Investigations of electrochemical oxygen transfer reaction on boron-doped diamond electrodes
ABSTRACT In this paper, the electrochemical oxygen transfer reaction (EOTR) is studied on boron-doped diamond electrodes using simple C1 organic compounds (methanol and formic acid). The kinetics of both oxygen evolution (side reaction) and organics oxidation (main reaction) has been investigated using boron-doped diamond microelectrodes-array (BDD MEA). Oxygen evolution, in the high-potential region, takes place with a Tafel slope of 120 mV dec−1 and zero reaction order with respect to H+. In the presence of organics, a shift of the polarization curves to lower potentials is observed while the Tafel slopes remain close to 120 mV dec−1. A simplified model of C1 organics oxidation is proposed. Both water discharge and organics oxidation are assumed to be fast reactions. The slowest step of the studied EOTR is the anodic discharge of hydroxyl radicals to oxygen. Further in this work, electrolysis of formic acid on boron-doped diamond macroelectrode is presented. In order to achieve 100% current efficiency, electrolysis was carried out under programmed current, in which the current density was adjusted to the limiting value.
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ABSTRACT: The electro-oxidation of ethanol, acetone, i-propanol, its fluorinated analogue hexafluoroisopropanol (HFiP) and cyclohexane in 1 M HClO4 was studied on a boron doped diamond (BDD) electrode by on-line differential electrochemical mass spectrometry (DEMS), using a dual thin layer cell. One can distinguish two oxidation pathways: at potentials below 2.5 V a direct electron transfer to the BDD takes place, while at potentials above 2.5 V OH radicals are produced and scavenged by the reactants. As a consequence, the oxygen evolution reaction is at least partially suppressed. The direct electron transfer to the electrode is observed for i-propanol, ethanol and cyclohexane. For acetone and HFiP, only the second, indirect, pathway with the participation of OH radicals is effective. For all the reactants except HFiP CO2 formation was observed generally at 2.5 V or higher, the potential for the oxygen evolution reaction (OER) in the pure supporting electrolyte. Hence OH radicals are instrumental in the cleavage of Csingle bondC bonds. For HFiP, the cyclic voltammograms of the supporting electrolyte with and without the reactant are identical. This indicates that the oxidation of HFiP is initiated by OH radicals followed by a further electron transfer to the electrode, similarly to the oxidation of CO (I. Kisacik, A. Stefanova, S. Ernst and H. Baltruschat, PCCP, 15 (2013) 4616). For both pathways, the reactivity follows the same trend as the homogeneous hydrogen abstraction reaction rates with OH radicals. The intermediate radicals formed in the reaction with the electro-generated OH radicals can react with oxygen present in the solution.Electrochimica Acta 11/2013; 110:560-569. DOI:10.1016/j.electacta.2013.05.104 · 4.09 Impact Factor
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ABSTRACT: In the present paper, the electrocatalytic abatement of urea in aqueous solutions has been studied by means of cyclic voltammetry and galvanostatic electrolysis, using different anodes such as Pt, Ti-Ru oxide, boron-doped diamond (BDD) and antimony-doped tin oxide. HPLC analysis, total organic carbon (TOC) and ionic chromatography have been used to evaluate the oxidation and the mineralization of the treated aqueous solutions. The results of the cyclic voltammetries have shown that, in the case of Pt and Ti-Ru oxides a decrease in current density in the oxygen evolution region can be observed in the presence of urea, due to the blockage of the electrode active oxygen evolution sites as a consequence of the reversible adsorption of urea. Instead, a notable increase in the current density has been observed in the region of the oxygen evolution for the BDD and antimony-doped tin oxide electrodes, in the presence of urea, indicating that the oxidation of urea involves hydroxyl radicals. The bulk electrolysis tests have shown that the complete removal of urea and TOC can only be achieved using a boron-doped diamond and that Pt, the Ti-Ru oxide and antimony-doped tin oxide only permit a partial oxidation of urea. On the basis of the TOC evolution and the identification of the organic intermediates and inorganic ions released during the treatment, a total mineralization has been proposed. Finally, electrolyses has been performed in the presence of chloride ions, which act as oxidation mediator, have been performed and a comparison has been done between direct and mediated electro-oxidation.Diamond and Related Materials 04/2014; 44. DOI:10.1016/j.diamond.2014.02.006 · 1.57 Impact Factor
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ABSTRACT: In recent years, new advanced oxidation processes based on the electrochemical technology, the so-called electrochemical advanced oxidation processes (EAOPs), have been developed for the prevention and remediation of environmental pollution, especially focusing on water streams. These methods are based on the electrochemical generation of a very powerful oxidizing agent, such as the hydroxyl radical ((•)OH) in solution, which is then able to destroy organics up to their mineralization. EAOPs include heterogeneous processes like anodic oxidation and photoelectrocatalysis methods, in which (•)OH are generated at the anode surface either electrochemically or photochemically, and homogeneous processes like electro-Fenton, photoelectro-Fenton, and sonoelectrolysis, in which (•)OH are produced in the bulk solution. This paper presents a general overview of the application of EAOPs on the removal of aqueous organic pollutants, first reviewing the most recent works and then looking to the future. A global perspective on the fundamentals and experimental setups is offered, and laboratory-scale and pilot-scale experiments are examined and discussed.Environmental Science and Pollution Research 04/2014; 21(14). DOI:10.1007/s11356-014-2783-1 · 2.76 Impact Factor