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

The electrochemical oxidation of acidic solutions of phenol on a Ti/IrO 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 of charge passed at 80 °C under galvanostatic conditions (50 mA cm) in absence of Cl. In contrast only 10 Ah L 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 CO was not significant unless harsh conditions (i.e. high temperatures and charges) were employed.