Nitrogen-doped cornstalk-based biomass porous carbon with uniform hierarchical pores for high-performance symmetric supercapacitors

The poor cycling stability of commercially used supercapacitors and the expensive activated carbon materials used in them have limited their large-scale use in energy storage. In this study, we successfully prepared nitrogen-doped cornstalk activated carbon (NCSAC) by high-temperature calcination using cornstalk, one of the three major crop wastes globally, as the biomass precursor. Potassium hydroxide was used as the activator and urea as the cheap nitrogen source. The as-prepared NCSAC showed a compact and homogeneous hierarchical porous structure composed mainly of mesopores and micropores with a large specific surface area of 2152 m 2 g −1 , which facilitated fast electrolyte ion transmission. The N doping content of 3.05 at% enhanced the surface wettability of the biomass porous carbon. In particular, the electrochemical performance of NCSAC as a biomass carbon electrode for supercapacitors was investigated. The NCSAC electrode showed a high specific capacitance of 350.4 F g −1 at the current density of 0.2 A g −1 . Additionally, the symmetric supercapacitor based on the NCSAC electrode material also showed the specific capacitances of 308 and 216 F g −1 at 0.2 and 20 A g −1 , respectively. Furthermore, it showed a high energy density of 10.01 W h kg −1 at the power density of 249.9 W kg −1 . Significantly, the NCSAC-based symmetric supercapacitor exhibited very high cycling stability with a capacitance retention of 99.8% after 10,000 cycles. Graphical abstract