Pt-free Fe-N-C Catalysts for the ORR in HT-PEMFC – Investigation of Carbon Black-based Fe-N-C and commercial Fe-N-C

Kurzfassung

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are promising candidates for the sustainable conversion of chemical into electrical energy with the option of utilizing sustainable fuels like green methanol. The use of methanol is beneficial if no hydrogen infrastructure is available and only possible due to the high operating temperature of 150-180 °C that increases the catalyst tolerance towards fuel impurities like CO. However, due to the partial deactivation of the Pt catalysts by phosphates in HT-PEMFC, high loadings of Pt with up to 1 mg cm-² on both electrodes are necessary in HT-PEMFCs.[1] Thus, the increasing Pt price limits a further commercialisation of HT-PEMFCs. Therefore, platinum group metal (PGM)-free catalysts are under investigation as replacement for the scarce noble metals. Promising candidates are Fe-N-C materials consisting of Fe-N sites which are incorporated into a graphitic carbon network. In this presentation an overview of Fe-N-C synthesis, characterisation and application in HT-PEMFC will be given. A carbon support-based synthesis with carbon blacks like Black Pearls® as matrix for Fe-N sites will we presented. Furthermore, physical characterization in terms of X-ray photoelectron spectroscopy (XPS) for analysis of surface elemental content and transmission electron microscopy (TEM) images with energy dispersive X-ray spectroscopy (EDS) for evaluation of the elemental distribution will be shown.[2] Next, activity data acquired with a rotating-ring disc electrode of a Black Pearl-based Fe-N-C and a commercial Fe-N-C from Pajarito Powder, which is fabricated through a sacrificial support method, will be compared. The commercial catalyst shows a slightly higher mass activity at 0.8 V of 2.2±0.4 A g-1 compared to the Black Pearl-based Fe-N-C with 1.1 ±0.1 A g-1 Finally, the application of the previous mentioned Fe-N-Cs in HT-PEMFC as cathode catalyst will be presented, showing significantly higher performance for the commercial Fe-N-C (Figure 1 b). These performance discrepancies can be attributed to differences in the catalyst’s activity on the one hand but are also evoked by the structure of the gas diffusion electrode, on the other hand. This talk will highlight our past work on Fe-N-Cs and the challenges to overcome with a catalyst able to compete with Pt/C.