Probing active sites in iron-based catalysts for oxygen electro-reduction: A temperature-dependent 57Fe Mössbauer spectroscopy study

- A Fe-N-C catalyst almost exclusively containing isolated iron atoms was synthesized.
- 57Fe Mössbauer spectroscopy identifies two quadrupole doublets, D1 and D2.
- D1 and D2, attributed to FeN4 moieties in N-doped carbon, do not vary down to 5 K.
- The Lamb-Mössbauer factors of D1 and D2 were evaluated for the first time.
- A correlation between O2 reduction activity and the content of doublet D1 is found.