V. L. Kornienko

Use of aqueous hydrogen peroxide solutions prepared by cathodic reduction of oxygen for indirect oxidation of chemical substances in situ: Achievements and prospects

The achievements and prospects in the use of aqueous hydrogen peroxide solutions prepared by cathodic reduction of oxygen in carbon black gas-diffusion and graphite electrodes for indirect oxidation of organic and inorganic substrates in situ are analyzed. Specific examples demonstrate the efficiency of using hydrogen peroxide solutions for in situ indirect electrocatalytic oxidation of organic and inorganic substrates to target products (indirect electrochemical synthesis), for decomposition (mineralization) of organic and inorganic pollutants in industrial waters and wastewaters, and for preparation of organic peroxy acids and inorganic peroxy solvates.

Indirect Electrooxidation of Organic Substrates by Hydrogen Peroxide Generated in an Oxygen Gas-Diffusion Electrode

Indirect electrooxidation of phenol, formaldehyde, and maleic acid in cells with and without a cation-exchange membrane, with a platinum anode and a gas-diffusion carbon black cathode, which generates hydrogen peroxide from molecular oxygen, proceeds with high efficiency and various oxidation depths, which depend on the intermediate nature: the process involving HO2- occurs selectively and yields target products, while the formation of HO2· and HO· leads to the destruction of organic compounds to CO2 and H2O.

Electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in solutions of mineralized exometabolites

The electrosynthesis of H2O2 in aqueous solutions (pH 1–9) of mineralized liquid and solid bio-wastes (exometabolites) for their processing in closed life-support systems was studied. It was shown that H2O2 can be obtained in these solutions by electrochemical reduction of oxygen in carbon black gas diffuse electrodes to concentrations of over 2 M with current efficiency 80%. The composition of the solution was found to affect the accumulation of H2O2 during the synthesis. The solutions can be concentrated further to 19 M H2O2. The results showed that the electrolytic method is promising for preparing H2O2 for closed life-support systems.

Indirect electrochemical oxidation of aliphatic alcohols to carboxylic acids by active oxygen forms in aqueous media

Indirect electrochemical oxidation of aliphatic alcohols (butanol, hexanol, nonanol, decanol) to the corresponding carboxylic acids by active oxygen forms (AOFs) generated in situ in electrochemical cells from O2, H2O2, H2O is carried out in aqueous electrolyte using anodes of lead dioxide, a nickel oxide electrode, and boron-doped diamond electrode (BDDE). It is found that selectivity of the process of indirect electrosynthesis of carboxylic acids depends on the chemical nature of the anode material and structure of the initial alcohol and is determined by the conditions of AOF generation. Coupled electrosynthesis with simultaneous in situ generation of AOFs on the cathode and anode occurs more effectively with formation of the corresponding carboxylic acids.

Pilot laboratory electrolyzer for electrosynthesis of hydrogen peroxide in acid and alkaline solutions

Results of a preparative electrosynthesis of hydrogen peroxide by cathodic reduction of oxygen in a carbon black gas-diffusion electrode in acid and alkaline electrolyte solutions in a versatile pilot laboratory three-chamber electrolyzer are presented.

Electrochemical oxidation of phenol on boron-doped diamond electrode

The process of phenol oxidation on a boron-doped diamond electrode (BDD) is studied in acidic electrolytes under different conditions of generation of active oxygen forms (AOFs). The scheme of phenol oxidation known from the literature for other electrode materials is confirmed. Phenol is oxidized through a number of intermediates (benzoquinone, carboxylic acids) to carbon dioxide and water. Comparative analysis of phenol oxidation rate constants is performed as dependent on the electrolysis conditions: direct anodic oxidation, with oxygen bubbling, and addition of H2O2. A scheme is confirmed according to which active radicals (OH·, HO2·, HO2−) are formed on a BDD anode that can oxidize the substrate which leads to formation of organic radicals interacting with each other and forming condensation products. Processes with participation of free radicals (chain-radical mechanism) play an important role in electrochemical oxidation on BDD. Intermediates and polymeric substances (polyphenols, quinone structures, and resins) are formed. An excess of the oxidant (H2O2) promotes a more effective oxidation of organic radicals and accordingly inhibition of the condensation process.

