Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction

Nancy Li; Ryan G Hadt; Dugan Hayes; Lin X Chen; Daniel G Nocera

doi:10.1038/s41467-021-24453-6

Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction

Nat Commun. 2021 Jul 9;12(1):4218. doi: 10.1038/s41467-021-24453-6.

Authors

Nancy Li¹, Ryan G Hadt^{2

3}, Dugan Hayes^{4

5}, Lin X Chen^{6

7}, Daniel G Nocera⁸

Affiliations

¹ Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
² Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA. rghadt@caltech.edu.
³ Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA. rghadt@caltech.edu.
⁴ Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA. dugan@uri.edu.
⁵ Department of Chemistry, University of Rhode Island, Kingston, RI, USA. dugan@uri.edu.
⁶ Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA.
⁷ Department of Chemistry, Northwestern University, Evanston, IL, USA.
⁸ Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA. dnocera@fas.harvard.edu.

Abstract

Iron alloying of oxidic cobaltate catalysts results in catalytic activity for oxygen evolution on par with Ni-Fe oxides in base but at much higher alloying compositions. Zero-field ⁵⁷Fe Mössbauer spectroscopy and X-ray absorption spectroscopy (XAS) are able to clearly identify Fe⁴⁺ in mixed-metal Co-Fe oxides. The highest Fe⁴⁺ population is obtained in the 40-60% Fe alloying range, and XAS identifies the ion residing in an octahedral oxide ligand field. The oxygen evolution reaction (OER) activity, as reflected in Tafel analysis of CoFeO_x films in 1 M KOH, tracks the absolute concentration of Fe⁴⁺. The results reported herein suggest an important role for the formation of the Fe⁴⁺ redox state in activating cobaltate OER catalysts at high iron loadings.

Grants and funding

DE-SC0017619/U.S. Department of Energy (DOE)