Water vapor exchange system installed in a polymer electrolyte fuel cell to enhance the performance without humidification

Abstract

Polymer electrolyte fuel cells (PEFCs) generally have external humidifiers to supply humidified hydrogen and oxidant gases, preventing dehydration of the membrane electrode assembly (MEA). If a PEFC could be operated without humidification, external humidifiers may be removed, resulting in a very simplified PEFC system with increased total efficiency and reduced cost. One of most important issues to advance the commercial viability of PEFCs is to develop high performance PEFCs that can operate without humidification. In the present study, a water vapor exchange system installed in the cell was developed to enhance the PEFC performance without humidification. A gas diffusion layer coated with a hydrophilic microporous layer, which consists of carbon black and polyvinyl alcohol (PVA), used at the cathode exchange area increases water transport from the wet cathode outlet gas to the dry anode inlet gas. This prevents dehydration of the MEA, thereby reducing the IR (ohmic) overpotential. The exchange area using interdigitated flow channels is effective to achieve further enhancement of water transport from the cathode to the anode, which significantly enhances the ability to prevent dehydration of the MEA. This results in a much higher output power density compared with that for a PEFC without the water vapor exchange area.