Full Factorial In Situ Characterization of Ionomer Properties in Differential PEM Fuel Cells

Abstract

The performance optimization of membrane electrode assemblies of PEM fuel cells requires accurate characterization and modelling of the relevant mechanisms. In this paper, the ionomer conductivities and permeation properties are characterized in situ in a differential cell setup by varying the operating conditions in a full factorial fashion in H2/N2 mode. Voltammetry methods are validated against online gas analysis and then used to record H2 crossover. The membrane and cathode catalyst layer (CCL) resistances are deconvoluted by fitting transmission line models (TLM) to electrochemical impedance spectroscopy (EIS) data. Based on this, we estimate activation energies of 20 kJ mol−1 for the H2 permeation, 7 kJ mol−1 for the membrane resistance and 9 kJ mol−1 for the ionomer resistance in the CCL. Through EIS measurements under load (H2/O2), we also evaluate the change in the ionomer resistances in course of water production. This effect is most pronounced under cold and dry conditions and implies that a subtraction of the protonic loss contributions from polarization curves only based on EIS measurements obtained in H2/N2 mode is not possible.