N/O Co-doped hierarchical nanoporous biochar derived from waste polypropylene nonwoven for high-performance supercapacitors.

How to efficiently treat municipal solid waste (MSW) has become one of the critical solutions in response to the call for "carbon neutrality". Here, the waste polypropylene nonwoven fabric of waste diapers was converted into hierarchical nanoporous biochar (HPBC) through pre-carbonization and activation processes as an ideal precursor for supercapacitors (SCs) with excellent performance. The prepared HPBC-750-4 with an ultrahigh specific surface area (3838.04 m g) and abundant heteroatomic oxygen (13.25%) and nitrogen (1.16%) codoped porous biochar structure. Given its structural advantages, HPBC-750-4 achieved a specific capacitance of 340.9 F g at a current density of 1 A g in a three-electrode system. Its capacitance retention rate was above 99.2% after 10 000 cycles at a current density of 10 A g, which indicated an excellent rate capability and long-term cycling stability. Furthermore, the HPBC-750-4//HPBC-750-4 symmetric SC exhibited a superb energy density of 10.02 W h kg with a power density of 96.15 W kg in a 6 M KOH electrolyte. This work not only demonstrates the enormous potential of waste polypropylene nonwoven fabric in the SC industry but also provides an economically feasible means of managing MSW.