Modeling of liquid water transport in cathode catalyst layer of PEM fuel cells

The performance of a polymer electrolyte membrane (PEM) fuel cell is significantly affected by liquid water generated at the cathode catalyst layer (CCL). Conversely, the ionic conductivity of PEM is directly proportional to its water content; it must have sufficient water. Therefore, it is essential to maintain a delicate water balance, which seems difficult without properly understanding liquid water transport from the CCL. In the present study, a one-dimensional analytical solution of liquid water transport across the CCL is derived from the fundamental transport equations. The effect of CCL wettability on liquid water transport and the effect of liquid water “flooding” on reactant transport have been investigated. It has been observed that hydrophilic characteristic of a CCL plays significant role on the liquid water transport. The liquid water saturation in a hydrophilic CCL can be reduced by increasing the surface wettability or lowering contact angle. Based on a dimensionless time constants analysis, it has been shown that liquid water production from the phase change process is negligible compared to water production from the electrochemical process.