Conductive Carbon Nanotube Networks Research Articles

The effect of interfacial resistance and crystallinity on heat transfer mechanism in carbon nanotube reinforced polyethylene

Thermoplastic nanocomposites were fabricated in order to deliver a suitable material for thermal management devices, commonly processed by injection molding or 3D printing. Scalable manufacturing of Carbon Nanotubes (CNTs) and multi-functional polymers with good thermal conductivity and ease of handling was demonstrated in the present study. The standard grade polyethylene reinforced with CNTs, was formed by melt mixing. Polyethylene glycol was used for concentrating CNTs in a masterbatch for its plasticizing properties, ensuring safe handling and even dispersion of CNTs. Through characterization of morphology and thermal properties, an interconnected CNTs network was established, which enhanced the heat transfer at high concentration by changing the main conduction path from polymer crystal lattice to CNTs conductive network. Moreover, it was shown that modification in the matrix crystallinity is key to maximize the phonon and electron conduction interfaces and achieve advances in thermal conductivity beyond 68% and 100% achieved for 15 wt% content of CNTs compared to neat PE and PE@PEG matrices, respectively, within this study.

High-sensitive flexural sensors for health monitoring of composite materials using embedded carbon nanotube (CNT) buckypaper

The health monitoring for the service status of the composite materials is particularly crucial, calling for highly sensitive piezoresistive strain sensors. This paper outlined the working mechanisms of CNT buckypaper sensor during loading and releasing processes by analyzing the electrical conduction mechanism of the adjacent CNT and developing the macroscopical and mesoscopic models of CNT electrical networks inside of the bukypaper. The CNT-based nanocomposite specimens underwent monotonic and cyclic flexural loading in low strain range to examine the dynamic stability and durability of the in-situ nano sensor. The different support span configurations were also employed and operated to obtain the recommended application scenarios. The long-term response behavior of the nano sensor was also concluded as three typical phases. The desirable agreement was demonstrated by comparing the responses of ΔR/R0 signals and phenomena of the breakage and propagation of micro cracks and the rearrangement and reconnection of CNT conductive networks within the Scanning electron microscope (SEM) images of the buckypaper. The proposed flexural nano sensor is suitable for potential health monitoring application of composite materials.

FeS2@CNT composite with synergistic battery/capacitor builds outstanding sodium-ion storage

Pyrite (FeS2) as one of the most promising anode material candidates for sodium ion batteries suffers from sluggish electrochemical kinetics and large volume expansion, leading to rapid capacity decline and poor rate performance. In this work, ultra-fine FeS2 nanoparticles anchored on carbon nanotube conductive network (FeS2@CNT) were synthesized by one-step pyrolysis combined with solid vulcanization method. On the one hand, the conductive network of CNT not only provides necessary expansion space for FeS2 during the sodiation/desodiation process, but also improves the conductivity of the composites. On the other hand, ultra-fine FeS2 nanoparticle (54 nm) shortens the diffusion paths of Na-ions and triggers the outstanding pseudocapacitance effect. Owing to the synergic effect of battery/capacitor hybrid energy storage, the obtained FeS2@CNT composites exhibit excellent sodium ion storage performance.

Construction of MnO2 nanosheets@graphenated carbon nanotube networks core-shell heterostructure on 316L stainless steel as binder-free supercapacitor electrodes

Carbon nanotubes are regarded as typical and promising electrode materials in supercapacitors. However, small specific capacitance of carbon nanotubes restricts the practical application in high energy density devices. Herein, MnO2 nanosheets@graphenated carbon nanotube networks are synthesized directly on 316L stainless steel as binder-free electrodes for high-performance supercapacitors. Graphenated carbon nanotube networks are grown in-situ on stainless steel by chemical vapor deposition method followed by annealing treatment. Subsequently, MnO2 nanosheets are uniformly deposited on graphenated carbon nanotube networks to construct core-shell heterostructure based on the facile hydrothermal reaction using KMnO4 as the precursor. Core carbon nanotube networks can offer a stable structural backbone and shell MnO2 nanosheets can shorten diffusion paths of ions. The MnO2 nanosheets@graphenated carbon nanotube networks exhibit a high specific capacitance of 575.4 F g−1 (areal capacitance of 274 mF cm−2) at the current density of 0.5 mA cm−2 and good cycling stability (93% of capacity retention after 6000 cycles), due to the synergistic effects between pseudocapacitive MnO2 nanosheets and conductive carbon nanotube networks. The developed synthetic strategy offers design guidelines for the construction of advanced binder-free electrodes for high-performance supercapacitors.

