N, P codoped carbon nanosheets derived from rice husk for supercapacitors with high energy density

Supercapacitors (SCs) have been widely used owing to their merits of long cycle life, excellent physiochemical stability and zero-carbon emission. However, the low energy density of SCs restricts their further applications. Herein, the N, P doped carbon nanosheets (NPCNs) were prepared by using silicon-removed carbon as carbon resource derived from rice husk. The as-prepared NPCN not only possesses a large surface area of 1701.6 m2 g-1 and a high ratio of mesopore volume to total pore volume (62.11 %) for adsorption and transfer of electrolyte ions, but also has a suitable nitrogen and phosphorus content for electron conduction and contribution of additional active sites to generate pseudo-capacitance through redox. Therefore, the excellent electrochemical properties have been obtained for NPCN-based SCs in the alkaline electrolyte, e.g. satisfactory capacitance of 396.1 F g-1 at 0.1 A g-1, outstanding rate properties of 319.2 F g-1 at 40 A g-1, long cyclability with capacitance decay of 0.95 % after 30,000 cycles. Additionally, the energy density of the NPCN-based SCs with neutral electrolyte and ionic liquid electrolyte increased 2.67-fold and 11-fold to 33.25 and 137.24 Wh kg -1, respec-tively. This study opens up a feasible route by crafting heteroatoms and using high voltage window electrolyte to obtain the high energy density for SCs.