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Abstract:
Transition metal oxides are promising materials for the development of cost-effective catalysts for the oxygen evolution reaction (OER) in alkaline media. Understanding the catalysts’ transformations occurring during the harsh oxidative conditions of the OER remains a bottleneck for the development of stable and active catalysts. Here, we studied redox transformations of core–shell Fe3O4@CoFe2O4 oxide nanoparticles over a wide range of potentials by using operando near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in total electron yield (TEY) detection mode. The analysis of the NEXAFS spectra reveals that the Fe3O4 core strongly affects the surface chemistry of the CoFe2O4 shell under the OER conditions. The spinel structure of the particles with Co (II) in the shell is preserved at potentials as high as 1.8 V vs RHE, at which Co (II) is expected to be oxidized into Co (III); whereas Fe (II) in the core is reversibly oxidized to Fe (III).
