Suitable epitaxial perovskite materials were selected at the start of the project and the analysis published as a review article that included the definition of prototypical mechanisms (doi: 10.1088/2515-7655/ab812f). Clear benchmark criteria for one of the prototypical mechanisms were enabled by calculation of Tafel slope and reaction order (doi: 10.1002/elsa.202100213). We clearly demonstrated a reduction of the Tafel slope by Co addition to a Mn oxide and thereby activated additional mechanistic steps (doi: 10.1002/celc.202200482); our analysis relates the change in metal redox to the change in Tafel slope.
We identified the requirements for beneficial restructuring from the erythrite crystal structure of a layered hydroxide and thereby turned corrosion in a beneficial process (doi: 10.1002/aenm.202101737). This opens the door to engineer the corrosion mechanism to improve other catalysts and ultimately to find repair mechanisms as an attractive alternative to the design of robust but usually less active electrocatalysts. Furthermore, we gained a better understanding of the formation of layered Ni hydroxide on LaNiO3 in collaborative work (doi: 10.1038/s41467-023-43901-z). In both cases, the restructured surface, i.e. a distinct active state that formed during operation, was beneficial for performance. Further information may be found in the press releases (
https://www.helmholtz-berlin.de/pubbin/news_seite?nid=23123;sprache=en;seitenid=1(s’ouvre dans une nouvelle fenêtre) https://www.helmholtz-berlin.de/pubbin/news_seite?nid=25906&sprache=en&seitenid=50901(s’ouvre dans une nouvelle fenêtre)). The reaction enthalpy of a layered Co oxide was obtained by analyzing the Eyring Polanyi equation where we innovated the treatment as three-dimensional data (doi: 10.1002/cctc.202301578). The precise experimental determination of reaction enthalpies is an important bridge to mechanistic work in the theory community.
X-ray absorption spectroscopy (XAS) was a key method to achieving the goals of the project. We reviewed combining electrochemistry and XAS, proposed a clear definition of operando for electrocatalysis and highlighted the importance of tracking states with sufficient time resolution (doi: 10.1002/anie.202211949). After the flow cell with a unique optical O2 detector had been commissioned, we jointly detected the evolved oxygen and spectral changes in XAS and UV-vis spectroscopy (doi: 10.26434/chemrxiv-2024-srmwb). The electronic structure of limiting states was elucidated by XAS and UV-Vis (doi: 10.26434/chemrxiv-2024-srmwb) which revealed that the availability of Co(IV) becomes important for the mechanism at high current density and pH, i.e. more applied electrochemical conditions.
Overall, results were disseminated to divers audiences at conferences, by peer-reviewed journal publications (Nat. Commun, Angewandte Chemie, Adv. Energy Mater, etc), press releases on publication highlights, public outreach activities (e.g. Berlin Science Week) and on social media.
