Nitrogen, fluorine and boron tri-doped flower-like porous carbon derived from sodium carboxymethyl starch for high-performance supercapacitors

Abstract

In this work, nitrogen, fluorine, and boron tri-doped flower-like porous carbons were prepared from sodium carboxymethyl starch (CMS) by using potassium hydroxide (KOH) as an activator and ammonium borofluoride (NH4FB4) as a heteroatomic dopant. The specific surface area (SBET), total pore volume (Vt), pore size distribution (PSD), heteroatom content and electrochemical performance of the samples were directly determined by the KOH content. The optimized material (CMS-F/B/N-4) showed a flower-like porous structure with a large SBET (666 m2 g−1) and an appreciable amount of heteroatoms (oxygen: 8.01 at.%, nitrogen: 1.56 at.%, fluorine: 2.22 at.% and boron: 0.75 at.%). Owing to these merits, the supercapacitor based on CMS-F/B/N-4 displayed a maximum specific capacitance (Cg) of 219.2 F g−1 at 1 A g−1 and a high performance, with more than 72.5% of initial capacitance was retained when the current density was increased from 1 to 10 A g−1. In addition, a symmetric cell was assembled with a wide voltage range of 2.0 in 1 M Na2SO4 aqueous electrolyte, delivering a relatively high energy density of 26.47 Wh kg−1 at 500 W kg−1 and stable performance of ∼99% retention after 10,000 cycles. This study demonstrated the feasibility of fabricating porous carbon with specific morphology and heteroatom doping from natural polysaccharide polymers. The findings indicate an avenue toward practical applications of carbon-based supercapacitors.