| AVS 62nd International Symposium & Exhibition | |
| In-Situ Spectroscopy and Microscopy Focus Topic | Tuesday Sessions |
| Session IS+AS+SS-TuA |
| Session: | Environmental TEM Studies for Catalytic and Energy Materials |
| Presenter: | Sophie Carenco, Lawrence Berkeley National Laboratory |
| Authors: | C.S. Bonifacio, University of Pittsburgh H.L. Xin, Brookhaven National Laboratory S.C. Carenco, Lawrence Berkeley National Laboratory M.B. Salmeron, Lawrence Berkeley National Laboratory E. Stach, Brookhaven National Laboratory J.C. Yang, University of Pittsburgh |
| Correspondent: | Click to Email |
Bimetallic nanoparticles (NPs) possess novel catalytic, optical, and electronic properties compared to their monometallic counterparts. These catalytic properties can be controlled by fine-tuning the NP structure and dimension, surface oxidation, and chemical composition. For instance, bimetallic NPs with a core-shell structure can allow for fine tuning of reactivity, averting sintering issues in the core, and even increase tolerance to high temperature exposure. Above all, elemental segregation in the core-shell structure has been demonstrated as a potential route of modifying the NPs catalytic properties through in situ gas reaction studies. To confirm this hypothesis, we have used in situ imaging and spectroscopy techniques to study Ni-Co core-shell NPs under environmental conditions to provide direct evidence of elemental redistribution during reaction . Two pairs of oxidation and reduction reactions were performed in an environmental transmission electron microscope (ETEM) at 0.3 Torr in O2 and H2 gas at 220°C and 270°C, respectively. Electron diffraction patterns and electron energy loss spectroscopy (EELS) maps showed a reaction-driven restructuring of the core-shell NPs with Ni species migrating to the NP surface by the 2nd reduction cycle. These results are in agreement with previous ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) studies of the same NPs under identical reaction conditions. Furthermore, the ETEM results confirm the NP structure without erroneous interpretations that may result from post-mortem analysis of the samples. Quantitative analysis of the EELS results is underway to identify the valence states during the oxidation-reduction reactions. Correlation of the reaction-driven restructuring of NPs with the electronic structure changes from ETEM and AP-XPS will be provide insight into the optimum reaction conditions, i.e., catalytic properties, of the Ni-Co core-shell NPs in challenging reactions such as selective CO2 reduction.