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Anodic oxidation of phenol on Ti/IrO2 electrode: Experimental studies

The electrochemical oxidation of acidic solutions of phenol on a Ti/IrO2 anode has been investigated by cyclic voltammetry and bulk electrolysis in a single-compartment cell. In the potential region of oxygen evolution, anodic oxidation resulted in electrode passivation (as evidenced by voltammetric measurements) allegedly due to the formation of a polymeric film on its surface. Phenol degradation increased with increasing temperature in the range investigated 30-80 degrees C and it was affected by the addition of Cl- and Br- anions in the supporting electrolyte. Complete conversion of 10 mM phenol was achieved after 37 Ah L-1 of charge passed at 80 degrees C under galvanostatic conditions (50 mA cm(-2)) in absence of Cl-. In contrast only 10 Ah L-1 were needed in the presence of 35 mM Cl-. The presence of chloride can induce reactions involving chlorohydroxyl radicals and electrogenerated oxidants such as free chlorine. On the other hand, addition of Br- slightly inhibited degradation possibly due to bromide scavenging of electrogenerated active species. Phenol degradation proceeded through the formation of three dominant, aromatic intermediates, namely 1,4-benzoquinone, hydroquinone and pyrocatechol, while total oxidation to CO2 was not significant unless harsh conditions (i.e. high temperatures and charges) were employed. (C) 2010 Elsevier B.V. All rights reserved.

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