Influence of the Gas Diffusion Layer Compression on the Oxygen Transport in PEM Fuel Cells at High Water Saturation Levels

Abstract

The impact of the gas diffusion layer (GDL) compression on the oxygen transport is investigated in single cell assemblies at 50°C, RH = 77%, 200 kPaabs and under differential flow conditions. For this, the oxygen transport resistance at low and high current densities is determined by limiting current density measurements at various oxygen concentrations for GDLs with and without microporous layer (MPL). At small current densities (≤0.4 A cm−2), where no liquid water in the GDL/MPL is present, a linear increase of oxygen transport resistance with GDL compression is observed, with the GDL without MPL exhibiting a significantly lower transport resistance. For low compressions of ≈8%, we find that the oxygen transport resistance for the GDL with MPL is increasing disproportionately high in the high current density region (>1.5 A cm−2), where water condensation in the porous media takes place. A similar trend is observed for a GDL without MPL at a typical compression of 22%. Based on these results, we hypothesize that a developing liquid water film is hindering the oxygen diffusion at the interface between MPL and cathode, analogous to what is known to be formed on the cathode surface for GDLs without MPL.

Anode Aging during PEMFC Start-Up and Shut-Down: H2-Air Fronts vs Voltage Cycles

“…Cathode degradation during SUSD.-To analyze the commonly reported SUSD-induced performance decay due to degradation of the cathode catalyst layer, Figure 2a shows the H 2 /air performance curves of a Gore MEA at BoT (after conditioning) and after the respective number of SUSD cycles. The ≈50 mV lower BoT performance at 2 A cm −2 in Figure 2a compared to the data shown by Simon et al using the same MEA (see Figure 8b in Simon et al) 23 is due to the approximately 20-25 m cm 2 lower HFR in the latter study, originating from the lower contact resistance (for details see Experimental section). In general, the MEA performance decreases compared to their BoT with increasing number of SUSD cycles.…”

Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation: A Voltage Loss Analysis

“…For each concentration, the O 2 mass transport resistance is calculated and plotted versus the respective limiting current density, as illustrated in Figure 10b for the low-loaded cathode MEAs at BOT and after 30000 SW cycles (for details on the analysis see Simon et al). 32 For all cathodes at BOT, the total oxygen mass transport resistance, R total O 2 , is essentially independent of the limiting current density at all pressures (see triangles in Figure 10b and its inset), as is expected under these conditions for the Freudenberg GDL. 65 Furthermore, the determination of the limiting current density at various pressures enables the separation of R total O 2 into a pressure dependent (R PD O 2 ) and a pressure independent (R PI O 2 ) oxygen mass transport resistance via a linear regression of R total O 2 versus the absolute pressure (Figure 10c).…”

Effects of mechanical compression on the performance of polymer electrolyte fuel cells and analysis through in-situ characterisation techniques - A review

“…Under these conditions, GDL pores get clogged and reactant gases do not reach the CLs leading to an increase in mass transport losses and therefore to a decrease in fuel cell performance caused by reactant starvation. These effects are more pronounced when mechanical compression is applied leading to a decrease in the porosity of GDL [111].…”