Investigation On Conductivity Relaxation Of Cathode Materials Containing Cobalt

A fuel cell is a device which can convert chemical energy directly to electric energy at a constant temperature. Because it is not limited by carnot cycle, it generates electricity in a high efficient and environmental friendly way. Furthermore, fuel is fed to the anode where it is oxidized and electrons are released to the external circuet.Solid Oixde Fuel Cell (SOFC), a kind of solid-only fuel cells which eliminates the problems that liquid electrolyte fuel cell face, is a promising fuel cell with many prominent advantages, such as no liquid, longevity. It becomes increasingly important to reduce the operation temperature of the fuel cells down to the range of 600 to 800oC. Howevers, there are significant barriers to intermediate temperature SOFC: electrolyte ohmic resistance and electrode overpotential, especially cathode overpotential. So a good performance cathode becomes the target. This thesis intends to reveal the property of cathode materials, aiming at developing practical intermediate temperatures SOFCs. The main work incudes the following dections:First, La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ composite oxide was prepared and characterized. Dilatometer and four-probe DC were exploited to investigate the thermal expansion and electrical conductivity, respectively. The thermal expansion curve was linear, but it became steeper at the high temperature region, as a result of the loss of lattice oxygen and the formation of oxygen vacancies. The conductivity increased with temperature up to about 600oC, and then decreased due to the loss of lattice oxygen. The chemical diffusion coefficient in La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δwas estimated by analyzing the conductivity relaxation behavior. The relaxation...