Investigation On The Doping Of Electrolyte Of BaCeO₃-based Proton-Conducting Solid Oxide Fuel Cells

Solid oxide fuel cells（SOFCs） as a new power generation device has attracted worldwide attention because of its advantages over traditional energy conversion systems including high power conversion efficiency, excellent fuel adaptability,reliability, low pollutant levels, long operating life and so on. The traditional oxide-ion conductor SOFCs must work at high temperature, while proton-conducting SOFCs promises to become low/intermediate-temperature SOFCs materials because of its low activation energy. Ba Ce O₃ based proton-conducting SOFCs has been a hot research field due to its very high proton conductivity. But the poor chemical stability of Ba Ce O₃ based proton-conducting SOFCs limits its development. In this study, the effects of different elements doping of Ba Ce O₃ based electrolyte on its sintering temperature, chemical stability and electrical conductivity was investigated.In Chapter 1, the components of SOFCs and its working principle are briefly reviewed. The key materials of SOFCs are introduced. In addition, current state of proton-conducting SOFCs research, as well as major studies in this thesis are described.In Chapter 2, chemicals and instruments required in the experiments are described. Characterization methods and testing methods are introduced.In Chapter 3, Ba Ce_0.8In_0.1Y_0.1O_3-δ（BCIY） electrolyte materials are synthesized via citrate combustion. The results show that the sintering activity of electrolyte samples is greatly improved by In doping comparing with Ba Ce_0.9Y_0.1O_3-δ（BCY）electrolyte materials. The BCIY sample can be sintered to a high density at 1250℃and complete densified at 1350℃, while BCY sample can be densified by sintering at1500℃. It is found that In doping is also useful for improving chemical stability by the structural characterizations after treating samples of BCIY and BCY electrolyte in CO₂ and boiling water respectively about three hours.In Chapter 4, citrate combustion combined with solid-phase reaction was used to synthesize Ba Ce_0.8Ta_0.1Y_0.1O_3-δ（BCTY） electrolyte materials and the effect of Ta doping on the chemical stability of electrolyte materials was studied. The structurewas characterized after treating samples of BCTY and BCY electrolyte materials in CO2 and boiling water respectively with 3 hours. It is found that the chemical stability of Ta doping electrolyte samples is greatly improved because the alkaline of BCTY is reduced due to the doping Ta with high electronegativity, which slows down its reaction with acid gas.In Chapter 5, Ba Ce_0.7Ta_0.1In_0.1Y_0.1O_3-δ（BCTIY） electrolyte materials were synthesized by citrate combustion combined with solid-phase reaction. The effect of co-doping of Ta and In on the properties of electrolyte materials was studied. The results show that BCTIY can be complete densified at 1350℃, while BCTY can be complete densified at 1500℃. It proves that the sintering performance of BCTIY is better than that of BCTY and In doping can greatly improve sintering activity of samples. The structural characterization was done after treating the obtained BCIY,BCTY, BCTIY in CO₂ and boiling water respectively about 3h, 6h, 12 h. The results show that chemical stability of BCTY and BCTIY is better than that of BCIY electrolyte, which proves that Ta doping plays an important role in improving chemical stability. By analyzing the electrical conductivity of samples of three electrolyte materials, it can be concluded that In or Ta doping won’t lead to much loss of electrical conductivity. All the results show that BCTIY electrolyte materials could be good candidates for stable low/intermediate-temperature SOFCs materials.In Chapter 6, a summary of this thesis is presented and the outlook is given.