Upcycling PET in parallel with energy-saving H₂ production via bifunctional nickel-cobalt nitride nanosheets

We describe here an electro-reforming strategy to upcycle polyethylene terephthalate (PET) waste with simultaneous hydrogen production by a bifunctional nickel-cobalt nitride nanosheets electrocatalyst. PET plastics are digested in alkaline solution giving an electrochemically active monomer ethylene glycol (EG). The introduction of Co in Co-Ni₃N/carbon cloth (CC) promotes the redox behavior of Ni²⁺/Ni³⁺, which is beneficial for EG oxidation at an ultra-low potential (1.15 V vs. reversible hydrogen electrode (RHE)) and breaks through the limitation of high catalytic potentials of simple Ni-based electrocatalysts (1.30 V). In PET hydrolysate with Co-Ni₃N/CC couples, an integrated EG oxidation-hydrogen production system achieves a current density of 50 mA·cm⁻² at a cell voltage of 1.46 V, which is 370 mV lower than the conventional water splitting. The in-situ Raman and Fourier transform infrared (FTIR) spectroscopies and density functional theory (DFT) calculations identify the catalytic mechanism and point to advantages of heterostructure engineering in optimizing adsorption energies and promoting catalytic activities for EG oxidation.