Facile Fabrication of Nickel Aluminum Layered Double Hydroxide/Carbon Nanotube Electrodes Toward High-Performance Supercapacitors.

The electrode, as one of the key components in supercapacitors, has a pivotal effect on the overall performances. In this work, a series of composite electrode materials are proposed via the combination of nickel aluminum layered double hydroxides (NiAl-LDHs) and carbon nanotubes (CNTs). To begin with, materials with different ratios of the two compositions are fabricated with a coprecipitation method. After that, various characterization methods indicate that the NiAl-LDH/CNT composites exhibit an irregular thin platelet structure with a well-constructed conductive network inside. Furthermore, the effect of the CNT ratio on the electrochemical property is subsequently investigated, which proves that the conductive network of CNTs is beneficial for the transport of the electrons and strengthens the platelet structure. The results show that when the amount of CNTs reaches 1.5 wt %, it can yield a high specific capacitance of 2447 F g–1 at 2 A g–1, with a good cycling stability of 90.1% after 2500 cycles, indicating high application potential in positive electrodes of pseudocapacitors. The synergistic effects of NiAl-LDHs and CNTs are thought to be the main reasons for the good properties of NiAl-LDHs/CNTs composites.

Self-assembly of carbon nanotube/graphitic-like flake/BiOBr nanocomposite with 1D/2D/3D heterojunctions for enhanced photocatalytic activity

A self-assembled nanocomposite of lamellar BiOBr covalently bonded with conductive network of dispersive one-dimensional carbon nanotubes (1D CNT) and two-dimensional reduced graphitic-like flakes (2D GF) had been in situ constructed using one-pot facile solvothermal technique. Through self-assembly, BiOBr/CNT/GF (BiOBr/CG) displayed three-dimensional architectures in which a strong interfacial contact interaction and covalent banding between BiOBr nanostructures and CNT/GF network appeared. Furthermore, visible-light-driven catalytic activity of BiOBr/CG for RhB dye degradation was superior to that of pure BiOBr or BiOBr/C. Interestingly, the photodegradation activity of the BiOBr/CG nanocomposite could be improved further by subsequent facile annealing treatment, in which the annealed BiOBr/CG-DS had degraded almost 97.9% of RhB dye within only 100 min of visible-light irradiation. Moreover, analysis of the photodegradation mechanism revealed that the repression of electron-hole recombination in the nanocomposites, with sufficient covalent interfacial contact with CNT/GF as effective electron collecting and transferring system, were responsible for the outstanding photocatalytic performance. This effect, in turn, led to the continuous generation of O2− and OH reactive oxygen species for the degradation of RhB dye, which was verified by active species trapping and ESR spectra.

3D Printing of Highly Sensitive and Large-Measurement-Range Flexible Pressure Sensors with a Positive Piezoresistive Effect.

Piezoresistive composite-based flexible pressure sensors often suffer from a trade-off between the sensitivity and measurement range. Moreover, the sensitivity or measurement range is theoretically limited owing to the negative piezoresistive coefficient, resulting in resistance variation below 100%. Here, flexible pressure sensors were fabricated using the three-dimensional (3D) printing technique to improve both the sensitivity and sensing range through the positive piezoresistive effect. With the addition of carbon nanotubes (CNTs) and fumed silica nanoparticles (SiNPs) as a conductive filler and rheology modifier, respectively, the viscoelastic silicone rubber solution converted to a printable gel ink. Soft and porous composites (SPCs) were then directly printed in air at room temperature. The sensitivity and sensing range of the SPC-based pressure sensor can be simultaneously tuned by adjusting the conducting CNT and insulating SiNP contents. By optimizing the density of the CNT conductive network in the matrix, positive piezoresistive sensitivity (+0.096 kPa-1) and a large linear sensing range (0-175 kPa) were obtained. To demonstrate potential applications, the completely soft SPC-based sensor was successfully used in grasp sensing and gait monitoring systems. The 3D printed sensors were also assembled as a smart artificial sensory array to map the pressure distribution.

