Hybrid Films of Graphene and Carbon Nanotubes for High Performance Chemical and Temperature Sensing Applications

A hybrid composite material of graphene and carbon nanotube (CNT) for high performance chemical and temperature sensors is reported. Integration of 1D and 2D carbon materials into hybrid carbon composites is achieved by coupling graphene and CNT through poly(ionic liquid) (PIL) mediated‐hybridization. The resulting CNT/PIL/graphene hybrid materials are explored as active materials in chemical and temperature sensors. For chemical sensing application, the hybrid composite is integrated into a chemo‐resistive sensor to detect a general class of volatile organic compounds. Compared with the graphene‐only devices, the hybrid film device showed an improved performance with high sensitivity at ppm level, low detection limit, and fast signal response/recovery. To further demonstrate the potential of the hybrid films, a temperature sensor is fabricated. The CNT/PIL/graphene hybrid materials are highly responsive to small temperature gradient with fast response, high sensitivity, and stability, which may offer a new platform for the thermoelectric temperature sensors.     

A novel strain sensor based on graphene composite films with layered structure

The use of graphene for strain sensors has attracted enormous attention due to its prominent mechanical and electrical properties. In this paper, we report on the preparation and characterization of a novel type of strain sensor based on graphene composite films with layered configuration. Highly reliable and sensitive composite films strain sensors based on graphene were produced from solution processed graphene flakes by spray coating method. The layered strain sensor which could sustain a large tensile deformation (25% strain) demonstrated high sensitivity to mechanical strain with gauge factors of 6–35. And the sensitivity of this type of strain sensors can be tuned over a relatively wide range of values by adjusting the deposition parameters. What’s more, the layered composite films are more durable compared with the fragile pure graphene films. In addition the main mechanisms are investigated, resulting in theoretical models which predict very well the observed behavior.     

A Solution‐Processed High‐Performance Phototransistor based on a Perovskite Composite with Chemically Modified Graphenes

Phototransistors with a structure of a nitrogen‐doped graphene quantum dots (NGQDs)–perovskite composite layer and a mildly reduced graphene oxide (mrGO) layer are fabricated through a solution‐processing method. This hybrid phototransistor exhibits broad detection range (from 365 to 940 nm), high photoresponsivity (1.92 × 10⁴ A W^?1), and rapid response to light on–off (≈10 ms). NGQDs offer an effective and fast path for electron transfer from the perovskite to the mrGO, resulting in the improvement of photocurrent and photoswitching characteristics. The high photoresponsivity can also be ascribed to a photogating effect in the device. In addition, the phototransistor shows good stability with poly(methyl methacrylate) encapsulation, and can maintain 85% of its initial performance for 20 d in ambient air.     

Encapsulated Vanadium‐Based Hybrids in Amorphous N‐Doped Carbon Matrix as Anode Materials for Lithium‐Ion Batteries

Recently, researchers have made significant advancement in employing transition metal compound hybrids as anode material for lithium‐ion batteries and developing simple preparation of these hybrids. To this end, this study reports a facile and scalable method for fabricating a vanadium oxide–nitride composite encapsulated in amorphous carbon matrix by simply mixing ammonium metavanadate and melamine as anode materials for lithium‐ion batteries. By tuning the annealing temperature of the mixture, different hybrids of vanadium oxide–nitride compounds are synthesized. The electrode material prepared at 700 °C, i.e., VM‐700, exhibits excellent cyclic stability retaining 92% of its reversible capacity after 200 cycles at a current density of 0.5 A g^?1 and attractive rate performance (220 mAh g^?1) under the current density of up to 2 A g^?1. The outstanding electrochemical properties can be attributed to the synergistic effect from heterojunction form by the vanadium compound hybrids, the improved ability of the excellent conductive carbon for electron transfer, and restraining the expansion and aggregation of vanadium oxide–nitride in cycling. These interesting findings will provide a reference for the preparation of transition metal oxide and nitride composites as well.     

An All‐Stretchable‐Component Sodium‐Ion Full Battery

Stretchable energy‐storage devices receive considerable attention due to their promising applications in future wearable technologies. However, they currently suffer from many problems, including low utility of active materials, limited multidirectional stretchability, and poor stability under stretched conditions. In addition, most proposed designs use one or more rigid components that fail to meet the stretchability requirement for the entire device. Here, an all‐stretchable‐component sodium‐ion full battery based on graphene‐modified poly(dimethylsiloxane) sponge electrodes and an elastic gel membrane is developed for the first time. The battery exhibits reasonable electrochemical performance and robust mechanical deformability; its electrochemical characteristics can be well‐maintained under many different stretched conditions and after hundreds of stretching–release cycles. This novel design integrating all stretchable components provides a pathway toward the next generation of wearable energy devices in modern electronics.     

