Flexible Single-walled Carbon Nanotube Research Articles

High-sensitivity and energy-efficient chloride ion sensors based on flexible printed carbon nanotube thin-film transistors for wearable electronics

The advent of flexible single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) has transformed electronics, providing significant benefits like low operating voltage, reduced power consumption, cost-effectiveness, and improved signal amplification. This study focuses on leveraging these attributes to develop a novel flexible high-sensitivity and energy-efficient chloride ion sensors based on printed flexible SWCNT-TFTs utilizing polymers-sorted semiconducting SWCNTs (sc-SWCNTs) as the active layers and ion liquids-poly(4-vinylphenol as dielectric layers along with the evaporated deposition of aluminum electrodes and printed silver electrodes as the gate and source-drain electrodes, respectively. The sensors exhibit several operational advantages, including low voltage requirements (≤1 V), rapid response speed (5.32 s), significant signal amplification (Up to 702.6 %), low power consumption (0.31 μJ at 1 mmol chloride ion), good repeatability, high sensitivity for both low and high concentrations of chloride ion (up to 100 mmol/L) and excellent mechanical flexibility (No obvious changes after bending for 10,000 times with a 5 mm radius). The detection mechanism of chloride ions was analyzed using X-ray Photoelectron Spectroscopy (XPS). It was found that chloride ions react with silver nanoparticles (AgNPs) to form silver chloride (AgCl) on printed electrodes, impeding carrier transport and reducing the currents in SWCNT TFTs. Importantly, our sensors' compatibility with smart devices allows for real-time monitoring of chloride ion levels in human sweat, offering significant potential for daily health monitoring.

Universal Sublimation Strategy to Stabilize Single-Metal Sites on Flexible Single-Wall Carbon-Nanotube Films with Strain-Enhanced Activities for Zinc-Air Batteries and Water Splitting.

Single-metal-site catalysts have recently aroused extensive research in electrochemical energy fields such as zinc-air batteries and water splitting, but their preparation is still a huge challenge, especially in flexible catalyst films. Herein, we propose a sublimation strategy in which metal phthalocyanine molecules with defined isolated metal-N4 sites are gasified by sublimation and then deposited on flexible single-wall carbon nanotube (SWCNT) films by means of π-π coupling interactions. Specifically, iron phthalocyanine anchored on the SWCNT film prepared was directly used to boost the cathodic oxygen reduction reaction of the zinc-air battery, showing a high peak power density of 247 mW cm-2. Nickel phthalocyanine and cobalt phthalocyanine were, respectively, stabilized on SWCNT films as the anodic and cathodic electrocatalysts for water splitting, showing a low potential of 1.655 V at 10 mA cm-2. In situ Raman spectra and theoretical studies demonstrate that highly efficient activities originate from strain-induced metal phthalocyanine on SWCNTs. This work provides a universal preparation method for single-metal-site catalysts and innovative insights for electrocatalytic mechanisms.

Excellent Miniature Thin Film Dielectric Elastomer Sensors for Robot Fingers Used in Human-Robot Interaction

Traditional sensors used to measure properties such as deformation and pressure often use materials such as metals, ceramics, piezos and polymers. However, since many of these materials are hard, it can be difficult to measure them with a single sensor when the pressure or elongation applied to the object changes. In this experiment, a dielectric elastomer thin-film pressure sensor (0.2 mm) was fabricated using hydrogenated nitrile rubber with significantly improved hardness and elongation. This single sensor can accurately measure pressure from 1gf to 20kgf. Also, the response speed was 50ms, which was sufficiently fast. A dielectric elastomer stretch sensor was also developed. This sensor uses elastic and flexible single-walled carbon nanotubes as dielectric elastomer electrodes for the hydrogenated nitrile rubber. This greatly improved the mechanical flexibility and stretchability of the stretch sensor, making it possible to operate it as a sensor even at 400% elongation. By attaching this stretch sensor to the robot's finger closely, it is possible to detect the dynamic movement of the robot's finger and to detect the force (pressure) when the fingertip touches the target object with the above pressure sensor. In addition, by using the small diaphragm-type dielectric elastomer actuator, it was confirmed that the sensation of the robot's touching an object could be fed back to the human finger. As a result, it is thought that the feeling of the robot’s finger touching an object could be driven more realistically and accurately. In addition, both a dielectric elastomer stretch sensor and a dielectric elastomer pressure sensor were attached to the finger of the robot, and the movement of the human’s finger was sensed and the force (pressure) when the finger touched the object was also able to be detected.

