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

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

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

Autocatalysis by the intermediate surface hydroxide formed during H₂O₂ reduction on Ag(111) electrodes

The cathodic hydrogen peroxide, H2O2, reduction in HClO4 proceeds by two parallel mechanisms, the “normal” H2O2 reduction, and a remarkable autocatalytic reaction path. Chemisorbed hydroxyl groups OHad, formed as an intermediate on the silver electrode, are considered to constitute the autocatalytically active species. In order to obtain a clearer conception of the species OHad, the state of Ag(111) electrodes in inert electrolytes of varying pH is analysed with electrochemical and surface science tech-niques. Experiments with Second Harmonic Generation yield particularly valuable results. The surface studies, along with numerical simulations of the adsorption dynamics, indicate that the species OHad is identical with the discharged surface hydroxyl species formed as a relatively stable intermediate in the anodic oxidation of OH- to surface-Ag2O