Solution Adsorption Formation of a π‐Conjugated Polymer/Graphene Composite for High‐Performance Field‐Effect Transistors

Semiconducting polymers with π‐conjugated electronic structures have potential application in the large‐scale printable fabrication of high‐performance electronic and optoelectronic devices. However, owing to their poor environmental stability and high‐cost synthesis, polymer semiconductors possess limited device implementation. Here, an approach for constructing a π‐conjugated polymer/graphene composite material to circumvent these limitations is provided, and then this material is patterned into 1D arrays. Driven by the π–π interaction, several‐layer polymers can be adsorbed onto the graphene planes. The low consumption of the high‐cost semiconductor polymers and the mass production of graphene contribute to the low‐cost fabrication of the π‐conjugated polymer/graphene composite materials. Based on the π‐conjugated system, a reduced π–π stacking distance between graphene and the polymer can be achieved, yielding enhanced charge‐transport properties. Owing to the incorporation of graphene, the composite material shows improved thermal stability. More generally, it is believed that the construction of the π‐conjugated composite shows clear possibility of integrating organic molecules and 2D materials into microstructure arrays for property‐by‐design fabrication of functional devices with large area, low cost, and high efficiency.     

Detection of Nitric Oxide from Living Cells Using Polymeric Zinc Organic Framework‐Derived Zinc Oxide Composite with Conducting Polymer

Sensitive and selective detection of nitric oxide (NO) in the human body is crucial since it has the vital roles in the physiological and pathological processes. This study reports a new type of electrochemical NO biosensor based on zinc‐dithiooxamide framework derived porous ZnO nanoparticles and polyterthiophene‐rGO composite. By taking advantage of the synergetic effect between ZnO and poly(TTBA‐rGO) (TTBA = 3′‐(p‐benzoic acid)‐2,2′:5′,2″‐terthiophene, rGO = reduced graphene oxide) nanocomposite layer, the poly(TTBA‐rGO)/ZnO sensor probe displays excellent electrocatalytic activity and explores to detect NO released from normal and cancer cell lines. The ZnO is immobilized on a composite layer of poly(TTBA‐rGO). The highly porous ZnO offers a high electrolyte accessible surface area and high ion–electron transport rates that efficiently catalyze the NO reduction reaction. Amperometry with the modified electrode displays highly sensitive response and wide dynamic range of 0.019–76 × 10^?6m with the detection limit of 7.7 ± 0.43 × 10^?9m . The sensor probe is demonstrated to detect NO released from living cells by drug stimulation. The proposed sensor provides a powerful platform for the low detection limit that is feasible for real‐time analysis of NO in a biological system.     

Exploring the Nickel–Graphene Nanocomposite Coatings for Superior Corrosion Resistance: Manipulating the Effect of Deposition Current Density on its Morphology,Mechanical Properties,and Erosion‐Corrosion Performance

The use of graphene‐based composite as anti‐corrosion and protective coatings for metallic materials is still a provocative topic worthy of debate. Nickel–graphene nanocomposite coatings have been successfully fabricated onto the mild steel by electrochemical co‐deposition technique. This research demonstrates the properties of nickel–graphene composite coatings influenced by different electrodeposition current densities. The effect of deposition current density on the; surface morphologies, composition, microstructures, grain sizes, mechanical, and electrochemical properties of the composite coatings are executed. The coarseness of deposited coatings increases with the increasing of deposition current density. The carbon content in the composite coatings increases first and then decreases by further increasing of current density. The improved mechanical properties and superior anti‐corrosion performance of composite coatings are obtained at the peak value of current density of 9 A dm^?2. The incorporation of graphene sheets into nickel metal matrix lead to enhance the micro hardness, surface roughness, and adhesion strength of produced composite coatings. Furthermore, the presence of graphene in composite coating exhibits the reduced grain sizes and the enhanced erosion–corrosion resistance properties.