Tailoring sensing properties of smart cementitious composites based on excluded volume theory and electrostatic self-assembly

The excluded volume effect is the reduction in free volume of a matrix filled by secondary fillers, which can enhance the conductive network of carbon nanotubes (CNTs) composites and work effectively with microscale secondary fillers. Besides, the electrostatic self-assembly method has been proved effective for dispersing CNTs. Therefore, this study aims to assemble microscale TiO2 with CNTs to develop smart cementitious composites, in an effort to tailor the sensing properties based on the excluded volume theory and electrostatic self-assembly method. The results show the composites with CNT/TiO2 have a high sensitivity, a wide stress/strain monitoring range, and acceptable mechanical properties. In elastic state, the strain sensitivity of cementitious composites can reach 317. The composite can monitor the compressive stress from 0 to 80.7 MPa, with the maximum fractional change in resistivity as high as 84.09%. Furthermore, due to its low water absorption property, the CNT/TiO2 filler exhibits little negative effect on the mechanical properties of cementitious materials with best piezoelectric performance.

Hierarchical peony-like FeCo-NC with conductive network and highly active sites as efficient electrocatalyst for rechargeable Zn-air battery

Carbon materials featuring hierarchical pores and atomically dispersed metal sites are promising catalysts for energy storage and conversion applications. Herein, we developed a facile strategy to construct functional carbon materials with a fluffy peony-like structure and dense binary FeCo-N active sites (termed as f-FeCo-CNT). By regulating the metal content in precursors, a three-dimensional (3D) interconnected conductive carbon nanotubes network was in-situ formed throughout the atomically dispersed FeCo-NC matrix during pyrolysis. Taking advantage of rich pore hierarchy and co-existence of highly active FeCo-N sites and beneficial FeCo alloy nanoparticles, the f-FeCo-CNT material exhibited excellent bifunctional performance towards oxygen reduction reaction/oxygen evolution reactions (ORR/OER) with respect to the atomically dispersed FeCo-NC (SA-f-FeCo-NC) and commercial Pt/C+RuO mixture, surpassing the SA-f-FeCo-NC with a 20 mV higher ORR half-wave potential and a 100 mV lower OER overpotential (at 10.0 mA/cm). Remarkably, the f-FeCo-CNT-assembled Zn-air battery (ZAB) possessed a maximum specific power of 195.8 mW/cm, excellent rate capability, and very good cycling stability at large current density of 20.0 mA/cm. This work provides a facile and feasible synthetic strategy of constructing low-cost cathode materials with excellent comprehensive ZAB performance. [Figure not available: see fulltext.].

Selective Microwave Sintering to Prepare Multifunctional Poly(ether imide) Bead Foams Based on Segregated Carbon Nanotube Conductive Network

Carbon nanotube/poly(ether imide) (CNT/PEI) bead foam parts featuring a lightweight and segregated conductive network were prepared by a judicious combination of selective microwave (MW) sintering and carbon dioxide/tetrahydrofuran (CO₂/THF) co-foaming. This way endowed the CNT/PEI conductive foam with adjustable cellular structure and tunable performance by simply changing the CNT content and MW processing condition. Owing to its unique structure, the CNT/PEI conductive foam (0.28 g/cm³) with a CNT content of 0.90 vol % presented a good electrical conductivity (20.7 S/m) and electromagnetic interference (EMI) shielding performance (30.3 dB). In addition, the CNT/PEI conductive foam exhibited an ultralow percolation threshold (0.029 vol %) and presented superior piezoresistive performance under an applied pressure of 0–3.5 MPa and strain of 0–10%, due to the “condensation–recovery” transition mechanism of the integral CNT network of the conductive foam. This study provided an innovative approach to fabricate high-performance polymer bead foam parts with multifunctionality.

