Effects of catalyst layer structure and wettability on liquid water transport in polymer electrolyte membrane fuel cell

Abstract

Polymer electrolyte membrane (PEM) fuel cells are high efficiency and low-emission power sources suitable for portable and automotive applications, but their performance and cost must be improved significantly in order to be viable for commercial applications. Water management is a key factor hindering the PEM fuel cells to be competitive with portable and automotive applications. The performance of a PEM fuel cell is affected by the liquid water generated at the cathode catalyst layer (CCL), potentially causing water flooding. The ionic conductivity of PEM layer is also directly proportional to its water content. As such, it is important to have a good understanding of the liquid water transport in the CCL in order to maintain an optimum water balance, fuel cell performance and to prevent material degradation. This paper presented a newly developed two-dimensional two-phase catalyst layer model to investigate the effect of catalyst layer structure and its surface wettability on the liquid water transport. The model addressed the liquid water transport across the cathode catalyst and gas diffusion layers. Numerical simulations revealed that the liquid water saturation maintains the highest value inside the catalyst layer under the bipolar plate. The lowest value inside the CCL was observed under the flow channel. The wetting and geometric characteristics of the CCL were shown to play a significant role on the liquid water transport. It was concluded that the mobile liquid water saturation in a hydrophilic CCL can be reduced by increasing the surface wettability or lowering the contact angle. 17 refs., 2 tabs., 9 figs.