Suppressing oxygen evolution over Cu-doped NiO for efficient electro-upcycling of PET plastics

Electrochemical upcycling of polyethylene terephthalate (PET) into value-added chemicals offers a sustainable route for plastic waste valorization. However, at high current densities, the competing oxygen evolution reaction (OER) lowers faradaic efficiency (FE) and compromises catalyst stability. Herein, we report a Cu-doped NiO catalyst grown on nickel foam (Cu-NiO/NF) that markedly suppresses OER while promoting the selective oxidation of ethylene glycol (EG) to formate. The Cu-NiO/NF electrode achieves a high formate FE exceeding 96% at 1.45 V vs. RHE. By combining X-ray absorption spectroscopy, in situ Raman and ATR-FTIR spectroscopies with density functional theory calculations, we reveal that Cu incorporation modulates the local coordination environment and electronic structure of Ni sites. This modulation promotes the formation of active NiOOH species while inhibiting the deprotonation of OH* to O*, the rate-determining step of OER. When integrated into a membrane electrode assembly, the system efficiently produces formate and enables the recovery of terephthalic acid from real PET hydrolysate with reduced energy input. This work thus offers a rational design principle for suppressing the parasitic OER while enabling efficient PET electro-upcycling.