Winding-Locked Carbon Nanotubes/Polymer Nanofibers Helical Yarn for Ultrastretchable Conductor and Strain Sensor.

Wearable and stretchable electronics including various conductors and sensors are featured with their lightweight, high flexibility, and easy integration into functional devices or textiles. However, most flexible electronic materials are still unsatisfactory due to their poor recoverability under large strain. Herein, we fabricated a carbon nanotubes (CNTs) and polyurethane (PU) nanofibers composite helical yarn with electrical conductivity, ultrastretchability, and high stretch sensitivity. The synergy of elastic PU molecules and spring-like microgeometry enable the helical yarn excellent stretchability, while CNTs are stably winding-locked into the yarn through a simple twisting strategy, making good conductivity. By virtue of the interlaced conductive network of CNTs in microlevel and the helical structure in macrolevel, the CNTs/PU helical yarn achieves good recoverability within 900% and maximum tensile elongation up to 1700%. With these features, it can be used as a superelastic and highly stable conductive wire. Moreover, it also can monitor the human motion as a rapid-response strain sensor by adjusting the content of the CNTs simply. This general and low-cost strategy is of great promise for ultrastretchable wearable electronics and multifunctional devices.

Lightweight and Robust Carbon Nanotube/Polyimide Foam for Efficient and Heat-Resistant Electromagnetic Interference Shielding and Microwave Absorption.

Excellent electromagnetic interference (EMI) shielding ability, light weight, and good heat resistance are highly required for practical applications of EMI shielding materials, such as in areas of aerospace, aircraft, and automobiles. Herein, a lightweight and robust carbon nanotube (CNT)/polyimide (PI) foam was developed for efficient and heat-resistant EMI shielding. Thanks to poly(vinyl pyrrolidone) (PVP) as a surfactant that not only promotes the uniform dispersion of CNTs to form perfect CNT conductive networks but also can be removed in situ during the polymerization process, the density of resultant CNT/PI foam is only 32.1 mg·cm-3, and the EMI shielding effectiveness (EMI SE) is up to 41.1 dB, which represents one of the highest EMI SE values compared to previously reported polymer-based foams. The CNT/PI foam also achieves the absorption coefficient (A) of up to 82.3%, which is very impressive in CNT/polymer foams at comparable EMI SE levels. The PI matrix endows the foam with excellent heat resistance. The as-prepared CNT/PI foam presents a higher EMI SE than 35 dB even after being subjected to the flame of an alcohol burner. Moreover, the compressive strength and compressive modulus are up to 240.9 and 323.9 kPa. These results indicate its certain application potential in the harsh requirement of aeronautics and aerospace industries as a highly efficient and lightweight EMI shielding material.

Cu2SnSe3/CNTs Composite as a Promising Anode Material for Sodium-ion Batteries

Metal selenides as anode materials for sodium-ion batteries have attracted considerable attention owing to their high theoretical specific capacities and variable composition and structures. However, the achievement of long cycle life and superior rate performance is challenging for these selenide materials due to the volume variation upon cycling. Herein, a composite composed of a new binary-metal selenide[Cu2SnSe3(CSS)] and carbon nanotubes(CNTs) was constructed via a hydrothermal process followed by calcination at 600 °C. Benefited from the unique structure of binary-metal selenide and the conductive network of CNTs, the Cu2SnSe3/carbon nanotubes(CSS/CNT) composite exhibits excellent electrochemical performance when used as an anode material for sodium-ion batteries. A reversible specific capacity of 399 mA·h/g can be maintained at a current density of 100 mA/g even after 100 cycles. This work provides a promising strategy for rational design of binary-metal selenides upon delicate crystal phase control as electrode materials.

3D confined zinc plating/stripping with high discharge depth and excellent high-rate reversibility

Confining Zn plating and stripping in a robust and conductive 3D carbon nanotube network results in an electrode, which shows excellent reversibility at high depth of discharge and enables zinc-ion batteries with high-rate and long-term performance.

