Study on Water Transport Phenomena in MEA of PEM Electrolysis

Abstract

This paper investigates water transport phenomena in PEM (Polymer Electrolyte Membrane) electrolysis cell. Experimental result showed that the cell voltage is less affected by the concentration overpotential even at quite high current densities, although significant amount of produced gas is observed in the water flow channels. Impedance measurement indicated that water content in the membrane increases with an increase in current density. The water flux measured at the cathode exit was almost identical to the osmotic flux in the membrane with saturated water content. In order to discuss the mechanism of the enough water-supply under the high current density conditions, numerical analysis was conducted on the water transport in the anode catalyst layer and the membrane. The result showed that the order of the water hydration rate into Nafion ionomer is greater than 1×10-4 m/s, and sufficient amount of water is supplied from pores in the catalyst layer to the ionomer surrounding catalyst particles at the anode side. This water supply mechanism results in the membrane water-content close to the saturated state, and the water in the membrane is mainly transported by osmotic force. It was also shown that water content in the membrane at the cathode boundary has little influence on the water flux and overall water distribution through the membrane.