Cooperative utilization of beet pulp and industrial waste fly ash to produce N/P/O self-co-doped hierarchically porous carbons for high-performance supercapacitors

Preparation of three-dimensionally hierarchical porous carbons (HPCs) with biomass wastes for high-performance supercapacitors has being the hotspot subject in the past decade from sustainable and renewable points of view. In this paper, an industrial biomass waste of beet pulp (BP) is used as precursor to purposely prepared N/P/O co-doped HPCs by a simple yet efficient two-step method. Another industrial solid waste of fly ash (FA), containing inorganic oxides (mainly SiO2, Al2O3, Fe2O3, and CaO) with varied sizes, is utilized as the ingredient acting as pore-forming template to regulate the morphology and increase the porosity of the resulting HPCs (derived from BP and FA, which are designated as BFCs). The optimal sample of BFC-2 exhibits an exceptionally high specific capacitance up to 522.1 F g−1 at 1.0 A g−1 in 6 M KOH electrolyte. Furthermore, the symmetric supercapacitor assembled with BFC-2 can deliver large energy densities in both 1 M Na2SO4 (39.3 Wh kg−1) and EMIMBF4 (97.9 Wh kg−1) with satisfactory rate retentions, as well as prominent cycling durabilities. These exciting results show a low-cost, environmentally benign, and waste profitable idea to prepare HPCs for high-performance supercapacitors, which is in good accordance with the principle of " changing waste into wealth " in the green energy resources. [Display omitted] •Beet pulp-derived hierarchically porous carbons (BFCs) are prepared.•Fly ash is recycled to regulate morphology and develop porosity of the BFCs.•The optimal BFC-2 delivers a large energy density of 97.9 Wh kg−1 in EMIMBF4.•This work provides a waste profitable idea to prepare HPCs for supercapacitors.