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

Russian Academy of Sciences, Moskva, Moscow, Russia
Russian Journal of Electrochemistry (Impact Factor: 0.76). 01/2004; 40(2):148-152. DOI: 10.1023/B:RUEL.0000016327.07214.69


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 HO
occurs selectively and yields target products, while the formation of HO2
and HO leads to the destruction of organic compounds to CO2 and H2O.

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    • "Superoxide anion and the hydroperoxide ion (HO 2 − ), the conjugated base of hydrogen peroxide (pKa = 11.62 at 25°C), may reach the anode and undergo a reverse reaction of 6, 8, and 9 on the cathode in an undivided cell, which consumes a lot of energy and greatly decreases the electrolysis efficiency, as the superoxide anion and hydroperoxide ion also compete with the organics for anodic reactions (Brillas et al., 2003; Kornienko et al., 2004). To avoid this disadvantage, many types of diaphragms, such as, glass frit (Do and Yeh, 1996; Harrington and Pletcher, 1999) and cationic exchange member (Kornienko et al., 2004), were used to separate two-chamber electrolysis reactors, which could reduce the degradation time and increase the total current efficiency. The mechanism of radical generation on the cathode mentioned earlier may be useful for the development of new cathode material and an efficient reactor that generates more oxidizing radicals, to mineralize organic compounds. "
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    ABSTRACT: The generation and transformation of radicals on the cathode of indirect electrochemical oxidation were studied by chemiluminescence (CL) and UV-Visible spectra in the reactor with a salt bridge that connected the separated chambers. The CL intensity of 4 x 10(-9) mol/L luminol on the cathode with bubbling oxygen was about seven times that of the intensity without it, which was because of the generation of reactive oxygen species (ROS). The existence of ROS, especially the generation of the superoxide radical, could be affirmed by the fact that the CL intensity of 4 x 10(-9) mol/L 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one with bubbling oxygen was about four times that of the intensity without it. However, there was no chemiluminescence on the anode under the same condition. The change in the UV-Visible spectra of nitro blue tetrazolium and N,N-dimethyl-4-nitrosoaniline at the cathode chamber affirmed the transformation from oxygen to superoxide and hydroxyl radicals. The mechanism of the superoxide and hydroxyl radical generation and transformation on the cathode was discussed with the help of the experimental results and relative references.
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    ABSTRACT: The electrochemical oxidation of toluene and acetone at the high-pressure of oxygen was investigated. Oxidation of toluene and ace-tone at electrolysis under the pressure of oxygen occurs not only on the anode, but also on the cathode due to the generation of active particles of ions O À 2 ; HO À 2 , radicals HO Å 2 ; HO Å etc. Increasing the oxygen pressure showed an increase in the process efficiency.
    Full-text · Article · Mar 2007 · Electrochemistry Communications
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