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 °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 °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.