Degradation Effect of Gas Diffusion Layer on Water Transport in Polymer Electrolyte Membrane Fuel Cell

Abstract

Hydrogen is converted to electric power by proton exchange membrane fuel cells (PEMFCs), which have received significant attention for transportation applications because of their high energy efficiency. In order to ensure the long-term stability, understanding about their long-term durability is essential because the operating performance deteriorates over time. Gas diffusion layers (GDLs) manage the transport of water generated from the CL during chemical reactions, and the degradation of the GDL significantly deteriorate the fuel cell performance. Compared to the fresh GDL, the water transport characteristics of GDL aged by inserting hydrogen peroxide solutions are investigated. The dynamic movement of the water meniscus inside the GDL is visualized using synchrotron X-ray imaging. Unlike the pristine GDL having snap-off patterns, water continuously transports through the degraded GDL representing the piston-like movement, and pressure fluctuations are not observed. This difference shows the change of the dominant local transport mechanisms due to GDL degradation. The temporal pressure variations are simultaneously measured, and the pressure and time at breakthrough (BT) are compared. The aged GDL exhibits a larger BT pressure and requires a longer time to achieve the first BT. Longer BT time in the degraded GDL can reflect a higher water saturation level. GDL degradation leads to the loss of polytetrafluoroethylene (PTFE) which is commonly treated to ensure efficient mass transport by restraining water clogging in the GDL pores due to the increase of hydrophobicity. Despite the reduction in hydrophobicity, The PTFE loss can increase BT pressure by reducing the pore size and the actual path length of the water flow. The increase in the BT time and BT pressure, as well as continuous transport, can disrupt fuel supply to chemical reaction sites, thereby deteriorating the PEMFC performance. This study provides a comprehensive understanding of the effect of GDL degradation on mass transport in PEMFCs. Figure 1