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.
Highlights
Chair of Technical Electrochemistry, Department of Chemistry and Catalysis Research Center, Technical University of Munich, D-85748 Garching, Germany
It was shown that material properties like substrate type and thermal conductivity of the gas diffusion layer (GDL) have a significant influence on the effective diffusion and the formation of liquid water, which appears as an increase in oxygen transport resistance from a low plateau at dry conditions to a higher plateau at wet conditions.[3]
This view of a transition from absence of water to high water saturation in the GDL/microporous layer (MPL) with increasing current density was proven by Owejan et al by comparing the local water saturation in the GDL extracted from neutron imaging in an operating fuel cell with limiting current density measurements
Summary
An experimental method to quantify the mass transport resistance of oxygen is the measurement of limiting current densities for various oxygen concentrations Based on these measurements, Baker et al developed a technique to separate the impact of flow field channels, GDL, MPL as well as other sources and presented a model to extract effective diffusion coefficients at the so-called dry conditions at low current densities.[23] There exist several studies that utilized this approach to quantify the influence of different GDL materials, MPLs, catalyst loadings, and operating conditions on the oxygen transport resistance on the cathode side.[3,4,32,33,34,35,36,37] It was shown that material properties like substrate type (paper, non-woven, etc.) and thermal conductivity of the GDL have a significant influence on the effective diffusion and the formation of liquid water, which appears as an increase in oxygen transport resistance from a low plateau at dry conditions (i.e., absence of liquid water in GDL/MPL) to a higher plateau at wet conditions (i.e., at high water saturation levels in GDL/MPL).[3] This view of a transition from absence of water to high water saturation in the GDL/MPL with increasing current density was proven by Owejan et al by comparing the local water saturation in the GDL extracted from neutron imaging in an operating fuel cell with limiting current density measurements.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
