Fabrication Of La₁₀Si_5.8Mg_0.2O_26.8 Electrolytes And Their Supporting Anodes

As clean and efficient power generation devices, solid oxide fuel cells (SOFCs) enable the direct conversion of the chemical energy which stored in the fuel (such as H2、CH4、and gas)into electrical energy through oxidation reaction in anode and through reduction reaction in the cathode(such as O2in the air into O--).Apatite-type lanthanum silicates have been considered promising candidates due their high oxide ionic conductivities, low activation energy, low thermal expansion coefficient, high chemical stability and good oxide ionic conductor in a wide range of oxygen partial pressure at moderate temperatures. This paper reports on fabrication of apatite-type lanthanum silicate La10Si5.8Mg0.2O26.8electrolyte films by RF-magnetron sputtering and the impact of gas pressure on the structures of the films. XRD, SEM, EPMA and Surface Profiler are used to characterize the phase, surface morphology, composition and thickness of the films respectively. The best experimental parameters are:pressure:1.4Pa; annealing temperature:1100℃; annealing time:6h; substrate temperature:room temperature; power supply:80W. The La10Si5.8Mg0.2O26.g film on the porous composite anode (anode-10) substrate can get apatite phase before and after annealing.SOFCs mainly include four important components which are anode, electrolyte, cathode and interconnecting materials. Anode which provides position for electrochemical oxidation affects the rate of energy conversion. Nanosized La10Si5.8Mg0.2O26.8powder was prepared through Sol-Gel method by using citric acid and nitrates in this thesis. The powder was mixed with different amount of NiO and starch, NH4HCO3as pore-forming agent. Porous composite anodes of Ni/La10Si5.8Mg0.2O26.8were fabricated through sintering at1400℃and then being reduced in H2atmosphere at600℃. Phases, surface morphology and porosity of the samples were characterized by XRD, FE-SEM and Archimedes method, respectively. Resistance of the anodes at room temperature was determined by ac impedance spectroscopy. The results show that the prepared Ni/La10Si5.8Mg0.2O26.8porous composite anodes are micro-crack free and the mean thermal expansion coefficient before reduction is10.7×10-6K-1.Considering all these characteristics including phases, surface morphology, porosity and resistance, the anode made with the pore-forming agent in amount of30wt%NH4HCO3is the best.