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In order to properly understand the power generation performance of polymer electrolyte fuel cells (PEFCs), it is necessary to have accurate data on water management, such as the diffusion coefficient of water through the membrane electrode assembly (MEA) and gas diffusion layer (GDL), electro-osmotic coefficient through MEA, and power loss data such as the activation and resistance overpotentials. In this study we measured these data with the aim of analyzing our experimental results from PEFC power generation tests done using our two-dimensional simulation code. Our code simultaneously solves mass, charge, and energy conservation equations, and the equivalent electric-circuit for PEFC to obtain numerical distributions of hydrogen/oxygen concentrations, cell potential, current density, and gas/cell-component temperatures. The current density distributions calculated with our simulation code were compared with the distribution measured using a segmented electrode cell. The distributions measured under various operating conditions agreed well with the calculated ones, demonstrating that our code is reliable. The concentration overpotential through GDL was also estimated with the parallel fine-pore model, but the estimated concentration overpotential was very small. Also, the cathode flooding is discussed with the calculated distribution of saturation degree along the channel flow, in comparison with experimental stability.

Keywords: PEFC (polymer electrolyte fuel cell), membrane properties measurement, overpotential measurement, current distribution analysisIn order to grasp properly the power generation performances of PEFC (Polymer Electrolyte Fuel Cell), it is necessary to know the water management data, such as diffusion coefficient of water vapor through MEA (Membrane Electrode Assembly) and GDL (Gas Diffusion Layer), and electro-osmotic coefficient of MEA, and to know power loss data, such as activation and resistance overpotentials. In this study we have measured these data to analyze our experimental results of PEFC power generation tests by our two-dimensional simulation code. These data were adopted in our simulation code.It is desirable to of develop the simulation code of PEFC power generation performance. By developing the simulation code of PEFC some experiments might be taken place by numerical simulations and could save the developing time and money. Therefore we have made a simulation code as a useful supporting tool of to develop PEFC. Our code considers simultaneously the mass, charge and energy conservation equations, and the equivalent electriccircuit for PEFC (Fig. 1) to get numerical distributions of hydrogen/oxygen concentrations, current density, cell potential, and gas/cell-component temperatures along gas flow. In this study current distributions of PEFC under a wide operating conditions have been calculated and compared with experimental distributions by our segmented electrode cell. The measured distributions under various operating conditions agreed well as shown in Fig. 2 with the calculated ones showing that our code is verified experimentally.The current distributions shown in Fig. 2 were measured at an operating condition of low dew point temperature, medium O 2 utilization ratio and co-flow type. In this condition the membrane resistance is high at cell entrance due to the dry anode and cathode gases, and at the middle of the cell the membrane is humidified by the generated water, keeping the same resistance along flow direction until the cell outlet. The concentration overpotential through GDL was also estimated by the parallel fine pores model, however the estimated concentration overpotential was very small to be neglected in the power generating performance of PEFC.

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SUMMARYGlobal warming is mainly caused by CO 2 emission from thermal power plants, which burn fossil fuel with air. One of the countermeasure technologies to prevent global warming is CO 2 recovery from combustion flue gas and the sequestration of CO 2 underground or in the ocean. SOFC and other fuel cells can produce high-concentration CO 2 , because the reformed fuel gas reacts with oxygen electrochemically without being mixed with air, or diluted by N 2 . Thus, we propose to operate the multistage SOFCs under high utilization of reformed fuel for obtaining high-concentration CO 2 . In this report, we have estimated the multistage SOFCs' performance considering H 2 diffusion and the combined cycle efficiency of multistage SOFC/gas turbine/CO 2 recovery power plant. The power generation efficiency of our CO 2 recovery combined cycle is 68.5% and the efficiency of conventional SOFC/GT cycle is 57.8% including the CO 2 recovery amine process.

Fuel cells have been developed rapidly due to its fewer pollutant emission than other power generation methods. Solid oxide fuel cell (SOFC) can be composed by solid components for a stable operation, and high power generation efficiency is obtained by using high temperature exhaust heat for both fuel reforming and bottoming power generation by gas turbine.Global warming is mainly caused by CO 2 emission from thermal power plants, which burn fossil fuel with air. One of the countermeasure technologies to prevent the global warming is CO 2 recovery from the combustion flue gas and the sequestration of CO 2 at the underground or in the deep ocean. SOFC and other fuel cells can produce high concentrated CO 2 , because the reformed fuel gas reacts with oxygen electrochemically without being mixed by air, or diluted by N 2 . So we propose to operate the multi-staged SOFCs under high utilization of reformed fuel for getting high concentrated CO 2 .In this report, we have estimated the multi-staged SOFCs performance considering H 2 diffusion, and further the combined cycle Fig. 1. SOFC/GT combined cycle for CO 2 recovery efficiency of multistage SOFC/gas turbine/CO 2 recovery power plant as shown in Fig1. We divided the high utilization SOFC into 4 blocks to avoid the current constriction at upstream. H 2 diffusion along flow direction has made the current distribution uniform, and maximum concentration overpotential was estimated to be 65 mV at the 4th stage SOFC. We also have estimated a conventional SOFC/GT cycle with CO 2 recovery amine process. The power generation efficiency of our CO 2 recovery SOFC/GT combined cycle is 68.5% and the efficiency of a conventional SOFC/GT cycle with the CO 2 recovery amine process is 57.8%. In the case of our CO 2 recovery combined cycle, the net output reform gas turbine is decreasing, however total power generation efficiency of our CO 2 recovery combined cycle is about 10% higher than that of the conventional SOFC/GT cycle, because the compressor power for CO 2 liquefaction is decreasing and the high fuel utilization SOFC produces 12.3% of total power. Therefore, this report showed a possibility to simplify the CO 2 recovery method by SOFC/GT cycle and further to improve the power generation efficiency.-5 -