     

Folding Large Graphene‐on‐Polymer Films Yields Laminated Composites with Enhanced Mechanical Performance

A folding technique is reported to incorporate large‐area monolayer graphene films in polymer composites for mechanical reinforcement. Compared with the classic stacking method, the folding strategy results in further stiffening, strengthening, and toughening of the composite. By using a water–air‐interface‐facilitated procedure, an A5‐size 400 nm thin polycarbonate (PC) film is folded in half 10 times to a ≈0.4 mm thick material (1024 layers). A large PC/graphene film is also folded by the same process, resulting in a composite with graphene distributed uniformly. A three‐point bending test is performed to study the mechanical performance of the composites. With a low volume fraction of graphene (0.085%), the Young's modulus, strength, and toughness modulus are enhanced in the folded composite by an average of 73.5%, 73.2%, and 59.1%, respectively, versus the pristine stacked polymer films, or 40.2%, 38.5%, and 37.3% versus the folded polymer film, proving a remarkable mechanical reinforcement from the combined folding and reinforcement of graphene. These results are rationalized with combined theoretical and computational analyses, which also allow the synergistic behavior between the reinforcement and folding to be quantified. The folding approach could be extended/applied to other 2D nanomaterials to design and make macroscale laminated composites with enhanced mechanical properties.     

Bending‐Tolerant Anodes for Lithium‐Metal Batteries

Bendable energy‐storage systems with high energy density are demanded for conformal electronics. Lithium‐metal batteries including lithium–sulfur and lithium–oxygen cells have much higher theoretical energy density than lithium‐ion batteries. Reckoned as the ideal anode, however, Li has many challenges when directly used, especially its tendency to form dendrite. Under bending conditions, the Li‐dendrite growth can be further aggravated due to bending‐induced local plastic deformation and Li‐filaments pulverization. Here, the Li‐metal anodes are made bending tolerant by integrating Li into bendable scaffolds such as reduced graphene oxide (r‐GO) films. In the composites, the bending stress is largely dissipated by the scaffolds. The scaffolds have increased available surface for homogeneous Li plating and minimize volume fluctuation of Li electrodes during cycling. Significantly improved cycling performance under bending conditions is achieved. With the bending‐tolerant r‐GO/Li‐metal anode, bendable lithium–sulfur and lithium–oxygen batteries with long cycling stability are realized. A bendable integrated solar cell–battery system charged by light with stable output and a series connected bendable battery pack with higher voltage is also demonstrated. It is anticipated that this bending‐tolerant anode can be combined with further electrolytes and cathodes to develop new bendable energy systems.     

On‐Chip Rolling Design for Controllable Strain Engineering and Enhanced Photon–Phonon Interaction in Graphene

On‐chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled‐up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through strain‐induced Raman G band splitting, while distinct blueshifts of characteristic peaks (G⁺, G^?, or 2D) can be well regulated on an asymmetric tubular structure with a strain variation. In addition, due to the strong confinement of the local electromagnetic field under 3D tubular geometry, the photon–phonon interaction is highly strengthened, and thus, the Raman scattering of graphene in rolled‐up tubes is enhanced. Such an on‐chip rolling approach leads to a superior strain tuning method in 2D materials and could improve their light–matter interaction in a tubular configuration, which may hold great capability in 2D materials integration for on‐chip applications such as in mechanics, electronics, and photonics.     

N,S co-doped lignin-based carbon microsphere functionalized graphene hydrogel with ‘‘sphere-in-layer” interconnection as electrode materials for supercapacitor and molecularly imprinted electrochemical sensors

This work reports a three-dimensional N, S co-doped lignin-based carbon microsphere/graphene composite hydrogel (GH-NSCMS) as an electrode material for supercapacitors and a signal enhancement material for tetracycline molecularly imprinted electrochemical sensors (MIECS). As a supercapacitor electrode, GH-NSCMS electrode has a specific capacitance of 434.6 F g^?1 at 0.5 A g^?1, which can still maintain 94.15% after 5,000 cycles. In addition, a highly sensitive MIP electrochemical sensor for tetracycline detection is prepared based on GH-NSCMS composite material due to the synergistic effects of the high recognition accuracy of the imprinting method, and excellent conductivity of the composite hydrogel material. The sensor has a wide linear range (0.1–50 μM) and a significant detection limit (5 × 10^?8 mol L^?1). Therefore, the 3D GH-NSCMS composites described herein have potential application prospects in supercapacitor electrode materials and tetracycline molecular imprinting detection.     

