Preparation And Interfacial Reaction Of Spinel Type High Entropy Oxides For Interconnect Coating

Solid oxide fuel cells（SOFCs）are clean and efficient high-temperature fuel cells It shows a promising application prospect due to the advantages of not using precious metal catalyst,wide range of available fuel and high energy efficiency.The interconnect plays a vital role in the stability of the fuel cell stack.It used to connect the anode and cathode electrode materials,isolate the fuel and air,and conduct the current.Ferritic stainless steel is considered the most promising interconnect material.However,the Cr element in the ferritic stainless steel matrix is easily diffused and volatilized to the electrode,resulting in cathode poisoning.It is a simple,economical,and effective solution to applying a spinel coating to the interconnect.Spinel coatings have excellent high-temperature conductivity and a coefficient of thermal expansion that matches the material.However,there are still issues such as insufficient ability to prevent Cr outward diffusion and oxygen inward diffusion,as well as poor interface stability between the metal and the coating.In recent years,high-entropy materials have attracted widespread attention due to their excellent properties such as high-entropy effect,lattice distortion effect,hysteresis diffusion effect,and"cocktail"effect.This paper introduces the design method of high-entropy new materials into spinel coating materials.A series of chromium-free spinel-type high-entropy oxides were designed and synthesized from equimolar ratios to non-equimolar ratios,and their formation mechanism and single-phase formation ability were studied.The interface reaction between high-entropy spinel oxide materials and chromium oxide was studied using the diffusion couple method,and the resistance to Cr diffusion performance and mechanism were investigated.The main conclusions obtained are as follows:The Equimolar ratio high-entropy spinel（Mn Fe Co Ni Cu）₃O₄was synthesized using the solid-phase method.It was found that the rock salt structured Ni O and the Cu O with a chalcocite structure combined to form a rock salt phase structure under entropy-driven effects,making it unable to form a single-phase solid solution.By adjusting the cation ratio,single-phase non-equimolar high-entropy spinel(Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄could be obtained at 750°C.The phase composition,microstructure,valence state of elements,and conductivity of the two high-entropy spinels were characterized and analyzed.The element distribution was uniform,and there was no obvious segregation phenomenon.The conductivity of the non-equal molar ratio high-entropy spinel can reach 15.77 S·cm^-1at 800°C.Four kinds of spinel bulk materials,including equal molar ratio high-entropy spinel（Mn Fe Co Ni Cu）₃O₄,non-equal molar ratio high-entropy spinel(Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄,manganese-cobalt spinel（Mn Co₂O₄）,and quaternary spinel（Mn Fe Co Ni）₃O₄,were synthesized using the vacuum hot-press sintering and re-oxidation method.They were combined with Cr₂O₃to form diffusion couples,and the interface stability of each spinel material was studied by diffusion oxidation at 900°C.The results show that in both equimolar and non-equimolar high-entropy spinels,due to the fastest diffusion rate of copper,Cu and Co inside the high-entropy spinel diffuse outward to the surface of chromium oxide to form a copper-cobalt-chromium oxide reaction layer.The Quaternary spinel material without copper had the lowest thickness of the reaction layer with chromium oxide,which may be attributed to the synergistic effect of multiple elemental components.