Solid oxide fuel cells pressure

Fig. 13.27. Potential vs. current density plots for state-of-the-art fuel cells, o, proton exchange membrane fuel cell , solid oxide fuel cell , pressurized phosphonic acid fuel cell (PAFC) a, direct methanol fuel cell, direct methanol PAFC , alkaline fuel cell. (Reprinted from M. A. Parthasarathy, S. Srinivasan, and A. J. Appleby, Electrode Kinetics of Oxygen Reduction at Carbon-Supported and Un-supported Platinum Microcrystal-lite/Nafion Interfaces, J. Electroanalytical Chem. 339 101-121, copyright 1992, p. 103, Fig. 1, with permission from Elsevier Science.)...

Iritani J, Kougami K, Komiyama N, Nagata K, Ikeda K, and Tomida K. Pressurized 10 kW class module SOFC. In Yokokawa H, Singhal SC, editors. Proceedings of the Seventh International Symposium on Solid Oxide Fuel Cells (SOFC-VII), Pennington, NJ The Electrochemical Society, 2001 2001(16) 63-71. 

Siemens-Westinghouse Power Corporation, of Pittsburgh, PA, with a subcontract to Allison Engine Company, evaluated a pressurized solid oxide fuel cell coupled with conventional gas turbine technology without a steam plant. The system was operated at a pressure of 7 atm. The fuel cell generated 16 MW of power and the gas turbine generated 4 MW of power. The process showed 67 % efficiency as developed. An efficiency of 70 % is deemed achievable with improvement in component design. The COE is predicted to be comparable to present day alternatives. NOx levels were less than 1 ppm. 

Siemens-Westinghouse Power Corporation, Pittsburgh, PA, and Solar Turbines developed a conceptual design of an economically and technically feasible 20-MW, 70-% efficient natural gas-fueled power system that employs solid oxide fuel cells operating at elevated pressure in conjunction with an Advanced Turbine System gas turbine. The fuel cell, operated at 9 atm pressure, generated 11 MW of power. Two Solar Mercury 50 gas turbines were used to generate 9 MW of power. The results of the study indicated a system efficiency near 60 %. A low COE relative to conventional power generation is predicted. 

Kanamura K., Yoshioka S., Takehara Z., 1991. Dependence of entropy change of single electrodes on partial pressure in Solid Oxide Fuel Cells. Journal of the Electrochemical Society 138(7), 2165-2167. 

Satisfactory conductivity is maintained up to 1800 °C in air but falls off at low oxygen pressures so that the upper temperature limit is reduced to 1400 °C when the pressure is reduced to 0.1 Pa. A further limitation arises from the volatility of Cr2C>3 which may contaminate the furnace charge. The combination of high melting point, high electronic conductivity and resistance to corrosion has led to the adoption of lanthanum chromite for the interconnect in high temperature solid oxide fuel cells (see Section 4.5.3). 

The low ionic resistivities of these materials (reported to be under 10 Q cm at 1000°C in some compositions) make them very attractive candidates for use in electrochemical devices such as the solid oxide fuel cell. Their proton conductivity is highly dependent on the partial pressure of water in the atmosphere. Whether these materials exhibit longterm stability in highly oxidizing and/or highly reducing atmospheres remains to be seen. Many of the preparation techniques discussed for the oxygen ion conductors should be applicable to this relatively new class of ionic conductors. 

The solid oxide fuel cell (SOFC) have been under development during several decades since it was discovered by Baur and Preis in 1937. In order to commercialise this high temperature (600 - 1000°C) fuel cell it is necessary to reduce the costs of fabrication and operation. Here ceria-based materials are of potential interest because doped ceria may help to decrease the internal electrical resistance of the SOFC by reducing the polarisation resistance in both the fuel and the air electrode. Further, the possibility of using less pre-treatment and lower water (steam) partial pressure in the natural gas feed due to lower susceptibility to coke formation on ceria containing fuel electrodes (anodes) may simplify the balance of plant of the fuel cell system, and finally it is anticipated that ceria based anodes will be less sensitive to poising from fuel impurities such as sulphur. 

Since these first reports, Iwahara and other investigators have studied the conductivities (both ionic and electronic), conduction mechanism, deuterium isotope effect, and thermodynamic stability of these materials. The motivation for most of this work derives from the desire to utilize these materials for high temperature, hydrogen-fiieled solid oxide fuel cells. In a reverse operation mode, if metal or metal oxide electrodes are deposited onto a dense pellet of this material and heated to temperature T, the application of an electric potential to the electrodes will cause a hydrogen partial pressure difference across the pellet according to the Nemst equation ... 

After the analysis of PCFB-1.0 plant design documentation, the circuit of new hybrid co-generation power plant with use of PCFB gasifier, solid oxide fuel cells, and gas turbine power plant with built-in air recuperator was proposed (see Fig. 7). Thermal capacity of power plant will be 1.14 MW at gasifier operation under pressure of 0.35 MPa and Ukrainian bituminous coal consumption of 222.6 kg/h. Electric capacity of solid oxide fuel cell module will be 375 kW and of electric capacity of high-speed gas turbine plant will be 125 kW. 

The endothermic reaction is favored by high temperature and low pressure and is accelerated by the presence of nickel or iron catalysts. NH3 can be burned directly in combustion engines or used in solid oxide fuel cells without preprocessing [238]. In alkaline and PEM fuel cells, the ammonia has first to be decomposed according to the above reaction. For the PEM cell, even trace amounts of ammonia left in the gas after decomposition must be removed [239]. 

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