Yanbing Yang

Core-Double-Shell, Carbon Nanotube@Polypyrrole@MnO2 Sponge as Freestanding, Compressible Supercapacitor Electrode

Design and fabrication of structurally optimized electrode materials are important for many energy applications such as supercapacitors and batteries. Here, we report a three-component, hierarchical, bulk electrode with tailored microstructure and electrochemical properties. Our supercapacitor electrode consists of a three-dimensional carbon nanotube (CNT) network (also called sponge) as a flexible and conductive skeleton, an intermediate polymer layer (polypyrrole, PPy) with good interface, and a metal oxide layer outside providing more surface area. These three components form a well-defined core-double-shell configuration that is distinct from simple core-shell or hybrid structures, and the synergistic effect leads to enhanced supercapacitor performance including high specific capacitance (even under severe compression) and excellent cycling stability. The mechanism study reveals that the shell sequence is a key factor; in our system, the CNT-PPy-MnO2 structure shows higher capacitance than the CNT-MnO2-PPy sequence. Our porous core-double-shell sponges can serve as freestanding, compressible electrodes for various energy devices.

Carbon nanotube-polypyrrole core-shell sponge and its application as highly compressible supercapacitor electrode

A carbon nanotube (CNT) sponge contains a three-dimensional conductive nanotube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole (PPy) core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance (> 90% of initial value). Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.

Controlled Synthesis of Core–Shell Carbon@MoS2 Nanotube Sponges as High-Performance Battery Electrodes

Heterogeneous inorganic nanotube structures consisting of multiwalled carbon nanotubes coated by long, continuous MoS2 sheets with tunable sheet number are synthesized using a carbon-nanotube sponge as a template. The resulting 3D porous hybrid sponges have potential applications as high-performance freestanding anodes for Li-ion batteries with excellent specific capacity and cycling stability.

Multifunctional graphene sheet–nanoribbon hybrid aerogels

Graphene sheets and nanoribbons are graphene-based nanostructures with different dimensions. Here, we show that these two materials can be combined to form highly porous, ultra-low density, compressible yet elastic aerogels, which can be used as efficient adsorbents and supercapacitor electrodes. The pore walls consist of stacked graphene sheets embedded with uniformly distributed thick nanoribbons unzipped from multi-walled carbon nanotubes as effective reinforcing skeletons. Owing to the large pore-size, robust and stable structure, and the nanoribbon-adhered pore walls, these hybrid aerogels show very large adsorption capacity for a series of organic solvents and oils (100 to 350 times of aerogel weight), and a specific capacitance of 256 F g−1 tested in a three-electrode electrochemical configuration, which is further improved to 537 F g−1 by depositing controlled loading pseudo-polymers into the aerogels. Our multifunctional graphene sheet–nanoribbon hybrid aerogels may find potential applications in many fields such as environmental cleanup and as flexible electrodes for energy storage systems such as supercapacitors and batteries.

Hierarchically Designed Three-Dimensional Macro/Mesoporous Carbon Frameworks for Advanced Electrochemical Capacitance Storage

Mesoporous carbon (m-C) has potential applications as porous electrodes for electrochemical energy storage, but its applications have been severely limited by the inherent fragility and low electrical conductivity. A rational strategy is presented to construct m-C into hierarchical porous structures with high flexibility by using a carbon nanotube (CNT) sponge as a three-dimensional template, and grafting Pt nanoparticles at the m-C surface. This method involves several controllable steps including solution deposition of a mesoporous silica (m-SiO2 ) layer onto CNTs, chemical vapor deposition of acetylene, and etching of m-SiO2 , resulting in a CNT@m-C core-shell or a CNT@m-C@Pt core-shell hybrid structure after Pt adsorption. The underlying CNT network provides a robust yet flexible support and a high electrical conductivity, whereas the m-C provides large surface area, and the Pt nanoparticles improves interfacial electron and ion diffusion. Consequently, specific capacitances of 203 and 311 F g(-1) have been achieved in these CNT@m-C and CNT@m-C@Pt sponges as supercapacitor electrodes, respectively, which can retain 96 % of original capacitance under large degree compression.

Smart, stretchable and wearable supercapacitors: prospects and challenges

Among the various energy storage systems, supercapacitors are considered to be the most promising alternative to batteries due to their high power density, long cycle life and fast charge–discharge process. Especially, flexible electrochemical supercapacitors with their unique advantages such as flexibility, shape-conformability, and light weight are attracting ever-increasing attention to meet the current requirements for portable and wearable electric devices in modern energy storage markets. In this perspective, we summarize the most recent progress in flexible all-solid supercapacitors from the point of view of flexible electrode materials. Various flexible electrode materials like carbon nanotubes, graphene, and pseudo capacitive materials are discussed and their performance is comprehensively analyzed. In addition, an overview of the latest progress in strategies to improve the energy and power density is discussed. Further research targets in multifunctional integrated systems and challenges in realizing idealized flexible energy storage systems are also proposed.

Recent progress in flexible and wearable bio-electronics based on nanomaterials

Flexible and stretchable biosensors that can monitor and quantify the electrical or chemical signals generated by specific microenvironments have attracted a great deal of attention. Wearable biosensors that can be intimately attached to skin or tissue provide a new opportunity for medical diagnostics and therapy. In recent years, there has been enormous progress in device integration and the design of materials and manufacturing processes for flexible and stretchable systems. Here, we describe the most recent developments in nanomaterials employed in flexible and stretchable biosensors. We review successful examples of such biosensors used for the detection of vital physiological and biological markers such as gas released from organisms. Furthermore, we provide a detailed overview of recent achievements regarding integrated platforms that include multifunctional nanomaterials. The issues and challenges related to the effective integration of multifunctional nanomaterials in bio-electronics are also discussed.

Coaxial TiO2–carbon nanotube sponges as compressible anodes for lithium-ion batteries

Carbon nanotubes (CNTs) have been combined with TiO2 to improve its performance in applications such as lithium ion batteries; previous CNT/TiO2 hybrid structures were usually in the powder form which requires a polymeric binder and carbon black to make electrodes. Here, we fabricate freestanding bulk electrodes by depositing TiO2 onto a CNT sponge via a simple in situ hydrolysis method, creating coaxial units of TiO2-wrapped CNTs. The built-in CNT framework supports a uniform thin crystalline TiO2 layer, forming a highly porous, conductive and compressible composite sponge. As an anode material for Li-ion batteries, the TiO2–CNT sponges exhibit stable charging/discharging plateau voltages, excellent cycling stability and rate performance. In particular, these sponges can be compressed to much smaller volumes with significantly improved areal capacity, which cannot be achieved by powder-form electrodes. Our hierarchical sponges with optimized microstructures may serve as stable and compressible electrodes for various energy storage systems such as Li-ion, Na-ion and Li–S batteries.

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

A Switchable and Compressible Carbon Nanotube Sponge Electrocapillary Imbiber

Carbon nanotube sponges are lightweight, conductive, highly porous, and flexible. An integration of these properties is suitable for constructing high-performance electrocapillary imbibers. Water imbibition into the sponges can be initiated at low potentials with tunable uptake rates and switched on and off reversibly. These controllable nanoporous imbibers have potential applications in a wide range of flexible micro- and nanofluidic systems.