Nitrogen-Enriched Hollow Porous Carbon Nanospheres with Tailored Morphology and Microstructure for All-Solid-State Symmetric Supercapacitors

We develop a straightforward and highly efficient approach to design N-enriched hollow porous carbon nanospheres (N-HPCNs) based on the self-polymerization of dopamine in mixed water/ethanol solvents. The control of the morphology, pore parameters, and nitrogen content of N-HPCNs can be effectively achieved by simple tuning of the volume ratios of water/ethanol and the amounts of the solvents. The representative N-HPCNs exhibit the characteristics of spherical and hollow geometry with a uniform diameter (∼400 nm), high surface area (1789 m2 g–1), abundant ultramicropores with reasonable supermicro- and mesopores, and high-level nitrogen content (up to 6.86 wt %). N-HPCNs as supercapacitor electrodes in 6 M KOH electrolyte show outstanding electrochemical performances including a high specific capacitance (353 F g–1 at 0.5 A g–1), superb rate capability (214 F g–1 at 20 A g–1), and excellent cycling stability (91.9% capacitance retention at 1.0 A g–1 after 10,000 cycles). Furthermore, the assembled symmetric all-solid-state supercapacitor based on N-HPCN electrodes and poly­(vinyl alcohol)/KOH gel electrolyte exhibits high integrated energy–power density of 10.42 W h kg–1 at 250 W kg–1. This study provides promising prospects to design N-doped carbons with tailored morphology and microstructure for high-performance supercapacitors.