Study On High-entropy Alloys Nanocomposites And Their Energy Applications

Recently,due to the excellent properties and great potential of high-entropy alloys in many fields such as mechanics,heat,electricity,magnetism,and corrosion resistance,they have attracted extensive attention in related fields around the world.With the gradual understanding of high-entropy alloys and the synthesis of high-entropy alloy nanomaterials,researchers have found that the unique high-entropy effect and cocktail effect make HEAs also extraordinary in the field of catalysis.However,the current research on high-entropy alloys mainly focuses on mechanics,corrosion resistance and etc.,and the preparation of high-entropy alloy nanomaterials and their applications in energy storage,catalysis,and other fields are still less explored.In order to further develop new energy utilization and energy storage technology,it is of great significance to synthesize more efficient and economical materials and explore the theoretical mechanism of energy utilization.Therefore,the electronic structure of high-entropy alloys and their applications in energy fields deserve further study.In this study,from both the experimental and theoretical perspectives,by developing a simple and controllable synthesis technique to prepare homogeneous HEA nanoparticles,combined with advanced characterization techniques,the influencing factors of the physical and chemical properties of HEA in energy storage and catalysis were analyzed.Based on theoretical modeling,the electronic structure properties of HEAs and the mechanism of action of HEAs properties were discussed in depth.The research mainly includes the following five aspects:（1）Developing the preparation technology of high-entropy alloy nanomaterials.High-entropy alloy nanocomposites were prepared by carbothermal shock method,pyrolysis reduction method and rapid heating and cooling method,respectively.Carbothermal shock method:The oriented nanofibers are prepared by electrospinning technology with polyacrylonitrile as precursor,and then the oriented carbon fiber substrate is obtained by pre-stabilization and carbonization.After adding the mixed solution of different metal chlorides to the carbon nanofiber substrate.The prepared high-entropy alloy nanoparticles have particle diameters around20 nm and good uniformity.Pyrolysis reduction method:High-entropy alloy nanoparticles supported on amorphous carbon were prepared by pyrolysis and hydrogen reduction of a mixture of guanine and nitrate.Quickly heating and cooling method:High-entropy alloy nanoparticles supported on biomass carbon were prepared by rapid heating and rapid cooling.Firstly,nitrogen-rich biomass porous carbon was obtained after carbonization and activation of waste biomass corks.And high-entropy alloy nanoparticles with good particle size uniformity and controllable were prepared on the biomass carbon.（2）Exploring the electronic structure shift phenomenon of high-entropy alloys.HEA nanoparticles were synthesized on two different carbon substrates by carbon thermal shock and in situ reduction methods.The relationship between the positive and negative displacement of the core energy level and the change of electron density for each component of the quinary high-entropy alloy was studied by using X-ray photoelectron spectroscopy analysis and first-principles electronic structure calculation.Among them,the core level shift of copper is negative,while the core level shifts of iron,cobalt,magnesium,chromium and manganese were positive.Combining the experimental data and the Bader charge calculation results,it is found that the core level shift phenomenon of these elements originates from the charge transfer between atoms.In addition,although experiments show that the core level shift of nickel is obviously positive,the density of states calculation analysis shows that this is caused by the shift of the Fermi level.The results show that the electron density redistribution in the alloy occurs between different electronegative elements,and the electron transfer between different elements leads to the change of the electronic structure in the alloy.This has important implications for guiding the design of high-entropy alloys and expanding their potential applications in mechanics,medicine,catalysis,and energy storage and energy conversion.（3）Exploring the application of high-entropy alloys in supercapacitors.Usually,heterojunction nanoparticles/carbonaceous nanomaterials could promote mass transfer and charge transfer at the electrode/electrolyte interface,and thus have excellent performance in supercapacitor energy storage.However,the application of high-entropy alloy nanoparticle materials in supercapacitors has hardly been reported.This study is the first to synthesize uniform high-entropy alloy nanoparticles on super-aligned electrospun carbon nanofibers by the carbon thermal shock method.The key to this method is to couple the alignment direction of the oriented carbon nanofibers with the appropriate CTS current direction,where the current direction along the direction of the fiber is more conducive to the formation of high-entropy alloys.For the electrochemical performance,the Fe Ni Co Mn Mg HEA-NPs/ACNFs electrode with a metal chloride salt solution concentration of 5 m M exhibited a high capacitance of 203 F/g and a specific energy density of21.7 Wh/kg.The HEA-NPs/ACNFs still have good charge-discharge efficiency after 2000 cycles.Combined with the microstructure characterization results after the experiment,the high-entropy alloy nanoparticle composite carbon fiber material has excellent stability.These findings provide important references and guidance for HEA-NPs/carbonaceous nanomaterials as energy storage applications.（4）Exploring the application of high-entropy alloys in water-splitting for hydrogen production.Noble metals have played an important role in the oxygen evolution reaction due to their excellent properties and stability.However,the high cost of materials limits the application of noble metal catalysts.The development of high-entropy alloy materials provides us with a feasible way to combine high performance with low cost,by tuning the electronic structure of electrocatalysts to obtain excellent electrocatalysts for efficient oxygen evolution reactions.Therefore,ruthenium-containing high-entropy alloy nanoparticles were synthesized on carbon nanofibers.Among them,Ru_0.2@CNFs exhibited the best catalytic oxygen evolution reaction performance and extraordinary stability for 1000 cycles.In addition,the density of states and d-band centers were analyzed by theoretical modeling and computational analysis of high-entropy alloys,indicating that Ru_0.2@CNFs have excellent electrocatalytic potential,which may benefit from the high-entropy effect leading to stronger electronic interactions between atoms effect.The maximum configurational entropy of Ru_0.2 HEAs reasonably explains the remarkable stability of OER electrocatalysis.In addition,the adsorption energy results between the high-entropy alloys and the reactants indicate that there are abundant active sites on the surfaces of the high-entropy alloys.Therefore,the high-entropy alloy composites can be used as potential low noble metal nanocatalysts in practical applications.（5）Exploring the application of high-entropy alloys in biomass pyrolysis for hydrogen production.Biomass is the most widespread and available renewable energy,with huge development value and application potential.The use of biomass pyrolysis and gasification to produce hydrogen is a high-potential and economically viable hydrogen production technology.In this study,a simple in situ reduction method was used to synthesize nickel-rich medium-entropy alloy nanoparticles on nitrogen-oxygen co-doped carbon supports.The prepared face-centered cubic Ni Ce La Fe Co medium-entropy alloy nanoparticles have nanometer size（average particle size of 21.1 nm）and medium mixing entropy（1.31 R）.To expand the application of MEA nanoparticles,we performed toluene cracking experiments on toluene conversion and hydrogen generation.The catalyst loaded with Ni-rich（～55.26%）MEA nanoparticles exhibited high catalytic performance（over 80%toluene conversion and 7293 ppm hydrogen yield）at 500°C for 2 h.In the steam reforming reaction,the Ni-rich Ni Ce La Fe Co catalyst has very good catalytic performance at a low temperature of 400°C（the conversion rate of toluene reaches 99%and the hydrogen yield is 78960 ppm）,and the steam reforming has a good effect on carbon deposition.inhibition.This study provides a simple and convenient method for the synthesis of functionalized carbon-based multicomponent alloy nanoparticles and shows their excellent catalytic performance in toluene cracking and hydrogen production.