Electrochemical Preparation Of Spinel Coatings With Metallic Connectors And Their High Temperature Properties

Solid oxide fuel cells have high energy conversion rate and are friendly to environment,so they have a good development prospect.However,at high temperature,Cr element in ferritic stainless steel connector is easy to diffuse outward,resulting in"cathodic poisoning",and ferrite at high temperature oxidation resistance is poor.Therefore,spinel coating on the surface of stainless steel will be an effective improvement scheme.In order to protect SOFC from chromium poisoning and reduce surface specific resistance(ASR),Cu-Mn,Ni-Mn and Cu-Ni composite coatings were prepared on the surface of ferritic stainless steel by direct current electrodeposition method.These three coatings were oxidized at 750°C for 100h,300h and 500h,respectively.The surface composition and phase of the thermal growth coating were analyzed,and its high temperature oxidation resistance and electrical properties were also studied.After 100h,300h and 500h oxidation of Cu Mn composite coating at 750°C,the oxidation products are Mn2O3,Mn3O4,CuMn₂O₄ and Cu O.CuMn₂O₄ spinel coating can effectively prevent the internal diffusion of O2 and external diffusion of Cr at high temperature,showing excellent oxidation resistance at high temperature.The high temperature conductivity of CuMn₂O₄ spinel coating was tested by four probe surface specific resistance(ASR)test.The results show that the Cu1Mn1 composite coating oxidized for 500h after holding at 800°C has a stable ASR value of 83.44 m?·cm^-2,which has excellent high temperature conductivity and oxidation resistance.After Ni-Mn and Ni-Mn-Ni-Mn composite coatings were oxidized at 750°C for 100h,300h and 500h,the two composite coatings produced the same oxidation products,mainly NiMn₂O₄,Ni O,Mn2O3 and Fe oxides.The two kinds of oxidation coatings can inhibit the external diffusion of Cr element and have good high temperature oxidation resistance.After500h of oxidation,the ASR value of Ni-Mn coating measured at 800°C is 1294.25 m?·cm^-2,showing poor conductivity.However,the four-layer structure of the coating can fully diffuse in the oxidation process,and the electrical conductivity is relatively good.After 500h of Ni-Mn-Ni-Mn oxidation,the stable ASR value of 800°C is 129.45 m?·cm^-2,which is better than that of the Ni-Mn coating.When Cu-Ni and Cu-Ni-Cu-Ni coatings were oxidized at 750°C for 100h,300h and500h,the oxidation products were mainly NiO and CuO.The coating can inhibit the external diffusion of Cr element after oxidation,but Cu and Ni can not react with each other to form spinel oxide in the oxidation process.Therefore,the ASR of Cu-Ni coating and Cu-Ni-Cu-Ni coating after 500h of oxidation at 800°C is very large,which are 827.91m?·cm^-2 and 1059.41 m?·cm^-2 respectively,and have poor conductivity at high temperature.In summary,it is found that Cu-Mn coating will produce CuMn₂O₄ spinel structure with excellent electrical conductivity after long time high temperature oxidation,which improves the high temperature electrical conductivity and high temperature oxidation resistance of the coating.Although the oxidation products of Ni-Mn coating have good oxidation resistance,less spinel is generated due to the easy diffusion of Ni in the oxidation process,and the electrical conductivity of NiMn₂O₄ spinel is inferior to that of CuMn₂O₄,so the surface specific resistance value is very large.Cu-Ni structure coating is because it can not form spinel after oxidation,the natural surface specific resistance is relatively high.Therefore,Cu-Mn structure is superior to Ni-Mn and Cu-Ni structure.