PdFe alloy nanoparticles supported on nitrogen-doped carbon nanotubes for electrocatalytic upcycling of poly(ethylene terephthalate) plastics into formate coupled with hydrogen evolution

Abstract

The escalating plastic pollution and potential energy crisis necessitate upcycling plastic waste into high-value-added chemicals and fuels. Combining the hydrogen evolution reaction (HER) with a thermodynamically feasible and sustainable anodizing reaction provides a sustainable option for the electrochemical appreciation of plastic waste. Herein, a hybrid electrocatalyst, i.e., PdFe alloy nanoparticles supported on nitrogen-doped carbon nanotubes (denoted as PdFe/N-CNTs), is proposed for the electrochemical upcycling of polyethylene terephthalate (PET) waste at the anode with simultaneous generation of hydrogen at the cathode. Benefiting from the distinctive structural characteristics of N-doped carbon nanotubes and downshift in the d-band center created by alloying Fe with Pd, the resultant PdFe/N-CNT bifunctional catalyst exhibits superior electrocatalytic performance for both the ethylene glycol oxidation reaction (EGOR) and the HER in 1.0 M KOH electrolyte, affording low overpotentials of 32 mV (vs. RHE)@10 mA cm⁻² and 1.22 V (vs. RHE)@10 mA cm⁻² for the respective HER and EGOR with a high faradaic efficiency (FE) of 87% for formate production. Besides, a two-electrode integrated system is constructed by coupling PET hydrolysate oxidation with the HER, which not only enables the concurrent generation of formate acid (FA) at the anode and H₂ at the cathode but also achieves a current density of 500 mA cm⁻² at a cell voltage of 1.68 V, lower than that of conventional water splitting. The conversion of PET into FA is studied by in situ electrochemical Fourier-transform infrared (FTIR) spectroscopy measurements and density functional theory (DFT). This work is expected to provide meaningful guidance for the upcycling of PET plastic waste by rationally designing highly efficient electrocatalysts.