Hierarchical Nanostructures of Nitrogen-Doped Porous Carbon Polyhedrons Confined in Carbon Nanosheets for High-Performance Supercapacitors

Interconnected close-packed nitrogen-doped porous carbon polyhedrons (NCPs) confined in two-dimensional carbon nanosheets (CNSs) have been prepared through a sustainable one-pot pyrolysis of a simple solid mixture of zeolitic imidazolate framework-8 (ZIF-8) crystals and with organic potassium as the precursors. The hierarchically organized framework of the NCP–CNS composites enables NCPs and CNSs to act as well-defined electrolyte reservoirs and mechanical buffers accommodating large volume expansions of NCPs, respectively. Among the unique composite nanostructures, the NCPs with vast micropores provide electric double-layer capacitances, while the CNSs bridge the individual NCPs to form a conductive pathway with a hierarchical porosity. As a result, the NCP–CNS composites with high electrical integrity and structural stability are used as electrode materials for high-performance supercapacitors, which exhibit excellent electrochemical capacitive characteristics in terms of an outstanding 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. This work therefore presents a one-pot and efficient strategy to prepare an ordered arrangement of ZIF-8-derived porous carbons toward new electrode materials in promising energy storage systems.