Improvement of the electrocatalytic activity of platinum in oxidation of aromatic compounds

The electrochemical oxidation of aromatic compounds (ACs) at pre-treated platinum electrodes was studied by cyclic voltammetry (CV). An understanding of the mechanism of the different electrochemical processes is possible only if taking into account the state of the Pt electrode surface, which is strongly affected by oxide formation and reduction. Long-time treatment by CV yields increased Pt oxide coverage and leads to very important electrocatalytic properties towards many organic electro-oxidation reactions. Three aromatic compounds were studied: phenol, hydroquinone and p-benzoquinone. The results show that the increase of the charge Q which characterizes the surface quality of the pre-treated Pt electrodes entails an increase in active sites with respect to the discharge of water to form PtOH species which typically starts at ca. 0.12 V. Once such species are formed they react with both free and adsorbed molecules. It results in the multiplication of the oxidation current by factors of 46 and 21 for phenol and p-benzoquinone, respectively, when Q increases from 0.3 to 4 mC. In the case of hydroquinone this factor is only about 3 for the same increase of Q. The oxidation of hydroquinone is not catalyzed by the PtOH species because it takes place at potential lower than 0.12 V. The results show that phenol is quantitatively oxidized by CV on a pre-treated platinum electrode to produce by the intermediary of catechol, hydroquinone, p-benzoquinone, oxalic and maleic acids, whose degradation leads to carbon dioxide.