In-situ diagnostic tools for PEM fuel cells: Advanced methods for liquid water profiling

The control of the distribution and movement of liquid water is crucial for increased reliability and durability of PEM fuel cells: whereas the proton exchange membrane requires a minimum amount of liquid water for optimum operation, water excess in the GDL will impede reactant gas access to the catalyst layer thereby reducing performance. In order to understand the relationships between water management on one hand and fuel cell performance and durability on the other, Ballard has been developing a number of minimally invasive techniques that can throw light on the role of liquid water for both cell performance and durability. This paper introduces a novel measurement method that can provide information about the amount and distribution of liquid water under operation. It is shown how the MEA Resistance and Electrode Diffusivity (MRED) method can be used to determine i) the amount of liquid water in the fuel cell, ii) the pure ohmic cell resistance and iii) the O2 -diffusivity of the cathode. Furthermore, through a combination of the MRED method with current mapping it is possible to determine spatially resolved MEA resistance profiles.