Encapsulating tin oxide nanoparticles into holey carbon nanotubes by melt infiltration for superior lithium and sodium ion storage

Design and development of alternative anode materials is of essential importance to power electronic vehicles and portable devices. As a promising candidate, tin oxide (SnO2) shows great potential for lithium and sodium storage due to its relatively high capacity and excellent safety. However, the SnO2 anode is suffering from its poor conductivity and large volume variation during charge/discharge process. Herein, a controllable and effective strategy is proposed by encapsulating SnO2 nanoparticles into the interior space of holey carbon nanotubes (hCNT). Such a conductive carbon nanotube networks could not only enhance the electronic conductivity of SnO2, but also provide abundant void space to accommodate the volume variation. As a result, the SnO2@hCNT electrode exhibits superior lithium and sodium ion storage performance. At a discharge current density of 100 mA g−1, the SnO2@hCNT could deliver reversible discharge capacity of 1192 mA h g−1 and 223 mA h g−1 for lithium and sodium ion storage, respectively. Even at high current density of 2000 mA g−1, the SnO2@hCNT also shows excellent rate performance and cyclic stability. Our results suggest that storing and transporting Li/Na ions in the interior space of hCNT should be one of the promising approaches to develop novel anode materials.

Integrated electrochromic supercapacitors with visual energy levels boosted by coating onto carbon nanotube conductive networks

Conductive polymer polyaniline (PANI) demonstrates potential applications in developing integrated smart energy devices based on the bi-functional electrochromic optical modulation and electrochemical energy storage. One challenge is to improve the structural stability of PANI films in response to repeating doping and dedoping of anions during the electrochemical redox process. Herein, a facile and effective approach is developed for improving the electrochemical performance of PANI by coating onto the carbon nanotube (CNT) conductive networks. The introduction of CNT firstly provides multiple directions for electron transfer and thus enhances the charge capacity of PANI. Then, the polymerization of PANI onto the CNT (PANI@CNT) contributes to the formation of a 3D network film, which effectively reduces the structural failure caused by anions intercalation and extraction. Compared with compact PANI film, a substantial promotion of bi-function achieves in the porous PANI@CNT one, whose optical transmittance modulation increases to over 40% and the specific capacitance of the initial cycle is almost tripled. On the basis of reversible and stable chromatic transitions between different charged states, the PANI@CNT electrode is further developed to be a smart electrochromic supercapacitor exhibiting visual energy storage level. We expect that this work may lead to new designs of robust smart energy storage devices.

High energy density and low self-discharge of a quasi-solid-state supercapacitor with carbon nanotubes incorporated redox-active ionic liquid-based gel polymer electrolyte

To achieve a quasi-solid-state supercapacitor (SC) with high energy density and low self-discharge, a redox-active poly(vinyl alcohol) (PVA)-based gel polymer electrolyte (GPE) is synthesized by the addition of 1-butyl-3-methylimidazolium bromide (BMIMBr) ionic liquid (IL) and carbon nanotubes (CNTs) into a PVA aqueous solution, followed by the addition of Li2SO4 and then the removal of excess water. The influences of BMIMBr-to-PVA and CNTs-to-PVA mass ratios on the ionic conductivity of GPE are discussed. The maximum ionic conductivity of GPE can reach 61.1 mS cm−1. A SC consisting of the optimized GPE and a pair of activated carbon (AC) electrodes exhibits a high energy density of 43.1 Wh kg−1, which can be assigned to the wide working voltage of 1.8 V as a result of the strong solvation effect of Li+ cations and SO42− anions, pseudocapacitance contribution from the redox reaction of Br−/Br3− at the electrolyte/electrode interface, and the three-dimensional (3D) conductive network of CNTs throughout the PVA matrix providing transport channel to facilitate ion transport. And the self-discharge is greatly suppressed due to the presence of 3D network of CNTs in the GPE. Additionally, the SC presents excellent cyclic stability.

