Polyatomic self-doping millet-derived porous carbon for supercapacitor.

The selecting of supercapacitor electrode materials, has seen a growing interest in biomass-derived carbon materials due to their surface functional groups and unique pore structure. In this study millet-derived porous carbon (MIC-PxRy) with heteroatoms including nitrogen (N), oxygen (O), phosphorous (P), and sulfur (S) was synthesized through a successive pre‑carbonization and chemical activation process. The structure and distribution of heteroatoms in the MIC-PxRy were effectively controlled by adjusting the pre‑carbonization and activation temperatures. When the pre‑carbonization and activation temperatures are both at 600 °C, the resulting sample (MIC-P6R6) exhibited a high specific surface area (1798.79 m2g−1) was co-doped with oxygen atoms (10.77 %), nitrogen atoms (1.40 %), sulfur atoms (0.76 %) and phosphorus atoms (0.26 %). In a three-electrode system, the MIC-P6R6 demonstrated a specific capacitance of 458.6 Fg−1 at 1 A g−1, which remained stable at 336.2 F g−1 even under higher current densities up to 20 A g−1. In a two-electrode system with KOH electrolyte, it exhibited an impressive specific capacitance of 314.2 F g−1 along with an energy density of 10.91 Wh kg−1 (at 250 W kg−1, 1 A g−1). Furthermore, after undergoing durable 20,000 cycling tests (at 5 A g−1), the MIC-R6A6 demonstrated exceptional capacitance retention rate of 92.1 %. This study provides a novel self-doped activated carbon material with multiple heteroatoms at a lower activation temperature, which can improve the performance of symmetric supercapacitors. [Display omitted] • Polyatomic N/O/P/S co-doped porous carbon was obtained by heat treatment of Millet. • Optimized carbonization and activation temperature are both low at 600 °C. • MIC-P6R6 exhibits low charge transfer resistance of 0.66 Ω. • MIC-P6R6 exhibited excellent specific capacitance and durability. [ABSTRACT FROM AUTHOR]