Fabrication Of Anode Functional Layer And Thin Film Electrolyte For Low-intermediate Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells?SOFCs?are electric energy generating devices that directly convert the chemical energy of fuel and oxides into electric energy.It has many advantages such as high energy conversion rate,no harmful products and convenient operation.For traditional solid oxide fuel cells,high operating temperature limits their production and utilization.Therefore,low and intermidiate temperature solid oxide fuel cells?400-800??have become the focus of research about SOFCs in recent years.At present,there are two main technical routes to make SOFCs work at low and intermidiate temperature:one is to reduce the thickness of electrolyte.The other is to develop new materials of electrolyte with high conductivity of oxygen ions at low and intermidiate temperature.In this thesis,the thin electrolyte is prepared by RF magnetron sputtering.The electrolyte material is apatite lanthanum silicate(La₁₀Si₆Mg_0.2O_26.8)with relative high conductivity of oxygen ions at low and intermidiate temperature.In this paper,apatite lanthanum silicate powder is prepared by sol-gel method.Apatite lanthanum silicate and nickel oxide?NiO?composite anode is prepared by dry pressing.The anode functional layers are prepared by screen printing,and the apatite lanthanum silicate electrolyte is prepared by RF magnetron sputtering.The dense electrolyte can not be prepared on the original porous anode substrate.Therefore,an anode functional layer of high flatness and small pore size is introduced to the interface between the electrolyte layer and the anode substrate.The powder of screen printing paste?the powder of anode functional layer?is La₁₀Si_5.8Mg_0.2O_26.8:NiO=4:6 mixed powder.The binder is ethyl cellulose and the solvent is terpineol.The ratio of anode functional layers powder to solvent is kept at 3:2 and the content of binder is 12.5%.In this paper,the effect of physical volatilization,decomposition and auto-ignition of terpineol and decomposition and auto-ignition of ethyl cellulose on the morphology of functional layer is investigated.The effect of substrates on the morphologies of sputtered electrolyte film,annealed and sintered electrolyte films is investigated.The surface morphologies of anode functional layers and electrolyte film are observed by scanning electron microscope?SEM?.The phases of anode functional layers and electrolyte film are characterized by X-ray diffraction?XRD?.The slurry of anode functional layers is analyzed by differential scanning calorimetry?DSC?,thermogravimetric analysis?TGA?and infrared absorption spectroscopy.The results of these analysises above provide the basis for establishing heat treatment processes of functional layer.Isothermal treatment processes of anode functional layers are formulated according the the results of these analysises.The porosity of anode functional layers is measured by image method.The experimental results show that the anode functional layers with maximum pore size of 1?m and porosity of 16%can be obtained after isothermal treatment.The apatite lanthanum silicate electrolyte is prepared by RF magnetron sputtering on the anode substrate and the anode functional layers with a maximum pore size of 2?m.The sputtering pressure is 0.9 Pa and the sputtering power is 80 W.The experimental results show that the sputtered dense film whose thickness is 5.2-6.0?m can be prepared on the anode substrate,and there are cracks in the electrolyte film after being annealed at 1100?,and after being sintered at 1500?,the cracks are eliminated,but the pore appear,and the thickness of the film is 4.4-4.9 um.The electrolyte film with a few cracks alone grain boundaries can be prepared on the functional layer with a maximum pore size of 2?m after being annealed at1100?,and after being sintered at 1500?,the cracks are eliminated,but the pore appear.