| A fuel cell is a device that can convert chemical energy to electricity. It generates electricity from fuel such as hydrogen, natural gas and other hydrocarbons. Though it is composed by electrolyte, anode and cathode like normal cell, it is obviously distinguished with others. Normal cell is just a kind of energy container, the fuel cell is an energy exchange device. On this hand the fuel cell is a better electrical chemical dynamo. It is different from traditional generators, fuel cell has advantages of higher energy conversion efficiency and lower polluted gases emission over the traditional generator for it is not limited by the Carnot cycle. Recently with the natural resource exhaustion and environment deterioration, developing efficient and environmental friendly energy techniques is necessary. Since fuel cell just matches such requirements, it attracts the interests all over the world.As the fourth generation fuel cell, SOFC (Solid Oxide Fuel Cell) has many outstanding advantages. Firstly, equipped with all solid components, it eliminates the problems that liquid electrolyte fuel cell faces, such as corrosion and leakage of liquid electrolytes. Secondly, operating at high temperatures, its electrode reaction is so fast that it is unnecessary to use noble metals as electrodes. Thus the cost of the cells can be minimized. At the same time, the high quality heat it emits can be fully used. The overall energy conversion efficiency of the thermal-electric system can be added up to 80%. The most outstanding advantage of SOFC is that it uses a large scale of fuels, from the hydrogen, carbon monoxide to the natural gas or even other combustive gases. 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 cathode microstructure are determined by the cathode reaction mechanism. To improve the cathode performance, proper materials should be selected while perfect preparation technique should be employed at the same time.For IT-SOFC operate at relatively lower temperature between 600℃ and 800℃, it provide more choices of cell materials,facilitate the make technology and stabilize the cell. Thus study and find new kinds electrolytes and relative electrode materials will be very significant to the development of IT-SOFC. In this thesis, we focused on the cathode material's properties and the cathode preparation techniques. Serials of work have been done in order to improve the cathode performance by searching materials having excellent properties and the optimal preparation conditions. Prepared La0.7Sr0.3Co1-xCuxO3-δ(x=0,0.05,0.1,0.15,0.2,0.25,0.3) by solid-state reaction method, measured their physical properties such as crystal structure, electrical conductivity and thermal expansion, their differences in micro-mechanism were discussed and observed, finally compared and discussed the samples' electrochemistry activity by measuring the samples' over potential. Summarily LSCC have faster reactive velocity than LSM and better catalytic activity at interim and low operate temperature, it suits to be an IT-SOFC cathode material. The SOFC's properties can be improved if choose suited electrolyte. According to front consideration, we chose CeO2 as electrolyte. By sol-gel method,Ce0.8Sm0.2O1.9(SDC) were prepared, its crystal structure, TEC, resistance were measured. The results show that SDC by sol-gel method is very compact after sintered at 1400℃,the sinter temperature is lower that by solid-state reaction method,the TEC and conductivity are better too.To improve the cathode ionic conductivity,doping electrolyte is usual method. Doping YSZ into LSM and CGO into LSFC are most frequently reported. In this thesis,we doped SDC into LSCC to expand react area. The results show that this method can enhance the material's ionic conductivity and improve its activity,at the same time it can reduce the TEC. Of them 10%SDC content in LSCC perform the highest conductivity and chemical activity.
|
PDF Full Text Request