Study On Electrical Properties And Optimization Of Samarium Doped Ceria-carbonate Composite Electrolyte

In order to improve electrical properties of samarium doped ceria-carbonate, three new types of composite electrolyte materials are synthesized in this work through optimization of SDC-carbonate. XRD, SEM, TG-DTA, EIS and D.C. four-probe techniques were applied to characterize the microstructure, morphology and electrical performance of new materials.In chapter2, Ce0.8Sm0.15Sr0.05O2-δ(SSDC) and SSDC/Na2CO3(NaSSDC) powders were prepared by coprecipitation technique using sodium carbonate as precipitant. The effects of calcination temperature of precursors on the conductivity of the composite electrolytes were examined. The conductivities of SSDC and NaSSDC were compared through EIS and D.C. four-probe method. SSDC and NaSSDC diffraction patterns are same as those of the pure ceria, Na2CO3is amorphously distributed. The results showed that the highest conductivity was obtained after sintered at800oC. Sodium carbonate not only promotes O2-and H+conduction, but also suppresses the electronic conduction.In chapter3, Ce0.78Sm0.2Sr0.02O2-δ(SSDC) powders were synthesized through oxalate coprecipitation route. Then30wt%binary eutectic salt ((Li0.52Na0.48)2CO3) was added to form SSDC-30LN composite electrolyte. SDC and SDC-30LN powders were prepared by the same method for comparison. The O2-and H+conductivities were compared by D.C. four-probe technique. The results showed that SDC, SDC-30LN, SSDC and SSDC-30LN all have cubic fluorite-type structure, no extra peaks were observed. Co-doping technique enhances the amount of oxygen vacancies, decreases the activation energy of SDC and facilitates O2-conduction. Carbonate phase improves both H+and O2-conductivities. The interface between carbonate and ceria can promote the H+conduction. What’s more, a single fuel cell based on SSDC-30LN composite electrolyte was fabricated with a tri-layer co-pressing technique, using NiO as anode and LiNiO2as cathode. The performance of the fuel cell was investigated at500~650oC. The effect of CO2supply in cathode side on performance of cell was also studied.In chapter4, Er0.4Bi1.6O3(ESB) was prepared through solid state reaction route, and SDC was synthesized by oxalate coprecipitation method. Then ESB-SDC-LN composite electrolytes with different composition were formed by mixing oxides method. Composite electrolytes retains fluorite structure, and there are no reactions among SDC, ESB and carbonate. The influences of the amount of ESB and carbonate on H+and O2-conductivities were respectively studied by D.C. four probe method. SEM showed that the distribution of the two phases increased with the decrease of the amount of the carbonate. The H+and O2-conduction enhanced with the increase of carbonate or ESB, which indicated that carbonate favored H+and O2-conduction, ESB benefited O2-conductivity, and the interface of two phases improved H+conduction.