LiCoO₂-Derived Ni-Doped Catalysts for Electrochemical Upcycling of Polyethylene Terephthalate Waste to Formic Acid.

Abstract

The electrochemical upcycling of polyethylene terephthalate (PET) into high-value products is essential for tackling "white pollution" and enhancing environmental protection. However, significant challenges remain, including the need for low-cost, highly efficient electrocatalysts, and the expensive electrolyte recovery in alkaline systems. This study presents a simple doping method to produce Ni octahedral-doped Co₃O₄ electrocatalysts (NiCo₂O₄) from spent LiCoO₂ (SLCO), enabling sustainable PET upcycling to formic acid (FA) under economic conditions. The NiCo₂O₄ catalyst exhibits outstanding electrocatalytic activity for the ethylene glycol oxidation reaction (EGOR), achieving a Faradaic efficiency of 90.5% for FA at a potential of 1.50 V versus RHE. When integrated into an anion-exchange membrane (AEM) reactor, the system displayed an average current density of 173.5 mA/cm² and a Faradaic efficiency of 84.7% at a cell voltage of 1.70 V. Systematic characterizations and DFT calculations indicate that Ni doping alters the spin-state electron density of Co, increases the localized electrons around Co sites, and significantly reduces the charge transfer resistance (<i>R</i>_ct from 44.10 Ω to 10.23 Ω) of EGOR. Moreover, the Co-Ni dual sites enhance EG adsorption compared to individual Co or Ni sites. Finally, along with our electrochemical recovery and separation system (ERSS), a KOH recovery rate of 98.9% is achieved, yielding a return of $440.50 per ton of recycled PET─approximately a 4-fold profit increase compared to the traditional acid-base neutralization process (ABNP). This work describes a closed-loop model that simultaneously addresses battery recycling, plastic pollution reduction, and eco-friendly chemical production.