Biocompatible Mesoporous Hollow Carbon Nanocapsules for High Performance Supercapacitors

Abstract

A facile and general method for the controllable synthesis of n-doped hollow mesoporous carbon nanocapsules (NHCNCs) with four different geometries has been developed. The spheres (NHCNC-1), low-concaves (NHCNC-2), semi-concaves (NHCNC-3) and wrinkles (NHCNC-4) shaped samples were prepared and systematically investigated to understand the structural effects of hollow particles on their supercapacitor performances. Compared with the other three different shaped samples (NHCNC-1, NHCNC-2, and NHCNC-4), the as-synthesized semi-concave structured NHCNC-3 demonstrated excellent performance with high gravimetric capacitance of 326 F g −1 (419 F cm −3 ) and ultra-stable cycling stability (96.6% after 5000 cycles). The outstanding performances achieved are attributed to the unique semi-concave structure, high specific surface area (1400 m 2 g −1 ), hierarchical porosity, high packing density (1.41 g cm −3 ) and high nitrogen (N) content (up to 3.73%) of the new materials. These carbon nanocapsules with tailorable structures and properties enable them as outstanding carriers and platforms for various emerging applications, such as nanoscale chemical reactors, catalysis, batteries, solar energy harvest, gas storage and so on. In addition, these novel carbons have negligible cytotoxicity and high biocompatibility for human cells, promising a wide range of bio applications, such as biomaterials, drug delivery, biomedicine, biotherapy and bioelectronic devices.Supercapacitors have drawn increasing attention due to their high power density, fast charge/discharge capability, long cycle life, low cost and environmental friendliness among various electrochemical energy storage devices 1 . Carbon materials are the most promising supercapacitor electrode materials, due to their high specific surface area, high electrical conductivity, tailorable pore structures and excellent chemical stability 2 . The pore structures and the surface properties of carbon materials have significant effects on the electrode performances 3 . In order to increase the volumetric capacitance of the electrode materials 4,5 , it is vital to optimize the morphology and reduce the void volume of the hollow porous carbon materials.Hollow carbon nanocapsules (HCNCs) are an interesting class of carbon materials, due to their unique properties such as high surface-to-volume ratio, low densities, large void space and high electrical conductivity 6,7 . The hollow macropore cavities and interior space of the HCNCs can act as anion-buffering reservoirs to shorten the diffusion distance of electrolyte ions 8 , while the mesopores and micropores in the shell can promote ion transport, minimize diffusion pathways from the electrolyte to the micropores, and increase the specific surface area to maximize the electric double layer capacitance 9 . For high-rate performances, HCNCs are particularly interesting as they have ultrahigh specific surface area, large surface-to-volume ratio, large void space along with an appropriate interconnected pore channels to facilitate ion ...

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