Experimental and theoretical study of the water management in polymeric fuel cells (PEFC) under dehydration conditions / Estudio experimental y teórico de la gestión del agua en Pilas de Combustible Poliméricas (PEFC) bajo condiciones de deshidratación

Kurzfassung

The study of the phenomena associated to the water management in PEFC polymeric fuel cells has been one of the key issues for the development of these devices in recent years. The rather narrow gap of stability shown by these devices makes especially important the analysis of the parameters associated to the effects of water management over the stability of the operation. These highly interacting features generate significant problems in the design of control systems for this kind of fuel cells. This dissertation describes an experimental work on the stability of a PEFC single-cell under unfavorable hydration conditions. Such conditions give rise to unstable (nonsteady) processes of the single-cell characterized by non-steady values of the main parameters (electric current, voltage and resistance). This study has been focused on the effects of the variables related to the water management on the time evolution of the current density distributions, in particular during the two most important processes which may arise as a consequence of an inadequate water management, namely, flooding and dehydration. Additionally, the way these processes affects the membrane resistance has been also studied. The analysis of the oscillatory behavior observed under dehydration conditions in the cathode has been also received special attention. These particular conditions allow the use of additional tools to study the stability of the PEFC cell response, providing a deeper understanding of the associated dehydration process in the single-cell. Finally, the dehydration processes induced into the segmented single-cell PEFC have been experimentally characterized, and the results have been analyzed by means of a theoretical consideration of the characteristic times associated to the main phenomena. In concluding, one model is proposed which represents the voltage evolution under total dehydration conditions.