Preparation And Performance Researches Of Cathodes Of Solid Oxide Fuel Cell(SOFC)

Fuel cell is a device that can convert chemical energy directly to electricity. It uses hydrogefl or natural gas as fuels to generate electricity. Because it is not limited by carnot cycle, it generates electricity in a high efficient and environmental friendly way. Solid Oxide Fuel Cell (SOFC) if the fourth generation of fuel cell family. Compaied to other fuel cell systems, Solid Oxide Fuel Cell (SOFC) is composed of solid materials, which eliminates the problems that liquid electrolyte fuel cell face, such as corrosion and the leakage of liquid electrolytes. Because it operates at high temperatures (800?1000 慍), the electrode reaction is very fast and it has no need tO use noble metals as electrodes, which minimizes the cost of the cell. At the same time, the heaf emitted is of high quality and thus can be supplied for warming or stean~ engines to generate electricity. The overall energy conversion efficiency can be up tO 800/0. T1~e most outstanding advantage of SOFC is that it can use a large scale of fuels: SOFC ~an not only use hydrogen, carbon monoxide as fuels, it can also use natural gas (m~thafle), syngas, hydrocarbon or even other gases combustive, such as NH3, H2S etc. Currently the problem SOFC faces is caused by high temperature and th~ britt1en~S5 of the ceramics. If the temperature can be reduced to intermediaW temperature (600?00 IC), stainless steel can be used as fuel cell stack components~ such as interconnector or gas manifolds and there is no problem of carbon deposition. ~ I tfl n?I抦nm.n..c, ohmic 鏴sistance and electrode overpotential, especially cathode overpotential. So, how to prepare a good performance cathode becomes the target of scientists. In this thesis, many electrochemical techniques, such as AC impedance spectruni and polarization were employed to research the performance of LSM-YSZ cathode. Various cathode preparation conditions were investigated, such as different screefl printing meshes, binders, cathode sintering temperatures and the particle size of LSM. The effect of YSZ additions on cathode performance was investigated too. Th~ TV electrochemical performance of the single layer LSM-YSZ was improved when a certain amount of YSZ was added due to the increase of the triple phase boundary (TPB) by addition of YSZ, while excessive YSZ addition (60%) caused a decrease in performance, because the in-phase resistance of the electrode increased so high, leading to a reduced effective electrode area. The problem was eliminated by a double-layer LSMILSM-YSZ composite electrode, in which a pure LSM layer functioned as a current collector and reduced the in-phase resistance. As a result, both large TPB area and low ohmic resistance were assured in this kind of structure. At 950 C, the double-layer composite electrode with 50 tw.% YSZ has the lowest polarization resistance of 0.3 ~.cm2, while at 800 慍, the electrode still has the polarization resistance of 1.74 acm2. There is a lot of work to do to make a good cathode.