An integrated oxygen electrode derived from a flexible single-walled carbon nanotube film for rechargeable Zn-air batteries produced by electropolymerization

The development of low-cost, high-activity, and durable integrated bifunctional flexible air electrodes for use in Zn-air batteries is both challenging and important. We report a simple and scalable electropolymerization method used to prepare an electrode material comprising heavily N-doped carbon covering single-walled carbon nanotube (N/C-SWCNT) networks. The resulting core/shell structure of the hybrid electrode enabled the flexibility, mechanics, and three-dimensional interconnected porous structure of SWCNT films while containing abundant pyridinic N, which provided excellent catalytic activity for both the oxygen reduction and evolution reactions (overpotential gap = 0.76 V). A binder-free Zn-air battery using the N/C-SWCNT film as an oxygen electrode was assembled and showed a high peak power density of 181 mW/cm2, a high specific capacity of 810 mAh/g and stable discharge‒charge cycling performance. We also constructed a flexible solid-state Zn-air battery featuring not only a high power density of 22 mW/cm2 but also good flexibility and stability.

Single‐Walled Carbon Nanotube Film as an Efficient Conductive Network for Si‐Based Anodes

AbstractSilicon‐based anodes are considered ideal candidate materials for next‐generation lithium‐ion batteries due to their high capacity. However, the low conductivity and large volume variations during cycling inevitably result in inferior cyclic stability. Herein, a dry method without binders is designed to fabricate Si‐based electrodes with single‐walled carbon nanotubes (SWCNTs) network and to explore the different mechanisms between SWCNT and multiwalled carbon nanotubes (MWCNTs) as a conductive network. As expected, higher initial discharge capacity (1785 mAh g−1), higher initial Coulombic efficiency (ICE, 81.52%) and outstanding cyclic stability are obtained from the SiOx@C|SWCNT anodes. Furthermore, its lithium‐ion diffusion coefficient (DLi+) is 3–4 orders of magnitude higher than that of SiOx@C|MWCNT. The underlying mechanism is clarified by in situ Raman spectroscopy and theoretical analysis. It is found that the SWCNTs can maintain good contact with SiOx@C even under tensile stresses up to 6.2 GPa, while the MWCNTs lose electrical contact due to alternating compressive stress up to 8.9 GPa and tensile stress up to 2.5 GPa during long‐term cycling. Under such very large stresses, the more flexible SWCNTs and their stronger van der Waals forces ensure that SiOx@C still has good contact with SWCNTs.

Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

Photovoltaic-Driven Flexible Single-Walled Carbon Nanotubes for Self-Powered and Polarization-Sensitive Infrared Photodetection

Photovoltaic-Driven Flexible Single-Walled Carbon Nanotubes for Self-Powered and Polarization-Sensitive Infrared Photodetection

Photosensitive-Stamp-Inspired Scalable Fabrication Strategy of Wearable Sensing Arrays for Noninvasive Real-Time Sweat Analysis.

Wearable sweat sensing is essential to the development of personalized health monitoring in a noninvasive manner with molecular-level insight. Hence, there is an increasing demand for convenient, facile, and efficient fabrication of wearable sensing arrays. Inspired by a photosensitive stamp (PS), we present herein a simple, low-cost, and eco-friendly vacuum filtration-transfer printing method (termed PS-VFTP) for the scalable preparation of single-walled carbon nanotube (SWCNT) based flexible electrode arrays. This method can economically yield customized flexible SWCNT arrays with praiseworthy performance, such as high reproducibility, precision, uniformity, conductivity, and mechanical stability. In addition, the flexible SWCNT arrays can be easily functionalized into high-performance electrochemical sensors for the simultaneous monitoring of sweat metabolites (glucose, lactate) and electrolytes (Na+, K+). The integration of wearable sensing arrays with a signal acquisition and processing circuit system in the intelligent wearable sensors empowers them to realize noninvasive, real-time, and in situ sweat analysis during exercise. More meaningfully, such a PS-VFTP strategy can be easily expanded to the economical manufacturing of other flexible electronic devices.

