Nature-motivated pressure sensors have been greatly important components integrated into flexible electronics and applied in artificial intelligence. Here, we report a high sensitivity, ultrathin, and transparent pressure sensor based on wrinkled graphene prepared by a facile liquid-phase shrink method. Two pieces of wrinkled graphene are face to face assembled into a pressure sensor, in which a porous anodic aluminum oxide (AAO) membrane with the thickness of only 200 nm was used to insulate the two layers of graphene. The pressure sensor exhibits ultrahigh operating sensitivity (6.92 kPa–1), resulting from the insulation in its inactive state and conduction under compression. Formation of current pathways is attributed to the contact of graphene wrinkles through the pores of AAO membrane. In addition, the pressure sensor is also an on/off and energy saving device, due to the complete isolation between the two graphene layers when the sensor is not subjected to any pressure. We believe that our high-performance pressure sensor is an ideal candidate for integration in flexible electronics, but also paves the way for other 2D materials to be involved in the fabrication of pressure sensors.Keywords: anodic aluminum oxide; flexible electronics; graphene; pressure sensor; wrinkled structures;

With the increasing demand for compact storage systems for portable and wearable electronic devices, flexible supercapacitors with high volumetric performance have attracted considerable attention. Here, we report a simple method to fabricate a sandwich-like carbon nanotubes (CNTs)/NiCo2O4 hybrid paper electrode, consisting of a layer of conductive CNT buckypaper coated with honeycomb-like NiCo2O4 nanosheets at both sides. Owing to the high conductivity of the CNT skeleton and vertically aligned structure of NiCo2O4 nanosheets, the free-standing hybrid paper possesses an ultra-high specific capacitance of 1752.3 F g−1 and excellent cycling performance. A flexible all-solid-state symmetrical supercapacitor has been further assembled based on the hybrid paper. The device exhibits excellent volumetric energy and power densities (1.17 mW h cm−3 and 2430 mW cm−3) and deformability, even under bending at an angle of 180°. The hybrid paper can serve as a freestanding and flexible electrode for various energy devices.

It is unavoidable to form wrinkles, which are folds or creases in a material, in graphene, whenever the graphene is prepared by micromechanical exfoliation from graphite or chemical vapor deposition (CVD). However, the controllable formation and structures of graphene with nanoscale wrinkles remains a big challenge. Here, we report a liquid-phase shrink method to controllably fabricate large-area wrinkled graphene (WG). The CVD-prepared graphene self-shrinks into a WG on an ethanol solution surface. By modifying the concentration of the ethanol solution, we can easily and efficiently obtain WG with a uniform distribution of wrinkles with different heights. The WG shows high stretchability and can withstand more than 100% tensile strain and up to 720° twist. Furthermore, electromechanical response sensors based on double-layer stacking of WG show ultrahigh sensitivity. This simple, effective, and environmentally friendly liquid-phase shrink method will pave a way for the controllable formation of WG, which is an ideal candidate for application in highly stretchable and highly sensitive electronic devices.Keywords: graphene; interface interaction; morphological controls; stretchable sensors; wrinkles

Flexible supercapacitors, which can sustain large deformations while maintaining normal functions and reliability, are playing an increasingly important role in portable electronic devices. Here we report the preparation of a three-dimensional α-Fe2O3/carbon nanotube (CNT@Fe2O3) sponge electrode with a porous hierarchical structure, consisting of a compressible, conductive CNT network, coated with a layer of Fe2O3 nanohorns. The specific capacitance of these hybrid sponges has been significantly improved to above 300 F g−1, while the equivalent series resistance remains at about 1.5 Ω. The highly deformed CNT@Fe2O3 sponge retains more than 90% of the original specific capacitance under a compressive strain of 70% (corresponding to a volume reduction of 70%). The hybrid sponge still works stably and sustains a similar specific capacitance to the initial value even after 1000 compression cycles at a strain of 50%. The outstanding properties of this hybrid sponge make it a highly promising candidate for flexible energy devices.

In order to improve the understanding of laser interactions of materials with homogeneous nano-structures, pulsed laser induced plasma from a low density, high-porosity multiwall carbon nanotube (CNT) sponge and a dense graphite block have been investigated by combinational spectroscopy approaches. We observe distinct differences in the laser-induced light emission of the CNT sponge and graphite block which we attribute to the occurrence of a phase explosion caused by the lower thermal conductivity and weaker mechanical strength of the CNT sponge. Furthermore, spectroscopy plasma analysis reveals that differences in the surface of the two systems play a key role in the generation of negative carbon ions. We observe a more effective production of negative ions for the CNT sponge as compared to the graphite block due to the greater number of surface defects of the CNT sponge.

