Closed-Loop Upcycling of PET Waste into Defect-Engineered Ni@C Electrocatalysts for Efficient Formate Production

Abstract

To address the challenges of polyethylene terephthalate (PET) recycling, we propose a closed-loop upcycling system based on deep eutectic solvent (DES) mediated alkaline hydrolysis PET into terephthalic acid (TPA) and ethylene glycol (EG). The TPA was used as a precursor to prepare a carbon-supported nickel-based electrocatalysts (Ni@C/NF), which was subsequently applied for the electrochemical oxidation of EG into formate. Carbon defects increase electron deficiency in the catalyst substrate, enhancing EG adsorption and promoting interfacial enrichment. Simultaneously, oxygen vacancies create coordinatively unsaturated Ni sites that facilitate OH adsorption and the formation of Ni δ+ -(OH) ads intermediates.Surface oxygen vacancies accelerate the pre-oxidation of γ-NiOOH active species through localized electronic effects, driving selective C-C bond cleavage in EG. Density functional theory calculations further confirm that the strengthened EG adsorption and reduced energy barrier for the Ni²⁺/Ni³⁺ redox transition synergistically promote the catalytic reaction.Benefiting from the synergistic effects of defect and vacancy engineering, the catalyst delivers outstanding performance with a current density exceeding 400 mA cm⁻² at 1.5 V (vs. RHE), 83% Faradaic efficiency and a formate production rate of 3.52 mmol cm⁻² h⁻¹. This closed-loop upcycling strategy provides an environmentally sustainable and industrially viable approach for the high-value conversion of PET waste.