Controllable Preparation Of Nanoscale High-Entropy Alloys And Their Applications In Electrocatalytic Small Molecule Reduction

High-entropy alloys(HEAs)as the emerging materials have the advantages of strong hardness,corrosion resistance,and resistance to oxidation compared with other traditional alloys.With the advent of the energy crisis and the deterioration of the global environment,high-entropy alloys had the application in the field of energy catalysis.Due to their large composition and wide tunable surface electronic structure,highentropy alloys are expected to be highly active electrocatalysts.However,the highentropy alloys prepared by traditional synthesis methods are mainly bulk and thin-film materials,which is contrary to the characteristics of small particle size and large specific surface area of catalysts.Therefore,high-entropy alloys prepared by traditional methods are rarely used in the field of electrocatalysis.In this thesis,a new method of nanocrystallization of alloying materials—the plasma shock method is proposed for preparing nano-scale high-entropy alloys.And by this method,a series of carbonaceous layer-coated nano-high-entropy alloys were successfully prepared for electrocatalysis.Firstly,we selected a single metal as the experimental subject,and used large particle metal powder as the raw material to prepare carbonaceous layer-coated nano-unitary metal materials.Then,binary,ternary,and up to hexahydroxy high-entropy alloys are prepared by increasing the type and quantity of metals.The prepared materials have the characteristics of small particle size(nanoscale),carbon coating,and uniform dispersion,which proves the universal applicability of the plasma shock method for the preparation of nanoscale alloy materials.In addition,we also focus on the preparation and research of two types of nano-HEAs for electrocatalysis:(1)refractory nano-high entropy alloys.(2)Nanometer high-entropy precious metal alloys.We prepared refractory TiNbTaCrMo nano-high-entropy alloys by the plasma shock method with an equimolar ratio of high melting and boiling point metals(Ti,Nb,Ta,Cr,Mo powder)as raw materials.Its microscopic morphology shows a regular hexagonal structure.The outer layer is wrapped with several layers of graphene-like carbon layers,and the particle size is only about 13 nm.Refractory nano high-entropy alloys have the advantages of high temperature resistance and corrosion resistance,and they are used for electrocatalytic hydrogen production from seawater.The seawater electrolysis overpotential of the nano-high entropy alloy catalysts is significantly smaller than that of the single-metal catalysts.Theoretical calculations show that the alloying effect makes the upshift of d-band electron center,which is closer to the Fermi level.It would be conducive to the combination,activation,and dissociation of the active sites on the catalyst surface and water molecules,thereby accelerating the catalytic reaction.And the alloyed nano-high entropy alloy catalyst has a long-term stability and stays stable even after 25 hours of continuous electrolysis.Similarly,we used seven kinds of precious metals(Au,Ag,Pt,Pd,Rh,It,and Ru)as raw materials,and prepared a series of senary precious metal-based nano-high entropy alloys by the same method.Its microscopic morphology is shown as uniform spherical nanoparticles with an average particle size of less than 10 nm,with a small amount of carbonaceous layer covered.We used a series of noble metal nano-highentropy alloys as electrocatalysts for CO2 reduction reaction.The senary noble metal nano-high-entropy alloy AuPtPdRhIrRu catalyst without metal Ag outperforms the others.The ratio of carbon monoxide and hydrogen produced in the H-type electrolytic cell reaches 1:1,and the partial current density of carbon monoxide is also significantly higher than that of other nano-HEAs.In the flow-type electrolysis cell,the catalyzed yield of carbon monoxide reaches 80%,and it has a wider electrochemical window.Its excellent catalytic performance may be attributed to the smaller and more uniform size of the Ag-free noble metal nano-HEAs compared with other catalysts.This is attributed to have a larger specific surface area and a larger number of active sites.In addition,the adjustment of the d-band electron center after the alloying of the six metals(Au,Pt,Pd,Rh,Ir,and Ru)is more conducive to the adsorption and activation of carbon dioxide.