Multiresponsive Graphene‐Aerogel‐Directed Phase‐Change Smart Fibers

Wearable devices and systems demand multifunctional units with intelligent and integrative functions. Smart fibers with response to external stimuli, such as electrical, thermal, and photonic signals, etc., as well as offering energy storage/conversion are essential units for wearable electronics, but still remain great challenges. Herein, flexible, strong, and self‐cleaning graphene‐aerogel composite fibers, with tunable functions of thermal conversion and storage under multistimuli, are fabricated. The fibers made from porous graphene aerogel/organic phase‐change materials coated with hydrophobic fluorocarbon resin render a wide range of phase transition temperature and enthalpy (0–186 J g^?1). The strong and compliant fibers are twisted into yarn and woven into fabrics, showing a self‐clean superhydrophobic surface and excellent multiple responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion. Such aerogel‐directed smart fibers promise for broad applications in the next‐generation of wearable systems.     

Microtopography‐Guided Conductive Patterns of Liquid‐Driven Graphene Nanoplatelet Networks for Stretchable and Skin‐Conformal Sensor Array

Flexible thin‐film sensors have been developed for practical uses in invasive or noninvasive cost‐effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ‐conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin‐conformal sensor array (144 pixels) is fabricated having microtopography‐guided, graphene‐based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin‐like stretchability (<48%), high cyclic stability or durability (over 10⁵ cycles), and the signal amplification (≈5.25 times) via structure‐assisted intimate‐contacts between the device and rough skin. Furthermore, given the thin‐film programmable architecture and mechanical deformability of the sensor, a human skin‐conformal sensor is demonstrated with a wireless transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse‐waveforms and evolved into a mechanical/thermal‐sensitive electric rubber‐balloon and an electronic blood‐vessel. The microtopography‐guided and self‐assembled conductive patterns offer highly promising methodology and tool for next‐generation biomedical devices and various flexible/stretchable (wearable) devices.     

Substrate Doping Effect and Unusually Large Angle van Hove Singularity Evolution in Twisted Bi‐ and Multilayer Graphene

Graphene has demonstrated great potential in new‐generation electronic applications due to its unique electronic properties such as large carrier Fermi velocity, ultrahigh carrier mobility, and high material stability. Interestingly, the electronic structures can be further engineered in multilayer graphene by the introduction of a twist angle between different layers to create van Hove singularities (vHSs) at adjustable binding energy. In this work, using angle‐resolved photoemission spectroscopy with sub‐micrometer spatial resolution, the band structures and their evolution are systematically studied with twist angle in bilayer and trilayer graphene sheets. A doping effect is directly observed in graphene multilayer system as well as vHSs in bilayer graphene over a wide range of twist angles (from 5° to 31°) with wide tunable energy range over 2 eV. In addition, the formation of multiple vHSs (at different binding energies) is also observed in trilayer graphene. The large tuning range of vHS binding energy in twisted multilayer graphene provides a promising material base for optoelectrical applications with broadband wavelength selectivity from the infrared to the ultraviolet regime, as demonstrated by an example application of wavelength selective photodetector.     

Heterogeneous Integration of Carbon‐Nanotube–Graphene for High‐Performance,Flexible, and Transparent Photodetectors

Low‐dimensional carbon materials, such as semiconducting carbon nanotubes (CNTs), conducting graphene, and their hybrids, are of great interest as promising candidates for flexible, foldable, and transparent electronics. However, the development of highly photoresponsive, flexible, and transparent optoelectronics still remains limited due to their low absorbance and fast recombination rate of photoexcited charges, despite the considerable potential of photodetectors for future wearable and foldable devices. This work demonstrates a heterogeneous, all‐carbon photodetector composed of graphene electrodes and porphyrin‐interfaced single‐walled CNTs (SWNTs) channel, exhibiting high photoresponse, flexibility, and full transparency across the device. The porphyrin molecules generate and transfer photoexcited holes to the SWNTs even under weak white light, resulting in significant improvement of photoresponsivity from negligible to 1.6 × 10^?2 A W^?1. Simultaneously, the photodetector exhibits high flexibility allowing stable light detection under ≈50% strain (i.e., a bending radius of ≈350 µm), and retaining a sufficient transparency of ≈80% at 550 nm. Experimental demonstrations as a wearable sunlight sensor highlight the utility of the photodetector that can be conformally mounted on human skin and other curved surfaces without any mechanical and optical constraints. The heterogeneous integration of porphyrin–SWNT–graphene may provide a viable route to produce invisible, high‐performance optoelectronic systems.     

