Nitrogen-Doped Hierarchical Nanoporous Carbon Materials from Discarded Polyurethane Sponges via One-Step Double-Activation Method for Double-Layer Capacitors

The self-induced N-doped micropore and mesopore hierarchical nanoporous carbon (NPC-CZ) was synthesized from a discarded shock-proof polyurethane sponge by using a one-step physical/chemical double-activation method with the introduction of ZnCl2 and CO2. ZnCl2 activation generated numerous micropores and mesopores, while subsequent CO2 treatment further enhanced the microporosity and pore volume of NPC-CZ. Besides, the carbonation process formed oxygen-containing functional groups and converted the self-contained abundant amino groups in a shock-proof polyurethane sponge to N atom doping, which generated additional active sites and improved the surface wettability ability. NPC-CZ has a high specific surface area of 1108.9 m2 g–1 and an abundant hierarchical nanoporous structure. The specific capacitances of NPC-CZ were found to reach 211.7 F g–1 at a current density of 0.5 A g–1 in a 2 M KOH electrolyte solution, while operating within a potential window of −1 to 0 V. Additionally, the excellent cycle stabilization of NPC-CZ was demonstrated by an impressive capacitance retention of 84.2% after undergoing 20000 cycles at a higher current density of 5 A g–1. Furthermore, when employed as electrode materials in symmetric supercapacitors, NPC-CZ achieved a power density of 600 W kg–1 while maintaining an energy density of 6.33 Wh kg–1. This research offers innovative perspectives on the transformation of discarded polyurethane sponges into highly potential nanostructured materials for capacitor electrodes.