Controlled Synthesis And Electrochemical Performance Of MIL-88A（Fe）microrods Modified By Heteropoly Acids

With the growing global energy crisis and environmental pollution,development and application of energy technologies has aroused widespread concern around the world.Polyoxometalates（abbreviated as POMs）are a class of anionic metal clusters formed by connecting the highest valence transition metals（such as Mo,W,and V,etc.）with oxygen.POMs have many advantages,such as excellent thermodynamic and chemical stability,reversible redox,controllable size and precise structure.Therefore,the excellent properties of POMs in the fields of photocatalysis,electrochemistry and energy have attracted extensive attention in the fields of coordination chemistry and materials science.However,POMs are easily soluble in the electrolyte,poor conductivity,uneven dispersion and easy agglomeration and crystallization,etc.,which lead to poor cycle stability and rate performance when used as electrode materials,and limit the further development of POMs as electrode materials.Therefore,realizing the uniform and firm load of POMs and simultaneously improving the conductivity,specific surface area and porosity of POMs-based electrode materials is of great significance for the research of POMs in the electrochemical field.Therefore,in this paper,the classic Keggin-type and Dawson-type polyacids are used as the research object,and the hydrothermal synthesis method is used to use POMs that can carry out reversible multi-electron transfer and easy functionalization,and further combine them with metal organic framework materials（MOFs）phase recombination.Later,we also studied the application of these POMs-based composite materials in electrochemical hydrogen evolution and energy storage.The specific work is as follows:1.We propose a new method to synthesize Pt-POMFe electrocatalyst by anchoring POMs and Pt NPs on the surface of MIL-88A（Fe）.Due to the layered structure and the presence of POMs and Pt NPs,the charge transfer efficiency and catalytic reactivity are greatly improved.The prepared catalyst（0.30 wt%of Pt loading）showed excellent HER performance,long-term electrochemical stability and reproducibility of up to 1000 potential sweeps,which was comparable to commercial Pt/C catalysts.2.By optimizing the carbonization temperature,we successfully synthesized hollow porous capsule shell materials with P₂W₁₈,Fe₃O₄ and C components.The solid carbon shell is beneficial to improve the conductivity of sulfur cathode material,and the rich porous structure can enhance the diffusion and transfer kinetics of lithium ion.In addition,the porous structure of carbon shell can be used to reduce the volume expansion of sulfur particles in the process of lithium and lithium removal,so as to maintain the structural stability.In addition,P₂W₁₈ has strong chemical bond and effective catalytic activity for polysulfides（LiPSs）,which can promote the kinetics of LiPSs redox reaction and inhibit the"shuttle effect"of LiPSs.Therefore,The positive electrode has high reversible capacity,excellent rate performance and long cycle stability.3.A kind of hollow carbon shell material was prepared to load selenium.The excellent electronic conductivity of hollow carbon shell and the fast ion transfer rate of multi acid can significantly improve the electrochemical performance of lithium selenium battery.When used as selenium host,it can limit the reaction area of selenium in the battery cycle,reduce the probability of multi selenide dissolving into the electrolyte,and inhibit the"shuttle effect",At the same time,the gap in the capsule shell can effectively alleviate the volume change of sulfur cathode in the process of lithium removal,and ensure a higher selenium load.The results show that the composite materials have excellent specific capacity and cycle stability in ether electrolyte.