Yu. V. Saltykov

The Dependence of the PdCl42−/Pd0 Electrode Potential on the Dispersity of Metallic Palladium

It was found that metastable equilibrium in the heterogeneous reaction PdCl42− + 2e = Pd0 + 4Cl− in H2PdCl4-hydrochloric acid solutions at 60°C depended on the dispersity of metallic palladium. It was shown experimentally that the dependence of the shift of the PdCl42− /Pd0 redox potential on the dispersity of palladium(0) was described by the Thomson equation.

On the Operation of a Porous Hydrophobized Electrode in an Indirect Electrosynthesis

Application of porous hydrophobized electrodes (HPE) in direct electrosyntheses of organic and inorganic species from liquid and gaseous source reagents poorly soluble in aqueous electrolytes was discussed in [1‐3]. At present, porous HPE are tentatively employed in indirect electrosyntheses where a high-reactivity intermediate is electrochemically generated in the porous space of HPE and then enters chemical reactions with organic and inorganic substrates in the electrolyte bulk [4‐6]. Naturally, in such a case, a problem arises of where the chemical reaction occurs and what its fraction in the porous space of HPE and the electrolyte bulk outside the porous space amounts to. Our theoretical estimates for a second-order reaction at a rate constant of ≅ 0.02 l/s mol showed that almost the entire chemical reaction occurs in the HPE porous space. We experimentally checked this assumption in an indirect formaldehyde oxidation to formic acid in situ by H electrochemically generated in a gas-diffusion carbon-black HPE in an alkaline solution. The experiment has demonstrated beyond any doubt that the chemical reaction between H and CH 2 O does occur practically entirely in the electrode porous space. This result opens pathways for new applications of HPE in indirect electrosyntheses. For example, it appears feasible to carry out processes of indirect electrochemical oxidation which require a higher oxidant concentration than that accumulated in the electrolyte outside the electrode porous space. Note that, in electrosynthesis of H 2 O 2 from O 2 , the H 2 O 2 concentration in the HPE porous space is several times that in the catholyte [7, 8].

Estimation of the Relative Thickness of Gas-Diffusion Electrodes of Carbon-Black Blends in the Course of Electrosynthesis of the Peroxide Ion from Oxygen

The results of a study of electrosynthesis of hydrogen peroxide from oxygen in an alkaline electrolyte on gas-diffusion electrodes of acetylene carbon black and blends of acetylene carbon black and furnace black are compared. The relative thickness of gas-diffusion hydrophobic electrodes operating under inner-kinetic conditions is estimated from polarization curves. Improving the hydrogen peroxide removal from pores of the gas-diffusion electrodes made of carbon black blends with various hydrophilic and hydrophobic properties stabilizes the relative thickness of the electrodes in comparison with the electrodes of acetylene carbon black.

The effect of structural characteristics of porous hydrophobized electrodes on selectivity of electrolysis of organic substances

A theoretical study of the effect of the electrode structure on the electrosynthesis in hydrophobized electrodes (HPE) for a case of further electrochemical conversion of the target product is performed by the example of nitromethane electroreduction to methyl hydroxylamine followed by its reduction to methylamine. The effect of the electrode structure on the selectivity of electrosynthesis in HPE was shown to be related to the effective diffusivity and conductivity.

Polarization Curve of a Porous Hydrophobized Electrode for Electrosynthesis Involving a Side Electrochemical Reaction

A polarization curve, suggested for electrosynthesis in a porous hydrophobized electrode operating in an inner-kinetic mode at a current efficiency for the target product below 100%, depends on the balance between exchange currents and slopes of the side and target reactions and the difference between the equilibrium potential of the side reaction and the steady-state electrode potential. At different slopes of the side and the target reactions, the current efficiency depends on the polarization. Experimental and calculated data satisfactory agree.

Location of Chemical Reaction of Indirect Electrochemical Synthesis in a Porous Hydrophobized Electrode

Location of chemical reaction of IES performed in a porous hydrophobized electrode is considered. Depending on the rate constant and order of the reaction, it can proceed in the electrodes porous space and in the electrolyte chamber.

Testing the Product Accumulation in the Porous Volume of Hydrophobized Electrodes during Electrosynthesis by Cyclic Voltammetry

Cyclic voltammograms (CVA) for the hydrogen peroxide electrosynthesis from oxygen in gas-diffusion hydrophobized electrodes (GHE) of acetylene black A437-E, furnace black P805-E, and their mixtures in an alkaline electrolyte are compared in order to test the product accumulation in their porous volumes. The increase in the area of the peak in an anodic branch of CVA during hydrogen peroxide accumulation depends on the GHE type. The removal of hydrogen peroxide in the GHE is facilitated by using a mixture of blacks. The CVA method is convenient for testing the product accumulation in the porous volume.

Mechanism of Removal of a Gaseous Difficultly Soluble Product from a Hydrophobized Electrode during Electrosynthesis

Differences in the mechanisms of removal of gaseous products from porous hydrophilic and hydrophobized electrodes are analyzed. The formulated notions are utilized to consider a possible mechanism of removal of gaseous difficultly soluble product—trifluorochloroethylene—from a porous hydrophobized electrode, during its synthesis from 1,1,2-trifluorotrichloroethane. The experimental facts testify in favor of the suggested mechanism.

Distribution of a Soluble Product During Its Electrosynthesis in the Porous Hydrophobic Electrode

The distribution of the concentration of a product, which is soluble in the electrolyte, inside a porous hydrophobic electrode is calculated. During the electrosynthesis under inner-kinetic conditions, the electrode obeys regularities observed in hydrophobic electrodes of fuel cells. The product distribution depends mainly on the polarization at the electrode front, the electrolyte conductivity, and the diffusion coefficient, and slightly depends on the electrode structure. An approximate equation describing the distribution of the product concentration inside the electrode is suggested.