excellent performance in hydrogen evolution.In this paper,we use solvothermal synthesis and liquid exfoliation method to acquire the few layers MoS₂ nanosheet loaded on CdS nanorods to form a composite catalytic system of MoS₂/CdS.On the basis of this system,we use transition metal ions doping method and the control of microscopic morphology to further enhance the performance of photoelectrochemical and photoelectrocatalytic hydrogen evolution of the composite materials.The main research contents of this paper are as follows:?1?The MoS₂/Cu-CdS composite catalytic material was prepared by a two-step solvothermal method.The characterization of XRD,XPS,TEM indicates that Cu²⁺has been successfully doped into the crystal lattice of CdS and replaced Cd²⁺.The UV-vis DRS and PL tests show that the photoresponsive region of the catalyst is broadened?from 520 nm to 540 nm?and the phenomenon of rapid recombination of photogenerated charge carriers has suppressed.The photoelectrochemical performance tests and photoelectrocatalytic hydrogen evolution reaction tests were carried out by the means of coating the catalysts samples on the surface of ITO conductive glass?the loading amount is 1 mg/cm²?as a photoanode.The test results show that when the doping ratio of Cu²⁺is 7%,the photocurrent density of MoS₂/Cu-CdS reaches 43?A/cm²,which is 7.1 times and 1.6 times that of CdS and MoS₂/CdS,respectively.At the same time,the diameter of the semicircular portion at the high-frequency region of the Nyquist diagrams is the smallest,which means the most effective surface electron transfer.And the photoelectrocatalytic hydrogen evolution rate of MoS₂/Cu-CdS reaches10.18 mmol h^-1g^-1,which is 48 times that of CdS.?2?In this chapter,Cu-MoS₂/CdS composite materials were successfully synthesized by two-step solvothermal method and liquid exfoliation method.CdS nanorods were decorated by fewer layers MoS₂ doped with Cu²⁺.The properties of the composite materials such as microstructure,crystal structure and crystal type,element valence state and energy band structure were obtained by XRD,XPS and TEM.The UV-vis DRS and PL tests show that the catalyst material has good photocatalytic properties?the photoresponse region is broadened from 520nm to 575 nm?,and the recombination of photogenerated charge carriers was controlled.The photoelectrochemical tests results show that Cu-MoS₂/CdS sample has the highest instantaneous photocurrent density?77?A/cm²?,which is12.8 times and 2.8 times that of CdS and MoS₂/CdS,respectively.In the EIS tests,the Cu-MoS₂/CdS composite has the lowest interfacial resistance and the best interfacial charge transfer capability,which is due to ion doping and the inherent high conductivity of the MoS₂ material itself.At the same time,when the doping ratio of Cu²⁺is 5%,the photoelectrocatalytic hydrogen evolution rate of Cu-MoS₂/CdS reaches 12.78 mmol h^-1g^-1,which is 60 times that of CdS.