Hydroxide Adsorption on Ag(110) Electrodes:  An in Situ Second Harmonic Generation and ex Situ Electron Diffraction Study

Abstract

The adsorption of hydroxide on the Ag(110) surface has been studied with cyclic voltammetry, in situ second harmonic generation (SHG), and ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED). OHis found to be adsorbed on the Ag(110) surface at potentials negative of the potential of zero charge, forming small antiphase domains of c(2 × 6) symmetry. Further adsorption leads to longer-range order and the removal of antiphase domain boundaries and is associated with a current peak in the cyclic voltammogram (CV). Concurrently, a change in symmetry patterns is observed in SHG. A c(2 × 2) pattern gradually replaces the c(2 × 6) pattern as the potential, and the OHcoverage, is increased. At the beginning of the second current wave, another symmetry change takes place which is accompanied by a sharp change in the LEED pattern from a c(2 × 2) pattern to a (1 × 1) pattern with strong background, indicating a disordered adlayer. However, RHEED results show that some patches of c(2 × 2) structure remain on the surface. The correlation between SHG and diffraction measurements and comparison of the information obtained from each technique allow us to develop a detailed picture of the structures and electronic effects at the Ag(110)|alkaline electrolyte interface.

A Comparative Study of Hydroxide Adsorption on the (111), (110), and (100) Faces of Silver with Cyclic Voltammetry, Ex Situ Electron Diffraction, and In Situ Second Harmonic Generation

“…SHG is a surface specific technique; thus, only the response of the top few layers of atoms of the surface is measured and it has been shown to be very sensitive to small changes at the electrode/electrolyte interface. SHG has been used to study Ag single-crystal electrodes in the absence of adsorbates, in the presence of metal under-potential deposition (upd),9c in the presence of halides, in alkaline fluoride electrolytes, as well as at silver electrodes covered by organic films . Changes in the electronic structure of the surface due to adsorbates can be detected in the intensity of the SH light produced and in its anisotropy.…”

“…The anisotropic part of the signal gives an insight into changes of symmetry on the surface. A varying phase difference between the isotropic and anisotropic contributions to the signal may also indicate changes in surface structure. ,11d …”

Impedance study on the capacitance of silver electrode oxidised in alkaline electrolyte

“…The real surface area of the polycrystalline Ag electrodes was calculated on the basis of the double-layer capacitance determined from EIS measurements at potentials of hydrogen evolution region (HER) (−1100 to −1300 mV), where the electrode surface is oxide-free. At higher potentials, the C dlm measurements may be complicated by adsorption of anions [15,35,54,55] or pre-monolayer surface oxidation, suggested in [56]. Further on, the C dlm varies with the electrode potential between the onsets of the surface oxidation and HER [19,57].…”

“…Silver oxidation in an alkaline electrolyte starts at ca. 10 mV vs. Hg|HgO; the usually reported oxidation products are Ag 2 O and AgO, depending on the oxidation potential [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. AgO is described as a mixture of Ag(I) and Ag(III) species [11,39,40].…”

Adsorption and Oxidation Dynamics of Disperse Orange 3 on a Polycrystalline Pt Electrode Studied by In Situ Second Harmonic Generation

“…Over the past three decades, the adsorption and reaction mechanism of molecules on a Pt electrode surface have been widely studied by various classical electrochemical methods and in situ spectroscopic techniques. ,− Of all the spectroscopic techniques, second-order nonlinear optical spectra, such as second harmonic generation (SHG) and sum-frequency generation (SFG), exhibit unique advantages in the study of buried interfaces because of their intrinsic interfacial selectivity and sensitivity, which allows the extraction of information about adsorption − and electrochemical reactions. ,− To date, these studies on adsorption have mainly focused on the influence of adsorption on single-crystal electrode symmetry, ,− the relative surface coverage and the orientation of the adsorbates as a function of applied potential, − adlayer structures, , and adsorption kinetics. , It has been proven that the surface coverage and configuration of adsorbed molecules could vary with the applied potential. Liu et al studied the nonequilibrium adsorption process of 4-(4-(diethylamino)­styryl)- N -methyl­pyridinium iodide (D289) molecules at polycrystalline Pt electrode/electrolyte interfaces using SHG spectra, indicating that the adsorption of D289 from bulk solution onto Pt electrodes follows a fast adsorption and a slow reorientation step .…”