Pathways towards reduction of Pt-loading in HT-PEMFC

Kurzfassung

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) needs high Pt-catalyst loadings between 0.7-1.0 mgPt cm-2[1] at the electrodes due to phosphate-induced deactivation of Pt. In order to decrease the material costs of HT-PEMFC the reduction of expensive Pt-catalyst loading is needed. At this point our group has focused two pathways to lower the amount of Pt in membrane electrode assemblies (MEAs). On the one hand, the development of Pt-free metal-nitrogen-carbon (M N C) catalysts as alternatives and on the other hand, the improvement of catalyst layer (CL) for better catalyst accessibility. We will present our recent catalyst fabrication including alternative carbon supports in Fe-N-Cs e.g. activated biomasses [2] and aerogels as well as metal-organic framework (MOF)-based M-N-Cs and M-M-N-Cs like Fe-Sn-N-C. A comparison of mass activities determined from rotating-disc electrode (RDE) measurements show high activity of MOF based Fe-Sn-N-C catalyst of 8.3 A g-1(at 0.8VRHE in 0.5 mol L-1 H3PO4) compared to commercial catalyst PMF 011904 (3.3 A g-1). Next to the catalyst synthesis, three optimisation approaches of Fe-N-C-based catalyst layer (CL) will be shown. First, a comparison of two coating methods – ultrasonic spray- and doctor blade-coating – for gas diffusion electrode (GDE) fabrication is presneted. There, no significant impact on the HT-PEMFC performance is observed.[2] Second, the variation of PTFE binder amount in the CLs, which indicate an optimal binder of 20 wt.% and higher is shown.[3] Third, the effect of a non ionic additive (TergitolTM) on the ink stability and GDE performance is presented. Aside from complete Pt-free electrodes, hybride cathodes containing PtNi/C and Fe-N-C with reduced Pt-loading are investigated in HT PEMFC. Slower activation behavior of hybrid MEA and promissing performance is observed.[4] Moreover, Pt-loading reduced anodes are tested. All in all, this overview will provide novel insight into Pt-loading reduction for HT-PEMFC.