Microwave-plasma induced one-step synthesis of Ni(PO3)2 nanosphere-loaded bio-waste derived N, P co-doped carbon for an asymmetric supercapacitor with prolonged life

Abstract

Despite significant advancements, supercapacitors are still struggling to showcase their successful commercial presence because they suffer either from low energy storage performances due to sluggish reaction kinetics or use complex and less affordable manufacturing processes. Therefore, here, we introduce a controlled microwave-plasma induced single-step process to produce a nitrogen (N) and phosphorus (P) co-doped sheet-like multilayer graphitic carbon (NPGC) coupled with an ultrasmall (average particle size of ∼6.2 nm) nickel phosphate (NiP₂O₆) nanosphere (NiPO) based composite (NPGC–NiPO) electrode with optimized compositions which exhibits a remarkable capacitance (417 F g⁻¹ and 300.6 mF cm⁻² at 1 A g⁻¹) with ultralong cycle life (93% capacitance retained even after 10 000 cycles at 5 A g⁻¹). Moreover, the fabricated all-solid-state asymmetric supercapacitor (ASC) of the NPGC–NiPO composite and NPGC exhibits a prolonged cycle life (96% capacitance retained even after 10 000 cycles at 7.6 A g⁻¹) with high capacitance values (48.1 F g⁻¹ and 383.3 mF cm⁻² at 0.6 A g⁻¹) while operating within 1.6 V. This NPGC–NiPO composite is the first of its kind and easy to manufacture through a one-step, quick and affordable microwave process which can be further extended for developing different composites from different bio-wastes and transition metal precursors for various energy storage applications.