Investigations of electrochemical oxygen transfer reaction on boron-doped diamond electrodes
Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, SwitzerlandElectrochimica Acta (Impact Factor: 4.5). 12/2007; 53(4):1954-1961. DOI: 10.1016/j.electacta.2007.08.066
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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- "Because no significant effect was observed in the solution with 200 mg/L p-BQ as the current density increased from 20 mA/cm 2 to 32 mA/cm 2 , current densities of 32 and 45 mA/cm 2 were applied to determine the effects of current density on electro-degradation of 1000 mg/L p- BQ in aqueous solution of pH 6 at 25 C. Fig. 6 demonstrates that increases in current density do not produce significant effects on the p-BQ electro-degradation rate, likely because increases in initial p-BQ concentration promote mass transfer control of the process . Any increase in current density will produce oxygen through hydroxyl radical decomposition  . Fig. 6 also shows that the current efficiency increases from 37.33% to 57.4% and from 48.2% to 78.4% at applied current densities of 45 and 32 mA/cm 2 , respectively, as a result of increasing the initial p-BQ concentration from 200 mg/L to 1000 mg/L. "
ABSTRACT: In this work, p-benzoquinone (p-BQ) electro-degradation in three carbon black diamond (CBD) composite electrodes is studied under conditions of 200 mg/L initial concentration, 45 mA/cm2 applied current density, pH 3, and 0.25 M Na2SO4 as a supporting electrolyte. The performance of the CBD electrodes was compared with that of a platinum electrode. Results showed that the optimal p-BQ degradation, COD removal efficiency, and current efficiency may be obtained from the CBD electrode containing 20% carbon black (20CBD). After 20 min of electro-degradation, p-BQ removal on 20CBD reached 96% at pH 6 and 61.5% at pH 3. However, after 180 min of p-BQ degradation, COD removal on this electrode reached 45% at pH 6 and 70% at pH 3. Increases in applied current during p-BQ electro-oxidation were related to the initial p-BQ concentration. Significant differences were observed in the solution containing 200 mg/L p-BQ as the current density was increased from 20 mA/cm2 to 45 mA/cm2 ; no such effects were observed in the solution with 1000 mg/L p-BQ.Electrochimica Acta 07/2015; 169. DOI:10.1016/j.electacta.2015.04.037 · 4.50 Impact Factor
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- "During anodic polarization of the BDD, hydroxyl radicals are generated from water discharge and react further to oxygen, or participate in the oxidation process of the compounds. The formation of hydroxyl radicals on BDD electrodes was confirmed by spintrapping experiments , coumarin oxidation , and a Tafel-slope of 120 mV/dec in the potential region above 2.4 V for the oxygen evolution reaction (OER) in perchloric acid  and for the oxidation of methanol and formic acid . The oxidation of H 2 O 2 as well as carbon monoxide and small aliphatic organic molecules such as MeOH, EtOH, formic and acetic acid, was studied in order to clarify the oxidation processes on BDD electrodes in aqueous media   . "
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 · 4.50 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). DOI:10.1007/s12613-013-0700-0 · 0.79 Impact Factor
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