Modification of expanded graphite resulting in enhancement of electrochemical activity in the process of phenol oxidation

The aimed modification of expanded graphite electrodes (EG) was divided into two independent parts consisting of chemical treatment in the mixture of concentrated H2SO4/HNO3 and subsequent heat treatment performed at elevated temperature in air. The electrochemical features of modified samples were examined in the model process of phenol electrooxidation which was realized in alkaline medium by the cyclic voltammetry technique. Taking into account the charges of anodic peaks corresponding to the phenol oxidation it was found that a two-step treatment of EG brought about over two-fold improvement of its electrochemical activity as compared to the initial cycle of regarded process. The reason for such a behavior can be ascribed to the changes in chemical composition of the EG surface as well as the changes in porous structure including almost a two-fold development of specific surface area and by a four-fold increase of the sample volume affected by the thermal treatment. According to the X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy data, the modification of EG resulted in a significant increase of the surface oxygen groups containing C-O.