Interfacial water at a co-predosed platinum electrode: A surface enhanced infrared study with strong hydrogen evolution reaction control

Attenuated total reflection surface-enhanced infrared absorption spectroscopy, in conjunction with Gram-Schmidt intensity response and 2-dimensional correlation IR analyses, has been extended to study the structure and interaction of interfacial H₂O at a CO-predosed platinum electrode in 0.1 M HClO₄ with its potential navigated from the double-layer region to the strong hydrogen evolution reaction (HER) region. The strong HER enables at least part of the outer interfacial H₂O layers to be effectively expelled by tremendous amounts of H₂ bubbles dynamically formed on the Pt surface. The H₂ bubbles could effectively survive during a fairly fast potential excursion to a positive limit for CO stripping at which a single-beam spectrum was then acquired and used as the reference, facilitating the analysis of "quasi-absolute" spectra of the initial interfacial H₂O and CO at the Pt electrode prior to the significant HER. As a result, the broad vOH band may be deconvoluted into four peaks at ca. 3630, 3550, 3250, and 3450 cm^-1, assignable, respectively, to the innermost H₂O layer with hydrogen bonding broken (H₂O_free) and interacted with the underlying CO adlayer, the second layer of H₂O with hydrogen bonding partially broken, the outer icelike water layers, and the liquid-like water layers. The interaction of H₂O_free with the CO adlayer is much stronger than that expected simply from the hydrophobic effect of the latter as deduced from the stability of rather stable CO and H₂O_free co-structure even with a drastic HER condition, suggesting that a sort of chemical bonding may be involved.