Synthesis And Electrocatalytic Performance Of MOFs-Derived Sulfides/Molybdenum Disulfide Composites

The increasingly exhausted fossil energy and the serious ecological environmental problems make people pay more attention to sustainable clean energy such as hydrogen.Hydrogen production from water electrolysis is a promising way to produce hydrogen,among which highly active,low-cost and stable electrocatalysts are crucial for producing hydrogen through water electrolysis.MoS₂ possesses approximate free energy of hydrogen adsorption to that of Pt,as well as the low costs and abundant resources,so it is regard as a promising catalyst for HER to substitute Pt.However,the number of catalytic active sites of the pristine MoS₂ is insufficient and the conductivity is poor,thus the catalytic performance of MoS₂ is still far from the Pt-based catalysts and it is necessary to modify MoS₂.In this paper,we focus on the modification of MoS₂,and the catalytic activity of MoS₂ is improved by increasing the number of active sites and the conductivity.The specific method is to use MOFs as the sacrificial templates.By virtue of the advantages of MOFs and their derivatives,the doping and recombination of MoS₂ can be realized,finally generating Zn_xCo_1-xMoS₃,CoS_x@MoS₂,CoS_x/CNTs@MoS₂electrocatalysts.The effects of the doping of heteroatoms,the formation of heterostructures,the introduction of carbon and the synergistic effect between different components on the electrocatalytic properties of the products were discussed.The main contents of this paper are as follows:?1?The water-soluble[?CH₃?₂NH₂][Zn_xCo_1-x?HCOO?₃]?x=0,1/4,1/3,1/2,2/3,1?precursors were synthesized by using formic acid as the ligand and dimethylamine as the cation template,which were reacted with?NH₄?₂MoS₄ water solution quickly to generate insoluble precipitates.Through succedent annealing treatment,Zn_xCo_1-xMoS₃ microboxes were finally obtained,so the doping of the Zn and Co atoms was successfully realized.The HER tests showed that,among the series Zn_xCo_1-xMoS₃ samples,Zn_1/3Co_2/3MoS₃ had the best HER performance,with a low overpotential of 160 mV at a current density of 10 mA cm^-22 and a small Tafel slope of85 mV dec^-1,as well as excellent durability in 0.5 M H₂SO₄.The synergism of Zn–Co–Mo–S,the hollow cubic structure and the incorporation of Zn and Co atoms were the key to the enhanced catalytic performance.?2?[?CH₃?₂NH₂][Co?HCOO?₃]was synthesized by a simple liquid precipitation method at room temperature at first.Then the Co-MOF was reacted with thioacetamide?TAA?to generate Co₉S₈ under solvothermal conditions.Through hydrothermal treatment,numerous MoS₂ nanosheets grew on the surface of CoS_x vertically and uniformly,finally generating CoS_x@MoS₂ heterostructures.As a bifunctional electrocatalyst,CoS_x@MoS₂ exhibited remarkable HER and OER performance at the same time.The HER overpotential was 239 mV at a current density of 10 mA cm^-22 and the Tafel slope was 103 mV dec^-1 in 0.5 M H₂SO₄.The OER overpotential was 347 mV at a current density of 10 mA cm^-22 and the Tafel slope was 147 mV dec^-1 in 1 M KOH.The enhanced electrocatalytic activities of CoS_x@MoS₂ could be ascribed to their unique heterostructures and the synergism between CoS_x and MoS₂.?3?On the basis of the previous chapter,carbon materials were further introduced to enhance the catalytic reaction kinetics of the products.The small-sized[?CH₃?₂NH₂][Co?HCOO?₃]was synthesized by microemulsion method at first.The Co₉S₈/CNTs binary composite was then prepared by adding carbon nanotubes?CNTs?additionally in the reaction system of Co-MOF and TAA.Finally,Co₉S₈/CNTs was used as a template to load MoS₂,generating CoS_x/CNTs@MoS₂ ternary composite.As a bifunctional electrocatalyst,CoS_x/CNTs@MoS₂ exhibited remarkable HER and OER performance at the same time.The HER overpotential was 206 mV at a current density of 10 mA cm^-22 and the Tafel slope was 69 mV dec^-1 in 0.5 M H₂SO₄.The OER overpotential was 296 mV at a current density of 10 mA cm^-22 and the Tafel slope was 92 mV dec^-1 in 1 M KOH.Compared with single component catalysts and binary composites,CoS_x/CNTs@MoS₂ had significantly improved catalytic performance,which could be attributed to the synergistic effect among CoS_x,CNTs and MoS₂.CNTs not only significantly enhanced the catalytic reaction kinetics,but also contributed to the improved catalytic activity.