This study uses atom probe tomography to investigate the 3D structure of 10 nm Co₂FeO₄ and CoFe₂O₄ nanoparticles during the oxygen evolution reaction (OER). Nanoscale spinodal decomposition is revealed in pristine Co₂FeO₄, with interfaces of Co-rich and Fe-rich nanodomains acting as trapping sites for hydroxyl groups, enhancing OER activity. However, Co₂FeO₄ activity decreases due to irreversible transformation to Co₃O₄ and Fe dissolution. CoFe₂O₄ shows negligible elemental redistribution but surface transformation to (FeIII, CoIII)₂O₃. The study provides 3D compositional insights into active sites and electrocatalyst deactivation during OER.

Weikai Xiang, Nating Yang, Xiaopeng Li, Julia Linnemann, Ulrich Hagemann, Olaf Ruediger, Markus Heidelmann, Tobias Falk, Matteo Aramini, Serena DeBeer, Martin Muhler, Kristina Tschulik, Tong Li