Electrocatalytic conversion of waste polyamide-66 hydrolysates into high-added-value adiponitrile and hydrogen fuel

Abstract

To reduce environmental pollution and plastic recycling costs, polyamide-66 (PA-66) as the most consumed engineering polymer needs to be recycled effectively. However, the existing recycling methods cannot convert waste PA-66 into valuable chemicals for upcycling under ambient conditions. Here, we report an integrated hydrolysis and electrocatalytic process to upcycle waste PA-66 into valuable adiponitrile (ADN), adipic acid, and H₂ commodities, thereby closing the PA-66 loop. To enable electrooxidation of the PA-66 hydrosylate hexamethylenediamine (HMD), we fabricated anode catalysts with hierarchical Ni₃S₂@Fe₂O₃ core-shell heterostructures comprising spindle-shaped Ni₃S₂ cores and Fe₂O₃ nanosheet shells. The unique core-shell architecture and synergy of the Ni₃S₂ and Fe₂O₃ catalysts enabled the selective dehydrogenation of C–N bonds from HMD to nitrile C≡N bonds, forming ADN with near-unity Faradaic efficiency at 1.40 V during the 100-h stability test even at 100 mA cm⁻². X-ray photoelectron spectroscopy revealed that the Ni(Fe) oxy(hydroxide) species formed were in the active state during oxidation, accelerating the activation of the amino C–N bond for dehydrogenation directly into the C≡N bonds.