Beyond Treatment: Electrochemical Phenol Oxidation in Methanol under Different Cell Configurations and Its Implications for Valorization

This study explores electrochemical phenol oxidation in methanolic and aqueous media as a strategy to shift adsorption-based treatments from pollutant removal toward chemical valorization. Using 3D-printed single- and divided-cell reactors with alkaline electrolytes to enhance conductivity, methanol clearly outperformed water: phenol conversions exceeded 50% after 3 h (vs <15% in water), with higher Faradaic efficiencies (>21%) and energy efficiencies up to 3-fold greater, especially in anion exchange membrane (AEM) systems. Speciation analysis revealed that methanol favors diverse, industrially relevant intermediates, including carboxylates (oxalate, malonate, succinate, tartrate, maleate) and methoxylated aromatics, whereas aqueous media predominantly formed benzoquinone and tetrahydroxybenzene, consistent with rapid hydroxyl-radical-driven mineralization. The strong influence of membrane type on phenol transport (AEM > PEM) and the distinct degradation pathways observed (hydroxylation/cleavage in water vs methoxylation/fragmentation in methanol) highlight the critical role of solvent-membrane coupling. Overall, the results demonstrate that electrochemical processing in methanol promotes the formation of identifiable value-added products, indicating potential implications for future resource-oriented wastewater treatment strategies.