S C

IE N

T IF

IC H

IG H

LI G

H T

S S

T R

U C

T U

R E

O F

M A

T E

R IA

L S

1 3 7 I H I G H L I G H T S 2 0 2 1

PRINCIPAL PUBLICATION AND AUTHORS

Electrochemical Strain Dynamics in Noble Metal Nanocatalysts, R. Chattot (a), I. Martens (a), M. Mirolo (a), M. Ronovsky (a), F. Russello (a), H. Isern (a), G. Braesch (b), E. Hornberger (c), P. Strasser (c), E. Sibert (b), M. Chatenet (b), V. Honkimäki (a), J. Drnec (a), J. Am. Chem. Soc. 143, 17068-17078 (2021); https:/doi.org/10.1021/jacs.1c06780 (a) ESRF (b) Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble (France) (c) Electrochemical Energy, Catalysis and Material Science Laboratory, Department of Chemistry, Technische Universität Berlin, Berlin (Germany)

REFERENCES

[1] I. Martens et al., ACS Appl. Energy Mater. 2 (11), 7772-7780 (2019).

(oxygen reduction and fuel oxidation) and stability (oxidation and dissolution), the measurement of the lattice parameter using this simple diffraction approach allows experimental access to this descriptor during measurements under operando conditions in device- relevant sample environments. This constitutes a major advantage compared to spectroscopic techniques, and is expected to find a wide range of applications.

In light of previous Density Functional Theory (DFT) calculations, this work shows that the strain variation amplitude associated with molecular adsorption is not expected to significantly alter the electro-catalytic properties of nanoparticles in the case of the Oxygen Reduction Reaction (ORR) on Pt.

Facile oxygen transport at the metal support interface improves the stability of single-atom Pd/CeO2 catalysts

Catalysis by atomically dispersed noble metals is a new frontier in heterogeneous catalysis. Stability against sintering under reaction conditions remains a significant challenge. By combining in-situ spectroscopy tools, it is revealed how oxygen migration from reducible ceria supports stabilises Pd single atoms, the active sites for low-temperature CO oxidation.

Isolated metal atoms stabilised by a support represent a new class of heterogeneous catalysts for which the use of expensive transition metals is maximised [1]. Atomically

dispersed noble metals supported on CeO2 can be used to catalyse low-temperature CO oxidation, reducing automotive emissions during cold start [2]. In order to apply single-atom catalysts (SAC) in practice, it is pivotal to improve their stability, as the atomically dispersed metal atoms are prone to clustering under reaction conditions. The usual approach to increase stability is to deposit very low amounts of the catalytically active metal (< 0.1 wt.%) on a support [3], but this can severely limit overall activity.

An alternative approach involves the use of flame spray pyrolysis (FSP) to prepare single-atom Pd/CeO2 catalyst with a much more realistic metal loading (1 wt.% Pd, 1PdFSP). This catalyst is already active in CO oxidation well below 100°C. Detailed characterisation shows that part of the Pd atoms are dissolved in the ceria

Fig. 118: a) Pd 3d NAP-XPS spectra during CO oxidation at 300°C. b) Evolution of Pd K-edge XANES and the CeO2 unit-cell parameter of a 5PdFSP catalyst during temperature-programmed reduction in CO monitored by in-situ XAS/WAXS.