Electrocatalytic Properties Of Nanoporous High-Entropy Alloys Prepared By Dealloying

Modern life is dependent on the use of fossil fuels,which brings increasingly serious environmental pollution.New energy technology has attracted more and more attention.The development of new energy resources like lithium ion battery,fuel cell and metal-air battery is also progressing.However,catalysts as an important factor greatly limit the development of fuel cells and metal-air batteries.Excessive reliance on noble metal,poor stability and other factors seriously affected the promotion of these new energy technologies.To develop a catalyst with good stability and using noble metal as little as possible is very important.High-entropy alloys are defined as alloys formed by alloying five or more alloy elements at or near the same atomic ratio.Due to the primary effect（including high entropy effect,the lattice distortion effect,hysteresis effects of diffusion and cocktail effect）,high-entropy alloys are different from the traditional alloy,showing a series of unique physical and chemical properties,such as high strength,high hardness,good thermal stability,excellent wear and corrosion resistance and so forth.At present,the research on high entropy alloys is mainly focused on the field of structural materials.To make nanoscale high-entropy alloys for catalysis/electrocatalysis,herein,we introduced a commonly used which is a simple and convenient for the preparation of nano-porous alloy materials on a large scale.The principle of preparation of nano-porous metal materials by dealloying is that the active elements with the lowest electrode potential are selectively corroded away through the different electrochemical electrode potentials of each component of the alloy,and the remaining stable elements will diffuse/self-assemble to form a uniform doublecontinuous nano-porous metal structure.By introducing aluminum and some metals which are insoluble in alkaline solution,aluminum based high-entropy alloy strips can be obtained through traditional melt spinning technology.Aluminum can be selectively removed in alkaline solution to prepare the nano-porous high-entropy alloy.First,we applied the idea to high-entropy alloys containing noble metals.Due to the stability of noble metal,it is easier to get the desired results.We designed different component alloys Al_97.5Ni_0.5Cu_0.5Pt_0.5Pd_0.5Au_0.5 and Al_97.2Ni_0.4Cu_0.4Pt_0.4Pd_0.4Au_0.4Co_0.4Fe_0.4.The results showed that both of the alloys can be used to prepare nanoporous high-entropy alloys,demonstrating the versatility of the dealloying method.The nanoscale six-element alloy exhibits superior catalytic performance for both oxygen reduction reaction and CO oxidation reaction.To prepare noble metal-free nanoporous high-entropy alloys,we designed five-component alloys composed of Al₉₇Ni_1.5Co_0.5Fe_0.5X_0.5（X: Mo,Cu,Mn,Cr,V,Zr and Nb）,with a series of ternary,quaternary and hexagonal alloys for comparison.We found that the severe oxidation of nanometer non-noble metals occurs.Due to the tuned electronic properties by mixing five components and the possible high entropy effect,the performance and stability of the five-element alloy Al Ni Co Fe X（Mo,Cr,Nb）are excellent for oxygen evolution reaction.The experimental results show that the nanoscale high entropy alloys/oxides can be prepared by this simple dealloying method.The materials also have superior performance for various catalytic reactions.