Preparation Of Defective MoS₂-based Photocatalyst And Hydrogen Evolution Performance

Molybdenum disulfide（MoS₂）is considered as a promising alternative to precious metal co-catalysts due to its abundance and low cost.However,the catalytic active center of MoS₂ is only along the edge of the MoS₂ layer.Less edge exposed active sites and inherent low conductivity greatly limit the speed of charge transfer,thus limiting its catalytic hydrogen evolution performance.In addition,the conductivity and electron mobility of the stable 2H phase of MoS₂ are poor,which greatly limits the efficiency of the MoS₂ catalytic hydrogen evolution reaction.Therefore,people may propose a lot of design and improvement methods on how to expose more edge structure MoS₂ catalysts and optimize the active edge sites on the inert substrate plane sites:engineering nanostructured MoS₂,phase transition from 2H to 1T,Chemical substitution,formation of heterostructures,defect engineering,etc.,to improve the catalytic activity of hydrogen precipitated.Both theoretical and experimental studies have shown that defect engineering can increase the active site of MoS₂ and has superior activity in catalytic reactions.In this paper,the photocatalytic performance of hydrogen evolution was studied by using the method of redox to prepare MoS₂ with rich defects to increase the active sites.The main research contents of this paper are as follows:（1）A novel Mo_1-xS₂(Mo_1-xS₂/Ti O₂)photocatalyst with controllable Mo vacancies was successfully synthesized by the NaBH₄ reduction method,which exhibits significantly enhanced hydrogen evolution reaction（HER）activity with lower overpotential and smaller Tafel slope in alkaline electrolyte.Compared to pure Ti O₂and MoS₂/Ti O₂,the H₂ release rate of Mo_1-xS₂/Ti O₂ heterostructure photocatalyst was significantly increased.At optimal molar ratio of 2.5:1 Mo_1-xS₂/Ti O₂,the H₂ release rate achieves 1561μmolg^-1h^-1,which is approximately 5.3 and 2.7 times of pure Ti O₂and MoS₂/Ti O₂,respectively.Through electrochemical analysis and first-principle density functional theory calculations,the rapid charge separation,transfer as well as high HER activity are believed to increase photocatalytic H₂ activity.（2）MoS₂ with surface defects（Mo）vacancies was prepared by KMnO₄ oxidation method.Defect MoS₂/CdS composite material with high hydrogen evolution performance was prepared by hydrothermal method.The results show that the H₂release rate of Defect MoS₂/CdS composite material is 11750μmolg^-1h^-1,which is a defect-free（Mo）vacancy MoS₂/CdS composite material(9018μmolg^-1h^-1)and pure CdS(768μmolg^-1h^-1)1.3 and 15.3 times.KMnO₄ is a strong oxidant that can oxidize part of Mo⁴⁺in MoS₂ to Mo⁶⁺,so that there are defects（Mo）vacancies on the surface of MoS₂.Defect（Mo）vacancies not only enhance the separation and transport capacity of photogenerated electrons,but also expose more active sites.The synergistic effect of Defect MoS₂/CdS composites shows significant photocatalytic hydrogen evolution performance.（3）A novel precious metal-free composite photocatalyst（Defect MoS₂/Ti₃C₂/CdS）with high hydrogen evolution performance was synthesized by hydrothermal method.Pure CdS shows a low photocatalytic hydrogen evolution rate(0.768 mmolg^-1h^-1).The Defect MTC catalyst showed a very high H₂ generation rate(14.168 mmolg^-1h^-1),which is 18.5 and 1.6 times that of CdS and MTC,respectively.A large number of active sites with enhanced H₂ generation can be induced by introducing Mo vacancies into the MoS₂ in Defect MoS₂/Ti₃C₂/CdS composites,and the presence of molybdenum vacancies can also inhibit carrier recombination.Ti₃C₂with good electron transfer ability can prevent light-induced carrier recombination,while the accordion-like multilayer structure can provide more reaction sites.In addition,it was found that the presence of Ti₃C₂ and MoS₂ acts as a dual co-catalyst to enhance the electronic conductivity of the metal,leading to an increase in the efficiency of electron transfer.At the same time,the mechanism of improving the catalytic performance was discussed.Figure[47]table[8]reference[137]...