Preparation And Electrochemical Performance Of Molybdenum Sulfur Compound 3D Electrode

Growing concern about the energy crisis and environmental contamination urgently demands the development of clean and sustainable energy sources as feasible alternatives to traditional energy sources.Owing to its high energy density and environmental friendliness,hydrogen is an attractive and promising energy carrier to meet future global energy demands.Electrolyzing water is a sustainable and environmental route for the future hydrogen economy,in which electrocatalysts play a crucial role in its hydrogen evolution reaction.Generally,Pt is the the current state-of-the-art hydrogen evolution reaction?HER?electrocatalyst.However,the limited reserves and high cost limit their commercial large-scale applications.Therefore,it is highly desirable to explore low cost and earth-abundant catalyst materials to realize highly efficient water splitting in the future.Among many hydrogen evolution catalytic materials,molybdenum sulfide has attracted much attention due to its high abundance of earth and Gibbs free energy similar to Pt.However,the poor conductivity of the molybdenum sulfide and the inertness of the base surface restricts its HER activity.Therefore,polypyrrole arrays and Ni?OH?₂ arrays were introduced on the conductive flexible carbon cloth?CC?.A series of molybdenum sulfide composite 3D electrode structures were prepared by simple hydrothermal method,and their electrochemical properties were studied.The main research contents of this paper are as follows:?1?Firstly,the vertically arranged polypyrrole arrays were synthesized on CC by electrodeposition,and then converted into nitrogen-containing carbon by high temperature carbonization process,which improved the conductivity of the material and provided a large specific surface.Then,the defect-rich MoS_x supported by the carbon nanofiber array was synthesized by a simple hydrothermal method?MoS_x/CF/CC?.The effect of molybdenum-sulfur ratio on product structure and HER performance was also discussed.The experimental results show that increasing the amount of thioacetamide in the precursor solution may interfere with the formation of the MoS₂ sheet structure and cause a change in its growth direction,thereby forming a horizontal coverage of the defect-rich MoS_x on the carbon nanofiber array.The presence of defects gives MoS_x more active sites,while CF/CC provides a large specific surface area and enhances the conductivity of MoS_x,so the HER performance of the composite 3D electrode is significantly improved.The product MoS_x/CF/CC-2 had an initial overpotential as low as 107 mV,an overpotential of only 187 mV at a current density of 100 mA cm^-2,and the sample had a lower Tafel slope of 51 mV dec^-1.In addition,when the overpotential is 300 mV,the TOF value is as high as 20.6 s^-1.The preparation of the composite 3D electrode provides a new strategy for increasing the HER activity of MoS₂.?2?Based on the prior work,the?NH₄?₂Mo₃S₁₃?2H₂O powder having a polysulfide valence similar to that described above was prepared by an oil bath method.To further improve the HER performance of MoS₂ under alkaline conditions,two Ni?OH?₂/CC arrays with porous and vertical sheet structures were introduced on CC basis.Then Ni₃S₂-MoS₂/Ni?OH?₂/CC composite electrode materials were prepared by hydrothermal method,and the effects of hydrothermal temperature on the morphology,composition,valence and electrochemical properties of the products were discussed.The experimental results show that the Ni?OH?₂/CC of the sheet structure is more beneficial to improve the electrochemical properties of the material,and the difference of hydrothermal temperature will affect the structure of the synthesized product.The synthesis product at 140 ? is dominated by Ni?OH?₂ and MoS_x complexes,and has excellent HER properties under acidic conditions,confirming the results of the previous work.The electrode material composition prepared at 180? is Ni₃S₂-MoS₂/Ni?OH?₂/CC.The material not only has good HER performance under acidic conditions,but also excellent HER and oxygen evolution reaction catalytic activity under alkaline conditions.Its initial overpotentials are 90 mV,83 mV and 1.44V,respectively.This work provides new ideas for the development of cost-effective dual-function catalysts.