Electro-Upcycling Polyethylene Glycol Aqueous Solutions in a Proton Exchange Membrane Electrolyser

This study addresses the electro-upcycling, at low temperature and neutral pH conditions, of aqueous solutions of polyethylene glycol (PEG). For this purpose, a Proton-Exchange Membrane (PEM) reactor with Pt/C-based electrodes has been used. The electrooxidation performances of ethylene glycol (EG) and PEG were evaluated for various concentrations in aqueous solutions, temperatures and PEG molecular weights (MW). PEG was successfully electro-oxidized from 0.4 V, reaching current densities above 100 mA cm^-2 at 0.8 V and 80 °C using oligoethylene glycols up to 400 g mol^-1. Size-exclusion chromatography and NMR analysis evidenced the possibility to cleave –C–O–C– bonds of heavy PEG (1000, 4000 g mol^-1), proving the possibility of depolymerizing PEG and recovering the monomer at low cell voltages and low temperatures. The production and purity of hydrogen in the cathode compartment of the electrolyser was confirmed by mass spectrometry. These results may open new perspectives in the development of electro-upcycling of PEG in water effluents.