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 νOH 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 (H2Ofree) 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 H2Ofree 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 H2Ofree co-structure even with a drastic HER condition, suggesting that a sort of chemical bonding may be involved.