Zhenbo Cai

Twisting carbon nanotube fibers for both wire-shaped micro-supercapacitor and micro-battery.

Energy storage systems including supercapacitors and lithium ion batteries typically appear in a rigid plate which is unfavorable for many applications, especially in the fi elds of portable and highly integrated equipments which require small size, light weight, and high fl exibility. [ 1–3 ] As a result, fl exible supercapacitors and batteries mainly in a fi lm format have been widely investigated, while wire-shaped energy storage devices are rare. [ 4 , 5 ] However, compared with the conventional planar structure, a wire device can be easily woven into textiles or other structures to exhibit unique and promising applications. The limitation is originated from the much stricter requirement for the electrode such as a combined high fl exibility and electrochemical property in wire-shaped devices. [ 6 , 7 ] It remains challenging but becomes highly desired to obtain wire-shaped supercapacitors and batteries with high performances. On the other hand, due to the unique structure and remarkable mechanical and electrical properties, carbon nanotubes (CNTs) have been widely studied as electrode materials in conventional planar energy storage devices. [ 8 , 9 ] However, CNTs are generally made in a network format in which the produced charges had to cross a lot of boundaries with low effi ciencies. It is critically important to improve the charge transport in CNT materials. [ 8–13 ]

An Integrated “Energy Wire” for both Photoelectric Conversion and Energy Storage†

The use of solar energy has the potential to provide an effective solution to the energy crisis. Generally, the solar energy is converted into electric energy which is transferred through external electric wires to electrochemical devices, such as lithium ion batteries and supercapacitors, for storage. To further improve the energy conversion and storage efficiency, it is important to simultaneously realize the two functions, photoelectric conversion (PC) and energy storage (ES), in one device. Recently, attempts have been made to directly stack a photovoltaic cell and a supercapacitor into one device which can absorb and store solar energy. However, these stacked devices exhibited low overall photoelectric conversion and storage efficiencies. In addition, the planar format in such stacked devices has limited their applications, such as in electronic textiles where a wire structure is required. Herein, an integrated energy wire has been developed to simultaneously realizes photoelectric conversion and energy storage with high efficiency. The fabrication is schematically shown in the Supporting Information, Figure S1. A titanium wire was modified in sections with aligned titania nanotubes on the surface. Active materials for photoelectric conversion and energy storage were then coated onto the modified parts with titania nanotubes. Aligned carbon nanotube (CNT) fibers were finally twisted with the modified Ti wire to produce the desired device. The Ti wire and CNT fiber had been used as electrodes. Figure 1a schematically shows a wire in which one part capable of photoelectric conversion and one part capable of energy storage. This novel wire device exhibits an overall photoelectric conversion and storage efficiency of 1.5%. Aligned titania nanotubes were grown on the Ti wires by electrochemical anodization in a two-electrode system. Figures 1b and 1c show typical scanning electron microscopy (SEM) images of titania nanotubes. The diameters of titania nanotubes ranged from 50 to 100 nm with the wall thickness varying from 15 to 50 nm, and their length was about 20 mm (Figure S2). In this case, titania nanotubes were mainly used to improve the charge separation and transport in photoelectric conversion and increase the surface area in energy storage. Aligned CNT fibers were spun from spinnable CNTarrays which had been synthesized by chemical vapor deposition. They could be produced with lengths of hundreds of meters through the continuous spinning process, and were typically ranged from 10 to 30 mm in diameter. Figure 1d shows a typical SEM image of a CNT fiber which has a uniform diameter of 10 mm. Figure 1e further shows that the CNTs are highly aligned in the fiber, which enables combined remarkable properties including tensile strength of 10– 10 MPa, electrical conductivity of 10 Scm , and high electrocatalytic activity comparable to the conventional platinum. In addition, the CNT fibers were flexible and could be easily and closely twisted with each other or with the other fiber materials (Figure S3), which was critical for the success in a wire-shaped device. Photoactive materials were deposited onto the titania nanotube-modified parts on the Ti wire, for photoelectric conversion, while the desired gel electrolyte was coated onto the other sections for energy storage. Aligned CNT fibers were then twisted with both photoelectric-conversion and energy-storage parts to produce an integrated wire-shaped device. For simplicity, an “energy wire” which was composed of one photoelectric conversion section and one energy storage section had been mainly investigated in this work. Figure 2a shows a typical photograph of a wire with the left Figure 1. a) Schematic illustration of the integrated wire-shaped device for photoelectric conversion (PC) and energy storage (ES). b),c) Scanning electron microscopy (SEM) images of aligned titania nanotubes grown on a Ti wire by electrochemical anodization for 2 h at low and high magnifications, respectively. d),e) SEM images of a CNT fiber at low and high magnifications, respectively.

Intertwined Aligned Carbon Nanotube Fiber Based Dye-Sensitized Solar Cells

Metal wires suffer from corrosion in fiber-shaped dye-sensitized solar cells (DSSCs). We report herein that stable, ultrastrong, and highly flexible aligned carbon nanotube fibers can be used not only as catalytic counter electrodes but also as conductive materials to support dye-loaded TiO(2) nanoparticles in DSSCs. The power conversion efficiency of this fiber solar cell can achieve 2.94%. These solar power fibers, exhibiting power conversion efficiency independent of incident light angle and cell length, can be woven into textiles via a convenient weaving technology.

Conducting polymer composite film incorporated with aligned carbon nanotubes for transparent, flexible and efficient supercapacitor

Polyaniline composite films incorporated with aligned multi-walled carbon nanotubes (MWCNTs) are synthesized through an easy electrodeposition process. These robust and electrically conductive films are found to function as effective electrodes to fabricate transparent and flexible supercapacitors with a maximum specific capacitance of 233 F/g at a current density of 1 A/g. It is 36 times of bare MWCNT sheet, 23 times of pure polyaniline and 3 times of randomly dispersed MWCNT/polyaniline film under the same conditions. The novel supercapacitors also show a high cyclic stability.

