STRUCTURE OF MATERIALS

142 ESRF

Introducing Highly Redox-Active Atomic Centers into Insertion-Type Electrodes for Lithium-Ion Batteries, Y. Ma (a,b), Y. Ma (a,b), G. Giuli (c), H. Euchner (d), A. Groß (d), G. Orazio Lepore (e), F. d Acapito (e), D. Geiger (f), J. Biskupek (f), U. Kaiser (f), H.M. Schütz (a,b), A. Carlsson (g), T. Diemant (h), R.J. Behm (a,h), M. Kuenzel (a,b), S. Passerini (a,b) and D. Bresser (a,b),

Adv. Energy Mater. 10, 2000783 (2020); https://doi.org/10.1002/aenm.202000783. (a) Helmholtz Institute Ulm (HIU) (Germany) (b) Karlsruhe Institute of Technology (KIT), Karlsruhe (Germany) (c) School of Science and Technology Geology Division, University of Camerino (Italy) (d) Institute of Theoretical Chemistry, Ulm

University (Germany) (e) CNR-IOM-OGG, Grenoble (France) (f) Central Facility for Electron Microscopy, Ulm University (Germany) (g) Thermo Fisher Scientific, Eindhoven (The Netherlands) (h) Institute of Surface Chemistry and Catalysis, Ulm University (Germany)

[1] M. Armand et al., J. Power Sources 479, 228708 (2020). [2] N. Loeffler et al., Johns. Matthey Technol. Rev. 59, 34 (2015).

DEGRADATION OF LaFe1-xPdXO3±δ PEROVSKITE-TYPE OXIDES IN BASIFIED AQUEOUS ETHANOL

Materials used for the generation of energy and chemical products often have to function in solvents that contain other chemicals. Here, an aqueous ethanol solvent, when combined with a base, causes a variety of degradative changes to a perovskite catalyst under mild conditions and even before any catalytic chemistry is considered.

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

CeO2 and Ce0.9Fe0.1O2 before and after lithiation (Figures 123a,b). For both materials, the data clearly reveal the reduction of Ce4+ to Ce3+, which is in line with the general solid solution- type de-/insertion mechanism. In the case of Ce0.9Fe0.1O2, however, the incorporated iron, occupying an off-centred position in the cubic structure compared to the cerium (Figure 123d in excellent agreement with theoretical calculations), is completely reduced to the metallic state, as highlighted by the comparison of the XANES data for pristine and lithiated Ce0.9Fe0.1O2 at the Fe K-edge (Figure 123c). This finding was rather surprising especially since the corresponding comparison of pristine and once lithiated and delithiated Ce0.9Fe0.1O2 via ex-situ high-resolution transmission electron microscopy (HRTEM) did not show any difference, thus confirming a well maintained crystal structure. The careful inspection of the ex-situ EXAFS data (Figures 123d,e) revealed that the metallic iron in the lithiated state forms extremely small subnanometric clusters

of about 2-4 Fe in close vicinity; but nothing larger than that, as would be expected in the case of a conversion-type reaction, resulting in the degradation of the crystal structure.

Summarising these findings, the following model is proposed: Besides the very homogeneous Fe distribution, there are presumably always two Fe3+ cations in direct vicinity, which is reasonable with regard to the need of balancing the aliovalent doping-induced point defects. In the reduced state, these iron atoms experience an increased attractive interaction, thus getting closer without destroying the crystalline host structure. Simultaneously, there are at least three Li+ needed close to the Fe dopant to reduce it from Fe3+ to Fe0, while its off-centred position allows for the required space. In this way, the available sites for lithium cations are substantially increased, which is eventually observed as greatly enhanced Li+ storage capability by about 200% compared to pure CeO2.

Perovskites are a much-researched class of materials for areas including catalysis [1], electro-catalysis [2] and solar applications [3]. Often, in these applications, they may be required to operate in contact with a liquid of non-neutral pH. For instance, in carbon- carbon coupling catalysis, where perovskite- type oxides have been shown to be active and selective materials [4], basic compounds are required to be present in excess. Moreover, the pharmaceutical industry, where carbon-carbon

coupling catalysis is an essential foundation, has formulated guides regarding preferred solvent systems; among which are mixtures of primary alcohols and water [5]. There is significant interest in understanding how some of these solvents, and the adjuncts that must be added to them to facilitate the desired chemistry, interact with catalytic materials, in the current case a LaFe1-xPdxO3±δ (where x = 0.1) perovskite-type oxide.