From Editors of Special Issue

Russian Journal of Electrochemistry -     

Intensification of the Nitrate Anion Reduction on a Membrane Palladium Electrode

Polarization curves of electroreduction of nitrate anions in sulfuric acid aqueous solutions on a Pd/Pd palladium electrode with the opposite side kept at different constant potentials in the region of Pd–H -phase formation are compared. The reduction rate of nitrate anions is shown to be substantially higher on a membrane electrode, provided the conditions of hydrogen supply from the membrane's opposite side to the reaction zone are realized. This phenomenon is caused by the reduction of a chemisorbed intermediate (a certain N(III) form) by hydrogen diffused through the membrane. It is shown that the measurements of hydrogen diffusion currents through a membrane can be used in plotting hydrogen sorption isotherms in the Pd–H -phase.     

Effect of Ammonium Ions on the Electroreduction of Anions at a Mercury Electrode

The effect of ammonium ions on the electroreduction of peroxodisulfate (S₂O^2- ₈) and perbromate (BrO^- ₄) anions is found to be commensurate with that of potassium ions. Ammonium ions accelerate the reduction of iodate (IO^- ₃), bromate (BrO^- ₃), and chromate (CrO^2- ₄) anions in nonbuffered solutions and does not, in buffered ones. In the former case, the effect is connected with the pH change in the near-electrode layer during the reaction and with the participation of ammonium ions in hydrolytic equilibriums, rather than with a simultaneous transfer of ammonium ions and electrons in an elementary act. The conclusions in the literature in favor of a simultaneous transfer of the proton and electron in the proton-consuming reactions of reduction of anions is shown to be ambiguous.     

Activationless Reduction of the Hexacyanoferrate Anion on a Mercury Electrode

Polarization curves for the electroreduction of [Fe(CN)₆]^3– on a mercury electrode in solutions containing different amounts of surface-inactive supporting cations are simulated on the basis of modern theory of charge transfer in polar media combined with quantum-chemical approaches. The conclusions about an activationless nature of the process in the overvoltage range 1.2 to 2.0 V accessible experimentally, which were drawn from the results of earlier calculations made within simpler models, are confirmed. The maximum contribution to the current is shown to be made by energy levels of metal that lie considerably (up to 1 eV) lower than the Fermi level. To establish the reasons for the anomalous behavior of the current in the activationless region at high overvoltages, the effect various factors sensitive to the electrode charge exert on the model curves at high negative charges of the electrode surface is analyzed. In connection with this, the stability of the results of a calculation of the electron overlap metal/reactant to a model of the interface is considered. The plausibility of the model proposed for the reaction layer and the approaches used for computing the activation energy and the preexponential factor is corroborated by good agreement between the temperature effect found for the region of a minimum current and its experimental value.     

Electroreduction of peroxodisulfate anion at platinum rotating disc electrode in the cyclic voltammetry mode

Electroreduction of peroxodisulfate anion at smooth polycrystalline and platinized (at different deposition potentials) platinum in perchloric acid and sulfuric acid solutions is studied by rotating disc electrode and cyclic voltammetry techniques. Dependences of the process rate on the electrode rotating velocity, the potential scan rate, the anodic limit of the scanning, the peroxodisulfate anion concentration in the solution and the platinizing conditions are found. The suggestion on the complications in the peroxodisulfate anion reduction caused by adsorbate formation is corroborated, at least, for certain potential region. The reaction structure sensitivity is evidenced, which makes it possible to use the reaction for characterization of the platinized Pt surface structure. The comparing of obtained results with literature data concerning smooth platinum and the single-crystal platinum basis faces allows concluding that the peroxodisulfate anion reduction maximal rate in sulfuric-acid solutions occurs at the potentials close to those observed for the (110) face. When the platinized Pt surface roughness factor exceeds ~30, the peroxodisulfate anion reduction reaction proceeds under the inner-diffusion limitation control. The platinized-Pt rotating disc electrode can serve as model tool in the studying of properties of disperse material microdeposits.     

Adsorption and electrooxidation of dimethyl ether on platinized platinum electrode in sulfuric acid solution

Adsorption and oxidation of dimethyl ether (DME) on the Pt/Pt electrode from 0.5 M H₂SO₄ is studied by measuring transients of current and potential, charging curves, and curves of electrooxidation in the adsorbed layer and also by cyclic voltammetry and steady-state polarization measurements. The DME adsorption is accompanied by dehydrogenation and destruction of its molecules to form a chemisorbed adsorbate that mainly consists of C1 species (HCO_ads and/or CO_ads) with (under certain conditions) a small amount of species that desorb at cathodic polarization. The adsorption and electrooxidation of DME are inhibited by adsorbed oxygen. The possible schemes of DME oxidation, where the reaction of DME chemisorption products with adsorbed oxygen-containing species is the limiting stage, are discussed.     

Workshop on Electrochemistry of Electroactive Polymer Films

Russian Journal of Electrochemistry -