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, Switzerland
Electrochimica 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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    • "A competing reaction, the oxygen generation reaction, occurs on the anode surface in the electrochemical cell during electrolytic discharge of water as a secondary anodic reaction [33]. Thus, the increase in applied current density consistently causes increases in the rate of the secondary anodic reaction (oxygen generation reaction), which decreases the current efficiency [34] [48]. The inset of Fig. 5(a) shows that the current efficiency at 8 mA/cm 2 is 96% for the first hour of electrolysis but decreases to only 88% and 82% when the applied current density is increased to Fig. 3 "
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    ABSTRACT: A carbon black diamond composite electrode with 20% carbon black (20CBD) and activated carbon composite (ACC) electrode were prepared and used as anodes for 2-chlorophenol electro-oxidation. The electro-oxidation behaviors of 200 mg/L 2-chlorophenol on 20CBD and ACC anodes were investigated by cyclic voltammetry in aqueous solutions of 0.5 M H2SO4 (pH 0.55) and 0.25 M Na2SO4 (pH 7). Results indicated that the 20CBD and ACC electrodes are more active at low pH than at high pH and that no oxidation peak appears on the ACC electrode. The performance of the 20CBD and ACC electrodes during degradation of 200 mg/L 2-chlorophenol was investigated in an aqueous solution of pH 3 with 0.25 M Na2SO4 as the supporting electrolyte and applied current density of 30 mA/cm2. Results showed that the 20CBD electrode produced the best degradation rate, COD removal efficiency, and current efficiency. The degradation efficiencies of the 20CBD and ACC electrodes after 6 h were 96% and 82.5%, respectively. The effects of solution pH, current density, and supporting electrolyte on the performance of the 20CBD were further investigated, and results showed that higher degradation rates are obtained at lower pH and with Na2SO4 as the supporting electrolyte. Removal efficiency also increased with increasing current density.
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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 [25]. Any increase in current density will produce oxygen through hydroxyl radical decomposition [18] [24]. 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. "
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    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 [8], coumarin oxidation [9], 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 [10] and for the oxidation of methanol and formic acid [11]. 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 [12] [13] [14]. "
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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 · 4.50 Impact Factor
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