In Situ Infrared Study of Water−Sulfate Coadsorption on Gold(111) in Sulfuric Acid Solutions

Abstract

Potential-dependent reorientation of a water molecule, adsorption of sulfate, and interactions between water and sulfate on a highly ordered Au(111) electrode surface in sulfuric acid solutions have been investigated in situ as a function of applied potential by means of surface-enhanced infrared absorption spectroscopy. The spectrum of the water layer at the interface changes in both intensity and frequency as the applied potential changes due to the reorientation of water molecules. The orientations deduced from infrared spectra are in good agreement with the predictions made by molecular dynamics simulations at potentials below and around the potential of zero charge (pzc) of the electrode where sulfate adsorption is negligible. At potentials above the pzc, sulfate anion is adsorbed at 3-fold hollow sites on the (111) surface via three oxygen atoms. When the potential is increased and the fractional coverage of sulfate reaches to about one-half of full coverage, adsorbed sulfate anions start to form short-ranged domains and greatly change the water layer structure. Water molecules stabilize the sulfate domains by bridging neighboring sulfate anions via hydrogen bonding. The weak tunneling spots observed in the reported scanning tunneling microscopy images of the well-ordered (√3×√7) sulfate adlayers on (111) metal surfaces are attributed to water molecules that bridge adjacent adsorbed sulfate anions.

Hydrogen adsorption and hydrogen evolution reaction on a polycrystalline Pt electrode studied by surface-enhanced infrared absorption spectroscopy

“…Since the feature around 1250 cm -1 is commonly observed also for other metals deposited on Si [35,40,41] and not on Ag and Cu deposited on Ge [42], this band may be assigned to a S-O stretching mode of Si oxide on the prism. The potential dependence of the bipolar feature may not be due to an electrochemical reaction because the prism was fully covered by the Pt thin film and not in direct contact with the solution.…”

“…The potential dependent frequency shift clearly demonstrates that this band arises from adsorbed species. The band around 1700 cm -1 that grows as the potential is made more negative is the asymmetricδ(HOH) mode of H 3 O + ion [27,35]. The H 3 O + band appears to be shifted to lower frequencies as the potential is made more negative and merge into the δ(HOH) mode of water.…”

“…The bipolar bands at 3700-2500 and 1620 cm -1 are assigned to the OH stretching, ν(OH), and HOH bending, δ(HOH), modes, respectively, of water molecules at the interface [27,35]. Since the spectrum of interfacial water depends on applied potential through the changes in orientation and interactions with coadsorbed ions [27,35], the water bands are bipolar in shape.…”

Oriented Attachment and Membrane Reconstitution of His-Tagged CytochromecOxidase to a Gold Electrode: In Situ Monitoring by Surface-Enhanced Infrared Absorption Spectroscopy

“…The enhancement decays rapidly with the distance from the surface (<8 nm), which eliminates the bulk contribution to the IR spectrum and selectively detects signals from the adsorbed monolayer even when the surface is immersed in water. [19][20][21][22][23][24] In this work, we employ SEIRAS to demonstrate the successful reconstitution of an oriented monolayer of cytochrome c oxidase (CcO) into a lipid bilayer along the solid surface of gold. SEIRAS, which exploits the surface enhancement, monitors each single step of the surface modification in situ.…”

Two-Dimensional Correlation Analysis Useful for Spectroscopy, Chromatography, and Other Analytical Measurements

“…For example, time-dependent evolution and subsequent relaxation of the spectral signals arising from various excited constituents of the system as a consequence of the applied perturbation may be observed. It is also very common to collect dynamic signals as a direct function of the quantitative measure of the imposed physical effect itself, such as temperature, 13 pressure, 14 concentration, 15 stress, 16 electrical field, 19 and so on. Thus, dynamic signals need not intrinsically be time-dependent responses of the system to the applied perturbation, as long as they represent the systematic changes of analytical signals in the responses of the system to the given perturbation.…”