Few-layer MoS2 nanosheets anchored by CNT network for superior lithium storage

A novel self-assembled porous network of carbon nanotubes (CNTs) attached to molybdenum disulfide (MoS2) nanosheets is prepared via a one-step atmospheric pressure chemical vapor deposition (APCVD) method. The conventional APCVD method cannot be used to uniformly deposit three-dimensional (3D) structures. Instead, an alternative method is used to overcome the disadvantage of conventional APCVD, whereby molybdenum oxide (MoO3) is decomposed by a molybdate ion (MoO42−) using in situ sulfuration. The synergy between the highly conductive CNT network and the layered MoS2 nanosheets contributes to the formation of high-efficiency ion/electron channels and improves the electrode durability and stability. The as-prepared C-MoS2/CNT composite exhibits both high rate stability and long-term capacity in lithium-ion batteries (LIBs). The C-MoS2/CNT electrode has a much higher initial discharge capacity of 1430 mAh g−1 at 100 mA g−1 and an impressive rate capability (885 mAh g−1 at 4000 mA g−1). Moreover, the C-MoS2/CNT composite also exhibits a long cycle life of 1260 mAh g−1 after 200 cycles at 500 mA g−1 and 1066 mAh g−1 at 1000 mA g−1 after 250 cycles. The mechanism and design strategy presented in this work may provide ideas for the development of other electrode materials.

Flexible and conductive scaffold-stabilized zinc metal anodes for ultralong-life zinc-ion batteries and zinc-ion hybrid capacitors

The merits of zinc metal anodes such as high chemical stability, low cost and ultrahigh volumetric capacity endow Zn based batteries/hybrid capacitors with great potential applications for electronic products. However, unstable stripping/plating of zinc anodes tends to cause the formation of protuberances/dendrites and side reactions such as water decomposition on anode surfaces, eventually leading to the failure of Zn based electrochemical energy storage devices. Herein, we report the fabrication of free-standing, highly flexible and conductive carbon nanotube (CNT)/paper scaffolds to stabilize zinc metal anodes. The free-standing CNT scaffolds only need to be placed between zinc anodes and separators when assembling zinc anode-based batteries/hybrid capacitors. On the surface of the zinc electrode, the scaffolds’ porous skeleton mechanically regulates Zn2+ deposition sites and their conductive CNT networks maintain a stable electric field during Zn stripping/plating processes, thus retarding the formation of protuberances/dendrites and the occurrence of side reactions. The scaffold-stabilized zinc anodes displayed small polarization voltages, a long cycling life over 1800 h and superior capability for fast charging-discharging. In addition, benefiting from the high electrochemical stability and reversibility of the scaffold-stabilized zinc anodes, zinc-ion batteries/hybrid capacitors with ultralong cycle lives were successfully constructed. This work provides a scalable approach to stabilize zinc metal anodes for long-life zinc-ion batteries and zinc-ion hybrid capacitors.

α-MnO2 nanofibers/carbon nanotubes hierarchically assembled microspheres: Approaching practical applications of high-performance aqueous Zn-ion batteries

Rechargeable Zn-ion batteries (ZIBs) have attracted extensive attention, but their practical application is hindered by the limited cycling life and complicated preparation process of cathode materials. Here, we develop a facile yet scalable chemical precipitation/spray-granulation combined methodology for the fabrication of α-MnO2 nanofibers/carbon nanotubes hierarchically assembled microspheres (α-MnO2/CNT HMs) as the cathode material for aqueous ZIBs. The α-MnO2 evenly anchoring to the CNTs-based framework shows significantly increased tap density compared with pristine α-MnO2, which can effectively enhance the electrochemical stability. Owing to the synergistic merits of highly conductive carbon nanotubes network and α-MnO2 nanofibers with desirable structure features, within our knowledge, the highest areal energy density of 0.98 Wh cm−2 at 0.2 A g−1 and the record cycling stability with 96% capacity retention over 10000 cycles at 3 A g−1 among the reported cathodes for ZIBs are achieved. Zn2+ and H+ co-insertion reaction mechanism with high reversibility is further revealed. Fast kinetic of the H+ insertion/extraction process renders the cell excellent cycling stability. Facile preparation of nanofibrous α-MnO2 based micro-composite, cost benefit of the source materials, and the superior battery performance provide new approaches for the practical applications of ZIBs.