Process of phenol electrooxidation on the expanded graphite electrode accompanied by the in-situ anodic regeneration

• Electrochemical activity of regenerated expanded graphite depends on concentration of KOH solution.
• In-situ regeneration of expanded graphite modifies its structural properties and chemical composition of its surface.
• In-situ regeneration of expanded graphite restrains its deactivation in cyclic process of phenol electrooxidation.

The investigations reported in this paper, were devoted to electrochemical regeneration of spent expanded graphite (EG), carried out in-situ during the process of electrochemical oxidation of phenol. The electrochemical process of phenol oxidation followed by the anodic regeneration of EG electrode was investigated by cyclic voltammetry technique in electrolytes composed of 0.1 M phenol dissolved in 0.5 M and 6 M KOH. The obtained results undoubtedly revealed that, owing to the considerable potential lowering of electrochemical decomposition of water, the anodic oxidation of phenol in 6 M KOH partially proceeded within the potentials of violent oxygen evolution. The active oxygen and/or hydroxyl radicals, generated during oxygen evolution, impacted both as phenol oxidation supporting oxidants and as in-situ synthesized regenerating agents of spent electrode material. Owing to this feature, the established process may be continued during the consecutive cycles. The enhanced level of electrochemical activity of EG remains almost unchanged during the initial 3 cycles of voltammetric process of phenol oxidation. On farther scanning, the EG activity decreases reaching in tenth cycle activity on significantly higher level compared to the process performed in 0.1 M phenol in 0.5 M KOH. The higher activity of EG demonstrated in 0.1 M phenol in 6 M KOH is proved by the higher decline in phenol concentration and lower value of total organic carbon. It cannot be excluded that partial damage to the EG structure is responsible for the noted decrease.