title: Scalable synthesis of hierarchically structured carbon nanotube-graphene fibres for capacitive energy storage.
abstract: Micro-supercapacitors are promising energy storage devices that can complement or even replace batteries in miniaturized portable electronics and microelectromechanical systems. Their main limitation, however, is the low volumetric energy density when compared with batteries. Here, we describe a hierarchically structured carbon microfibre made of an interconnected network of aligned single-walled carbon nanotubes with interposed nitrogen-doped reduced graphene oxide sheets. The nanomaterials form mesoporous structures of large specific surface area (396 m(2) g(-1)) and high electrical conductivity (102 S cm(-1)). We develop a scalable method to continuously produce the fibres using a silica capillary column functioning as a hydrothermal microreactor. The resultant fibres show a specific volumetric capacity as high as 305 F cm(-3) in sulphuric acid (measured at 73.5 mA cm(-3) in a three-electrode cell) or 300 F cm(-3) in polyvinyl alcohol (PVA)/H(3)PO(4) electrolyte (measured at 26.7 mA cm(-3) in a two-electrode cell). A full micro-supercapacitor with PVA/H(3)PO(4) gel electrolyte, free from binder, current collector and separator, has a volumetric energy density of ∼6.3 mWh cm(-3) (a value comparable to that of 4 V-500 µAh thin-film lithium batteries) while maintaining a power density more than two orders of magnitude higher than that of batteries, as well as a long cycle life. To demonstrate that our fibre-based, all-solid-state micro-supercapacitors can be easily integrated into miniaturized flexible devices, we use them to power an ultraviolet photodetector and a light-emitting diode.
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Dingshan
authors.initials: D
authors.lastname: Yu
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Kunli
authors.initials: K
authors.lastname: Goh
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Li
authors.initials: L
authors.lastname: Wei
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Wenchao
authors.initials: W
authors.lastname: Jiang
authors.affiliation: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, 1 Tsinghua Road, Beijing 100084, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Liming
authors.initials: L
authors.lastname: Dai
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Yuan
authors.identifier: 0000000190593839
authors.initials: Y
authors.lastname: Chen
mesh_terms: D025802:Electric Capacitance; D006108:Graphite / Q000737:chemistry*; D037742:Nanotubes, Carbon / Q000737:chemistry*
chemical_list: D037742:Nanotubes, Carbon; D006108:Graphite