Glucose-derived nitrogen-doped hierarchical hollow nest-like carbon nanostructures from a novel template-free method as an outstanding electrode material for supercapacitors

Abstract

Nitrogen-doped hierarchical hollow nest-like carbon (NHHNC) nanostructures were fabricated from glucose with a novel template-free method. A hollow nest-like precursor, Ni(OH)₂@N-polysaccharide, was first formed through a hydrothermal treatment of glucose in the presence of NiSO₄ and hexamethylenetetramine (HMT), with glucose serving as the carbon source, HMT as the precipitant and nitrogen source, and NiSO₄ as the main structure-directing reagent. The hierarchical porous carbon structure was created through thermal carbonization and activation followed by acid etching, of the hollow nest-like precursor. The NHHNC was a hierarchical porous structure composed of three-dimensionally intercepting N-doped porous carbon sheets and possessed micropores, mesopores, and macropores. This unique hierarchical hollow nest-like porous structure is ideal for applications as electrodes for supercapacitors, with the micropores offering large surface areas to accommodate electric double layer capacitances, the mesopores as fast ion transport channels, and the macropores as the electrolyte reservoir for fast ion supply. These advantageous structural features, together with the fast charge transport ability of the partially graphitized carbon sheets and extra pseudocapacitances generated through superficial redox reactions of the N-doped sites, led to outstanding capacitive performances of the NHHNC. The NHHNC electrode exhibited a high specific capacitance of 322 F g⁻¹ at 1 A g⁻¹, an excellent high rate capability of 54% capacitance retention at 20 A g⁻¹, and an outstanding cycling stability of only 2% loss in specific capacitance after 10 000 cycles at a current density of 10 A g⁻¹, among the best reported. The present template-free process, however, unlike the often cumbersome templating ones, is well suited for mass production and thus practical applications.