Graphitized carbon materials for electrosynthesis of Н2О2 from О2 in gas-diffusion electrodes

New graphitized carbon materials: technical carbon N220, С140, and СН85 (Omsktekhuglerod) were studied as catalysts of electrosynthesis of alkaline solutions of hydrogen peroxide from oxygen in gasdiffusion electrodes (GDEs). The kinetic parameters of oxygen reduction in alkaline solution and the capacity of gas-diffusion electrodes based on technical carbon N220, С140, and СН85 were determined. Data on the kinetics of hydrogen peroxide accumulation were obtained at different current densities. The fraction of current γ spent on the reduction of oxygen to hydrogen peroxide was determined. The rate constants of hydrogen peroxide decomposition under the given conditions were calculated.

Indirect electrosynthesis of peracetic acid using hydrogen peroxide generated in situ in a gas diffusion electrode

Indirect electrochemical oxidation of acetic to peracetic acid in aqueous solutions using hydrogen peroxide generated in situ from O2 in a gas diffusion electrode was studied. The use of sulfuric acid and ammonium molybdate as catalysts accelerated the formation of peracetic acid during the electrolysis, and the use of both catalysts allowed us to prepare 0.02 M solutions. The limiting stage of the electrosynthesis of peracetic acid was the chemical interaction of the substrate with the generated H2O2. The desired product mainly formed during the storage of the reaction mixture after the electrosynthesis. In electrolytes with more than 3.5 M acetic acid, the electrochemical activity of the gas-diffusion cathode decreased.

Effects of the composition of acid solutions and the presence of organic acids on oxygen electroreduction to hydrogen peroxide in a carbon black gas-diffusion electrode

This paper reports on the effects of the K2SO4, H2SO4, NaCl, HCl, and tetrabutylammonium bromide concentrations (0.01–0.0002 M) and the presence of formic, acetic, and butyric acids in the electrolyte on the kinetic characteristics of oxygen reduction to H2O2 in a carbon black gas-diffusion electrode (GDE) and on the H2O2 accumulation kinetics in electrolyte at current densities of 30–100 mA/cm2. The introduction of K2SO4 and tetrabutylammonium bromide in the electrolyte led to an increase in the transfer coefficient α and a decrease in the coefficients in the Tafel equation. The concentration and the current efficiency of H2O2 decreased with the salt to acid concentration ratio. The organic acids reduced the current efficiency of H2O2 and increased the electrode polarization. Peracids with a current efficiency of up to 0.27% and concentration of up to 7.5 mM were obtained. Solutions of H2O2 with concentrations of 0.6–3.3 M and current efficiencies of 17–75% were obtained at current densities of 30–100 mA/cm2 in electrolytes with salt and inorganic acid concentrations of 0.9–40 g/l and in the presence of organic acids.

New accelerated method of impregnation by aqueous electrolyte of carbon black gas-diffusion electrodes to study their structural and electrochemical characteristics

A new method of fast impregnation of carbon black gas-diffusion hydrophobized electrodes is suggested under their cathodic polarization in an alkaline aqueous solution of tetrabutylammonium bromide (TBAB) at the potentials of hydrogen evolution. As dependent on the quantitative content of polytetrafluoroethylene (PTFE) in the electrode, current density, time, TBAB concentration, various degree of electrode wetting is observed, up to nearly complete electrode flooding in just several hours. When electrodes are stored, their original electrolyte porosity is not recovered. the electrode with 8 wt % of PTFE was used to show the effect of the electrode flooding degree on the double layer capacity, average diameter of electrolyte pores, their surface area and activity in the case of oxygen reduction. This method may be used for simulation of the process of flooding of gas-diffusion electrodes by electrolyte in the course of their prolonged operation.