Transition and noble metal oxides for sustainable energy conversion and storage applications

3D transition metals (Ni, Co, Fe) and noble metals (Ir, Ru) and their oxides exhibit promising activity and stabilty towards oxygen evolution reaction (anode reaction in water electrolyzers). A full understanding of how these electrocatalysts work and degrade is essential for the knowledge-based design of electrode materials for hydrigen production. Here, we employ mulitmodal approaches to shed light on the activation and degradation processes of the electrocatalysts during reactions. For example, we used APT with X-ray-based-spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy and electrochemical measurements to investigate structural and compositional changes of 10 nm-sized Co-Fe spinel oxides after different cycles during oxygen revolution reaction. APT-data shows Co-rich and Fe-rih nanodomains in Co₂FeO4 nanoparticles due to the miscibility gap. We unveiled the temporal compositional and structural changes of oxide nanoparticles, at the atomic scale, clarifying how they degrade during oxidation and reduction cycles.

Publication:

W. Xiang, N. Yang, X. Li, J. Linnemann, U. Hagemann, O. Ruediger, M. Heidelmann, T. Falk, M. Aramini, S. DeBeer, M- Muhler, K. Tschulik, T. Li; 3D atomic-scale imaging of mixed Co-Fe spinel oxide nanoparticles during oxygen evolution reaction, Nature Communicatoins 13(1) (2022) 179. 

We also employed APT to reveal the three-dimensional structure of the first few atomic layers of electrochemically grown iridium oxide during OER. We revealed the formation of confined, non-stichiometric Ir-O species during oxygen evolution, and these metastable species gradually transform to IrO₂, providing stability improvement but a decrease in activity. Additionally, the elctrochemical growth of oxide in deuterated solutions allowed us to trace the hydroxy-groups and water molecules present in the regions of the oxide layer preferable for the oxygen evolution and Ir dissolution reactions.

Publication:

T. Li, O. Kasian, S. Cherevko, S. Zhang, S. Geiger, C. Scheu, P. Felfer, D. Raabe, B. Gault, K. Mayrhofer, Atomic-scale insights into surface species of electrocatalysts in three dimensions, Nature catalysis, 1(4) (2018) 300-305.