Hierarchical hollow microspheres of carbon nanorods with enhanced supercapacitor performance

A hollow spherical superstructure of carbon nanorods (HSSCNs-900) electrode enables excellent capacity, rate capability, and cycle stability of a symmetric supercapacitor. The HSSCNs-900 has ultrahigh surface area, large pore volume, and hierarchical porosity, and chestnut-like morphology. 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 (S BET = 2249 m 2 g −1 ), large pore volume with a hierarchical porosity (2.5 cm 3 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.