Project C05

C05 - Controlling electron-driven chemistry by intercalation Understanding multi-electron transfer reactions at manganite spinel surfaces is the focus of this project. After successful demonstration of both in situ Li intercalation and deintercalation during the first funding period, we succeeded to control the rate of oxygen evolution by tuning the composition of LixMn2O4 in the second funding period. However, we uncovered that an established property-activity relationship, namely the octahedral eg occupancy as a descriptor, does not work for all variations of composition, prompting the need for in situ studies during catalytic activity.

Fig1 Figure. Combining quantitative electrochemistry, high-resolution spectroscopy and imaging with the simulations performed in project C03 will reveal the mechanisms controlling the oxygen evolution reaction (OER) at the surface of LiMn2O4.

C05 - Kontrolle Elektronen-getriebener Chemie durch Interkalation Ein besseres Verständnis von Vielelektronentransferreaktionen an Manganat-Spinelloberflächen ist der Fokus dieses Projektes. Nach erfolgreicher Demonstration sowohl von in situ Li-Interkalation als auch Deinterkalation in der ersten Förderperiode konnten wir in der zweiten Förderperiode die Rate der Sauerstoffentwicklung durch Variation der Zusammensetzung von LixMn2O4 kontrollieren. Wir fanden jedoch, dass eine etablierte Eigenschaft-Aktivitätsbeziehung, nämlich die oktaedrische eg Besetzung als Deskriptor, nicht für alle Variationen der Zusammensetzung funktioniert, was die Notwendigkeit von in situ Studien während katalytischer Aktivität erforderlich macht.

Fig2 The Cover Feature illustrates the interplay between the activity for the oxygen evolution reaction and the battery charge state of LiMn2O4 when used as a catalyst. The electrocatalyst remains in the discharged battery state at pH 14, whereas a charged battery state is observed as manganese oxidizes at lower pH values, which leads to catalyst deactivation. More information can be found in the Article by M. Baumung et al. in ChemPhysChem on page 2981 in Issue 22, 2019.

Grafik_C05-1_kleiner The cover art illustration shows lithium manganese oxide particles, a commonly used electrode material. One of the long-standing challenges is the microstructural characterization of the electrode material itself and identifying the influence of the different microstructures on the (de)intercalation of Li ions. Using atom probe tomography, it was possible to identify different phases, phase segregation as well as a lamellar microstructure and their effect on charging/discharging. Using this information, it should be possible to further improve electrode materials. You can read more in the Full Paper by Johannes Maier et al. in the Journal Energy Technology on page 1565 in Issue 12, 2016 (DOI: 10.1002/ente.201600210).

Video of in-situ lithiation of a single crystalline LMO specimen in the TEM. The lithium tip is visible in the lower left corner. Strain and microstructural contrast reveal a sharp interface between the untransformed single crystal on the top right and the lamellar structure in the transformed region on the bottom left. More information can be found in the Article by T. Erichsen et al. ACS Appl. Energy Mater. on page 5405 in Issue 3, 2020.