Structure of Water at the Electrified Platinum−Water Interface:  A Study by Surface-Enhanced Infrared Absorption Spectroscopy

Abstract

Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode is used to examine the structure of water on a polycrystalline Pt electrode in H2SO4 and HClO4 as a function of applied potential. The electrode surface covered with CO is used as the reference in recording spectra, which enables us to obtain the absolute infrared spectrum of the interfacial water layer (monolayer or bilayer) in contact with the surface with negligible interference from the bulk water. The spectrum of the interfacial water is largely different from that of bulk water and changes around the potential of zero charge of the electrode. The spectral changes are ascribed to the potential-dependent reorientation of water molecules from a weakly hydrogen-bonded oxygen-up orientation at the negatively charged surface to a strongly hydrogen-bonded nearly flat orientation at the positively charged surface in agreement with theoretical simulations reported in the literature. Clear experimental evidence of the formation of a stable ice-like structured water on the positively charged surface is reported.

The effect of pH on the electrocatalytic oxidation of formic acid/formate on platinum: A mechanistic study by surface-enhanced infrared spectroscopy coupled with cyclic voltammetry

“…and a medium strong band at ~1850 cm -1 assigned to linear CO (CO L ) and bridge-bonded CO (CO B ), respectively. The dip at 1610 cm -1 is the bending mode of water that was removed from the interface upon adsorption of CO [42]. The CO bands disappear at around 0.8 V due to the oxidative removal of CO ads and a new band emerges at 1325 cm -1 at around 0.5 V. This band has been assigned to the symmetric O-C-O stretching mode of bridge-bonded adsorbed formate [9], while the asymmetric O-C-O stretching mode of the bridge-bonded adsorbed formate, expected around 1590 cm -1 , is not observed in the spectra due to the surface selection rule in SEIRAS [43].…”

On the oxygen reduction reaction in phosphoric acid electrolyte: Evidence of significantly increased inhibition at steady state conditions

“…To the best of our knowledge no previous investigations of the time dependence of these processes were performed that highlight the significant differences between the behavior of sulfuric and phosphoric acid. In contrast in general it is assumed that anion adsorption from phosphoric and sulfuric acid act similar, while perchloric acid exhibits only weak or no blocking [1,2,[23][24][25][26][27].…”

ATR-SEIRAS study of CO adsorption and oxidation on Rh modified Au(111-25 nm) film electrodes in 0.1 M H2SO4

“…They were identified as the OH stretching of isolated interfacial water molecules (ν OH1 ) [52,53], the OH stretching of the hydrogen bonded water (ν OH2 ) and the bending mode of interfacial water (δ HOH ), respectively. The band intensities of all the three water bands increased with time during CO adsorption, indicating the coadsorption of water with the CO adlayer, as described by Osawa [54], with one (isolated) OH bond buried in CO adlayer and the other (hydrogen bonded) OH pointing up into solution. Moreover, we stress that they did not disappear after purging with Ar, proving that they are related to CO adsorbed on Rh sites.…”