A 3D hierarchical hybrid nanostructure of carbon nanotubes and activated carbon for high-performance supercapacitors

Novel carbonaceous hybrid materials are fabricated through the in situ growth of open-tipped mesoporous carbon nanotubes (CNTs) on low-cost activated carbon (AC) substrates with cobalt (Co) nanoparticles as the growing seeds via a chemical vapor deposition process. The CNTs are strongly bonded with the surface of the AC supports using the fine Co nanoparticles (<10 nm) as the joints. The unique three-dimensional hybrid architectures enable the resultant materials to exhibit a considerable specific capacitance of up to 440 F g(-1) at 1 A g(-1) as well as an excellent rate performance (97% retention ratio at 5 A g(-1) compared to 1 A g(-1)). In addition, the hybrid materials have an impressive cycling stability with an initial capacitance retention of 98.4% after 3000 cycles at 5 A g(-1). Besides the high specific surface area, such an excellent capacitive performance is mainly attributed to the combination of (i) the well-dispersed open-tipped CNTs (5-12 nm) that could provide more effective ion channels, (ii) the interconnected CNT conducting networks facilitating the transport of electrons, and (iii) superfine Co nanoparticles (3-9 nm) offering pseudocapacitance, indicating the synergistic effect of both the electrical double layer capacitance and pseudocapacitive reactions.