Structure and activity relations in the hydrogen peroxide reduction at silver electrodes in alkaline NaF/NaOH electrolytes

The electrochemical interface between polycrystalline silver and alkaline NaF/NaOH electrolytes at various pH values has been studied by means of cyclic voltammetry and ac-impedance spectroscopy. Hydroxide electrochemisorption has been observed in a wide potential range (between −1.1 and 0 V SCE depending upon pH). Study of the hydrogen peroxide reduction at silver rotating-disc electrodes in alkaline NaF/NaOH electrolytes has proved the existence of a slow chemical step in the reaction mechanism, its rate being strongly affected by the submonolayer surface oxidation. The reaction scheme is proposed for the hydrogen peroxide reduction, which takes into consideration the structure of the adsorbate layer at the electrode/electrolyte interface at the variable potential

In situ Raman spectroscopy studies of the interface between silver(111) electrodes and alkaline NaF electrolytes

The electrochemical interface between Ag(111) single crystal and NaF + NaOH electrolytes at various pH values has been studied using cyclic voltammetry and in situ Raman spectroscopy. Submonolayer oxidation starts well below bulk silver oxide formation at potential about -0.6V vs. HglHgO electrode at pH 11. Two potential-dependent Raman bands v1 at 540 to 560cm-1 and v2 at 803 to 819 cm-1 in basic NaF electrolytes are attributed to Ag-OH stretching and AgO-H bending vibrations of electrochemisorbed hydroxide species. Strong isotope effect is observed in D20 solutions, v2 being shifted to values of 550 to 570cm-1. Fluoride stabilizes the adsorption of hydroxide species. A multistep scheme is proposed that describes the mechanism of formation of hydroxide/oxide species at the considered silver-electrode surface

Electrochemical SHG at a Ag(111) single-crystal electrode using the hanging meniscus configuration

We combine in situ electrochemical second-harmonic generation (SHG) with voltammetry measurements using the hanging meniscus configuration. This setup is used to investigate the interface between a Ag (111) electrode and an alkaline electrolyte. The study offers a new in situ insight into the electrochemical processes at the Ag (111) electrode during OH adsorption and subsequent oxidation. The behavior of SHG isotropic and anisotropic contributions as a function of potential is discussed and related to the interfacial electric field.,Comparison of the results with previous investigations of the Ag underpotential oxidation in alkaline solutions shows that submonolayer oxidation is followed by bulk oxidation

XPS observation of OH groups incorporated in an Ag(111) electrode

An Ag(111) single crystal electrode emersed from NaF+NaOH electrolyte (pH 11) under anodic polarisation has been studied ex situ by means of X-ray photoelectron spectroscopy (XPS). “Underpotential” oxidation has been found at +0.2 and 0.0 V vs. Hg/HgO, that is by 0.2–0.4 V more negative than the reversible potential of the Ag2O phase formation. The generation of a number of surface and bulk oxygen-containing species, including surface Ag2O-like species, surface and bulk OH groups (OHads and OHbulk, respectively), surface and bulk atomic oxygen, has been observed on the emersed electrode. The present work provides the first direct evidence of the hydroxide incorporation in the bulk of an Ag(111) electrode in the course of underpotential oxidation. OHbulk is characterised by a O 1s peak at approximately 532.8 eV, while surface OHads manifests itself as the peak at ca. 531.6 eV. The origin of the positive binding energy shift is discussed. Surface and bulk OH groups demonstrate substantially different thermal stability. Surface species desorb below 470 K, while dissolved OH groups exhibit high stability towards prolonged annealing in vacuum at temperatures up to 750 K; they remain in the near-surface region even after sputtering by Ar+ and He+ ions. The oxide-like species is characterised by the O 1s peak at 529.5 eV and decomposes after heating in vacuum at a temperature of about 470 K. The He(I) and He(II) UP spectra of the emersed electrode along with the XPS data provide evidence that the coverage with surface oxide is less than 1 ML. A tentative scheme of Ag(111) underpotential oxidation is discussed

Ex situ scanning tunneling microscopy study of under-potential oxidation of a Ag(111) electrode in an alkaline electrolyte

A Ag(111) single crystal electrode emersed from NaF+NaOH electrolyte (pH 11) under potential control in the interval between -0.8 V and +0.2 V vs. Hg | HgO was studied by scanning tunneling microscopy (STM) in an inert atmosphere. The STM images show that the oxidation of the Ag(111) surface starts above the point of zero charge and exhibits a nucleation-growth mechanism. It starts at the steps and extends to the terraces as the electrode potential is scanned positive. Potential reversal restores the initial surface morphology. The reaction-induced features imaged in STM as dark spots are assigned as islands of chemisorbed oxygen-containing species. The irregular shape of the islands points to the diffusion of ad-species as the limiting step of the process

Electrocatalytic Reduction of Peroxodisulfate in 0.5 M NaOH at Copper Electrodes. A Combined Quartz Microbalance and Rotating Ring/Disc Electrode Investigation

From an electrochemical investigation by means of an electrochemical quartz microbalance, a rotating disc electrode, and a ring/disc electrode, two mechanisms for the reduction of S2O82- became apparent. Besides the well-known outer-sphere cathodic reduction, a catalytic mechanism of S2O82- reduction operates in a potential range between the surface oxide region (≈-0.5 V/SCE) and -1.0 V/SCE. It involves the chemical oxidation of the copper surface to a soluble Cu(I) species. The catalytic mechanism is concluded to result from the specific interaction between S2O82- and the Cu surface modified by the presence of subsurface oxygen