German Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities

New insights on the identification of iron structures in Fe-N-C catalysts by NIS and Mössbauer spectroscopy

18 Sept 2018, 16:00

1h 30m

Fakultät für Maschinenwesen der Technischen Universität München

Poster P9 Catalysis Poster session 2

Speaker

Stephan Wagner (Technische Universität Darmstadt, FG Catalysts and Electrocatalysts)

Description

In proton exchange fuel cells (PEFC) the hydrogen oxidation reaction and oxygen reduction reaction are catalysed by platinum-based catalysts. However, for economic reasons it is anticipated to replace platinum on the cathode for the oxygen reduction reaction (ORR). Fe N C catalysts are the most prominent substitute. Molecular FeN4 centres were identified by different groups as ORR active sites [1-5]. However, the oxidation state and structure remains under debate, but it is crucial for further improvement of Fe-N-C catalysts. Recently, we were able to show that sulphite ions can be used as poison for Fe-N-C catalysts [6]. The comparison of different catalysts gives indications of systematic changes in the iron signature. However, due to the ambident character of sulphite ions the interpretation is not straight forward.
In order to get additional insights, temperature dependent Mössbauer spectroscopy and Nuclear Inelastic Scattering (NIS), were used to refine our model of iron sites present in these catalysts. DFT calculations are used to modulate the partial density of iron states (pDOS).
On the basis of this we are able to identify some identic and some changing iron sites in the as-prepared and poisoned catalyst, that gives new insights on the nature of ORR activity in Fe-N-C catalysts.
Acknowledgement: The results based on the beamtimes at PETRA III (I-20160285 and I-20170383). Financial support by the BMBF within the cooperation project NUKFER (05 K16 RD1), Fe-N-C-StRedO (03XP0092) and from the TU Darmstadt Graduate School Energy Science and Engineering (ESE, GSC1070) is gratefully acknowledged. The authors are grateful for the beamtimes at the P01 beamline.

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