Polymer Electrolyte Membrane (PEM) fuel cells are considered as promising clean sources for automotive applications. A key challenge to reduce the cost of this technology is to increase the power density by operating PEM fuel cells at high current densities. One strategy is to improve the 3D structure of the gas diffusion layer (GDL) located between the channel and the catalyst layer (CL). At the cathode side, this GDL is used to evacuate the liquid water toward the channel while providing access to the oxygen to the CL [1]. Although innovative GDL structures have been proposed, a better understanding of the liquid water would help to design better GDL. In particular, few works have investigated the liquid water transport after several hours of steady state fuel cell operating conditions although changes in liquid water preferential pathway have been observed [2]. Such changes are not predicted in theory, and a physical explanation of these mechanisms is still required.

In this presentation, we investigate ex situ the change of liquid water preferential pathways through PEM fuel cell GDLs. Liquid water breakthough from the GDL to the fuel cell channels is mimicked using a microfluidic PDMS device with embedded GDLs. Liquid water is injected through the GDL to the microchannel, and changes in liquid water pathways are observed after several hours of operations. These changes in liquid water pathway are attributed to the dynamic of droplet eruption in fuel cell microchannel. To validate this assumption, a small capillary network with is built. It is shown that after the liquid water breakthrough, the pressure variation due to the growth of the water droplets in the microchannel enables the liquid water to invade smaller capillaries which at the end can change the preferential path. The experimental observations reported in this work show that the invasion percolation theory can be used to predict the preferential pathway at the onset of the liquid water breakthrough, but pressure-induced dynamic transport [3] due the water droplet eruption in the channel has also to be taken into account to predict the preferential pathway after long time of fuel cell operation.

References

[1] T. Yoshida, K. Kojima, Toyota MIRAI Fuel Cell Vehicle and Progress Toward a Future Hydrogen Society, Interface Mag. 24 (2015) 45–49.

[2] Z. Lu, M.M. Daino, C. Rath, S.G. Kandlikar, Water management studies in PEM fuel cells, part III: Dynamic breakthrough and intermittent drainage characteristics from GDLs with and without MPLs, Int. J. Hydrogen Energy. 35 (2010) 4222–4233.

[3] S. Chevalier, C. Josset, B. Auvity, Fluid dynamic breakthrough in two connected capillaries: From stationary to oscillating state, Phys. Fluids. 29 (2017) 102102.