Operando NRIXS and XAFS Investigation of Segregation Phenomena in Fe‐Cu and Fe‐Ag Nanoparticle Catalysts during CO2 Electroreduction

Operando nuclear resonant inelastic X-ray scattering (NRIXS) and X-ray absorption fine-structure spectroscopy (XAFS) measurements have been used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the CO 2 electrochemical reduction (CO 2 RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core-shell structure during CO 2 RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of ~ 36 % for CO in 0.1 M KHCO 3 at -1.1 V vs RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H 2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H 2 production. These results, together with the findings from NRIXS and XAFS, revealed that Ag is preferentially present on the surface of the FeAg NPs during CO 2 RR, while Cu is also likely to be mainly distributed on the surface of the FeCu NPs but with a larger degree of intermixing with Fe.