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

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 Fe-57 Mossbauer 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 CoFeOx films in 1M 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. The capturing of high valent iron in a catalytic reaction is important but difficult task. Here, the authors report identification of a high-valent Fe(IV)-species with different spectroscopic tools such as Mossbauer spectroscopy and X-ray absorption spectroscopy during the course of an oxygen evolving reaction.

Automated summary

The alloying of iron in oxidic cobaltate catalysts can enhance the oxygen evolution reaction activity, with Fe4+ showing the highest concentration in the 40-60% Fe alloying range, indicating its crucial role in activating the catalyst for oxygen evolution.