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

Sebastian Kunze,Beatriz Roldan Cuenya,Philipp Grosse,Ercan E Alp,See Wee Chee,Jiyong Zhao,Ilya Sinev,Miguel Bernal Lopez,Ioannis Zegkinoglou,Janis Timoshenko,Michael Y Hu,Hemma Mistry

doi:10.1002/anie.202010535

Abstract

Operando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO2 reduction (CO2RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO2RR 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 KHCO3 at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H2 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 H2 production.

Highlights

One of the most significant challenges in the field of catalysis is the development and optimization of experimental methods that allow the observation of a catalyst while at work.[1,2,3] This is especially difficult when nanomaterials are considered under realistic conditions, as for example, when trying to understand atomic segregation phenomena and ot-her structural/chemical modifications at liquid/solid interfaces during an electrochemical process.[4]
The formation of a core–shell structure during CO2RR for FeAg NPs was inferred from the analysis of the operando nuclear resonant inelastic X-ray scattering (NRIXS) data and X-ray absorption fine-structure spectroscopy (XAFS) measurements
After careful evaluation of the operando structural and chemical information extracted from two complementary synchrotron X-ray methods (XAFS and NRIXS), we demonstrate a significant reduction of iron oxide to metallic species under reaction conditions, accompanied by a structural transformation from an amorphous or atomically disordered phase to a crystalline structure

Summary

Introduction

One of the most significant challenges in the field of catalysis is the development and optimization of experimental methods that allow the observation of a catalyst while at work.[1,2,3] This is especially difficult when nanomaterials are considered under realistic conditions, as for example, when trying to understand atomic segregation phenomena and ot- Her structural/chemical modifications at liquid/solid interfaces during an electrochemical process.[4] A number of established methods are not directly applicable under reaction conditions due to decreased electronic mean free paths, scattering or lack of sufficient spatial resolution or chemical sensitivity. The structure and composition of the FeCu and FeAg catalysts during the reaction will be extracted from a synergistic combination of operando NRIXS and XAFS measurements and correlated with the selectivity trends of monometallic Cu, Ag and Fe NPs of similar size

Results and Discussion

Conclusion

Conflict of interest