| A fuel cell is a device which can convert chemical energy toelectricity directly. It generates electricity with a high efficiency and a lowpollution from fuels such as hydrogen, natural gas and other hydrocarbons .Different from the traditional cells that can only reserve energy, the fuelcells can convert energy continuously. The fuel cell is also called a cellbecause it is composed of electrolyte, anode and cathode, which are thesame for a normal cell. The electrolyte is sandwiched by the two electrodes.The fuel cell is also different from the traditional power generation methods.Because it is not limited by the Carnot cycle, fuel cell has advantages ofhigher energy conversion efficiency and lower polluted gases emission overthe traditional generator. Recently with the natural resource exhaustion andenvironment deterioration, developing efficient and environmental friendlyenergy techniques is necessary. Since fuel cell just matches suchrequirements, it attracts the interests all over the world.As the fourth generation fuel cell, SOFC (Solid Oxide Fuel Cell) hasmany outstanding advantages. Firstly, equipped with all solid components,it eliminates the problems that liquid electrolyte fuel cell faces, such ascorrosion and leakage of liquid electrolytes. Secondly, operating at hightemperatures, its electrode reaction is so fast that it is unnecessary to usenoble metals as electrodes. Thus the cost of the cells can be minimized. Atthe same time, the high quality heat it emits can be fully used. The overallenergy conversion efficiency of the thermal-electric system can be added upto 80%. The most outstanding advantage of SOFC is that it uses a largescale of fuels, from the hydrogen, carbon monoxide to the natural gas oreven other combustive gases. Currently the main difficulty that the SOFCfaces is the problem caused by high temperature and the ceramiccomponents' match.During a SOFC working, the electrolyte and the electrodes have awaste of the power output. The waste will cut down the efficiency of theconversion, which should be avoided. As the key component of SOFC,cathode plays a very important role in the performance of the whole cell.The cathode material's properties and the cathodic microstructure aredetermined by the cathodic reaction mechanism. To improve the cathodeperformance, proper materials should be selected while perfect preparationtechnique should be employed at the same time.In this thesis, we focused on the cathode material's properties and thecathode preparation techniques. New electrode materials that different fromtraditional ones was synthesized and investigated. The results that we canget from the experiments are good.First, The cathode material Sm1-xSrxCoO3-δ(x=0.2,0.3,0.4,0.5,0.6,0.7)was synthesized by a sol-gel method. We studied the propertiessuch as crystal structure(XRD), electrical conductivity, cathodicpolarization and single cell performance. Further,we compare theperformance of the cathodes with those of the other cathodes. Differentelectrolytes are also used to find which is more adaptable to the cathode wehave studied.The results show that the overpotential based on SDCelectrolyte is lower compared that based on SDC-YSZ compositeelectrolyte. The open circuit voltage based on SDC is low because the ionCe4+ is reduced into Ce3+in high temperature,thus the electron released bythe Ce4+ ion conduct electricity.So we use La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM)as electrolyte to study the single cell performance . Not only the opencircuit voltage based on LSGM is larger than that based on SDC but alsothe power output is much higher that based on SDC.The cathode material La0.7Sr0.3Ni1-xCuxO3-δ(x=0.1,0.3,0.5,0.7,0.9)wassynthesized by traditional a solid-state method. Investigation suggests thatLa0.7Sr0.3Cu0.7Ni0.3O3-δ has good electrical conductivity.its conductivity isabout 330S/cm at 800℃.As to electrochemical properties,its overpotentialbased on SDC is 0.1V with the current density of 0.1 A/cm2 at 800℃. |
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