Performance and Durability of Next Generation Automotive Membrane Electrode Assemblies in Automotive Short Stacks

Abstract

The space for polymer electrolyte membrane fuel cell (PEMFC) systems for the application especially in small cars is a limiting factor. Hence, high power density at high current density is required to fulfill the power demand and space requirements of a fuel cell system when installed into a car. Additionally, the fuel cell operation at elevated temperature supports this requirement facilitating smaller cooling systems. Hence, within the EU funded project GAIA (next Generation AutomotIve membrane electrode Assemblies), a consortium of leading OEMs, industrial partners and academic/research partners/organizations/institutions aimed to develop well beyond state of the art membrane electrode assemblies (MEAs) for high power application at elevated operating temperature.Therefore, electrocatalysts, membranes, ionomers, gas diffusion and microporous layers were developed with respect to minimizing the resistances by improving their interfaces. The potential of the developed next generation MEAs was determined using automotive short stacks aiming a beginning of life power density of 1.8 W/cm2 at 0.6 V. The durability target was defined with less than 10 % voltage loss of the beginning of life performance after 6000 operating hours (extrapolated from a testing time of 1000 h). For verification of the durability, an automotive drive cycle was adapted from real life driving data and applied for durability determination. This drive cycle contained very challenging operating conditions such as e.g., an applied current density up to 3 A/cm2 and an increased operating temperature of 105 °C at the stack outlet.In this study, the project achievements in performance and durability at high power and high temperature operation of the developed next generation automotive MEAs were demonstrated within automotive short stacks. During the projects progression, the application of a newly developed gas diffusion layer with increased degree of graphitization and a microporous layer with large pore structure significantly increased the performance at high current density. The stability of the catalyst coated membrane (CCM) was drastically increased by a membrane with a PBI-X reinforcement developed within the project, which replaced a standard PTFE reinforcement. Additionally, a new ionomer with increased high temperature stability was implemented that inhibited ionomer migration at high temperatures. The addition of a radical scavenger to the catalyst layer inhibited the destruction of the CCM by radicals as observed at high temperature operation with the state-of-the-art material. Finally, besides the improvement of the MEA material properties, the fuel cell operating parameters were optimized in-situ using an automated optimization algorithm to find the optimum operation parameters for the newly designed MEA. This optimization demonstrated a significant contribution to the achievement of the performance and durability target as it allowed the operation of the developed MEA at its “sweet spot”.