Flexible, weavable and efficient microsupercapacitor wires based on polyaniline composite fibers incorporated with aligned carbon nanotubes

A supercapacitor in a flexible wire format has potential advantages that are described in this paper. Polyaniline composite fibers incorporated with aligned multi-walled carbon nanotubes are first synthesized with high mechanical strength and electrical conductivity through an easy electrodeposition process, and two robust composite fibers have then been twisted to produce microsupercapacitor wires with a specific capacitance of 274 F g−1 or 263 mF cm−1. These energy storage wires are light-weight, flexible, strong and weavable for promising applications in various fields.

Nitrogen-Doped Carbon Nanotube Composite Fiber with a Core–Sheath Structure for Novel Electrodes

Carbon nanotubes (CNTs) have been recently investigated to be assembled into macroscopic fi bers which may pave the way for their practical applications. [ 1–5 ] The resulting fi bers maintain the remarkable mechanical and electrical properties of individual CNTs, e.g., high tensile strengths and electrical conductivities, because of the aligned structure of the building CNTs. [ 6 , 7 ] Therefore, they have been proposed as electrodes to fabricate a broad spectrum of optoelectronic devices such as novel organic solar cells with high performance. [ 8 ] On the other hand, certain electron-attractive elements such as nitrogen atoms have been doped into a carbon lattice of CNTs to further tune their electronic structure for desired electrocatalytic performances. [ 9 , 10 ] Herein, we fi rst design and fabricate a unique core–sheath composite fi ber with a core of aligned undoped CNTs with a sheath of network-like nitrogen-doped carbon nanotubes (NCNTs). The excellent 3D hopping conduction of the aligned undoped CNTs and the electrocatalytic property of the NCNT network are well combined and extend through the above structure, which provides them with unexpectedly good performance in a wide variety of application fi elds such as metal-free electrocatalysis of dioxygen electroreduction (DE) and sensitive detection of hydrogen peroxide. [ 11–13 ] The current density of the composite fi ber electrodes for DE easily reached 2.2 mA cm − 2 at –0.35 V in O 2 -saturated 0.1 M potassium hydroxide, compared with 0.45 mA cm − 2 at –0.05 V for a platinum wire-based electrode and is comparative to a CNT/ platinum-based electrode under the same conditions. [ 11 , 13 ] The sensitivity of the composite fi ber electrode for the detection of hydrogen peroxide is much higher than an undoped CNT fi ber electrode and a NCNT-modifi ed glassy carbon electrode. Furthermore, these composite fi bers can be easily scaled up with

A novel fabrication of a well distributed and aligned carbon nanotube film electrode for dye-sensitized solar cells†

Carbon nanotubes (CNTs) have been recently fabricated into macroscopic films to improve their practical applications in a wide variety of fields, e.g. electrode materials. In the current CNT electrodes however, CNTs are typically interconnected to form networks or are aligned as lots of bundles, and the resulting photovoltaic devices based on the CNT electrodes have typically shown low energy conversion efficiencies. Here we report a new and general drying approach to make a well distributed and aligned CNT film which exhibits a rapid charge separation and transport. As a demonstration, it has been used as a counter electrode to fabricate dye-sensitized solar cells with an energy conversion efficiency of 9.05%.

Synthesis of aligned carbon nanotube composite fibers with high performances by electrochemical deposition

To improve their practical applications, carbon nanotubes (CNTs) have recently been assembled into macroscopic fibers in which the CNTs are aligned to maintain their excellent properties. To further enhance the properties and expand the application of CNT fibers, it is critically important to introduce a second functional phase to produce high performance composite fibers. Herein, a general and efficient electrodeposition method has been developed to synthesize aligned CNT composite fibers into which a wide variety of components including metals and conductive polymers can be incorporated. The resulting composite fibers show remarkable mechanical and electrical properties, which enable promising applications in various fields. As a demonstration, CNT/silver composite fibers exhibit a high signal enhancement under weak laser irradiation when used as wire substrates for surface enhanced Raman scattering, and CNT/polyaniline composite fibers have been used to fabricate wire-shaped supercapacitors which achieve a specific capacitance of 2.26 mF cm−1, at least two orders of magnitude greater than that of bare CNT fibers, and ten times that of other fiber materials, such as plastic wires coated with zinc oxide nanowires.

Hierarchically Tunable Helical Assembly of Achiral Porphyrin‐Incorporated Alkoxysilane

A general assembly approach is developed to construct hierarchically tunable helical superstructures from an achiral porphyrin-incorporated alkoxysilane. The resulting superstructures can be controlled from film, rice, spindle, ribbon, to fiber in morphology and from nonhelical to helical in structure at a multiscale with excellent optoelectronic, electrical, and thermal properties.

Perpendicularly aligned carbon nanotube/olefin composite films for the preparation of graphene nanomaterials

There remains a common and critical challenge in the preparation of carbon nanotube (CNT) composite materials, i.e., random dispersion of CNTs in the second phase. Here we have reported a general method to prepare perpendicularly aligned CNT/olefin composite films through a conventional slicing technique. The thickness of a composite film can be accurately controlled from about fifty nanometers to fifty micrometers, and the diameter and density of CNTs may be varied in a wide range as required. In particular, due to the generated defect at the end during the slicing process, the separated CNTs from the composite film have been easily unzipped to produce graphenes in the forms of nanoribbons and nanosheets with a yield of almost 100% under ultrasonic treatment.