Water electrolysis is a promising and environmentally friendly means for renewable energy storage. Recent progress in the development of anion exchange membranes (AEMs) has provided new perspectives for high-performance anode catalysts based on transition metal oxides (TMOs) for the sluggish anodic oxygen evolution reaction (OER). Here, we report on core–shell nanoparticles (Fe3O4@CoFe2O4) which allow combining an electrocatalytic shell (CoFe2O4) with a conductive core (Fe3O4). Such an original approach significantly minimizes critical Co content in the catalyst and avoids addition of unstable conductive carbon black. The core–shell nanoparticles outperform Co(1−x)Fe(2+x)O4 nanoparticles and show an exceptional OER activity per Co unit mass (2800 A gcobalt−1 at 1.65 V vs. RHE) suggesting synergistic interaction between the core and the shell. Along with the core–shell structure, the size of the Fe3O4 core is a critical parameter, with a large conductive Fe3O4 core being beneficial for OER enhancement.

This project was financially supported by the Foundation for Frontier Research in Chemistry. We thank the Helmholtz-Zentrum Berlin für Materialien und Energie for the allocation of synchrotron radiation beamtime. The authors acknowledge Juan Velasco Velez for his help on the synchrotron beamline as well as Vinavadini Ramnarain, Barbara Freis and Théo Lucante for the TEM images. STEM and EELS measurements have been performed at the Laboratorio de Microscopías Avanzadas (LMA) at the Universidad de Zaragoza (Spain). I. M. acknowledges the funding from IdEx Université de Strasbourg. R. A. and S. H. acknowledge the funding from the Spanish MICINN (project grant PID2019-104739GB-100/AEI/10.13039/501100011033), from the Government of Aragon (project DGA E13-20R) and from the European Union H2020 program “ESTEEM3” (823717).

This article is part of the themed collection: Recent Open Access Articles.

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