Intermediate Temperature Conduction Properties And Applications Of Mg-doped ZrP₂O₇and Mn-doped La_0.6Sr_0.4FeO₃

As we all know, solid electrolyte materials are a kind of new functional materials, which have played an important role in various electrochemical devices, such as hydrogenation and dehydrogenation of some organic compounds, ammonia synthesis at atmospheric pressure, separation and purification of hydrogen, gas sensors, molecule pump and solid oxide fuel cell (SOFC), etc.The operating temperature higher than800℃for high temperature electrochemical devices may result in steep demand for electrode materials and connection materials, large energy consumption, high fabrication cost, etc. Therefore, intermediate temperature conductive materials, which operated at100-800℃, have attracted more attention of people. Recently, a new intermediate temperature solid electrolyte materials-pyrophosphate (MP2O7) has aroused a great interest. MP2O7based electrolyte materials have high proton conductivity in the temperature range of100-600℃, good thermal stability and insoluble in water. As a member of MP2O7, Mg-doped ZrP2O7ionic conductive ceramic materials have yet not been reported.Solid oxide fuel cell (SOFC) is a power generation device, which can convert chemical energy into electrical power directly by electrochemical reaction. It is called a new green power generation technology in twenty-first century for its high power generation efficiency, low emissions, environmentally friendly, long life, etc. A typical SOFC essentially is consisted of a porous anode material, cathode material, electrolyte material, connecting plate and seal material, etc. The cathode material as one of the most important parts of SOFC, mainly divided into metal cathode material, metal ceramic cathode material and perovskite composite metal oxide cathode material. Many novel perovskite mixed ionic-electronic conductors have been widely used as cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC), such as cobalt-doped perovskite-type cathode material La0.5Sr0.5CoO3-δ, 5, etc. However, cobalt is a rare element on the earth, Co-doped cathode materials exhibit high thermal expansion coefficients and poor chemical stability. That is difficult to find suitable electrolytes to match with cobalt-doped cathode materials. Mn is a cheaper element compared with Co, the ionic radius of Mn is close to Fe. So cobalt-free perovskite-type Mn doped Lao.6Sro,4Fe03-5as cathode material of SOFC has aroused our research interest.Based on the above, the synthesis, conduction properties and applications of Mg doped ZrP2O7cemaric and Mn doped perovskite Lao.6Sro.4Fe03-δ cathode material at intermediate temperature are investigated in this thesis. The main research work and results are as followed:(1) Chapter1-Introduction. We introduced briefly some typical functional ceramic materials, solid electrolyte materials, inorganic proton conductors, fuel cells, concerned defect chemistry, proton transference mechanism and their applications. In addition, we summarized the internal and external research background on Zri-xMgxP2O7intermediate temperature electrolyte materials and cobalt free perovskite La0.6Sr0.4Fe1-xMnxO3-δ cathode material, proposed the research content and significance of this thesis.(2) Chapter2-Preparation and intermediate temperature conduction properties of Zr1-xMgxP2O7ceramic. A new series of Zr1-xMgxP2O7(x=0.00,0.03,0.06,0.09,0.12) ceramic samples were prepared by solid-state reaction method, the dense ceramic samples were obtained after sintered at1250℃for5h. The doping limit of Mg in ZrP2O7was at least x=0.09. Densification increased with increasing of Mg doping level, the highest relative density reached97.1%for the sample of x-0.09. The doping content of x in the samples plays a significant effect on the conduction property of the sample. Conductivity increased in the order:a (x=0.00)<a (x=0.12)<σ (x=0.03)<σ (x=0.06)<σ (x=0.09). Among the ceramic samples studied, the highest conductivity was observed for the sample of Zr0.91Mg0.09P2O7to be1.34×10-4S cm-1in unhumidified air and1.08×10-4S cm-1in unhumidified hydrogen at600℃. The ionic conductive properties of the typical sample (Zr0.91Mg0.09P2O7) were studied by means of gas concentration cells.(3) Chapter3-intermediate temperature conducting properties and applications of Lao.6Sro.4Fe1-xMnxO3-δ cathode. A series of cobalt-free perovskite-type cathode materials La0.6Sr0.4Fe1-xMnxO3-δ (x=0.00,0.05,0.10,0.15) for IT-SOFCs were prepared by a citric-nitrate process. It was found that partial substitution of Mn for Fe site obviously enhances the conductivities of the cathode materials. Among the series of samples studied, La0.6Sr0.4Fe0.90Mn0.1003-δ(LSFM10) exhibits the highest conductivity to be160S cm-1in air at500℃. An anode-supported BaZr0.1Ce0.7Y0.2O3-d (BZCY) electrolyte membrane was successfully obtained by a simple, cost-effective spin coating process. A single cell with the configuration of Ni-BZCY/BZCY/LSFM10was fabricated. The maximum power density of the cell was475mW cm-2at700℃. The interfacial polarization resistance (Rp) was0.12Ω cm2at700℃. Long-term stability of the single cell with LSFM10cathode was studied. There is only a little degradation in performance after testing24h at600℃, indicating that the cobalt-free LSFM10was a stable promising cathode material for proton conducting IT-SOFCs.