Preparation And Characterization SDC Electrolyte And NiO-SDC Anode Materials For SOFC

A great attention has been paid on Solid Oxide Fuel Cell (SOFC) including solid anode, cathode and electrolyte for the advantages of high efficiency, clean, economic, and safety. SOFCs operated under lower than 800℃ are in prevail nowadays. Rare earth oxide doped ceria is a very promising material for the electrolytes of the low temperature SOFC, because it exhibits high oxide ion conductivity at low temperature. Among them, the Sm₂O₃ doped CeO₂ (SDC) system shows the great potential. High density and large grain size are demanded when SDC ceramics are used as electrolytes of SOFCs. However, as anode of SOFCs, a microstructure with porous and homogeneous distributions of Ni and SDC is desired of Ni-SDC cermet. It is well known that morphology, size and distribution of powders show effect on the sintering properties of ceramics. The powders with spherical and 50nm⁰.5μm in size are better for sintering of ceramics.Spray pyrolysis has advantages in preparing spherical powders whose particle size and distribution can be controlled by the process parameters. The process is simple and can satisfy the demand of industrialization. Thus, Spray pyrolysis is a suitable and effective technology when applied to prepare the SDC electrolyte and NiO-SDC anode powders.In this essay, Two spray solutions were prepared. NH₄HCO₃ was used as precipitation reagent in one spray solution (AHC) and (NH₄)₂CO₃ was used in the other (AC). XRD, SEM, TEM and TG-DTA were used to characterize the composition, morphology, grain size, and the density of the SDC ceramics. The results suggested that:1 Morphology and crystallinity of spray pyrolysis derived powders from two series were different caused by the difference in spray solutions. The powders by AHC showed flakiness in morphology and had the phase of Ce₂(CO₃)₃ 6H₂O. Another powders by AC were spherical and amorphous.2, SDC electrolyte powders were different in morphology from spray pyrolysis derived powders after calcinations. Flakiness morphology was remained in powdersprepared by AHC, and the sizes were about 3-5 um. The fine particles of the powders by AC agglomerated a little with open structures, and the agglomerates were about 0.5u,m in size. The differences were caused by the pH and the concentration of CO32' in two spray solutions.3^The densification and grain growth of the SDC ceramics were depended by the morphology of SDC electrolyte powders. The relative density and average grain size of SDC ceramics by AHC sintered at 1350°C for 4h were only about 80% and 0.5\im. The SDC electrolyte powders by AC calcined at 700°C can be sintered up to 94% of the theoretical under a low temperature of 1250°C, and the average grain size of ceramics was 0.86um.Generally speaking, the densification and grain growth of the SDC electrolyte ceramics were affected by the spray solution. The SDC ceramics by AC were believed to be suitable to utilize in preparing the high performance electrolytes of SOFCs.In this essay, two spray solutions were prepared. One was the mixture of Ni sols and Ce-Sm solution, and the other was of Ni solution and Ce-Sm sols. The process of preparing NiO-SDC anode powders was also investigated.1 > The particles size of NiO-SDC anode powders increased with the concentration of the spray colloidal solutions.2> The growth of NiO was easier than SDC. When NiO acted as nucleus, the crystallinities of two phases were close. The growth of NiO was much better than SDC when SDC acted as nucleus, although growth of two phases were not balanced, which result in the increase of the particle size. The reason was that the sols in colloidal solutions were acted as nucleus, which could control the growth of sol particle.3^ The NiO-SDC anode powders by Ni sols had primary particles of 30nm, aggregates of 250nm, narrow sizes distribution, balanced growth of two phases, and homogeneous phases distribution. The powders would be suitable to prepare the high performance anodes of SOFCs.