Development of MEA materials for PEMFCs with a focus on performance and durability: Results from EU IMPACT and IMPALA projects

Kurzfassung

The market presence and public acceptance of fuel cells is slowly increasing, however, the mass market penetration is mainly hindered by the high costs, to which the precious metal content, in particular platinum, contributes significantly. Since most scenarios predict a further increase of platinum prices due to an increasing demand, it must be a major goal to reduce the amount of necessary noble precious metal catalysts in fuel cells. This presentation gives an overview of the combined efforts in the developments of ionomers and membranes (perfluorosulfonic acid and hydrocarbon based), catalysts (platinum and alloys), gas diffusion layers (GDL) and the resulting MEAs, that were and are performed in the EU funded projects ‘IMPACT’ and ‘IMPALA’. The aim is to reduce the precious metal loading to 0.2 mg/cm² in fuel cells with a power density of 1 W/cm² and a durability of min. 5000 h. The research addresses various issues, e.g. membrane conductivity, hydrophobicity, degradation mechanisms, catalyst supports. Substantial effort was made in order to increase the chemical and electrochemical stability of the catalysts in a wide range of operating conditions of temperature and humidity levels. For instance, carbon-supported PtNi and PtCo cathode electro-catalysts were developed to evaluate their performance and stability in PEFC cathodes under various conditions. The PtCo alloy catalyst, with a recorded mass activity >0.46 A/mg at 0.9 V RHE and 80°C with 50% RH is adequate to reach the MEA performance milestones. The membrane development comprise reinforced 22 µm and 10 µm thick AQUIVION® PFSA membranes that are used in the fabricated MEAs. Additionally novel hydrocarbon membranes are being tested. In parallel to membrane development, new PFSA dispersions with EW as low as 720 g/eq have been developed. The approach to improve the GDL performance and degradation involves sophisticated modelling to deeply analyze the water management inside the GDL and the simulation of its effective transport properties as a function of its local properties. The predictability of these models will be checked by comparison to some experiments planned in IMPALA. The final aim is to use modeling to have a better understanding of water management in MEA and propose improvements of GDL. A joint workshop of the projects IMPACT and IMPALA with more detailed presentations is held on Monday 2nd February in Toulouse directly at the FDFC site. 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).