| Heretofore,noble metal is still the most effective catalysts for hydrogen evolution reaction（HER）,but the high price of noble metal restricts its practical application and production.Mo S2 is considered as a promising alternative to noble metal-based catalysts due to its simple preparation,large specific surface area,low cost,and high stability.However,the lack of active sites on the base surface of Mo S2 and low intrinsic conductivity are key reasons that limit its catalytic activity.Therefore,increasing the number of active sites of Mo S2 and improving the conductivity of Mo S2 are the core problems that need to be solved urgently.Introducing sulfur（S）vacancies on the inert basal plane of Mo S2 is an effective strategy to improve its HER activity.However,probing active sites at nanoscale and quantitatively analyzing the related electrocatalytic activity in electrolyte aqueous solution are still great challenges.In this study,we have successfully investigated the catalytic activity of the S vacancies defect on the Mo S2 base plane and the edge of Mo S2 by scanning electrochemical microscope（SECM）.Based on the research,the HER activity of Mo S2 based catalysts can be improved by creating defective Mo S2 nano sheets,preparing molybdenum disulfide quantum dots（Mo S2 QDs）with low electron interlayer transition barrier,high conductivity and exchange current density to improve the conductivity of Mo S2 by modifying metals and metal oxides.The main research contents are as follows.In this work,utilizing high-resolution scanning electrochemical microscopy,optimized electrodes and newly designed thermal drift calibration software,morphology information and the catalytic performance of Mo S2 were obtained by feedback mode and generation collection（SG/TC）mode,respectively.SECM confirmed that the edge of 2H-Mo S2 has significant HER activity.Excluding the influence of edge active sites,the HER activity of region with abundant S vacancies on Mo S2 inert surface was in-situ imaged with high resolution by using Pt tip with a radius of 14 nm,the minimum radius of the hydrogen flux obtained was 20 nm.In addition,we quantitatively measured the HER kinetic data of S vacancy by SECM under SG/TC mode,directly and accurately obtaining the electrochemical activity of S vacancies in actual catalytic environment,which has significant implications for optimizing the performance of Mo S2 catalysts.Additionally,the stability of S vacancies over the wide range of p H 0-13 was investigated.This study provides a viable strategy for obtaining the catalytic kinetics of nanoscale active sites on structurally complex electrocatalysts and evaluating the stability of defects in different environments for two-dimensional material-based catalysts.As a common defect type,S vacancy can increase the density of active center on Mo S2 surface,which will enhance the catalytic activity of Mo S2.However,excessive S vacancies have a tendency to strongly adsorb hydrogen protons,thereby diminishing the overall catalytic activity.Therefore,in this study,the number of active sites on the Mo S2base surface and the conductivity of the Mo S2 based catalyst were further increased by introducing non noble metal cobalt nano disks（Co Nds）on the Mo S2-x base surface containing S vacancies.The modification of Co Nds on Mo S2-x substrate can effectively adjust the surface electronic state of Mo S2,and the active sites on Mo S2-x surface can be retained as much as possible by using the layered structure of the nano disk.Meanwhile,the interaction of Co-S bond can activate the S atom on the inert group of Mo S2,achieving the reduction of H+on the S sites,further effectively regulating the adsorption capacity of Mo S2 for hydrogen protons.Co Nds/Mo S2-x exhibited excellent catalytic performance with low over potential at a current density of 10 m A cm-2(184 m V@η10m A cm-2),small Tafel slope(62.5 m V dec-1)and showed good electrochemical stability after 1000 cycles of voltammetry（CV）.Its catalytic performance is significantly better than that of pure 2H-Mo S2(627 m V@η10 m A cm-2,246 m V dec-1)and Mo S2-x(354m V@η10 m A cm-2,99.7 m V dec-1).This study provides a new approach for designing non-noble metal nanostructures with different morphologies as cocatalysts and a novel strategy for improving the catalytic performance of two dimensional materials.In addition to the S vacancies,edge sites also contribute significantly to catalytic performance of Mo S2.In this study,we use Co3O4-MOF framework with high porosity and large specific surface area was used to evenly load more Mo S2 QDs to fully expose the active edge sites,to achieve excellent catalytic performance of the material.Meanwhile,Co3O4-MOF would provide more active sites and increase the conductivity of Mo S2.The coupling effect of cobalt ions and S edges can increase the HER activity of Mo S2 by enhancing stability,shortening the transmission distance of electrons and accelerating charge transfer.In addition,we utilized reduced graphene oxide（RGO）with excellent electrochemical performance as substrate,combining advantages of Mo S2 QDs and Co3O4-MOF mentioned above,to prepare Mo S2 QDs/Co3O4-MOF@RGO catalyst.The catalyst showed a low over potential and Tafel slope(235 m V@η10 m A cm-2,77 m V dec-1).This study provides a new idea to improve the catalytic activity of Mo S2 based catalysts by developing synergistic structures and electronic modulation. |
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