Reaction Protocol for the Electro-Oxidation of Ethylene Glycol on Gold in PET Upcycling

The electro-oxidation of ethylene glycol (EG) toward value-added glycolic acid (GA) has excellent potential as an upcycling strategy in the chemical recycling of polyethylene terephthalate (PET). However, noble metal catalysts suffer from rapid deactivation during constant potential electrolysis (CPE), which diminishes productivity and impedes continuous operation. In order to enable long-term operation, the cause of deactivation is investigated, and reaction sequences are developed as countermeasures to deactivation. The catalyst performance was evaluated based on the charge passed during CPE and on the GA production rate. HPLC analysis confirmed the selectivity of the reaction and the validity of charge as an assessment parameter. It was found that the oxidation potential in CPE significantly determines the rate of deactivation, while convection does not improve catalyst productivity, but hinders regeneration. To efficiently operate long-term electro-oxidation of EG (EGOR), the CPE conversion was paired with electrochemical regeneration through potential sweeping experiments. A reaction protocol initiating regeneration at a current threshold during CPE improved the catalyst productivity significantly compared to non-regenerated or time-interval-based regeneration processes. The current threshold method enabled the timing of regeneration independent of the catalyst decay rate and allowed for long-term EGOR operation.