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Fig. 14 Polarization curves for a mildly oxidized BDD electrode, at different OA concentrations. Jnset elaboration of data in terms of Tafel plot

Figure 14 Polarization curves for a mildly oxidized BDD electrode, at different OA concentrations. Jnset elaboration of data in terms of Tafel plot

Related Figures (14)

Fig. 1 Polarization curves for the electroxidation of OA at the Pt electrode CV experiments at the GC electrode (Fig. 2) showed that OA is electroactive at this material, its oxidation taking place about 300-400 mV before the o.e.r. onset. In addi- tion, a signal centred at about 0.9 V (vs. SCE) was observed for OA concentrations >500 mM. The literature reports that OA oxidation takes place across a wide potential range (see, for example, ref. [1]); however, the effect is witnessed only by an increase in current density and a shift of quasi-steady polarization curves to less positive potential values, with increasing the OA
Fig. 1 Polarization curves for the electroxidation of OA at the Pt electrode CV experiments at the GC electrode (Fig. 2) showed that OA is electroactive at this material, its oxidation taking place about 300-400 mV before the o.e.r. onset. In addi- tion, a signal centred at about 0.9 V (vs. SCE) was observed for OA concentrations >500 mM. The literature reports that OA oxidation takes place across a wide potential range (see, for example, ref. [1]); however, the effect is witnessed only by an increase in current density and a shift of quasi-steady polarization curves to less positive potential values, with increasing the OA
Fig. 2 Magnification of CV curves for the GC electrode, in the presence of the pure supporting electrolyte and of different amounts of OA in solution. Inset the whole experimental picture 4 As shown in Fig. 5, at variance with the above experi- mental evidence, OA exhibits a quite important electroac- tivity at the Ti/IrO.,—2SnO, electrode: the organic oxidation onset can be placed at about 0.8 V versus SCE, thus 350- 400 mV prior to the beginning of the o.e.r. As data on IrO,-Ta,Os also indicate, this cannot be easily accounted for if only the role of the “active” component, IrO,, is considered. On the other hand, as elsewhere shown [39],
Fig. 2 Magnification of CV curves for the GC electrode, in the presence of the pure supporting electrolyte and of different amounts of OA in solution. Inset the whole experimental picture 4 As shown in Fig. 5, at variance with the above experi- mental evidence, OA exhibits a quite important electroac- tivity at the Ti/IrO.,—2SnO, electrode: the organic oxidation onset can be placed at about 0.8 V versus SCE, thus 350- 400 mV prior to the beginning of the o.e.r. As data on IrO,-Ta,Os also indicate, this cannot be easily accounted for if only the role of the “active” component, IrO,, is considered. On the other hand, as elsewhere shown [39],
Fig. 3 Polarization curves for the GC electrode, in the presence of the pure supporting electrolyte and of different amounts of OA in solution. Jnset elaboration of data in terms of Tafel plot
Fig. 3 Polarization curves for the GC electrode, in the presence of the pure supporting electrolyte and of different amounts of OA in solution. Jnset elaboration of data in terms of Tafel plot
Fig. 4 CV curves for a Ti/IrO.-Ta2Os electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV s7!
Fig. 4 CV curves for a Ti/IrO.-Ta2Os electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV s7!
Fig. 5 CV curves for a Ti/IrO.—2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV s_! To gain additional insight into these aspects, the elec- trochemical behavior of OA has been further investigated by quasi-steady polarization curves, and related diagnostic parameters. As shown in Fig. 8 (blank curve), at a Ti/IrO- Ta2O; the o.e.r. is anticipated with respect to what was observed at oxidized Pt surfaces (Fig. 1). Currents due to OA oxidation remain quite low up to the oxygen evolution and the features of J/E curves are affected by the presence of OA in a fairly complex way. Current values obtained in
Fig. 5 CV curves for a Ti/IrO.—2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV s_! To gain additional insight into these aspects, the elec- trochemical behavior of OA has been further investigated by quasi-steady polarization curves, and related diagnostic parameters. As shown in Fig. 8 (blank curve), at a Ti/IrO- Ta2O; the o.e.r. is anticipated with respect to what was observed at oxidized Pt surfaces (Fig. 1). Currents due to OA oxidation remain quite low up to the oxygen evolution and the features of J/E curves are affected by the presence of OA in a fairly complex way. Current values obtained in
