Membrane Electrode Assembly Development for HT-PEM Fuel Cells

Kurzfassung

High-temperature proton exchange membrane fuel cell (HT-PEMFC) electrodes have high Pt loading (0.7-1.0 mgPt cm-2) due to phosphate-induced deactivation of Pt. In order to decrease the electrode costs of HT-PEMFCs the reduction of expensive Pt-catalyst loading is needed. Moreover, the typically used phosphoric acid doped polybenzimidazole membrane (PBI) suffers from acid leaching and unsatisfactory mechanical properties leading to limited lifetime.[1] We will give an overview of our research pathways to lower the amount of Pt in membrane electrode assemblies (MEAs) and to increase the stability of the HT-PEM. This includes the investigation of bimetallic metal-nitrogen-carbon (M N C) catalysts as Pt-free alternatives and the application of hybrid Pt/Fe-N-C catalysts. Fe-Sn-N-Cs have fourfold higher mass activity in diluted 0.5 mol L-1 phosphoric acid compared to a commercial Fe-N-C (Fig 1).[2] However, they still suffer from low stability. We found that the stability of Fe-N-Cs can be fixed by introduction of small amounts of Pt into the catalyst. Next to the catalyst, also the electrode is improved by investigation of different coating methods and binders.[3] For increase of membrane stability different PBI-based membranes are tested including cross-linked and inorganic filler-based membranes. The introduction of silicon carbide filler shows an increase of stability as well as moderate tolerance towards reformate (Fig. 1).[4,5] Additional to the MEA development, novel MEAs are also tested for their tolerance toward different reformate purities.