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

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.