Hierarchical\nNanostructures of Nitrogen-Doped Porous Carbon Polyhedrons Confined\nin Carbon Nanosheets for High-Performance Supercapacitors

Abstract

Interconnected\nclose-packed nitrogen-doped porous carbon polyhedrons (NCPs) confined\nin two-dimensional carbon nanosheets (CNSs) have been prepared through\na sustainable one-pot pyrolysis of a simple solid mixture of zeolitic\nimidazolate framework-8 (ZIF-8) crystals and with organic potassium\nas the precursors. The hierarchically organized framework of the NCP–CNS\ncomposites enables NCPs and CNSs to act as well-defined electrolyte\nreservoirs and mechanical buffers accommodating large volume expansions\nof NCPs, respectively. Among the unique composite nanostructures,\nthe NCPs with vast micropores provide electric double-layer capacitances,\nwhile the CNSs bridge the individual NCPs to form a conductive pathway\nwith a hierarchical porosity. As a result, the NCP–CNS composites\nwith high electrical integrity and structural stability are used as\nelectrode materials for high-performance supercapacitors, which exhibit\nexcellent electrochemical capacitive characteristics in terms of an\noutstanding capacitance of 300 F g^–1 at 1 A g^–1, large energy density of 20.9 W h kg^–1, and great cycling performance of 100% retention after 6000 cycles.\nThis work therefore presents a one-pot and efficient strategy to prepare\nan ordered arrangement of ZIF-8-derived porous carbons toward new\nelectrode materials in promising energy storage systems.