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: 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; · 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; · 2.76 Impact Factor
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ABSTRACT: A pulse current technique was conducted in a boron-doped diamond (BDD) anode system for electrochemical wastewater treatment. Due to the strong generation and weak absorption of hydroxyl radicals on the diamond surface, the BDD electrode possesses a powerful capability of electrochemical oxidation of organic compounds, especially in the pulse current mode. The influences of pulse current parameters such as current density, pulse duty cycle, and frequency were investigated in terms of chemical oxygen demand (COD) removal, average current efficiency, and specific energy consumption. The results demonstrated that the relatively high COD removal and low specific energy consumption were obtained simultaneously only if the current density or pulse duty cycle was adjusted to a reasonable value. Increasing the frequency slightly enhanced the COD removal and average current efficiency. A pulse-BDD anode system showed a stronger energy saving ability than a constant-BDD anode system when the electrochemical oxidation of phenol of the two systems was compared. The results prove that the pulse current technique is more cost-effective and more suitable for a BDD anode system for real wastewater treatment. A kinetic analysis was presented to explain the above results.International Journal of Minerals Metallurgy and Materials 01/2013; 20(1). · 0.57 Impact Factor