Study of Localized Carbon Monoxide Behavior on Polycrystalline Pt Electrode Surface Using Compressive Sensing Sum Frequency Generation Microscopy Combined with Electrochemistry

Date

2021-05

Authors

Li, Hao

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Abstract

Surface science is an important discipline in physical chemistry due to the unique environment of the surfaces compared to a bulk volume. CO-Pt electrode system is a typically complicated system that involves multiple interfaces. The adsorption and oxidation process of CO on Pt electrode surface is of great importance to be studied in the fuel cell system to solve the anode poisoning problem. Spectroscopy and microscopy techniques are necessary to be applied to reveal the difference of CO behavior on a heterogeneous Pt surface for an in-situ study. Compressive sensing sum frequency generation microscopy (CS-SFGM) was applied to study the CO adsorption on the polycrystalline Pt electrode surface. The crystal facets of heterogeneous polycrystalline Pt domains were determined by electron backscatter diffraction (EBSD). The SFG images stack obtained from broadband IR system contains the spectroscopic information of CO for in-situ adsorption behaviors study. Localized SFG spectra of C≡O stretching mode revealed the difference of CO behaviors on different crystal domains compared to the average spectrum. The contact potentials between the domains caused by the different work functions change the electron density of each domain, which results in the redshift of C≡O vibrational peak. The Stark shift effect of each crystal domain was studied under potential control. The SFG spectra were fitted at every single pixel to map the peak wavenumber and Stark shift values distribution of C≡O stretching mode. The Stark shift values map shows the non-local distribution across the whole surface. CS-SFG Multi-scale Video (MUVI) was applied to study the CO oxidation process on the polycrystalline Pt electrode surface with a scanning potential. The optical flow technique was applied to improve the image quality and the time resolution of the MUVI. The Sum-to-one (STOne) pattern was applied to save the time of the optical flow calculation. An SFG MUVI experiment with the recording of the linear movement of an arrow-shaped gold film deposited on a silicon wafer was applied to test the improvement with the optical flow technique. The CO oxidation process was monitored at different potentials from the SFG MUVI experiment. The disappearance of the CO signal was captured with a blurry SFG image frame.

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Keywords

surface science, sum frequency generation spectroscopy, microscopy, compressive sensing, CO adsorption, CO oxidation, polycrystalline Pt electrode, nonlinear optical, laser

Citation

Portions of this document appear in: Li, Hao, Kevin F. Kelly, and Steven Baldelli. "Spectroscopic imaging of surfaces—Sum frequency generation microscopy (SFGM) combined with compressive sensing (CS) technique." The Journal of Chemical Physics 153, no. 19 (2020): 190901.