Enhanced Performance And Mechanism Of Electrocatalytic Hydrogen Evolution Of Highly Defective MoS

Electrocatalytic hydrolysis for hydrogen production is a green and sustainable technology for hydrogen energy production,and the search for efficient catalysts for electrocatalytic hydrolysis for hydrogen production is the key to move the technology toward practical application.Molybdenum disulfide（MoS₂）is currently the most promising catalyst for electrocatalytic hydrogen precipitation reaction（HER）due to its cheap price and abundant reserves.Compared with the semiconductor phase（2H-MoS₂）,the metallic phase（1T-MoS₂）exhibits higher electrical conductivity and superior catalytic activity.It has been shown that increasing the defect states by introducing a certain number of sulfur vacancies（Sv）is also able to further activate the inert basal plane of MoS₂.These defect states are responsible for H adsorption,but too high a concentration of sulfur vacancies（Sv%）can generate high surface energy,weakening the stability of the structure,which in turn leads to an upper limit of performance.To address this issue,this thesis is based on the study of MoS₂ in highly defective states to optimize the catalytic performance by forming van der Waals heterojunctions with MXenes using interfacial coupling to adjust the electronic properties of the two-dimensional structure,thus controlling the electronic properties of SV;and forming nanoscrolls structures using strain to change the electronic structure of MoS₂ itself to optimize the catalytic performance.The specific findings are as follows:（1）Ti₃C₂-F,Ti₃C₂-OH and Ti₃C₂-O MXene nanosheets with quasi-monolithic functional groups were obtained by HCl-LiF etching of Al layers,ethylene glycol（EG）solvent heat treatment and n-butyl lithium（n-Bu Li）reduction.A series of two-dimensional van der Waals（2D vd W）heterojunctions（Sv@1T-MoS₂/Ti₃C₂Tx）with stable structures and promising properties were successfully prepared by further compounding with high Sv%1T-MoS₂ nanosheets obtained by alkali ion intercalation exfoliation and metal Pd atom doping.Through systematic structural and performance characterization,it was confirmed that the MXene surface functional groups have a modulating effect on the properties of MoS₂ in the highly defective state.Theoretical calculations show that the hydroxyl modified heterojunction optimizes the electronic structure of sulfur vacancies and effectively promotes the transfer of hydrogen atoms,surface adsorption and activation.The performance of the catalyst can be further enhanced at Sv%up to 32%,with an overpotential of only 58 m V and a Tafel slope of60 m V dec^-1 at an exchange current density of 10 m A cm^-2（η10）under acidic conditions,and an overpotential of 111 m V（η10）and a Tafel slope of 81 m V dec^-1 at alkaline conditions.（2）Highly defective 1T-MoS₂ nanosheets doped with Pd atoms at 20 wt.%were used as substrates,and highly defective Pd@1T-MoS₂ nanowires（Pd@1T-MoS₂-NSs）were successfully prepared by high boiling point organic solvent-assisted lyophilization technique.Combined with the morphological characterization tests,the effects of the lamellae size and external stress on the roll formation effect were further explored to obtain the optimal synthesis scheme and electrochemical tests were performed on the best samples.In the acidic system,the Pd@1T-MoS₂-NSs catalyst has a large electrochemically active area with an overpotential of 90 m V（η10）and a Tafel slope of 99 m V dec^-1.