Development of Self-Management Water Separator for PEFC

Polymer electrolyte fuel cells (PEFCs) have water management issues such as the flooding phenomenon where condensate blocks the pores of the gas-diffusion-layer (GDL), and the plugging phenomenon where condensate blocks the gas channels. If the plugged water can be moved from the plugged area to the gas inlet of low humidity, the system efficiency is improved by reducing the energy consumption that is required for humidifying. Therefore, we have proposed the Self-Management Water Separator (SMWS) to solve those issues since 2006. Excess water was absorbed by the capillary action of a water absorption material, and it moved from the gas outlet to an arbitrary place in the gas channel through a bypass channel by a concentration difference of water. The previous study was able to confirm the transport phenomenon of water through the bypass channel and prove the effectiveness of the bypass channel. Therefore, this paper aims to confirm the effect of SMWS in the actual cell, to optimize the position of the bypass exit, and also to select a water absorption material. As a result, the optimum position of the bypass exit was at the upstream of the cell under a non-humidifying/heating condition because of prevention of the membrane drying. On the optimization of water absorption material, PVA was optimal from the viewpoint of the absorption and the speed of water absorption as an absorption material. On the durability test of about 300 hours, the cell voltage with the bypass channel was stable although that of the cell without the bypass channel was a little unstable and lower. The effectiveness of the bypass channel with PVA as the water absorption material was also proved by the actual cell test. Moreover, although Diatomite has excellent moisture adsorption/ desorption characteristics which was evaluated by the cell test as an advanced water absorption material, the performance of the cell with Diatomite was not able to exceed that of PVA.Y. Okahashi*, K. Tajiri, M. Tanaka, M. Yamakawa & H. Nishida