Preparation And Electrocatalytic Hydrogen Evolution Properties Of Amorphous Molybdenum Sulfide Matrix Composites

The environmental pollution problems and energy crisis caused by the burning of fossil fuels have attracted the attention of the world.Hydrogen,a renewable and clean energy,is one of the ideal candidates for replacing traditional fossil energy.Electrocatalysis water splitting is an important way to obtain high-purity hydrogen energy,but the required voltage during the electrocatalytic reaction is much higher than the theoretical value due to the existence of electrode overpotential.The development of electrocatalysts with low price,abundant reserves and excellent performance is the key to the development of hydrogen production from water electrolysis.Amorphous molybdenum sulfide(a-MoSx)has become one of the most promising materials for electrocatalytic hydrogen evolution reaction(HER)due to its unique physical and chemical properties.However,the a-MoSx exhibits poor electrochemical stability in acidic electrolytes due to its low crystallinity and the inherent low conductivity which also can inhibits the efficient electron transfer process.Based on the above,strategies such as coupling with conductive substrates,designing nanostructures with specific shapes and doping with transition metal atoms have carried out to improve the catalytic performance of MoSx materials for hydrogen evolution,and the preparation methods of amorphous molybdenum sulfide-based catalysts have been explored in this work.The electrocatalytic properties of as-prepared catalysts were systematically investigated.The main research contents and results are as follows:(1)Ti3C2Tx MXene nanosheets were obtained by etching the precursor Ti3AlC2 with a mixed solution of lithium fluoride and hydrochloric acid.MoSx/Ti3C2Tx composites were prepared by wet chemical method using ammonium tetrathiomolybdate as raw materials.the MoSx/Ti3C2Tx composite exhibits good electrocatalytic activity with an overpotential of 207 mV at the current density of 10 mA cm-2,and a Tafel slope of 46 mV dec-1.The introduction of Ti3C2Tx nanosheets can effectively improve the electrical conductivity of the composites and accelerate the charge transfer rate in the electrocatalytic hydrogen evolution process,and the abundant functional groups on its surface can serve as the nucleation sites of MoSx,so that MoSx can uniformly grows on the surface of Ti3C2Tx,which can expose more active sites.In addition,the strong interaction between MoSx and Ti3C2Tx can further promote the transfer of interfacial charges and improve the catalytic performance.(2)A series of Co-doped MoSx nanopolyhedral materials(CoMoSx NPs)were successfully prepared by a simple solvothermal method using metal-organic framework material ZIF-67 as the precursor and(NH4)2MoS4 as the multifunctional vulcanizing agent.Compare with other samples,the CoMoSx NPs(1/2)prepared by using the mass ratio between ZIF-67 and(NH4)2MoS4 of 1/2 shows the best catalytic activity with the lowest overpotential(η10=188 mV)and Tafel slope(b=65.4mV dec-1).The excellent catalytic performance of CoMoSx NPs can be attributed to their unique polyhedral structure,which is beneficial to expose more active sites.In addition,the doping effect of Co ions not only reduces the free energy of hydrogen adsorption(AGH*)at the active site for faster hydrogen adsorption kinetics,but also promotes the charge transfer between the electrolyte and the catalyst surface,and thus increasing the intrinsic conductivity of MoSx.(3)Co-N doped carbon polyhedra were obtained by direct carbonization of metal-organic framework material ZIF-67 at 800℃ in an inert atmosphere.MoSx nanoparticles were grown on the surface of polyhedron by wet chemical method,and a series of composite materials Co/NC@MoSx with special morphologies and structures were synthesized.Co/NC@MoSx exhibits excellent HER activity in 0.5 M H2SO4 electrolyte.The Co/NC＠MoSx(l/3)sample,prepared by a mass ratio of Co/NC to(NH4)2MOS4 of 1/3,only need 187 mV overpotential to reach the current density of 10 mA cm-2,its is only,and its Tafel slope is 55.6 mV dec-1.The introduction of Co-N doped carbon polyhedra not only improves the conductivity of the catalyst and accelerates the electron transfer rate,but also provides an effective support for the growth of nanocatalysts,which inhibits the occurrence of agglomeration,and thus exposing more active sites.In addition,Co nanoparticles interacted with MoS42-and the formed CoMoS phase can further enhance the overall electrocatalytic activity.