The Research Of The Electrolyte For Intermediate Temperature Solid Oxide Fuel Cells And Related Materials And Properties

Solid oxide fuel cell (SOFC) is an efficient, green energy conversion device, which can directly convert the fossil energy into electrical power, which has many advantages, such as high energy conversion efficiency, solid-state structure, and a wide range of adaptability of fuel gases, etc. As the core component of SOFC, the electrolyte is always the hot-pot. The basic theory, the state-of-art of SOFC and the electrolyte were reviewed in the Chapter 1. The fabrication of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ(BZCYYb), a new electrolyte for SOFC, were optimized and the BZCYYb with highest conductivity was got in the Chapter 3; In the Chapter 4, the theoretical density of BZCYYb was measured and calculated for the first time and we systematically studied the sinterability of BZCYYb, which is favorable for its application in other field. In the Chapter 5, we discussed the new electrolyte systems, NASICON materials and its application as an electrolyte in the SOFC, and Olivine and Garnet type lithium ion conductors were also discussed.The main results and the creative points could be concluded as below:(1) The different Y/Yb ratio BZCYYb materials were successfully fabricated by solid state reaction (SSR) method, and the X-ray diffraction shows all the powder has perovskite structure. And the conductivity is the highest when the amount of Yb is 10% in BZCYYb. The powder, which was fabricated by the precursor made ofμm CeO₂ and nm ZrO₂ and two times calcinations and the calcinations temperature is 1100oC, has no obvious impurities in the X-ray diffraction test and the corresponding pellets have the highest conductivity,.(2) The theorectical density of BZCYYb materials was calculated for the first time, and its value is about 6.211g·cm^-3.(3) The addition of a small amount (¹wt%) of NiO to BZCYYb, which was fabricated by SSR method, greatly promoted densification and grain growth, which is better than other sintering aids (LiF and Al₂O₃), achieving ⁹6% of the theoretical density (reducing the sintering temperature by ²00oC). Further, the sample showed high open circuit voltages (OCV) when used as the electrolyte membrane to separate the two electrodes under typical SOFC operating conditions, indicating that the electrical conductivity of the BZCYYb was not adversely affected by the addition of ¹ wt % NiO. The solid state reactive sintering method was conducted for the first time with NiO as sintering aid for the BZCYYb material, and the result showed that the conductivity is close to the BZCYYb pellets which are fabricated by the traditional solid state reaction method.(4) The Na₅GdSi₄O₁₂ (NGS) powder was successfully fabricated through the SSR method, and the pellets made from the powder after sintering at 1060oC were dense, and its conductivity was close to the literature. The NGS pellets were used as the electrolyte for SOFC for the first time, and it has high open circuit voltage, and its powder density could reach 0.5mW/cm2 at 500oC with the electrolyte thickness of 1.2mm. Further more, the NGS structure changed a lot after lithium ion exchange. And after lithium ion exchange, the conductivity of the pellet became lower and the activation energy became higher. The LiInGeO4 and LiIn1-xMxGeO4(M=Ti⁴⁺, Zr⁴⁺ and Nb5+,x=0.1-0.2) material were successfully fabricated via SSR method. The X-ray diffraction showed that when no dopant and the dopant is Zr+, x=0.1, the pure phase could be got. But, when the dopant is Ti⁴⁺ or Nb⁵⁺, there is always some impurity in the powder. The conductivity of LiInGeO4 and Li0.9In0.9Zr0.1GeO4 were low. The Li₇La₃Zr₂O₁₂ powder was successfully fabricated through SSR method. The X-ray diffraction shows that the Li₇La₃Zr₂O₁₂ had tetragonal structure after calcinations at 900oC and 1125oC. But after 1230oC sintering for a long time, the main phase changed to La₂Zr₂O₇. Furthermore, the structure of the experiment and the mechanism of the reaction were also discussed.