Defective nickel sulfide hierarchical structures for efficient electrochemical conversion of plastic waste to value-added chemicals and hydrogen fuel

Abstract

Valorizing plastic waste into value-added chemicals/fuels in a green manner (e.g., electrochemical reforming) is a sustainable way to address the global pressing problem of plastic pollution. For the electro-reforming of plastic waste (e.g., polyethylene terephthalate (PET)), the development of highly active and selective catalysts remains a challenge. Herein, we have designed a low-cost and highly defective nickel sulfide to selectively convert ethylene glycol (PET monomer) into formate, with the co-production of hydrogen fuel. The optimal B and Co co-doped Ni₃S₂ (B,Co-NiS) only takes 1.341 V compared to the reversible hydrogen electrode (RHE) at 100 mA cm⁻² for ethylene glycol oxidation, and it can realize high faradaic efficiency (>93%) and selectivity (>92%) for EG-to-formate conversion over a wide potential range. Furthermore, the bifunctional B,Co-NiS assisted real PET waste hydrolysate electrolysis in a membrane-electrode assembly (MEA) can generate 15.24 mmol formate per hour and attain H₂ production efficiency over 70 times compared to conventional water electrolysis. Mechanism analyses indicate that the excellent catalytic performance of B,Co-NiS stems from the hierarchical structure, rich S defective sites, regulated electronic properties, and the dopant-facilitated in situ formation of an active sulfide@oxyhydroxide phase. This work provides an integrated nanostructure controlled-composition regulation strategy to design cost-effective catalysts for plastic electro-upcycling and paves the way for low-carbon plastic waste management.