NiCo₂O₄/NF nanoneedle array enables low-potential ethylene glycol oxidation and upcycles waste polyethylene terephthalate into commodity chemicals

Abstract

Electrochemical upgrading of polyethylene terephthalate (PET) waste into value-added chemicals offers a promising route for plastic recycling. However, efficient oxidation of PET-derived ethylene glycol (EG) still requires low-cost catalysts with high activity and selectivity. Herein, a NiCo₂O₄ nanoneedle array grown on nickel foam (NiCo₂O₄/NF) was fabricated via a hydrothermal-annealing process and employed as an anode for EG electrooxidation. The NiCo₂O₄/NF electrode delivers 100 mA∙cm^–2 at 1.37 V (vs. RHE) and achieves a formate Faradaic efficiency of approximately 97.0% at 1.50 V (vs. RHE). It also retains 92.7% of its initial current after 50 h of continuous electrolysis. X-ray photoelectron spectroscopy analysis suggests electronic modulation around Ni and Co centers, and combined with electrochemical analyses, these results indicate that the Ni-Co interaction in the spinel framework may contribute to strengthened interfacial EG adsorption and promoted EG oxidation kinetics. Mechanistic studies further identify electrogenerated high-valent Ni/Co oxyhydroxides as the key redox-active species, with formate generated via oxygenated C₂ intermediates followed by C–C bond cleavage. Electrolysis using EG derived from real PET hydrolysates further demonstrates the conversion of PET powder into potassium diformate and terephthalic acid, underscoring the practical potential of this strategy for PET upcycling.

Graphical abstract

Keywords

electrochemistry / electrolysis / catalysis / oxidation / waste treatment

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