Electrochemical stability of the reconstructed Fe3O4(001) surface

D. Grumelli, T. Wiegmann, S. Barja, F. Reikowski, F. Maroun, P. Allongue, J. Balajka, G. S. Parkinson, U. Diebold, K. Kern, O. M. Magnussen

Instituto Nacional de Investigaciones Fisicoquimcas Teoricas y Aplicadas, Universidad Nacional de La Plata, CONICET La Plata, Argentine
Department Solid State Physics, Kiel University, 24118 Kiel, Germany
Departamento de Física de Materiales, Centro de Física de Materiales, University of the Basque Country (UPV/EHU-CSIC) Donostia-San Sebastián, Spain
Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain
IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
Laboratoire de Physique de la Matière Condensée, CNRS, IP Paris, 91128 Palaiseau, France
Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Max Planck Institute for Solid State Research, Stuttgart, Germany
Ecole Polytechnique Fédérale de Lausanne, Switzerland

Angew. Chem. Int. Ed. 59 (2020) 21904-21908

Establishing the atomic-scale structure of metal-oxide surfaces during electrochemical reactions is a key step to modeling this important class of electrocatalysts. Here, we demonstrate that the characteristic (√2×&ra;2)R45° surface reconstruction formed on (001)-oriented magnetite single crystals is maintained after immersion in 0.1 M NaOH at 0.20 V vs. Ag/AgCl and we investigate its dependence on the electrode potential. We follow the evolution of the surface using in situ and operando surface X-ray diffraction from the onset of hydrogen evolution, to potentials deep in the oxygen evolution reaction (OER) regime. The reconstruction remains stable for hours between -0.20 and 0.60 V and, surprisingly, is still present at anodic current densities of up to 10 mA cm-2 and strongly affects the OER kinetics. We attribute this to a stabilization of the Fe3O4 bulk by the reconstructed surface. At more negative potentials, a gradual and largely irreversible lifting of the reconstruction is observed due to the onset of oxide reduction.

Corresponding author: Doris Grumelli. Reprints also available from Gareth Parkinson (parkinson at iap_tuwien_ac_at).

Users with online access to Angewandte Chemie International Edition can load the article from the publisher.