Facile premixed flame synthesis C@Fe2O3/SWCNT as superior free-standing anode for lithium-ion batteries

Premixed flame configuration is considered as an effective method for the synthesis of carbon materials. In this work, flexible single-walled carbon nanotube network decorated by carbon-encapsulated Fe2O3 nanoparticles (C@Fe2O3/SWCNT) membrane was in-situ fabricated via a facile floating catalyst premixed ethanol flame method, and followed by annealing treatment. In this process, low-cost ethanol and ferrocene were used as carbon source and catalyst precursor for the synthesis of C@Fe2O3/SWCNT, respectively. Benefiting from the interconnected conductive network, the as-fabricated C@Fe2O3/SWCNT membrane was used as a free-standing anode for lithium-ion batteries. Structural characterization revealed that the ultrafine Fe2O3 nanoparticles homogeneously anchored on the SWCNT network, which facilitates the fast diffusion for electron. Furthermore, the carbon layers uniformly enwrap on Fe2O3 can effectively suppress the aggregation and buffer the volume change of Fe2O3 during the lithiation/delithiation process. Consequently, this material delivered an excellent lithium storage performance with a high reversible capacity of 1294.7 mAh g−1 at 50 mA g−1, and an excellent cyclability of 82.5% retention is obtained after cycles at 2 A g−1. This study provides a novel low-cost and fast method for preparing flexible advanced electrode for next-generation rechargeable batteries.

An Integrated Oxygen Electrode Derived from Flexible Single-Wall Carbon Nanotube Film for Rechargeable Zn-Air Batteries Produced by Electro-Polymerization

An Integrated Oxygen Electrode Derived from Flexible Single-Wall Carbon Nanotube Film for Rechargeable Zn-Air Batteries Produced by Electro-Polymerization

Confinement of hbox {CO}_{2} inside carbon nanotubes

We propose a preliminary study based on molecular dynamics calculations to investigate the adsorption of pure hbox {CO}_{2} on flexible single-walled carbon nanotubes (SWCNTs) of different sizes. The adsorption capacities of SWCNTs were simulated and the effect of chirality and diameter of SWCNTs was assessed, to check them as sizable carbon structured materials suitable for hbox {CO}_{2} confinement and storage. The potential energy surfaces, describing the intermolecular interactions involving hbox {CO}_{2}-SWCNT and hbox {CO}_{2}-hbox {CO}_2 pairs, have been described specifically by adopting the improved lennard jones model potential. The intramolecular interactions within the SWCNT were considered explicitly since they are responsible for out-of-plane movements of carbon atoms and the flexibility of nanotubes. These well-formulated potentials are well capable of defining hbox {CO}_{2} confinement through physisorption and guarantee a quantitative description and realistic results for the dynamics of the interactions. The flexible SWCNTs can adsorb up to 35 wt% at 273 K, a property that makes them potentially versatile materials competitive with other carbon-derived adsorbents to cope with hbox {CO}_{2} gas emission.Graphic abstract

Impedance spectroscopy of polyvinyl alcohol-coated carboxyl-functionalized single-walled carbon nanotube flexible film: a generic battery model

In this study, we demonstrate a simple technique to prepare a flexible single-walled carbon nanotube (SWCNT) array for battery application. The polyvinyl alcohol-coated unidirectional SWCNT flexible film has been prepared using a simple solution casting technique. The frequency variation of impedance spectroscopy of the composite film is investigated in a frequency spectrum of 20 Hz ≤ f ≤ 1 MHz and temperature range (373 ≤ T ≤ 413 K). The experimental data are simulated with a generic battery model equivalent circuit. The generalized model is based on impedance spectroscopy, which is suitable for practical application and able to interpret the existing battery model. The extracted parameters from the simulation of experimental data are tabulated. The temperature variation of the parameters is very significant for manufacturing a battery system. The study of electric modulus suggests a non-Debye-type relaxation behavior of the flexible battery system.

