N, P dual doped foamy-like carbons with abundant defect sites for zinc ion hybrid capacitors

To achieve high value-added use of biomass waste is still a big challenge. Besides, heteroatom-doped carbon materials have been charmed enormous interests due to their high conductivity and abundant defect sites. Herein, a simply and confined pyrolysis method is innovated to prepare N, P codoped foamy-like carbons (NPFC) with abundant defect sites from osmanthus flowers. The NPFC features uniform N, P doped, porous structures and big electric conductivity, which provide abundant defects and additional active sites for ion adsorption, shorten ion transfer distance, enhance transfer kinetics and supply highways for electron transfer. As cathode for zinc ion hybrid capacitor (ZHC), NPFC exhibits large energy density (85.7 Wh kg−1) with long cycle life (remains 97.4% after 20,000 cycles) in aqueous electrolyte. More interestingly, NPFC-based quasi-solid-state ZHC presents extremely big capacity of 163.6 mAh g−1 at 0.1 A g−1 and excellent power density of 35.9 kW kg−1. This study offers a universal method to synthesize heteroatom-doped carbon materials from biomass waste for hybrid capacitors.