Carbon nanotubes have the potential to construct highly compressible and elastic macroscopic structures such as films, aerogels and sponges. The structure-related deformation mechanism determines the mechanical behavior of those structures and niche applications. Here, we show a novel strategy to integrate aligned and random nanotube layers and reveal their deformation mechanism under uniaxial compression with a large range of strain and cyclic testing. Integrated nanotube layers deform sequentially with different mechanisms due to the distinct morphology of each layer. While the aligned layer forms buckles under compression, nanotubes in the random layer tend to be parallel and form bundles, resulting in the integration of quite different properties (strength and stiffness) and correspondingly distinct plateau regions in the stress–strain curves. Our results indicate a great promise of constructing hierarchical carbon nanotube structures with tailored energy absorption properties, for applications such as cushioning and buffering layers in microelectromechanical systems.

Development of sorbent materials with high selectivity and sorption capacity, easy collection and recyclability is demanding for spilled oil recovery. Although many sorption materials have been proposed, a systematic study on how they can be reused and possible performance degradation during regeneration remains absent. Here we report magnetic carbon nanotube sponges (Me-CNT sponge), which are porous structures consisting of interconnected CNTs with rich Fe encapsulation. The Me-CNT sponges show high mass sorption capacity for diesel oil reached 56 g/g, corresponding to a volume sorption capacity of 99%. The sponges are mechanically strong and oil can be squeezed out by compression. They can be recycled using through reclamation by magnetic force and desorption by simple heat treatment. The Me-CNT sponges maintain original structure, high capacity, and selectivity after 1000 sorption and reclamation cycles. Our results suggest that practical application of CNT macrostructures in the field of spilled oil recovery is feasible.Keywords: carbon nanotube; mechanical strength; recyclability; sorption and desorption; sorption capacity; spilled oil;

Electrical and thermal transportation properties of a novel structured 3D CNT network have been systematically investigated. The 3D CNT net work maintains extremely low thermal conductivity of only 0.035 W/(m K) in standard atmosphere at room temperature, which is among the lowest compared with other reported CNT macrostructures. Its electrical transportation could be adjusted through a convenient gas-fuming doping process. By potassium (K) doping, the original p-type CNT network converted to n-type, whereas iodine (I2) doping enhanced its electrical conductivity. The self-sustainable homogeneous network structure of as-fabricated 3D CNT network made it a promising candidate as the template for polymer composition. By in situ nanoscaled composition of 3D CNT network with polyaniline (PANI), the thermoelectric performance of PANI was significantly improved, while the self-sustainable and flexible structure of the 3D CNT network has been retained. It is hoped that as-fabricated 3D CNT network will contribute to the development of low-cost organic thermoelectric area.Keywords: CNT network; nanocompositing; thermal conductivity; thermoelectric;

The anisotropy in thermoelectric properties of three-dimensional carbon nanotubes (CNTs) and CNT/polyaniline (PANI) composites have been studied by utilizing an orderly aligned CNT arrays with a self-sustained construction. In the length direction of CNT, the electrical conductivity of the CNT array is ∼5 times larger as compared to the direction vertical to the alignment of CNTs, while the difference in thermal conductivity between these two directions is ∼25 times. As a result, strong anisotropic thermoelectric transportation has been also observed in the composites composed of PANI and CNT arrays. An enhanced thermopower in the composites, as compared to the pure PANI or CNTs, is only observed in the direction along the CNTs. This study helps the fundamental understanding on the un-conventional improved thermopower, which is more likely to be realized via adjusting the carrier transportation within the interface between CNTs and PANI rather than across it.

Flexible supercapacitors, which can sustain large deformations while maintaining normal functions and reliability, are playing an increasingly important role in portable electronic devices. Here we report the preparation of a three-dimensional α-Fe2O3/carbon nanotube (CNT@Fe2O3) sponge electrode with a porous hierarchical structure, consisting of a compressible, conductive CNT network, coated with a layer of Fe2O3 nanohorns. The specific capacitance of these hybrid sponges has been significantly improved to above 300 F g−1, while the equivalent series resistance remains at about 1.5 Ω. The highly deformed CNT@Fe2O3 sponge retains more than 90% of the original specific capacitance under a compressive strain of 70% (corresponding to a volume reduction of 70%). The hybrid sponge still works stably and sustains a similar specific capacitance to the initial value even after 1000 compression cycles at a strain of 50%. The outstanding properties of this hybrid sponge make it a highly promising candidate for flexible energy devices.

With the increasing demand for compact storage systems for portable and wearable electronic devices, flexible supercapacitors with high volumetric performance have attracted considerable attention. Here, we report a simple method to fabricate a sandwich-like carbon nanotubes (CNTs)/NiCo2O4 hybrid paper electrode, consisting of a layer of conductive CNT buckypaper coated with honeycomb-like NiCo2O4 nanosheets at both sides. Owing to the high conductivity of the CNT skeleton and vertically aligned structure of NiCo2O4 nanosheets, the free-standing hybrid paper possesses an ultra-high specific capacitance of 1752.3 F g−1 and excellent cycling performance. A flexible all-solid-state symmetrical supercapacitor has been further assembled based on the hybrid paper. The device exhibits excellent volumetric energy and power densities (1.17 mW h cm−3 and 2430 mW cm−3) and deformability, even under bending at an angle of 180°. The hybrid paper can serve as a freestanding and flexible electrode for various energy devices.