Determination of H Adsorption Sites on Pt/C Electrodes in HClO4 from Pt L23 X-ray Absorption Spectroscopy

• Published in: The journal of physical chemistry. B 2004-02, Vol.108 (7), p.2333-2344
• Main Authors: Teliska, M, O'Grady, W. E, Ramaker, D. E
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0356113

The adsorption of atomic hydrogen on a platinum electrode in 0.1 M HClO4 electrolyte was studied in situ with Pt L2,3 X-ray absorption spectroscopy (XAS). The Pt electrode was formed of highly dispersed 1.5−2.0-nm particles supported on carbon, and the Pt X-ray absorption fine structure data were collected at room temperature in transmission mode. A novel difference procedure utilizing the L3 spectra at different applied voltages was used to isolate the effects of H adsorption on the Pt electrode in the XAS spectra. The results obtained in this work are compared with similar results recently reported for H/Pt in the gas phase and with results obtained from real-space full-multiple-scattering calculations utilizing the FEFF8 code on model clusters. The data reveal a number of important points that are similar to those found in the gas phase:  (1) at low coverage the H is highly mobile and possibly delocalized on the surface, (2) at higher coverage it localizes into fcc sites, and (3) at very high coverage H is also found in atop sites presumably at or near edges. Point 3 is consistent with that found from previously reported spectroscopic data for Pt/C electrodes. Finally, a detailed interpretation of previously reported electrochemically modulated IR spectra, supporting the XAS analysis, suggests that the delocalized H exists at low coverage and has a profound affect on the water double layer.