Preparation and thermoelectric properties of flexible SWCNT/PEDOT:PSS composite film

Flexible single-walled carbon nanotube (SWCNT)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (CNT/PP) composite films have been fabricated by a simple dilution filtration method. The effects of SWCNTs content and dimethyl sulfoxide (DMSO) treatment on thermoelectric properties of the composite films have been investigated. With the content of SWCNTs increasing, both the electrical conductivity and Seebeck coefficient increase, leading to an enhancement of thermoelectric properties of the composite film. After the DMSO treatment, a maximum power factor of 108.7 μWm−1K-2 has been achieved at 340 K for the sample containing 80 wt.% SWCNTs. SEM and XPS analyses are applied to characterize morphologies and compositions of the composite films.

Radiation effects in printed flexible single-walled carbon nanotube thin-film transistors

In this study, the gamma ray radiation effect on the characteristics of inkjet-printed semiconducting single-walled carbon nanotubes (sSWCNTs) thin-film transistors (TFTs) is investigated. The devices with top gate dielectrics consisted of BaTiO3 and poly(methyl methacrylate) (PMMA) were characterized before and after 150 krad 60Co gamma radiation in air. It reveals that the radiation results in a positive threshold voltage shift from -0.5 to 3.6 V (with a drain voltage biased at -1 V). The hysteresis decreases slightly from 1.2 to 0.5 V, indicating that the BaTiO3/PMMA dielectric layer effectively encapsulates the sSWCNTs TFTs from absorbing molecules in the environment. Furthermore, the charge pumping current ICP is measured with a gate voltage pulsed at 100 kHz. The maximum ICP increases from 90 to 140nA, which translates to an increase in the interface trap density from 4.5×1011 to 1.1×1012 cm-2eV-1. The charge pumping measurements at the frequency of 10∼250 kHz show that the increase of ICP induced by radiation is obvious when f>30 kHz but is little when f<30 kHz, which indicates that the radiation induced charge traps locate near sSWCNTs. The BaTiO3/PMMA gate dielectric remains to be a good insulator with a leakage current of less than 60 pA after radiation. Such printed flexible TFTs with the polymer gate dielectric possess similar radiation tolerant compared to convention devices on rigid substrates.

High sensitive Polyimide-based single-walled carbon nanotube thermal film sensor for fluid shear stress measurements

A flexible polyimide-based single-walled carbon nanotube (SWCNT) thermal film sensor has been developed for wall shear stress measurements in both air and water. To ensure high sensitivity, vacuum thermal annealing and electrical aging are conducted to enhance the electric properties of the sensor with low-resistance and the high temperature coefficient of resistivity (TCR). The TCR of sensors can reach to 8040 ppm/°C to the author’s knowledge, which is the highest reported value of thermal sensors used for shear stress measurements. In calibration, the output voltage of the sensor is proportional to the one third power of wall shear stress with the sensitivity on the order of mV Pa−1 in the constant current operation mode. The repeatability error is no more than 1% in both air and water, which confirms the capability of the flexible SWCNT thermal film sensor for fluid wall shear stress measurements with high sensitivity.

Thermally stable near UV-light transparent and conducting SWCNT/glass flexible films

Flexible single wall carbon nanotube (SWCNT) transparent and conducting films (TCFs) are indispensable to a further development of flexible electronics. Here we describe thermally and mechanically stable near-ultraviolet (near-UV) transparent and conducting films on ultrathin flexible glass produced from Zn/Al complex-SWCNT inks by bar coating. Our SWCNT/glass TCF is flexible and its relative resistance remains almost constant with increasing bending angle up to ∼170°. Sheet resistance decreases from 80 Ω/sq to 68 Ω/sq after heating in vacuum and increases from 80 Ω/sq to 300 Ω/sq after heating in air from 300 to 523 K. Transmittance in the near-UV region is in the range of 80–90% and does not change with increasing temperature up to 523 K. We believe that this SWCNT/glass TCFs should be promising for thermally stable transparent and flexible electronics.

