Study On Electrocatalytic Hydrogen Evolution Reaction Of Molybdenum-based Carbides Regulated By Electronic Structure

The development of renewable energy is an effective way to solve the problems of resource depletion,environmental pollution,and ecological damage caused by the use of traditional fossil energy.Hydrogen energy has become a research hotspot because of its high calorific value of combustion and pollution-free combustion products.The electrolyzed water hydrogen production technology driven by electric energy converted by renewable energy has the advantages of high product purity,high cleanliness,and no pollution,which aligns with the concept of green and sustainable development.However,due to the small reserves and high cost of precious metal-based catalysts（such as Pt）,it is still difficult to widely use hydrogen production technology by electrolysis of water.Therefore,the development of non-precious metal catalysts is particularly important.Molybdenum carbide with a Pt-like electronic structure is one of the ideal candidates for hydrogen production by electrolysis of water instead of Pt-based catalysts due to its excellent electrical conductivity and corrosion resistance.However,compared with Pt-based catalysts,the hydrogen evolution activity of molybdenum carbide is still not high,and the stability needs to be enhanced.In view of the above problems in the hydrogen evolution reaction of molybdenum carbide,to further improve the hydrogen evolution performance of molybdenum carbide,we prepared boron-doped porous carbon-coated nickel/molybdenum carbide composites（Ni/Mo₂C-BC）,boron-doped molybdenum/molybdenum carbide composites（B-Mo/Mo₂C）and boron-doped Mo₂CT_x（MXene）composites modified with highly dispersed ruthenium nanoparticles（Ru@B-Mo₂CT_x（MXene））.Through the construction of heterostructures and effective doping of boron,the electronic structure of each electrocatalyst was regulated and the corresponding hydrogen evolution performance was optimized.The main research content includes the following three aspects:（1）The hydrogel precursor was prepared by the crosslinking reaction of a polyvinyl alcohol solution of sodium tetraborate,sodium molybdate,and nickel nitrate.The boron-doped porous carbon-coated nickel/molybdenum carbide composite was synthesized by simple lyophilization and calcination.The morphology and hydrogen evolution property of the composite were studied.The morphology of Ni/Mo₂C-BC was characterized by scanning electron microscopy（SEM）,and the pore size structure of the material was determined by N₂ adsorbent.The test showed that the catalyst has a loose multi-level pore morphology and a wide distribution of pore size.In 1.0 M KOH solution,Ni/Mo₂C-BC has an overpotential of 198 m V at a current density of 10 m A cm^-2.The catalyst can stabilize hydrogen evolution for 30 h at this current density.X-ray photoelectron spectroscopy（XPS）analysis showed that the Ni/Mo₂C composite structure in the catalyst was beneficial to electron transfer from Ni to Mo₂C.This electron transfer promotes hydrogen desorption by regulating the electronic structure of Mo.In addition,the introduction of boron also helps to improve the hydrogen evolution activity.The influence of boron introduction on the hydrogen evolution performance of the catalyst was explored by SEM and Raman.On the one hand,the hydrogel formed by the introduction of boron helps to produce a loose and porous morphology,so that the electrolyte and the catalyst can be effectively contacted.On the other hand,the introduction of boron in carbon materials increased the carbon defect.（2）Boron-doped molybdenum/molybdenum carbide composite（B-Mo/Mo₂C）was prepared by high-temperature boronization.Their morphology and wide p H hydrogen evolution properties were studied.SEM test showed that B-Mo/Mo₂C has a two-dimensional layer structure and evenly distributed pores on the layer structure,and.The N₂ adsorption test further analyzed the pore structure of the composite.The catalyst B-Mo/Mo₂C has a wide p H hydrogen evolution activity,with overpotentials of 108 m V(η₁₀)and 191 m V(η₁₀)in 1.0 M KOH and 0.5 M H₂SO₄ solutions,respectively.The catalyst has good hydrogen evolution activity and stability in alkaline solution and can stabilize hydrogen evolution for 30 h.The phase structure of the catalyst was analyzed by X-ray powder diffraction（XRD）.In addition,XPS studies showed that the formation of the Mo/Mo₂C heterostructures is helpful for the regulation of Mo electronic structure,then promoting hydrogen release,and optimizing hydrogen evolution performance.（3）A boron-doped Mo₂CT_x（MXene）composite modified with highly dispersed ruthenium nanoparticles was prepared by lyophilization and calcination of the mixed solutions of Mo₂CT_x（MXene）,RuCl₃·x H₂O,and H₃BO₃.The morphology and alkaline hydrogen evolution property were investigated.SEM and transmission electron microscopy（TEM）characterizations showed that ruthenium nanoparticles with a particle size of about 4 nm were uniformly distributed on the two-dimensional sheet structure of Ru@B-Mo₂CT_x（MXene）,and formed a multi-interface structure.Ru@B-Mo₂CT_x（MXene）has efficient hydrogen evolution activity in 1.0 M KOH solution,and the overpotential at a current density of 10 m A cm^-2 is only 45 m V.The relationship between the efficient hydrogen evolution activity and the structure of catalysts was explored by XPS,TEM,and electrochemical testing.The results show that the electronic structure of Mo can be regulated by boron doping modification and ruthenium nanoparticle decoration of Mo₂CT_x（MXene）.This regulation of Mo electron structure is beneficial to the improvement of hydrogen evolution performance.