Template-free fabrication of nitrogen-doped hollow carbon spheres for high-performance supercapacitors based on a scalable homopolymer vesicle

Presented in this article is the template-free fabrication of nitrogen-doped hollow carbon spheres (N-HCSs) as electrode materials for high-performance supercapacitors based on scalable homopolymer vesicles, which are self-assembled from an amphiphilic homopolymer, poly(amic acid) (PAA). This homopolymer can be massively produced by simple stepwise polymerization at room temperature with a fast polymerization rate. For the first time, PAA homopolymer vesicles are carbonized to form N-HCSs with tunable porous structures and nitrogen contents (from 1.3% to 7.4%) by controlling the content of the cross-linker (melamine). This template-free method for fabricating N-HCSs is more environmentally friendly and does not involve tedious synthetic procedures compared to traditional template-based methods. More importantly, the N-HCSs exhibit excellent electrochemical performance with a very high specific capacitance (266.9 F g^-1) after more than 1000 cycles when used as the active electrode material for the supercapacitor. The N-HCSs presented in this paper retain its specific capacitance as high as 84% at a very high current density (20 A g^-1). Given the potential massive production and excellent electrochemical properties, the N-HCSs based on the carbonization of scalable PAA homopolymer vesicles are promising candidate electrode materials for energy storage devices.