MnO₂-introduced-tunnels strategy for the preparation of nanotunnel inserted hierarchical-porous carbon as electrode material for high-performance supercapacitors

Nanotunnels inserted hierarchical-porous carbon (NTHPC) have been synthesized successfully via a MnO₂-introduced-tunnels strategy using MnO₂ nanorods as template, with agar and β-cyclodextrin serving as hybrid carbon precursors. The as-prepared NTHPC possesses a higher specific surface area of 1441 m² g⁻¹, a moderate pore volume of 1.23 cm³ g⁻¹, and the hierarchical-porous structure with inserted nanotunnels. Transmission electron microscopy has demonstrated that the width of the nanotunnels is between 20 and 100 nm, and the length ranges from 0.2 to 2.0 μm. Tests in a three-electrode system showed that the NTHPC has high specific capacitance (253.1 F g⁻¹, 5 mV s⁻¹), as well as good rate capability (203.3 F g⁻¹, 100 mV s⁻¹) and excellent cycling stability. More importantly, an assembled symmetric supercapacitor with NTHPC electrodes delivered an outstanding energy density of up to 34.9 Wh kg⁻¹ with power density of 755.2 W kg⁻¹. The remarkable electrochemical performance of the NTHPC is ascribed to the nanotunnels, which act as ion reservoirs and liquid transfer channels that can increase the ion transport rate and shorten the ion transfer distance. This study provides a novel method for the preparation of high-performance hierarchical-porous carbon and guidance for its potential applications in supercapacitors. © 2017 Elsevier B.V.