Efficient Anodic Degradation of Phenol Paired to Improved Cathodic Production of H₂O₂ at BDD Electrodes

Electrochemical degradation of phenol (PhOH) with simultaneous reduction of O₂(g) to H₂O₂ in acidic media was performed in an H-type divided cell (500 mL), separated with a cationic membrane (Nafion 424). Boron-doped diamond (BDD) electrodes were used as anode and cathode. The study was divided into three stages: (a) Electroanalytical study of the oxygen reduction reaction (ORR) to H₂O₂ by hydrodynamic linear-sweep voltammetry with a BDD-RDE in acidic and alkaline solutions; (b) galvanostatic ORR to H₂O₂ at BDD electrode in acidic solution (unpaired system); (c) pairing the anodic PhOH degradation with the H₂O₂ cathodic production at BDD electrodes. The best production of H₂O₂ under our conditions with the unpaired system was 250.1 mg L^-1 at 1.5 mA cm^-2 after 540 min of electrolysis, the highest reported to date for BDD electrode in acidic media. Total mineralization of 100 mg L^-1 of PhOH in the paired system required a higher current density (i.e., 2.5 mA cm^-2); in spite of this, the process is one order of magnitude faster than any electrochemical process previously reported.