Numerical Simulation of Liquid Water Behavior in PEFCs with Different GDL Wettability

Abstract

The performance of polymer electrolyte fuel cells (PEFCs) is greatly influenced by internal transport phenomena. Particularly, accumulation of liquid water due to electrochemical reaction is one of the main factors that prevents the transport of oxygen and increases the concentration overpotential, and thus, quick rejection of liquid water accumulation is important issue for improving performance. This study focuses on liquid water accumulation inside gas diffusion layers (GDLs), and investigates how wettability of the substrate surface alters the liquid water behavior using numerical simulation. In this study, a numerical simulation incorporating condensation phenomena was performed using three-dimensional structure of GDL substrate obtained from CT measurements. The cell temperature and the current density were set to 40° and 0.6A/cm2, and the contact angles of the substrate was set to 60°, 110°, 150°. The simulation results showed that in the hydrophobic cases of 110°, 150°, the droplets began to move between pores to minimize their surface energy as their size grew into pore scale of the substrate. While in the hydrophilic 60° case, the liquid water condensed near the catalyst layer only moved in such a way that the thickness of the liquid water increased, and no droplet-like structure were observed. In the 150° case, the contact area between the substrate and the droplets was smaller than that in the case of 110°, and the surface energy of the droplets was assumed to be larger. It was found that the liquid water accumulation is highest at the 60° case followed by 110°, 150°. Figure 1