Iron, a versatile and abundant element
The earth overshoot day illustrates in a very specific way that since decades we are living and active above our resources. Sustainability becomes of importance for processes but also with respect to the materials in use. In this respect, I have the vision that earth abundant elements as iron with a distinct chemical tuning of their environment are possible substituents for critical raw materials.
That the environment has a tremendous influence can be seen from a comparison of iron and so-called FeNC catalysts. From the Pourbaix diagram it can be directly seen that iron – as element - is not stable under acidic conditions in the potential regime of relevance for oxygen reduction reaction (ORR) catalysis. In contrast, the local environment of iron that is provided in FeNC catalysts enables a stabilization and the catalysts can be applied even at harsh conditions. The ORR is of relevance in various fuel cell applications as well as for metal air batteries.1-3 It is suspected that in the FeNC catalysts iron is coordinated by nitrogen donor atoms and these molecular units are embedded in a surrounding carbon matrix.4-7 Nonetheless, it need to be pointed out, that induced by the typical preparation approach (a high temperature pyrolysis), these catalysts usually contain multiple iron species that hinder an unambiguous active site assignment.5, 7
In this talk I like to address some of our recent achievements with respect to the development of FeNC catalysts.1,4,8 Motivated by these findings and other, in the Chemistry Department at TU Darmstadt the Collaborative Research Center 1487 Iron, upgraded! was initiated that explores iron in different environments to gain a fundamental understanding of the interplay between iron and its surrounding. I will address the concept of the CRC and our vision.
In the last part of the presentation iron is considered as energy storage material. The collaborative project CleanCircles addresses all aspects from fundamentals towards large scale applications and also considering a socio-economical evaluation. I will address the recent findings of our subproject on the oxidation behavior of iron probed by Mössbauer spectroscopy.
Thus, it can be concluded that iron is a multifaceted and high-potential element with a broad field of applications.
 Kübler, M.; Wagner, S., et al. Energy Technology 2020, 8 (9), 2000433, doi: 10.1002/ente.202000433.
 Zhang, H.; Chung, H. T., et al. En. & Environm. Sci. 2019, 12 (8), 2548, doi: 10.1039/C9EE00877B.
 Haller, S.; Gridin, V., et al. Energy Technology 2021, 9, 2001106, doi: 10.1002/ente.202001106.
 Gallenkamp, C.; Kramm, U. I.; Krewald, V., Chem. Comm. 2021, 57 (7), 859, doi: 10.1039/D0CC06237E.
 Ni, L.; Gallenkamp, C., et al. Adv. En. Sustain. Res. 2021, 2(2), 2000064, doi: 10.1002/aesr.202000064.
 Ni, L.; Theis, P., Paul, S.; et al. Electrochimica Acta 2021, 395, 139200, doi: 10.1016/j.electacta.2021.139200
 Wagner, S.; Auerbach, H., et al. Angew. Chem. Int. Ed. 2019, 58 (31), 10486, doi: 10.1002/anie.201903753.
 Prössl, C.; Kübler, M., et al. J. Mater. Chem. A 2022, doi: 10.1039/D1TA04668C.