Need for SOFC

Solid oxide fuel cells (SOFCs) are the most efficient devices invented for conversion of chemical fuels directly into electrical power. Originally the basic ideas and materials were proposed by Nernst and his colleagues in Gottingen at the end of the nineteenth century and considerable advances in theory and experiment are still being made over 100 years later.In simple words, SOFCs contains a solid oxide electrolyte made from a ceramic such as Yttria Stabilized Zirconia (YSZ) which acts as a conductor of oxide ions at temperatures from 600 to 1000°C. This ceramic material allows oxygen atoms to be reduced on its porous cathode surface by electrons, thu sbeing converted into oxide ions, which are then transported through the ceramic body to a fuel-rich porous anode zone where the oxide ions can react, say with hydrogen, giving up electrons to an external circuit. Only five components are needed to put such a cell together: electrolyte, anode,cathode and two interconnect wires.

This is almost magical in its elegance and simplicity, and it is astonishing that this process has not yet been commercialized to supplant the inefficient and polluting combustion heat engines which currently dominate our civilization.Largely, this failure has stemmed from a lack of materials knowledge and the absence of chemical engineering skills necessary to develop electrochemical technology. Our belief is that this knowledge and expertise is now emerging rapidly. The purpose of research is to present this up-to-date knowledge in order to facilitate the inventions, designs and developments necessary for commercial applications of solid oxide fuel cells.The benefit of the SOFC over competing fuel cells is the higher temperature of the exhaust heat which makes its control and utilization simple and economic.

During the past decades, many oxide formulations have been extensivel yexamined in the search for candidate SOFC electrolyte materials. Zirconia-based compositions are still the best electrolytes at present owing to their good stability under reducing atmospheres, low electronic conductivity, and acceptable oxide

ion conductivity above 800°C. The recent trend of SOFC development is to operate at lower temperatures. The lowest operation temperature limit of the cell, for thin YSZ electrolytes, is estimated to be about 700°C from YSZ conductivity and mechanical property data. Scandia-doped zirconia, which shows a higher conductivity than that of YSZ, could be preferred at temperatures below 700°C, if the cost of Scandia was acceptable.Ceria-based electrolytes could be used at 550°C or less. To operate at higher temperatures, a dual layer electrolyte, with a thin YSZ layer on Ceria doped electrolyte, has been proposed to avoid the electronic current leakage. The inter diffusion issues at the interface are important in this case for long-life electrolytes.Another possibility is to use Pyrochlore compositions. The most promising candidate at this time is Y₂Zr₂O₇ doped with Gd and Nb. Other possible such as Ba doped with Y₂Zr₂O₇. These candidates are proposed for detailed studies in this project.

Solid oxide fuel cell technology is very promising because of its intrinsic simplicity and efficiency. Several markets for SOFC systems have been identified including residential, commercial and industrial CHP, distributed generation, auxiliary power units for the transportation sector, and portable power. Benefits of SOFC technology are consistent with current trends such as liberalization of energy markets, growing environmental concerns and shift towards distributed utilities especially in Kerala. The most promising features of SOFC systems are high efficiencies, fuel flexibility and negligible harmful emissions like particulate matter, oxides of nitrogen, oxides of sulphur, unburned CO and hydrocarbons. Competitive systems, e.g. gas engines, gas turbines and combined cycle units, are setting thebase-line for economic and technical specifications. SOFC hybrids are better than existing technologies with respect to electrical efficiency, part-load efficiency and emissions: however, their control speed, control range, investment cost and lifetime have yet to be fully established. High SOFC system cost is the principal obstacle to successful commercialization. But current capital costs are considerably reduced as the development Intermediate Temperature Solid Oxide Fuel cells progress. Several researchers in India (CSIR-CMERI West Bengal) aim at development of small systems (1-10 kW)with shorter lead times and a versatile market. The major obstacle towards commercialization is the chasm between the visionaries and the technology enthusiasts in material research on one hand and the pragmatists and conservatives on the other. Crossing this chasm is the main challenge for successful IT-SOFC commercialization which requires reducing system costs, demonstrating system, reIiabiIity and lifetime, and identifying proper materials.