Nitrogen-enriched hierarchical porous carbons derived from biomass waste-discarded pear for ultra-high energy density supercapacitor in neutral aqueous electrolyte

Abstract Herein, nitrogen-enriched hierarchical porous carbons (HPCs) were synthesized by soaking, carbonization and pickling process using natural discarded pears (DP) as the precursor, ZnCl2 as a chemical etching agent and Mg(NO3)2·6H2O as a template. The ZnCl2 activation could produce abundant micropores, while Mg(NO3)2·6H2O can serve as mesopores template. Consequently, the as-prepared carbon material exhibits a three-dimensional interconnected porous structure with a high specific surface area (SBET) of 1642 m2 g−1 and a pore volume of 1.06 cm3 g−1 as well as high nitrogen content (1.7 at.%). On the basis of electrochemical tests, the SCs involve the final products as electrode material presented remarkable gravimetric capacitance (443.5 F g−1) and volumetric capacitance (285.2 F cm−3) at the current density of 1 A g−1 and excellent rate capability (45.1% capacitance retention from 0.5 A g−1 to 40 A g−1). Most attractively, the constructed DP-Zn-Mg-PC/DP-Zn-Mg-PC symmetric SC cell in 1 M Na2SO4 with a wide potential window of 2.2 V displays an ultra-high energy density of 95.8 Wh kg−1 at 550 W kg−1 together with superior cycling stability (98.6% retention after 10,000 cycles), which is outperform those of some similar peer reported biochars. Thus, this work provides an important guideline for preparing HPCs with high-energy density from eco-friendly and sustainable biomass precursors.