All‐Carbon Pressure Sensors with High Performance and Excellent Chemical Resistance

An all‐carbon pressure sensor is designed and fabricated based on reduced graphene oxide (rGO) nanomaterials. By sandwiching one layer of superelastic rGO aerogel between two freestanding high‐conductive rGO thin papers, the sensor works based on the contact resistance at the aerogel–paper interfaces, getting rid of the alien materials such as polymers and metals adopted in traditional sensors. Without the limitation of alien materials, the all‐carbon sensors demonstrate an ultrawide detecting range (0.72 Pa–130 kPa), low energy consumption (≈0.58 µW), ultrahigh sensitivity (349–253 kPa^?1) at low‐pressure regime (<1.4 Pa), fast response time (8 ms at 1 kPa), high stability (10 000 unloading–loading cycles between 0 and 1 kPa), light weight (<10 mg), easily scalable fabrication process, and excellent chemical stability. These merits enable them to detect real‐time human physiological signals and monitor the weights of various droplets of not only water but also hazardous chemical reagents including strong acid, strong alkali, and organic solvents. This shows their great potential applications in real‐time health monitoring, sport performance detecting, harsh environment‐related robotics and industry, and so forth.     

Ultraflexible Transparent Bio‐Based Polymer Conductive Films Based on Ag Nanowires

The unstable mechanical properties of flexible transparent conductive films (TCFs) make it difficult for them to meet the requirements for displays or wearable devices. Here, the relationship between the mechanism behind the bending behavior and the electrical properties, which is important for improving the mechanical stability of flexible TCFs, is explored. Flexible TCFs are reported based on silver nanowires (AgNWs) and bio‐based poly(ethylene‐co‐1,4‐cyclohexanedimethylene 2,5‐furandicarboxylate)s (PECFs), with a low sheet resistance (23.8 Ω sq^?1 at 84.6% transmittance) and superior mechanical properties. The electrical properties of the AgNW/PECFs composite film show almost no change after bending for 2000 times.     

Modular Graphene‐Based 3D Covalent Networks: Functional Architectures for Energy Applications

The development of ordered graphene‐based materials combining high stability, large surface areas, ability to act as absorbent of relevant chemical species, and solution processability is of significance for energy applications. A poorly explored approach relies on the controlled nanostructuration of graphene into robust and highly ordered 3D networks as a route to further leverage the exceptional properties of this unique material. Here, a simple yet effective and scalable one‐step method is reported to prepare graphene‐based 3D covalent networks (G3DCNs) with tunable interlayer distance via controlled polymerization of benzidines with graphene oxide at different reaction temperatures under catalyst‐ and template‐free conditions. The reduced form of G3DCNs is used as electrodes in supercapacitors; it reveals a high specific capacitance of 156 F g^?1 at a current density of 1 A g^?1 in a two‐electrode configuration and 460 F g^?1 at a current density of 0.5 A g^?1 in a three‐electrode configuration, combined with an excellent cycling stability over 5000 cycles. The present study will promote the quantitative understanding of structure–property relationship, for the controlled fabrication of 3D graphene‐based multifunctional materials.     

A Carbonyl Compound‐Based Flexible Cathode with Superior Rate Performance and Cyclic Stability for Flexible Lithium‐Ion Batteries

A sulfur‐linked carbonyl‐based poly(2,5‐dihydroxyl‐1,4‐benzoquinonyl sulfide) (PDHBQS) compound is synthesized and used as cathode material for lithium‐ion batteries (LIBs). Flexible binder‐free composite cathode with single‐wall carbon nanotubes (PDHBQS–SWCNTs) is then fabricated through vacuum filtration method with SWCNTs. Electrochemical measurements show that PDHBQS–SWCNTs cathode can deliver a discharge capacity of 182 mA h g⁻¹ (0.9 mA h cm⁻²) at a current rate of 50 mA g⁻¹ and a potential window of 1.5 V–3.5 V. The cathode delivers a capacity of 75 mA h g⁻¹ (0.47 mA h cm⁻²) at 5000 mA g⁻¹, which confirms its good rate performance at high current density. PDHBQS–SWCNTs flexible cathode retains 89% of its initial capacity at 250 mA g⁻¹ after 500 charge–discharge cycles. Furthermore, large‐area (28 cm²) flexible batteries based on PDHBQS–SWCNTs cathode and lithium foils anode are also assembled. The flexible battery shows good electrochemical activities with continuous bending, which retains 88% of its initial discharge capacity after 2000 bending cycles. The significant capacity, high rate performance, superior cyclic performance, and good flexibility make this material a promising candidate for a future application of flexible LIBs.