Studies on the Water Management within an H2/O2 Fuel Cell Using a KOH Impregnated Matrix G. GAVE* A. KHALIDI, B. LAFAGE, M. J. CLIFTON AND P. TAXIL** Summary: As part of studies concerning power-source systems intended for manned spacecraft, investigations have been performed concerning water management inside an HfO? fuel cell, aimed at optimizing its working conditions and thus improving its efficiency. The experimental cell has two plane porous electrodes enclosing a matrix impregnated with a seven molar potassium hydroxide (7M KOH) aqueous solution at 80°C. The reactions involved are well known. The water produced in the anode compartment is extracted from the cell by a hydrogen flow rate in excess of the stoichiometric quantity required by the reaction. Flow rate and hygrometry of the hydrogen stream have to be optimized to avoid either drying of the matrix or flooding of the electrode. A numerical model has been developed to simulate the phenomenon by application of the mass transfer laws for porous media and using physicochemical data for the fluids in the system. This model has been validated using: the thermostated experimental cell, a hydrogen loop containing a humidifier unit and a water extractor, and a hygrometry sensor. The model appears to be in good agreement with the experimental results. Another aspect of the water-management problem is the weeping effect, observed at the cathode. This seems to be due to a strong vapor-pressure gradient induced by the high KOH concentration created at the electrode-electrolyte-gas interface when the cell is operating. The phenomenon has been experimentally investigated and ways of reducing this effect have been studied, such as humidifying the oxygen loop. Aim of the study As part of research on the use of fuel cells as a power source for future manned spacecraft, a study has been undertaken concerning the electrochemical H2/O2 cell using a basic immobilized electrolyte, in order to quantify all the fluid exchanges as a function of the electrical power delivered . The consumption of reactant gas (H2 and O2) and the elimination of the water produced were studied, to allow optimum cell operating conditions to be defined. This should give usefid information for the following tasks: • optimization of the electrochemical cell in terms of design and sizing of its different parts t*Centre National D'Etudes Spatiales CT/AE/SEIAC Avenue E. Belin 31055 Toulouse CEDEX France '**Laboratoire Genie Chimique et Electrochimie- URA CNRS 192, Universite Paul Sabatier Route de Narbonne 31062 Toulouse CEDEX France
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