Enhancement of the electron transfer rate in carbon nanotube flexible electrochemical sensors by surface functionalization

Thin films of single-walled carbon nanotubes (SWNTs) possess high potential for use in flexible electrochemical sensors in wearable medical devices. However, the electrochemical activity of such materials is not yet fully understood. We studied the enhancement in electrochemical activity of SWNT-based flexible electrochemical sensors. To exclude the effect of surface contaminations from the fabrication processes on the electrochemical activity, we introduced the dry process for high-quality and clean SWNT film formation and the clean device fabrication process with a protective layer. So-fabricated SWNT electrodes exhibited a low electron transfer rate. Electrochemical functionalization with an H2SO4 solution successfully enhanced the electrochemical activity of the SWNT electrode for the inner sphere probes such as [Fe(CN)6]4−/3−. This method is quite gentle and controllable, but also effective at increasing the electron transfer rate without either degrading the potential window. We found out that there was a correlation between the electron transfer rate and the amount of defects evaluated from Raman scattering spectroscopy. XPS analysis showed that the functionalization process introduced CO and CO species, suggesting that these species constituted active sites for inner sphere probes. The electrochemical functionalization was also effective for enhancing the limit of detection in dopamine detection with the flexible SWNT electrode. The limit of detection was ∼100 nM for functionalized electrode whereas it was ∼1 μM for as-fabricated electrodes.

A New Anode for Lithium-Ion Batteries Based on Single-Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design.

Carbon nanomaterials, especially graphene and carbon nanotubes, are considered to be favorable alternatives to graphite-based anodes in lithium-ion batteries, owing to their high specific surface area, electrical conductivity, and excellent mechanical flexibility. However, the limited number of storage sites for lithium ions within the sp2 -carbon hexahedrons leads to the low storage capacity. Thus, rational structure design is essential for the preparation of high-performance carbon-based anode materials. Herein, we employed flexible single-walled carbon nanotubes (SWCNTs) with ultrahigh electrical conductivity as a wrapper for 3D graphene foam (GF) by using a facile dip-coating process to form a binary network structure. This structure, which offered high electrical conductivity, enlarged the electrode/electrolyte contact area, shortened the electron-/ion-transport pathways, and allowed for efficient utilization of the active material, which led to improved electrochemical performance. When used as an anode in lithium-ion batteries, the SWCNT-GF electrode delivered a specific capacity of 953 mA h g-1 at a current density of 0.1 A g-1 and a high reversible capacity of 606 mA h g-1 after 1000 cycles, with a capacity retention of 90 % over 1000 cycles at 1 A g-1 and 189 mA h g-1 after 2200 cycles at 5 A g-1 .

An electrochemically modulated single-walled carbon nanotube network for the development of a transparent flexible sensor for dopamine

Transparent and flexible single-walled carbon nanotube (SWCNT) network electrodes were used for the determination of neurotransmitters. The surface of SWCNT network film was oxidised by multiple electrochemical anodic scans, thereby the electronic structure of SWCNTs network film was modulated with p-typed doping. Herein, we analysed the electronic structure in-depth by resonant Raman spectroscopy with two different wavelength lasers (514 and 633 nm) and UV–vis-NIR absorption spectroscopy. From this analysis, it is found that the electrochemical oxidation process selectively occurred on metallic SWCNTs surface in the mixture of metallic and semiconducting SWCNTs. Interestingly, after electrochemical oxidation, the charge transfer resistance was observed to have decreased by 52%, compared to that of a SWCNT network electrode before treatment (4.7 kΩ). This is probably due to the suppression of Schottky barrier of junctions between metallic and semiconducting SWCNT bundles. The enhanced electrocatalytic activity of a SWCNT network film by electrochemical doping (Eox-SWCNT network film) has enabled discrimination of dopamine (DA) from a mixture with ascorbic acid (AA) and uric acid (UA). The limit of detection was estimated to be 0.51 μM DA in the presence of 100 μM AA and 10 μM UA, and the DA sensing activity was not significantly affected even using a bent configuration of Eox-SWCNT network film. The simple and eco-friendly electrochemical doping with multiple cyclic voltammetric scans can be a powerful tool to modulate the electronic energy in the band structure of carbon-related materials.

Flexible single walled nanotube based chemical sensor for 2,4-dinitrotoluene sensing

In this work, we have attempted to fabricate flexible single walled carbon nanotube based sensor for detection of 2,4-dinitrotoluene (DNT) an explosive chemical. For analyte sensing study, the flexible sensor is fabricated by vacuum filtration method. These fabricated gas sensors are characterised by SEM and Raman spectroscopy. The sensor response is investigated toward the explosive chemicals which have NO2 group in their molecular structure. The fabricated sensor is able to detect the traces of DNT at room temperature. The sensor gives 0.28–0.32% repeatable response to 0.22 ppm of DNT. The response of sensor increases with increase in the vapour concentration of the DNT vapours.