Key Material Study And Numerical Simulation For Anode-Supported Intermediate Temperature Solid Oxide Fuel Cells

Fuel cells have drawn much attention of human beings due to its high efficientin energy conversion and environmental friendship. Intermediate Temperature SolidOxide Fuel Cells (IT-SOFC) is a kind of promising fuel cell technique. To realize anIT-SOFC, one effective way is to use new electrolytes with higher conductivity andthiner thickness. Planar structure with anode supported is the popular design modefor IT-SOFCs. This thesis aims at the development with DCO electrolytes, focusesmainly on the preparation of thin electrolyte films, anode supports, as well as thePEN multilayers, and tries to reveal the relationship among material compositions,microstructures, process parameters and properties of IT-SOFC components.The first step of cell assembly preparation is the. preparation of compositelydoped oxide nanopowders. In the paper three different methods of synthesizingprocedure of Sm_0.15Gd_0.05Ce_0.8O_1.9 particles have been made detailed discussion. Theeffects of sintering temperature, preparation methods, the species of organic chelates,and the total cation ions on the performance of SGDC powders were investigated.The results show that the performance of particles obtained by Glycine-NitrateProcess (GNP)is superior to that using pechini method under the same operatingconditions. The former method can achieve an improved monodispersed spheres. It isnoted that the shape and size of the particles are various such as needle, spindle andsphere when the powders were prepared under different conditions, which wasobtained by TEM and SEM. The sintering ability of the powder by wet-chemicalmethod is so good that the relative density of the pressed pellet sintered at 1400℃exceed 98ï¼…. The relative density of the SGDC samples prepared by solid phasereaction method is more than 96ï¼…at 1600℃. The relative density becomes higher,the sintering ability becomes better, and the porosity reduces with the decreasing ofthe total cation ions concentration.Perovskite-type La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode and NiO/GDC anodesupport were synthesized using the glycine-nitrate process (GNP) and the pechinimethod. The property and process of perovskite phase in LSCF material, themicrostructure, the sintering performance of the anode and cathode were investigated.The influences of the synthesis method, the starting powder and the sinteringtemperature on crystallization and the catalytic activity of electrode have beenstudied. The results indicate that the single phase of LSCF perovskite can beobtained at 650℃. The fine grains and crystallinity of cathode is obtained by milling the starting LSCF powder for 3h. LSCF cathode showed a worse catalytic activity asits sintering temperature increases. The finer microstructure and higher surface areafor O₂ reduction reaction is observed in LSCF cathode sintered at 1000℃. Thecrystal phase and size of the NiO/GDC anode are various with the different NiOdoped modes. The sintering shrinkage of NiO/GDC anode supports green tapesascend and the porosity of NiO/GDC anode supports decline with the increasing ofNiO contents.The anode support with the amylum of 5ï¼…mass fraction possess thebest porosity performance. The better crystal size could be obtained after effectivedispersion measures taken.Gd_0.2Ce_0.8O_1.9, Sm_0.2Ce_0.8O_1.9 and Sm_0.15Gd_0.05Ce_0.8O_1.9 thin DCO films werecoated on the anode supports by screen printing and spin coating methods. Theeffects of dispersion technique, preparation methods of thin electrolyte films, particlesize and distribution, and the sintering mode on the electrolyte performance wereinvestigated. The results show that the densification temperature of electrolytesamples preparated by spin coating method is siginificantly lower than that obtainedby screen printing technique. The SGDC samples with dry ball-milling dispersionmode exhibit the highest sintered density at the same temperature. The "sandwich"sintering technique used is efficient for making good electrolyte membrances.Among three different DCO electrolytes, GDC possess the highest sintering kinetics,the closest electrolyte thin membrance, and the best microstruce. Interaction will beoccurred between GDC and YSZ, if the operating temperature reached 1300℃.Thestudies indicate that agglomeration retards densification in the stage of sintering. Thepowders with better dispersion exhibit a higher sintered density at the sametemperature. After effective dispersion measures taken, SGDC can fully dense at thesintering temperature of 1300℃.A three-dimensional mathematical model of an anode-supported planarIT-SOFC, with pure hydrogen as fuel and air as oxidant, has been developed bycoupling the velocity field, the species concentration field, the pressure field and thecurrent density field with one-another. An analysis to the effects of the systemparameters (operating pressure, temperature, fuel concentration, porosity, tortuosity,and the species of oxidant) on the system performance is performed. Results showthat the performance curves predicted by this numerical modeling agreed well withthe published experimental data. The performance of an anode-supported fuel cell issuperior to that using cathode or electrolyte as the support under the same operatingconditions. The former can achieve an improved operating range of current density and the electric potential. The model results could provide some fundamentalguidelines for the design and operation optimization of anode-supported planarIT-SOFCs.