Preparation And Electrochemical Properties Of Porous High Entropy Compounds

Supercapacitors are highly efficient charging and discharging devices that are different from secondary batteries.They have the advantages of long cycle life,fast charging and discharging rates and high power density.Among them,pseudocapacitors are widely studied due to their high theoretical specific capacitance and high stability.The electrode material determines the overall performance of the pseudocapacitors.High entropy compounds are the new type of stable energy storage material and have good prospects for application in pseudocapacitor.However,current solutions for the preparation of high entropy compounds have shortcomings,such as high costs,high risks,complex operations and poor morphological control.Therefore,in this thesis,author use dealloying combined with different post-treatment schemes to prepare high entropy compounds with porous structures,and investigate the effects of dealloying schemes and post-treatment means on their properties,to provide new ideas for the controllable preparation of high entropy compounds.The specific studies and findings are as follows:（1）The aluminium-based Fe-Cr-Mn-Ni-Co alloy materials were prepared using arc melting and spin quenching techniques,followed by dealloying at different concentrations and time conditions,and then analysing the influence of the two-dimensional dealloying parameters on the microscopic morphology and testing the electrochemical properties of the materials.It was found that the high-entropy system has obvious self-coarsing,with the 3M-2h,2M-5h and 1M-18h materials having larger specific surface areas.The low concentration and long time favours the formation of fine structures,reaching a specific capacitance of 285.97 F/g and a voltage window of 0.6 V at 1 A/g.The short dealloying time allows the precursor material to exhibit excellent multiplicity,and the 3M-2h not only has a rich morphological structure but also has stability at high currents,resulting in an optimal overall performance.（2）The porous high-entropy oxide（FeCoNiCrMn）₃O₄ was prepared by a scheme of dealloying and high-temperature oxidation,with the uniform distribution of elements,the standard spinel structure and the specific surface area of 202.9 m²/g.Electrochemical tests show that the material properties decrease and then increase with increasing temperature,but the voltage window continues to decrease.900℃ is the optimum post-treatment temperature and the material has a high specific capacitance（639 F/g at 1 A/g）,and high multiplicity（80.77%at 10 A/g）,low internal resistance and good cycling characteristics（73.8%after 1000 cycles）.By comparing CoCr₂O₄ with the same structure,（FeCoNiCrMn）₃O₄ was found to have higher electrochemical properties.Density Functional Theory（DFT）calculations revealed that multiple elements work together to bridge the energy band gap,making the material conducive to electron transport,thus confirming that high entropy materials are more conducive to energy storage.（3）High entropy compound precursors were treated by the sulphidation scheme to successfully introduce sulphur into the high entropy crystal.High entropy compounds containing high entropy sulphides were prepared.The physical phase analysis of the material revealed that this material is a mixture of high entropy sulphides and high entropy oxides（HESs&HEOs）.Electrochemical tests showed that the material has the specific capacitance of 648.4 F/g（current density 1 A/g）,maintains rate capability of 65.2%at 10 A/g and stability of 85.6%after 1000 cycles.The product was paired with reduced graphene oxide（r GO）to assemble an asymmetric supercapacitor with a voltage window of 1.6 V and an energy density of 32.2 Wh/kg,and a power density of 802.4W/kg at this point,with a capacitance retention of 83.9%after 3000 cycles.This thesis contains 39 figures,4 tables and 140 references.