Study On Preparation And Properties Of Anode Materials For IT-SOFC

The preparation and properties of Ni-YSZ anode materials were studied in this paper. The multilayer anode-supported composite SOFC anode substrates were prepared by the tape-casting method. The aim of this study is to make the base for reducing the operating temperature.It was shown that the production efficiency of precipitation method using NH4HCO3 as a precipitant was high and the technology of NiO powders prepared by the oxidation of Ni metal was simple. The electrical conductivities of the Ni-YSZ cermet prepared by these two methods were 0.7 and 1.4 orders of magnitude less than that prepared by the precipitation method, using NH3(H2O as precipitant. Thus the precipitation method, using NH3(H2O as precipitant was chosen for preparing NiO powders. In order to raise the production efficiency, the pH value was controlled strictly. YSZ powders were obtained by the co-precipitation method, controlling the pH at 8.2. NH3(H2O was used as co-precipitant. The powder was calcined at 600(C in air for 1h to obtain the YSZ powder with the average particle size around 20nm. NiO-YSZ powders were prepared by the mechanical mixing method, coating precipitation method and the combustion synthesis method respectively. In the first route, NiO and YSZ were ball-milled in alcohol for 48h to obtain the homogeneous powders. The NiO-YSZ powders, which were prepared by the coating precipitation method, were calcined at 600(C and 800(C. NH3(H2O was used as co-precipitant, controlling the pH at 8.5~9.0. It is obvious that the two phases were well crystallized at 600℃. The particle size of the powder is about 20nm. Redox combustion reaction between metal nitrate and citric acid yielded ultrafine NiO-YSZ powders. When the c/n initial molar ratio was less than and close to the stoichiometric value 0.54, the combustion progressing of Sample C (c/n＝0.5) was the most intensive. Through the XRD patterns and TG and DSC analysis of synthesized sample C powder, the Ni phase was discovered. Because the c/n initial molar ratio of Sample A is minor, the combustion progress was slow. Also there was no reducing atmosphere. Ni phase was not discovered in Sample A.The density of the NiO-YSZ composite sintered at different temperatures and Ni-YSZ cermet was measured via the Archimedes method. Considering the influence of the sintering temperature on the anode material performance, the rational sintering system was 1400(C for 2h. The sintered NiO-YSZ composite was reduced at 800(C in H2 atmosphere for 4h into Ni-YSZ cermet entirely. The microstructure of the samples was investigated. The YSZ phases formed a continuous network while the Ni particles and pores were uniformly dispersed in the network.The influencing factors on the electrical conductivity of the Ni-YSZ cermet were considered. It was found that: 1) the electrical conductivity increased nearly linear with the elevation of the sintering temperature. The electrical conductivity reached above 103.4 S/cm for the sample sintered at 1400(C for 2h when testing from 600(C to 800(C. 2) the different technologies resulted in the different properties of the NiO powders, and then resulted in the difference of the electrical conductivity. 3) The electrical conductivity increased firstly then decreased with the c/n increasing during the combustion synthesis. The electrical conductivity of Sample C, whose c/n was 0.5, reached above 103.6 S/cm. 4) The electrical conductivity of the Ni-YSZ cermet prepared by the combustion synthesis method was 0.2 and 0.6 order of magnitude higher than that prepared by the mechanical mixing method and the coating precipitation method respectively.In order to optimize the anode microstructure and improve the anode performances, the multilayer composite anode films and the electrolyte films were prepared by the tape-casting method. The anode-supported composite SOFC anode substrates were obtained by co-sintering. The single layer anodes used the Ni/YSZ=55: 45 cermet. The double layer anodes consist of the interfacial layer and bulk layer. As the interfacial layer,...