Influence of the gas diffusion layer compression on the oxygen transport in PEM fuel cells at high water saturation levels

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 kPa_abs 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.