Porous ball-in-ball N-doped carbon loading Co nanoparticles for high-performance asymmetric capacitor

Porous carbon supported metal nanoparticles as supercapacitor electrode materials have attracted extensive attention. In this paper, cobalt nitrate/polystyrene microspheres/chitosan(Co(NO3)2/PS/CS) balls were fabricated by emulsion encapsulation and self-assembly process. After carbonization, Co nanoparticles (NPs) loaded on porous ball-in-ball N-doped carbon (Co/BNC) were prepared. Co/BNCs with high surface area profit formation of sufficient active sites and facilitate ion transport due to the interconnected and interpenetrating porous carbon structure. The electrochemical performances of Co/BNCs are affected by Co NPs content and the Co/BNC with the optimal Co NPs content (Co/BNC-2) possesses a commendable specific capacitance of 1120 F g⁻¹ at 1 A g⁻¹. Moreover, the capacitance retention of the asymmetric supercapacitors assembled by Co/BNC-2 and activated carbon is about 85.38 % after 5000 cycles. Remarkably, the device exhibits a maximum energy density of 60.9 Wh kg⁻¹ at 764 W kg⁻¹ and maintains 37.8 Wh kg⁻¹ at 7878 W kg⁻¹. Co/BNCs mentioned here have the potential to be candidates for high-performance supercapacitor electrode materials.