Development of Test Procedures and Lifetime Improvement of MEAs for Automotive Application

Kurzfassung

To meet the requirements of membrane electrode assemblies (MEAs) for polymer electrolyte fuel cells (PEMFCs) for automotive applications a durability of 5,000 h, corresponding to a degradation rate of 10 μV/h, and a high power density of 1 W/cm2 at 670 mV cell voltage are required. It is of great importance for the stack durability validation in PEMFC stacks to assure that results from different institutions are comparable. Therefore, the harmonization of PEMFC test procedures is of significant interest for industry and academia and important to fuel cell development. The preparation of required protocols for stack durability in automotive application was realized in the FCH JU project Stack-Test. The crucial parameters for reliable validation were identified and the fuel cell dynamic load cycle, based on the new European driving cycle, was specified considering the feedback from industrial institutions, from OEMs to stack manufacturers, and academia. Beside the load cycle, the importance of reproducible shut-down, refresh and restart procedures was demonstrated. The aspect of refresh procedures was analyzed in the FCH JU IMPACT project in detail to discriminate between reversible and irreversible degradation in order to propose a reliable and general procedure to quantitatively assess durability achievements for automotive PEMFC MEAs and stacks. To make the PEMFC competitive for automotive application, the IMPACT project was focused on the reduction of the Pt amount to 0.2 mgPt/cm2. The reduction of Pt loading leads to substantial performance losses and an increased degradation. To mitigate these issues and to maintain high performance and durability at low Pt loadings, in IMPACT the MEA core components, namely the membrane and the catalyst layer, have been improved. In the course of the project several generations of MEAs have been developed iteratively and tested in single cells and stacks. Thanks to this effort the irreversible degradation rate of a MEA with 0.21 mgPt/cm2 measured at 1 A/cm2 could be reduced by a factor >10 down to approximately 10 μV/h. The performance achieved by IMPACT at 0.25 mgPt/cm2 corresponds to the one of a commercial state-of-the-art MEA with 0.6 mgPt/cm2. The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303452 (Impact) and 303445 (Stack-Test).