Minghai Chen

Graphene patched CNT/MnO2 nanocomposite papers for the electrode of high-performance flexible asymmetric supercapacitors.

MnO2 has been widely studied as the pseudo-capactive electrode material of high-performance supercapacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO2, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO2 on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO2 nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO2/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO2 nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices.

Ultrastrong, Foldable, and Highly Conductive Carbon Nanotube Film

Preparation of strong, flexible, and multifunctional carbon-based films has attracted considerable interest not only in fundamental research areas but also for industrial applications. We report a binder-free, ultrastrong, and foldable carbon nanotube (CNT) film using aligned few-walled nanotube sheets drawn from spinnable nanotube arrays. The film exhibits tensile strengths up to ∼2 GPa and a Youngs modulus up to ∼90 GPa, which is markedly superior to other types of carbon-based films reported, including commercial graphite foils, buckypapers, and graphene-related papers. The film can bear severe bending (even being folded) and shows good structure integrity and negligible change in electric conductivity. The unique structure of the CNT film (good nanotube alignment, high packing density) provides the film with direct and efficient transport paths for electricity. As a flexible charge collector, it favors a magnesium oxide coating to exhibit high charge/discharge rate stability and an excellent electrochemical capacitance close to its theoretical value.

Electrochemical fabrication of carbon nanotube/polyaniline hydrogel film for all-solid-state flexible supercapacitor with high areal capacitance

Carbon nanotube (CNT) film is a favorable kind of substrate in flexible electric devices because of its superior flexibility, favorable mechanical strength and excellent electrical conductivity. Moreover, since the conductive polymer polyaniline (PANI) possesses a high capacitance and is easy to manufacture, it is always a favored material in the field of supercapacitors. In this research, CNT film synthesized via a floating catalyst chemical vapor deposition method could be further activated by its electrochemical re-expansion to achieve better porosity and higher specific area, in order to obtain an all-solid-state flexible supercapacitor with a higher area capacitance. In comparison with the pristine CNT film decorated with PANI, electrochemically fabricated CNT hydrogel film with PANI deposition had a higher specific area capacitance of 680 mF cm−2 at 1 mA cm−2. The all-solid-state supercapacitor that was synthesized from this composite film exhibited a high specific area capacitance of 184.6 mF cm−2 at 1 mA cm−2, which was higher than many similar supercapacitors. The rolling test showed that this supercapacitor maintained its high capacitance even under conditions of rolling. After 500 charge–discharge cycles, it also retained its high coulombic efficiency and specific area capacitance. This all-solid-state supercapacitor shows great potential in the field of energy storage devices.

Hierarchical CNT@NiCo2O4 core–shell hybrid nanostructure for high-performance supercapacitors

The mass integration of electrochemically active materials on nanosized conductive fillers is a promising strategy to achieve an ideal electrode structure for energy storage devices. In this research, a one-dimensional CNT@NiCo2O4 nanosheet core–shell structural nanocable was constructed by a facile chemical co-deposition route combined with post-calcination in air. The subsequent thermal treatment led to the transformation of the hydroxide nanosheet precursor to NiCo2O4 nanosheets, during which process the overall morphology and structure were well retained. By selecting CNTs as conductive support for ultra-thin NiCo2O4 nanosheets, a high-performance electrode for supercapacitors was obtained. Notably, the as-prepared CNT@NiCo2O4 nanocables have a high capacitance of 1038 F g−1 at a current density of 0.5 A g−1. Furthermore, the specific capacitance of the product was almost 100% retained after 1000 cycles, which indicates excellent structural and cycling stability. More importantly, a relatively high mass loading of active materials on CNTs was also achieved, making the practical application of such electrode materials possible. Consequently, this CNT@NiCo2O4 nanocable is a promising electrode for high-performance supercapacitors.

Facile Assembly of Ni-Co Hydroxide Nanoflakes on Carbon Nanotube Network with Highly Electrochemical Capacitive Performance

Herein, we demonstrate the high-density assembly of Ni-Co hydroxide nanoflakes on conductive carbon nanotube (CNT) network through a simple and rapid chemical precipitation method, presenting a low-cost and high-performance scaffold for pseudosupercapacitor. It is found that the Ni-Co layered double hydroxide (LDH) nanoflakes prefer to proliferate around large-diameter CNTs (diameter>50 nm), with conductive CNT network well-maintained. Such hierarchical nanostructures show greatly improved specific surface areas compared with bare CNT network and are freestanding without other organic binder, which can be directly employed as a binder-free compact electrode assembly. By optimizing the chemical composition of as-precipitated LDH nanoflakes, the resultant Co0.4Ni0.6(OH)2 LDH/CNT composite nanostructures exhibit the largest specific electrochemical capacitance and the best rate performance, with their capacitance up to 1843 F/g under a low current density of 0.5 A/g and maintained at 1231 F/g when the current density is increased 20 times to 10 A/g. Importantly, such hierarchical nanostructures tend to prevent the electrode from severe structural damage and capacity loss during hundreds of charge/discharge under a high rate (2 A/g), ensuring the electrode with high-energy density (51 W h/kg) at power density of 3.3 kW/kg.

