| The excessive energy depletion and the limited supply of fossil fuels combined with the ever-increasing environmental problems are driving the development of energy storage and conversion technologies.Among the existing energy storage and conversion technology,supercapacitor have attracted considerable attention owing to the fast charge/discharge processes,high power density,and long cycle life.As a low-cost and environmentally friendly electrode material,the N-doped graphene-like carbon nanosheets has broad research space and application prospect.Herein,melamine sponge and NaCl crystals were utilized to form a template to prepare the PGOCN and HGOCN-A material via solid-state pyrolysis method.The morphology,structure and composition of the resulting materials were characterized.The samples were assembled into three electrodes and two electrodes and characterized by cyclic voltammetry,galvanostatic charge-discharge,and electrochemical impedance spectroscopy.Moreover,the capacitance performance of the synthesized carbon material was analyzed based on the characterization and test results.The main results are as follows:?1?Macroscopic three-dimensional oxygenated carbon materials with enriched nitrogen are prepared by a two-step solid-state pyrolysis of a mixture of urea and glucose inside a template framework of melamine sponge in a N2 atmosphere without any functionalizing or crosslinking agents.Characterization by SEM,TEM and nitrogen adsorption–desorption isotherm measurements reveals that the prepared samples consist of a tetrapod framework embedded with crumpled graphene-like oxygenated N-doped carbon nanosheets,demonstrating a hierarchical porous structure of macro-,meso-and micropores.Considering the hierarchical porous structure combined with the presence of abundant oxygen and nitrogen,the application of the PGOCN materials in high-performance supercapacitors is investigated.In three electrode systems,the PGOCN electrodes show high specific capacitances of 348 F g-1 in acidic electrolytes and 308 F g-1 in alkaline electrolytes at a current density of 1A g-1,respectively.Remarkably,the PGOCN materials can be directly cut into thin sheets to assemble two-electrode supercapacitor devices without adding binders and conducting additives using 6 M KOH as the electrolyte.The two-electrode supercapacitor device exhibits a high specific capacitance of 220 F g-1 at 0.2 A g-1 anda power density of 1.2 kW kg-1 at an energy density of 3.4 Wh kg-1 as well as outstanding cycling stability after 2000 cycles.?2?Robust 3D hierarchical porous graphene-like N-doped ultrathin carbon nanosheets have been prepared via an in situ solid-state pyrolysis of a mixture of urea and glucose combined with a template framework of NaCl crystals in a N2 atmosphere with KOH activation?designated as HGOCN-A?.In three electrode systems,the HGOCN-A electrodes shows a specific capacitances of 456 F g-1 and 366 F g-1at a current density of 20 A g-1in 1M H2SO4 electrolytes,respectively.Furthermore,an all solid-state two-electrode symmetric supercapacitor has been fabricated using PVA/KOH gel electrolyte.The two-electrode symmetric supercapacitor exhibits a capacitance of 212 F g-1for a current density of 0.5 A g-1and a power density of 5 kW kg-1 at an energy density of 4.8 Wh kg-1 as well as superior cycle stability with 98% capacitance retention after 2000 cycles. |
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