Fig. 7 CV curves for a Ti/RuO,—2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HCI1O,) and with OA in solution; data obtained at 100 mV s_! Fig. 6 CV curves for a Ti/Itp.67Rup.3302-2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV st
Fig. 7 CV curves for a Ti/RuO,—2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HCI1O,) and with OA in solution; data obtained at 100 mV s_! Fig. 6 CV curves for a Ti/Itp.67Rup.3302-2SnO, electrode, in the presence of the pure supporting electrolyte (1 M HC1O,) and with OA in solution; data obtained at 100 mV st
Fig. 8 Polarization curves for a Ti/IrO.-TaOs electrode, at different OA concentrations. /nset elaboration of data in terms of Tafel plot
Fig. 8 Polarization curves for a Ti/IrO.-TaOs electrode, at different OA concentrations. /nset elaboration of data in terms of Tafel plot
Fig. 9 Polarization curves for a Ti/IrO,—2SnO, electrode, at differen OA concentrations. /nset elaboration of data in terms of Tafel plot
Fig. 9 Polarization curves for a Ti/IrO,—2SnO, electrode, at differen OA concentrations. /nset elaboration of data in terms of Tafel plot
Fig. 10 Polarization curves for a Ti/Ito.¢7Rup.3302—-2SnO, electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
Fig. 10 Polarization curves for a Ti/Ito.¢7Rup.3302—-2SnO, electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
Fig. 11 Polarization curves for a Ti/RuO.—2SnO, electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
Fig. 11 Polarization curves for a Ti/RuO.—2SnO, electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
Fig. 13 Polarization curves for a strongly oxidized BDD electrode, at different OA concentrations. Jnset elaboration of data in terms of Tafel plot
Fig. 13 Polarization curves for a strongly oxidized BDD electrode, at different OA concentrations. Jnset elaboration of data in terms of Tafel plot
Fig. 12 Polarization curves for a F-BDD electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
Fig. 12 Polarization curves for a F-BDD electrode, at different OA concentrations. Inset elaboration of data in terms of Tafel plot
On the other hand, mechanism (1) + (3) implies super- imposition of the organic substrate electrosorption and at least the first step of the oxygen evolution reaction. Step (4) can account for the possibility of a “direct” chemical reaction between oxidized surface of the electrode and OA in a non-adsorbed state. increase in electrode potential allows the attainment of higher oxidation states of the metal cations at the electrode surface, accompanied by preferential electrosorption of hydroxyl groups, displacing OA species and still too stable to act as oxidation mediators themselves. This may well ead to the inhibition of OA oxidation in a more or less imited potential range in the vicinity of the o.e.r. onset, first, and then to a change of mechanism to the (1) + (3), mechanism (a), sustained by the higher reactivity attained by hydroxyl radicals. Reaction (4) cannot be ruled out either. Details of the effect are decided by the nature of the properties of the electrode surface.
On the other hand, mechanism (1) + (3) implies super- imposition of the organic substrate electrosorption and at least the first step of the oxygen evolution reaction. Step (4) can account for the possibility of a “direct” chemical reaction between oxidized surface of the electrode and OA in a non-adsorbed state. increase in electrode potential allows the attainment of higher oxidation states of the metal cations at the electrode surface, accompanied by preferential electrosorption of hydroxyl groups, displacing OA species and still too stable to act as oxidation mediators themselves. This may well ead to the inhibition of OA oxidation in a more or less imited potential range in the vicinity of the o.e.r. onset, first, and then to a change of mechanism to the (1) + (3), mechanism (a), sustained by the higher reactivity attained by hydroxyl radicals. Reaction (4) cannot be ruled out either. Details of the effect are decided by the nature of the properties of the electrode surface.
Related topics:
Chemical EngineeringChemistryInorganic ChemistryElectrochemistryApplied ElectrochemistryAnodic OxidationOxalic acidBoron Doped DiamondElectrochemical Incineration
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