Ultra-high current density water management in polymer electrolyte fuel cell with porous metallic flow field

Anode dry-out is the main mechanism identified to limit operation in an open metallic element (OME) PEFC. The fundamental water transport mechanisms in the OME PEFC were examined in order to engineer further improved performance and higher temperature operation required for efficient heat rejection. Specifically, the net water drag (NWD) was measured over a range of conditions and analyzed with respect to electrochemical impedance spectroscopy and performance. As the cell operating temperature was increased, the effect of back diffusion was reduced due to the diminishing liquid water content in the cathode catalyst layer, and at critical liquid water content, anode dry-out was triggered primarily through electro-osmotic drag. Addition of cathode humidity was shown to promote high temperature operation mostly due to improved water back diffusion. The same mechanism can be achieved by creating a pressure differential across the membrane, with higher pressure on the cathode side. Stable operation was demonstrated at 90 °C using a polymer electrolyte membrane. Real time NWD measurements during transient anodic dry-out conditions were consistent with gradual membrane dehydration. The trade-off between liquid water overshadowing cathode catalyst sites and its contribution in promoting back diffusion is a key factor in systems with anode dry-out limited operation.