Contact : Fouad Maroun
One of the research topics of the ECM team is the synthesis and characterization of thin oxide films for oxygen evolution (OER). This reaction is the rate-limiting step in the decomposition of water. A large number of publications have shown that transition metal oxides are good catalysts for OER without a clear fundamental explanation of the catalytic process. The ECM team has tackled this problem (as part of an ANR project with Prof. O. Magnussen’s team in Germany) with an original approach based on the fabrication and characterization of epitaxial and atomically flat oxide layers. The model nature of these layers and the operando characterizations allowed us to determine the state of the catalyst surface under reaction conditions. We have developed and refined synthesis methods to prepare 10-40 nm thick layers of Co3O4, CoOOH, CoFeOx and Fe3O4, electrochemically deposited on gold crystals [Pacheco2023]. We have demonstrated by operando X-ray diffraction (XRD) on Co3O4 films the reversible transformation of the film surface over a sub-nanometric thickness before the onset of the OER [Reikowski2019, Wiegmann2022]. We have characterized the surface redox state by operando X-ray absorption (XANES) at the Co threshold and shown that the oxidation state of Co on the surface of the film changes from 2.7 to 3. This shows that the phase that forms on the surface of Co3O4 during the OER is of the CoOOH type [Bouvier2023].
AFM images of Co3O4 deposits (top left), catalytic activity for oxygen evolution (top right), schematic representing surface transformation as a function of potential (bottom).
Recent theses : Ivan Pacheco Bubi (2021) and Mathilde Bouvier (2021)
Collaborations : Institute of experimental and applied physics, université de Kiel (Allemagne)
Funding : ANR EC-MEC
Recent publications :
[Bouvier2023] Bouvier, M., Bubi, I. P., Wiegmann, T., Qiu, C. R., Allongue, P., Magnussen, O. M., Maroun, F., Unraveling the Cobalt Oxidation State at the Surface of Epitaxial Cobalt Oxide Films during the Oxygen Evolution Reaction by Operando X-ray Absorption Spectroscopy/Surface X-ray Diffraction, ACS APPLIED ENERGY MATERIALS, 2023, 6, 7335-7345
[Pacheco2023] Pacheco, I., Bouvier, M., Magnussen, O. M., Allongue, P., Maroun, F., Growth of Ultrathin Well-Defined and Crystalline Films of Co3O4 and CoOOH by Electrodeposition, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 2023, 170, 012501
https://doi.org/10.1149/1945-7111/acafaa
[Reikowski2019] Reikowski, F., Maroun, F., Pacheco, I., Wiegmann, T., Allongue, P., Stettner, J., Magnussen, O. M., Operando Surface X-ray Diffraction Studies of Structurally Defined Co3O4 and CoOOH Thin Films during Oxygen Evolution, ACS CATALYSIS, 2019, 9, 3811-3821
https://doi.org/10.1021/acscatal.8b04823
[Wiegmann2022] Wiegmann, T., Pacheco, I., Reikowski, F., Stettner, J., Qiu, C. R., Bouvier, M., Bertram, M., Faisal, F., Brummel, O., Libuda, J., Drnec, J., Allongue, P., Maroun, F., Magnussen, O. M., Operando Identification of the Reversible Skin Layer on Co3O4 as a Three-Dimensional Reaction Zone for Oxygen Evolution, ACS CATALYSIS, 2022, 12, 3256-3268
https://doi.org/10.1021/acscatal.1c05169