Study Of The CoCu/Mn Co-Deposition Behaviour And Its High Temperature Oxidation And Electrical Performance

The Solid Oxide Fuel Cell（SOFC）is an environmentally friendly type of battery.Ferritic stainless steel is often used as the terminal body material,but in the high-temperature oxidizing working environment,the Cr element in ferritic stainless steel is easily diffused to the outside to cause"cathodic poisoning",reducing the performance of the battery.In order to reduce"cathodic toxicity",this thesis prepares CoCu co-deposited alloy layers and CoCu/Mn composite coatings on the surface of ferritic stainless steel by DC electrodeposition to reduce the external diffusion of Cr,improve the high-temperature oxidation resistance of stainless steel and reduce the surface resistivity.Firstly,the influence of process parameters on the co-deposition behaviour of the alloy is investigated.The main parameters selected are:complexing agent content,solution pH,current density,deposition time,etc.Based on L43 orthogonal optimisation experiments,a set of stable process solutions was generalised.The effects of different complexing agent contents and pH values on the co-deposited CoCu alloy layers were comparatively investigated by cyclic voltammetry with the aim of determining the optimum configuration of the CoCu co-deposition solution and producing coatings with uniform thickness and appropriate concentration distributions of Co and Cu.After determining the optimum parameters for CoCu co-deposition and CoCu/Mn layer deposition,the high temperature performance and electrical properties of the oxide coatings were generated after the research design coatings were thermally grown for 10h and 100h at the fuel cell operating temperature（750°C）.The main conclusions are as follows:（1）Study of the effect of complexing agents on the co-deposition behaviour using cyclic voltammetric curves.Sodium citrate（Na C₆H₅O₇·2H₂O）was used as a complexing agent to provide the ligand（C₅H₇O₅COO）^-and to form a copper citrate[Cu（C₅H₇O₅COO）]⁺coordination compound with Cu,which adsorbed on the cathode surface and increased the cathodic polarisation.The best CoCu co-deposition was achieved when the sodium citrate content in the solution was 30 g·l^-1,but the presence of excess sodium citrate led to strong hydrogen precipitation,while Co^2-was also complexed and the solution became less stable,with precipitation occurring,reducing the stability of the alloy co-deposition solution.（2）The effect of pH variation on the CoCu co-deposition behaviour.When the pH of the solution was higher,the content of complexes at the cathode site increased and colloids were formed,which hindered the electrodeposition of Co²⁺in the cathode region.The optimum pH value of 3.5 was finally chosen as the plating solution parameter.Experimental data with and without boric acid as a pH buffer were analysed and it was found that the addition of boric acid shifted the CoCu co-deposition potential to the right（positive）and increased the peak current,thus promoting the co-deposition of CoCu.（3）The high-temperature oxidation and electrical properties of the CoCu co-deposited layer and the CoCu/Mn composite coating are different;the oxidation products of the CoCu co-deposited layer are Cu O,Co O and Fe₂O₃,while the oxidation products of the CoCu/Mn composite coating are Mn₃O₄and CuMn₂O₄ spinel.The CoCu/Mn composite coating forms a continuous and thin CuMn₂O₄ spinel layer after 100 h of oxidation with high spinel formation efficiency.In comparison between the CoCu layer and the CoCu/Mn composite coating,the ASR value of the CoCu co-deposited layer is 41.67 mΩ·cm^-2 and the ASR value of the CoCu/Mn composite coating is 38.39 mΩ·cm^-2 after 100 h oxidation at 750°C in air.