Huisheng Peng

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 ]

A Highly Stretchable, Fiber-Shaped Supercapacitor†

Flexible and portable devices are a mainstream direction in modern electronics and related multidisciplinary fields. To this end, they are generally required to be stretchable to satisfy various substrates. As a result, stretchable devices, such as electrochemical supercapacitors, lithium-ion batteries, organic solar cells, organic light-emitting diodes, field-effect transistors, and artificial skin sensors have been widely studied. However, these stretchable devices are made in a conventional planar format that has largely hindered their development. For the portable applications, the devices need to be lightweight and small, though it is difficult for them to be made into efficient microdevices. In particular, it is challenging or even impossible for them to be used in electronic circuits and textiles that are urgently required also in a wide variety of other fields, such as microelectronic applications. Recently, some attempts have been made to fabricate wire-shaped microdevices, such as electrochemical supercapacitors. They have been generally produced by twisting two fiber electrodes with electrolytes coated on the surface. Several examples have been also successfully shown to make fiber-shaped supercapacitors with a coaxial structure. Compared with their planar counterparts, the wire or fiber shape enables promising advantages such as being lightweight and woven into textiles. Although the wire and fiber-shaped supercapacitors are also flexible with high electrochemical performance, they are not stretchable, which is critically important for many applications. For instance, the resulting electronic textiles could easily break during the use if they were not stretchable. To the best of our knowledge, herein we have, for the first time, developed a novel family of highly stretchable, fibershaped high-performance supercapacitors. Aligned carbon nanotube (CNT) sheets that are sequentially wrapped on an elastic fiber serve as two electrodes. The use of aligned CNT sheets offers combined remarkable properties including high flexibility, tensile strength, electrical conductivity, and mechanical and thermal stability. As a result, the fibershaped supercapacitor maintains a high specific capacitance of approximately 18 F/g after stretch by 75% for 100 cycles. Spinnable CNT arrays were first synthesized by chemical vapor deposition. A scanning electron microscopy (SEM) image of the array with height of 230 mm is shown in the Supporting Information, Figure S1, and the CNT shows a multi-walled structure with diameter of about 10 nm (Supporting Information, Figure S2). Aligned CNT sheets could be then continuously drawn from the array and easily attached to various substrates. Elastic fibers were used herein to offer the stretchability in the resulting supercapactiors, and rubber fibers have been mainly studied as a demonstration. For a typical fabrication on the fiber-shaped supercapacitor (Figure 1), a rubber fiber was first coated with a thin layer of

Flexible and Weaveable Capacitor Wire Based on a Carbon Nanocomposite Fiber

A flexible and weaveable electric double-layer capacitor wire is developed by twisting two aligned carbon nanotube/ordered mesoporous carbon composite fibers with remarkable mechanical and electronic properties as electrodes. This capacitor wire exhibits high specific capacitance and long life stability. Compared with the conventional planar structure, the capacitor wire is also lightweight and can be integrated into various textile structures that are particularly promising for portable and wearable electronic devices.

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.

Electrochromatic carbon nanotube/ polydiacetylene nanocomposite fibres

Chromatic materials such as polydiacetylene change colour in response to a wide variety of environmental stimuli, including changes in temperature, pH and chemical or mechanical stress, and have been extensively explored as sensing devices. Here, we report the facile synthesis of carbon nanotube/polydiacetylene nanocomposite fibres that rapidly and reversibly respond to electrical current, with the resulting colour change being readily observable with the naked eye. These composite fibres also chromatically respond to a broad spectrum of other stimulations. For example, they exhibit rapid and reversible stress-induced chromatism with negligible elongation. These electrochromatic nanocomposite fibres could have various applications in sensing.

Chromatic polydiacetylene with novel sensitivity.

Conjugated polymers have been investigated for a number of applications in optoelectronics and sensing due to their important electronic and optical properties. For instance, polydiacetylene (PDA) may change color in response to external stimuli and has been extensively explored as a material for chromatic sensors. However, the practical applications of PDA materials have been largely hampered by their irreversible chromatic transitions under limited stimuli such as temperature, pH, and chemical. As a result, much effort has been paid to improve the chromatic reversibility and increase the scope of external stimuli for PDA. In this tutorial review, the recent development of PDA materials which show reversible chromatic transition and respond to new stimuli including light and electrical current has been described.

Developing polymer composite materials: carbon nanotubes or graphene?

The formation of composite materials represents an efficient route to improve the performances of polymers and expand their application scopes. Due to the unique structure and remarkable mechanical, electrical, thermal, optical and catalytic properties, carbon nanotube and graphene have been mostly studied as a second phase to produce high performance polymer composites. Although carbon nanotube and graphene share some advantages in both structure and property, they are also different in many aspects including synthesis of composite material, control in composite structure and interaction with polymer molecule. The resulting composite materials are distinguished in property to meet different applications. This review article mainly describes the preparation, structure, property and application of the two families of composite materials with an emphasis on the difference between them. Some general and effective strategies are summarized for the development of polymer composite materials based on carbon nanotube and graphene.

Novel Electric Double‐Layer Capacitor with a Coaxial Fiber Structure

A coaxial electric double-layer capacitor fiber is developed from the aligned carbon nanotube fiber and sheet, which functions as two electrodes with a polymer gel sandwiched between them. The unique coaxial structure enables a rapid transportation of ions between the two electrodes with a high electrochemical performance. These energy storage fibers are also flexible and stretchable, and can be woven into and widely used for electronic textiles.

A Fiber Supercapacitor with High Energy Density Based on Hollow Graphene/Conducting Polymer Fiber Electrode.

A hollow graphene/conducting polymer composite fiber is created with high mechanical and electronic properties and used to fabricate novel fiber-shaped supercapacitors that display high energy densities and long life stability. The fiber supercapacitors can be woven into flexible powering textiles that are particularly promising for portable and wearable electronic devices.

Novel Graphene/Carbon Nanotube Composite Fibers for Efficient Wire‐Shaped Miniature Energy Devices

Novel nanostructured composite fibers based on graphene and carbon nanotubes are developed with high tensile strength, electrical conductivity, and electrocatalytic activity. As two application demonstrations, these composite fibers are used to fabricate flexible, wire-shaped dye-sensitized solar cells and electrochemical supercapacitors, both with high performances, for example, a maximal energy conversion efficiency of 8.50% and a specific capacitance of ca. 31.50 F g(-1). These miniature wire-shaped devices are further shown to be promising for flexible and portable electronic facilities.