Revealing failure modes and effect of catalyst layer properties for PEM fuel cell cold start using an agglomerate model

Abstract

We propose a dynamic model for cold start of proton exchange membrane fuel cell in account for transport, phase-change and electrochemical reactions within catalyst agglomerates. The competition between loss of in-agglomerate reactant concentrations and active electro-catalytic surface is shown to cause different failure modes dependent on start-up current densities. Critical ice fractions of failure were identified for different cathode catalyst layer (CL) thickness and ionomer to carbon ratios (I/C) at 0.4 A cm−2. In contrast to thicker CLs that uplift the critical ice fraction, larger I/Cs decrease the CL porosity and agglomerate pore size, thus significantly reducing the critical ice fraction. Moreover, by utilizing the electro-osmotic drag effect, slightly thickening anode CLs provides effective internal heat source during cold start at high current densities with minimal impact on the nominal cell performance.