Integrated upcycling of PET waste via ethylene glycol oxidation and CO2 electroreduction: full-cell demonstration with techno-economic and environmental assessments

Abstract

The electrochemical CO₂ reduction reaction (CO₂RR) offers a sustainable strategy for converting CO₂ into valuable products while utilizing renewable energy sources. However, the oxygen evolution reaction (OER), which is commonly coupled with the CO₂RR, is a sluggish reaction that requires a high overpotential. To overcome this, we used the ethylene glycol oxidation reaction (EGOR) as an alternative anodic oxidation reaction, using ethylene glycol (EG) derived from waste poly(ethylene terephthalate) (PET). This strategy lowers the overall cell voltage and enables simultaneous carbon utilization and plastic waste valorization. The EGOR∥CO₂RR system was operated with a Ni_0.33Co_0.67(OH)₂/NF anode and an Ag-BTC/CP cathode. The as-prepared anode required less energy (135 mV) for the EGOR at 100 mA cm⁻² than for the OER. In the full cell, the EGOR at the anode achieved a faradaic efficiency (F.E.) of approximately 60% for formate production, while the CO₂RR at the cathode reduced CO₂ to CO with a F.E. exceeding 95% over a wide range of potentials. Furthermore, to elucidate the commercialization potential of the EGOR∥CO₂RR, we developed a rigorous process simulation with techno-economic and environmental assessments incorporating PET hydrolysis and downstream separation at an industrial scale. Three process configurations were designed and evaluated, revealing that hydrolysis and separation dominate the overall process efficiency rather than electrochemical performance alone. Moreover, we demonstrate that improvements in EGOR∥CO₂RR technology can approach cost parity with fossil-based terephthalic acid and achieve lower CO₂-equivalent emissions, thereby providing a viable pathway toward commercialization of the technology.