Water Management in Polymer Electrolyte Fuel Cells through Asymmetric Thermal and Mass Transport Engineering of the Micro-Porous Layers

For polymer electrolyte fuel cells (PEFCs) operating at very high current, prevention of anode dry-out through enhanced back flux of water and restriction of evaporation is required. In this work, back flux of water to the anode is engineered using an asymmetric anode and cathode micro-porous layer (MPL) configuration. Extensive experimental tests have been conducted to study the impact of thermal and mass transport resistances on the net water flux coefficient for extremes of wet and dry operating conditions. The net water drag coefficient was measured in the range of −0.17 to +0.18 depending on the operating conditions and material configurations. A simplified model has also been developed to investigate the effect of temperature gradient on the net water drag coefficient. It is shown that with an asymmetric configuration, the net flux of water can be reversed under certain conditions, greatly enhancing high current density performance. For wet operating conditions, the cell configuration with asymmetric mass transport resistance can be utilized to tailor the back flux of water. For dry operating conditions, the thermal resistance is the key controlling parameter to affect the net water drag.