Measurement of Water Distribution in Anode of Polymer Electrolyte Fuel Cell Under Low Humidity Conditions

Abstract

During low humidity operation of polymer electrolyte fuel cells (PEFCs), water management in anode electrode is essential for achieving sufficient membrane hydration and high proton conductivity. In this study, the water vapor condensation in an operating PEFC under low humidity conditions was experimentally visualized by using water sensitive paper (WSP), and the water distribution on the anode side was investigated. WSP is a test paper for detecting water droplets, fog and high humidity, which is coated with a yellow surface. This test paper was inserted between the anode electrode and separator in the transparent fuel cell. Furthermore, the dew-point temperature at the anode outlet was simultaneously measured using a hygro-thermometer, and the effects of operating conditions and flow configuration on the water transports between the anode and cathode electrodes were discussed. It was found that the water vapor concentration on the anode side increases considerably after the startup because of the back diffusion of the product water, and the water condensation occurs from the downstream section of the anode channel in the co-flow arrangement. However, at high current densities, the amount of water in the anode decreases due to the water flux driven by electro-osmotic drag. The difference of the water vapor concentrations between the anode and cathode electrodes arises significantly with cell temperature, and the back diffusion flux of water toward the anode increases. The counter-flow pattern of anode and cathode gases is effective in achieving uniform water distribution in the anode flow field. The dry H2 at the anode inlet is humidified by the water diffused through the membrane from the cathode outlet, and thus sufficient water can be supplied all over the anode flow field.