Résumé
The design of new active and cost-effective heterogeneous catalysts for the oxygen evolution reaction (OER) has been the subject of intense researches in the past decades.
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Nevertheless, in contrary to other fields, no clear and handy physical parameters currently allow for the fast identification of new materials. A common approach developed so far was to consider the surface of the OER catalysts as stable and providing adsorption sites for the oxygen evolution to proceed, with the best catalyst binding oxygen neither too strongly nor to weakly. However, this simple and elegant approach is questioned by recent works demonstrating reconstruction and/or amorphization process for highly active transition metal oxide (TMO) catalysts.
2,3
It then becomes critical to understand if the TMO surface stability set up a boundary for the development of OER catalysts or if, in contrary, it can be used as a platform to potentially form new active surfaces alike what has been developed for bimetallic oxygen reduction reaction catalysts (PtNi, PtCu etc.).
4,5
More precisely, recent discoveries suggest that the surface of highly active TMO can participate to the OER mechanism with the possibility of a direct coupling of surface oxygen during the oxidation process, leading to a constant bond breaking/formation process on the surface.
6,7
Therefore, it is of prime importance to unambiguously determine the physical parameters governing the participation of the surface to the OER mechanism.
To alleviate such complex question, we designed OER catalysts with the perovskite structure that contain a sacrificial alkaline cation that can be selectively leached out from the perovskite structure at a given potential. This selective leaching not only allows for the modification of the electronic structure of the catalyst by oxidizing the transition metal, but we also demonstrate that it governs the surface reconstruction, both effects leading to the formation of a new surface with greater OER activity than the state-of-the-art IrO
2
catalyst. The effect of the electrochemical leaching/activation was studied by employing HRTEM coupled with XAS measurements, allowing for the determination of the crystal and electronic structures of the new surface. Combining these measurements with DFT calculations unlocked the fundamental understanding of the mechanism at play, and more precisely the activation of the lattice oxygen reactivity and its participation to the oxidation process.
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