Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC

Abstract

This study examines the effect of ink composition on the ionomer distribution in the catalyst layer of membrane electrode assemblies (MEA) prepared by decal transfer. We combine both structural and electrochemical characterization techniques to investigate the influence of the ionomer distribution on MEA performance determined by 50 cm2 active area single-cell proton exchange membrane (PEM) fuel cell measurements. Cathodic catalyst layers were prepared from inks with different alcohols (1-propanol or 2-propanol) and varying water content (16–65 wt% H2O). The H2/air performance of cathode catalyst layers prepared from the different inks with 700 EW ionomer differed drastically, particularly under wet operating conditions, whereby the best performance was obtained for an ink based on 16 wt% H2O in 1-propanol. This was successfully correlated with the observation of ionomer patches at the cathode electrode surface (i.e., the surface facing the diffusion medium) determined by scanning electron microscopy (SEM), with N2 adsorption analysis of the electrodes using a QSDFT model, and with dynamic light scattering data of ionomer/solvent mixtures. No correlation could be obtained between H2/air performance and the proton conductivity of the cathodes obtained by electrochemical impedance spectroscopy, and a model to rationalize this behavior will be proposed.