Carbon nanotube composite films with switchable transparency.

A composite film with switchable transparency is fabricated by sandwiching a carbon nanotube (CNT) sheet within polyurethane (PU) films. The introduction of CNTs not only makes the composite film electrically conductive but also induces a rapid crystal melting of soft segments in the PU. As a result, the film can be switched from opaque to transparent in just several seconds after turning on voltage, and reversed back to opaque after turning off voltage. The film also possesses several other attractive properties, including excellent flexibility, low energy consumption, switching speed insensitivity to ambient temperature, and easy coloration, which make the film promising for a wide variety of practical applications.

One-step strategy to a three-dimensional NiS-reduced graphene oxide hybrid nanostructure for high performance supercapacitors

Metal sulfides are an emerging class of high-performance electrode materials for electrochemical energy storage devices. Here, a facile hydrothermal method is reported to assemble three-dimensional (3D) NiS-reduced graphene oxide (rGO) hybrid aerogels with strong coupling between the two compounds. It is intriguing to note that NiS nanoparticles are well anchored on the 3D porous and conductive scaffold constructed from wrinkled rGO nanosheets. When evaluated as binder-free electrode materials for supercapacitors, impressive electrochemical performances are presented. Specifically, the 3D NiS–rGO aerogel nanocomposite exhibits a high capacitance of 852 F g−1, 526 F g−1 based on the whole electrode mass (mNiS : mGO = 45 mg/50 mg) at a current density of 2 A g−1 and 15 A g−1, respectively. These satisfactory electrochemical behaviors, attributed to the introduction of reduced graphene oxide, suggest the great promise of fabricating graphene-supported hybrid electrode materials for high-performance energy applications.

Crack-Free and Scalable Transfer of Carbon Nanotube Arrays into Flexible and Highly Thermal Conductive Composite Film

Carbon nanotube (CNT) arrays show great promise in developing anisotropic thermal conductive composites for efficiently dissipating heat from high-power devices along thickness direction. However, CNT arrays are always grown on some substrates and liable to be deformed and broken into pieces during transfer and solution treatment. In the present study, we intentionally synthesized well-crystallized and large-diameter (~80 nm) multiwalled CNT (MWCNT) arrays by floating catalyst chemical vapor deposition (FCCVD) method. Such arrays provided high packing density and robust structure from collapse and crack formation during post solution treatment and therefore favored to maintain original thermal and electrical conductive paths. Under optimized condition, the CNT arrays can be transferred into flexible composite films. Furthermore, the composite film also exhibited excellent thermal conductivity at 8.2 W/(m·K) along thickness direction. Such robust, flexible, and highly thermal conductive composite film may enable some prospective applications in advanced thermal management.

Oxygen Evolution Assisted Fabrication of Highly Loaded Carbon Nanotube/MnO2 Hybrid Films for High-Performance Flexible Pseudosupercapacitors.

To date, it has been a great challenge to design high-performance flexible energy storage devices for sufficient loading of redox species in the electrode assemblies, with well-maintained mechanical robustness and enhanced electron/ionic transport during charge/discharge cycles. An electrochemical activation strategy is demonstrated for the facile regeneration of carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition strategy into a flexible, robust, and highly conductive hydrogel-like film, which is promising as electrode matrix for efficient loading of redox species and the fabrication of high-performance flexible pseudosupercapacitors. The strong and conductive CNT films can be effectively expanded and activated by electrochemical anodic oxygen evolution reaction, presenting greatly enhanced internal space and surface wettability with well-maintained strength, flexibility, and conductivity. The as-formed hydrogel-like film is quite favorable for electrochemical deposition of manganese dioxide (MnO2 ) with loading mass up to 93 wt% and electrode capacitance kept around 300 F g(-1) (areal capacitance of 1.2 F cm(-2) ). This hybrid film was further used to assemble a flexible symmetric pseudosupercapacitor without using any other current collectors and conductive additives. The assembled flexible supercapacitors exhibited good rate performance, with the areal capacitance of more than 300 mF cm(-2) , much superior to other reported MnO2 based flexible thin-film supercapacitors.

Electrochemical conversion of Ni2(OH)2CO3 into Ni(OH)2 hierarchical nanostructures loaded on a carbon nanotube paper with high electrochemical energy storage performance

Large-diameter carbon nanotube (CNT) paper was used as a porous and conductive template to obtain vertically aligned Ni2(OH)2CO3 nanowire array shells, which could be further converted into highly active Ni(OH)2 nanosheets by a cyclic voltammetry strategy. The as-prepared hierarchical nanostructure showed superior electrochemical performance for the electrodes of supercapacitors.