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Published February 2013 | public
Journal Article

High-resolution electron energy loss spectroscopy of anions chemisorbed on electrode surfaces: The effect of counter cations

Abstract

In the course of experiments that included Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS) on cation exchange at benzoquinone sulfonate chemisorbed on a Pd(111) electrode, it was found that, whereas the AES spectra remained invariant as the counter cation was varied from H^+ to K^+ to Cs^+, profound changes occurred in the HREELS spectra. Specifically, the intensity of the spectral features decreased noticeably when H^+ was replaced with K^+. And, when the K^+ ions were exchanged with Cs^+, nothing but a flat-line (dead) spectrum was observed; even the elastic peak was completely attenuated. When the Cs^+ ions were displaced by protons, the initial undiminished spectrum was fully restored. This outcome, while unrelated to cation-exchange selectivity, is of exceptional significance in surface electron spectroscopy. It appears that the positive ions on the surface attracted the low-energy incident electrons such that backscattering towards the energy analyzer was hindered; partially by K^+ but totally by the larger Cs^+ ion. The use of HREELS to examine the molecular integrity of chemisorbed anionic species must thus take cognizance of the possibility that the counter cation chosen to preserve interfacial-layer electroneutrality can have a profound effect. To circumvent such complication, low-valent and small-radii cations will have to be employed. In addition, although subject to instrument limitations, higher incident-electron energies could be adopted. AES, with incident-electron energies in the kV range, is impervious to the presence of counter cations.

Additional Information

© 2012 Elsevier B.V. Received 23 October 2012. Received in revised form 5 November 2012. Accepted 6 November 2012. Available online 15 November 2012. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, as follows: The surface spectral analysis was supported through the Office of Science of the U.S. Department of Energy under Award No. DE-SC0004993; the adlayer preparation and characterization were supported by The Welch Foundation (A-1064). JES would like to acknowledge a graduate fellowship provided by the National Institute of General Medical Sciences and the National Institutes of Health.

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023