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 (Rct 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.