Thin and Small N-Doped Carbon Boxes Obtained from Microporous Organic Networks and Their Excellent Energy Storage Performance at High Current Densities in Coin Cell Supercapacitors

Abstract

This work reports the thinnest and smallest hollow N-doped carbon boxes among recently reported hollow N-doped carbon materials. Hollow and N-rich microporous organic networks (H-NMONs) were prepared by the azide–alkyne Huisgen cycloaddition of tetra(4-ethynylphenyl)methane and 1,4-diazidobenzene on the surface of Cu2O nanocubes and the successive acid etching of inner Cu2O. The Cu2O nanocubes played roles of templates and networking catalysts. The networking reaction generated N-rich triazole rings in the MON. Heat treatment of H-NMONs under argon resulted in the formation of hollow N-doped carbon boxes (H-NCBs). The diameter and shell thickness of H-NCBs were 130 and 12 nm, respectively. The H-NCBs showed superior electrochemical performance in H2SO4 electrolyte as energy storage materials for supercapacitors, compared with that in KOH electrolyte. Among the H-NCBs, H-NCB-900 which was obtained by the heat treatment of H-NMON at 900 °C showed the best performance with capacitances of 286 and 251 F/g at current densities of 1 and 10 A/g in two electrode coin cell type supercapacitors and maintained the capacitances of 228 and 206 F/g at higher current densities of 50 and 100 A/g. Moreover, the H-NCB-900 showed excellent cycling stabilities with ∼95% retention of the first capacitance after 10 000 cycles. The excellent electrochemical performance of H-NCBs can be attributed to their efficient N-doping, hollow structure, and thin thickness of shells.