Closed-loop electro-upcycling of PET waste into formate and hydrogen via self-supported NiCo2O4 spinel arrays

Jiang, Mingkun, Yang, Yang, Wang, Yujie, Wang, Yajie, Ratova, Marina ORCID: https://orcid.org/0000-0003-4588-181X and Wu, Dan ORCID: https://orcid.org/0000-0001-5272-6581 (2025) Closed-loop electro-upcycling of PET waste into formate and hydrogen via self-supported NiCo2O4 spinel arrays. Green Chemistry, 27 (33). pp. 9978-9991. ISSN 1463-9262

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Abstract

The global accumulation of polyethylene terephthalate (PET) waste poses a severe environmental crisis and leads to severe underutilization of embedded carbon resources. In this work, a self-supported spinel NiCo2O4 electrocatalyst grown on nickel foam (NiCo2O4/NF) is developed for the electrochemical upcycling of PET-derived ethylene glycol (EG) into formate and hydrogen. The catalyst leverages a synergistic redox interaction between Ni and Co centers to enhance OH− and EG adsorption, accelerate interfacial charge transfer, and steer selective C–C bond cleavage. Operando and theoretical analyses reveal that EG oxidation proceeds via a surface-confined pathway, where Ni3+ modulates redox dynamics and Co3+ facilitates C–C scission while suppressing overoxidation. This enables a high formate faradaic efficiency of 96.7% and an industrial-level current density of 400 mA cm−2 at 1.34 V. Notably, post-consumer PET bottles can be directly converted into potassium diformate, terephthalic acid, and H2 under mild alkaline conditions. A technoeconomic analysis reveals a net profit of $774.56 per ton PET processed, underscoring the feasibility and sustainability of this closed-loop strategy. This work provides a promising pathway for high-value chemical and energy recovery from plastic waste using earth-abundant, non-noble metal catalysts.