Hierarchical hollow microspheres of carbon nanorods with enhanced supercapacitor performance

Abstract

A hierarchical hollow microsphere of carbon nanorods (HHMCNs) is constructed via facile carbonization for a hollow microsphere consisted of zinc metal-organic framework (Zn-MOF-74) nanorods. The spherical Zn-MOF-74 nanorods with a chestnut-like morphology are formed through a hydrothermal reaction of crystalline Zn-MOF-74 nanoparticles. When the HHMCNs carbonized at 900 °C, the obtained HHMCNs-900 possesses a ultrahigh specific surface area (SBET = 2249 m2 g−1), large pore volume with a hierarchical porosity (2.5 cm3 g−1), and an ideal oxygen content (5.1 at.%). Using the HHMCNs-900 as a supercapacitor electrode delivers a satisfying specific capacitance (287 F g−1 at 0.5 A g−1), excellent rate capability (165 F g−1 at 50 A g−1), superior energy density of 39.86 Wh kg−1 at a power density of 250 W kg−1, and a long-term cycling stability keeping 97 % of its initial capacity after 10 000 cycles at 20 A g−1. Furthermore, a symmetric cell (HHMCNs-900//HHMCNs-900) is assembled and demonstrates unexpected performances, showing a satisfying specific capacity (∼55 F g−1 at 0.1 A g−1), impressive rate capability (∼44 F g−1 at 5.0 A g−1), and superior stability with a capacitance retention of ∼95.3 % over 10 000 cycles at 10 A g−1. These remarkable electrochemical performances suggest that the hierarchical hollow microsphere of carbon nanorods (HHMCNs) is an ideal electrode material for supercapacitors.