Carbon Nanotube Aerogels Research Articles

Crosslinked Carbon Nanotube Aerogel Films Decorated with Cobalt Oxides for Flexible Rechargeable Zn-Air Batteries.

Air electrodes with high catalytic activity are of great importance for rechargeable zinc-air batteries. Herein, a flexible, binder-free composite air electrode for zinc-air batteries is reported, which utilizes a lightweight, conductive, and crosslinked aerogel film of carbon nanotubes (CNTs) functioned as a 3D catalyst-supporting scaffold for bifunctional cobalt (II/III) oxides and as a current collector. The composite electrode shows high catalytic activities for both oxygen reduction reaction and oxygen evolution reaction, resulting from the synergistic effect of nitrogen-doped CNTs and spinel Co3 O4 nanoparticles. Solid-state Zn-air batteries assembled using such free-standing air electrodes (without the need of additional current collectors) are bendable and show low resistances, low charge/discharge overpotentials, and a high cyclic stability.

Self-Expansion Construction of Ultralight Carbon Nanotube Aerogels with a 3D and Hierarchical Cellular Structure.

A novel and simple strategy is developed to construct ultralight and 3D pure carbon nanotube (CNT) aerogels by the spontaneous expansion of superaligned CNT films soaked in a piranha (mixed H2 SO4 and H2 O2 ) solution, followed by cryodesiccation. The macroscopic CNT aerogels have an extremely low apparent density (0.12 mg cm-3 ), ultrahigh porosity (99.95%), high specific surface area (298 m2 g-1 ), and a hierarchical cellular structure with giant and ultrathin CNT sheets as cell walls. The pure CNT aerogels show high adsorption abilities for various kinds of solvents, and have great potential in widespread applications such as energy storage, catalysis, and bioengineering.

Fabrication of α-FeOOH decorated graphene oxide-carbon nanotubes aerogel and its application in adsorption of arsenic species

Arsenic pollution has caused worldwide attention due to its mandatory toxicity. Chemical structures of the adsorbent and arsenic species greatly influence the arsenic adsorption efficiency. The goethite impregnated graphene oxide (GO)-carbon nanotubes (CNTs) aerogel (α-FeOOH@GCA) was prepared via a facile self-assembly method of GO-CNTs induced by in-situ Fe2+ reduction. α-FeOOH@GCA showed excellent adsorption capacities of 56.43, 24.43 and 102.11mgg−1 for As(V), DMA and p-ASA comparing with that of 25.71, 8.03 and 14.52mgg−1 of pristine α-FeOOH, respectively. The incorporation of GO-CNTs not only hinders the aggregation of GO-CNTs but also inhibits the growth of α-FeOOH nanoparticles greatly facilitating the diffusion and adsorption capacity of arsenic species. α-FeOOH@GCA shows wide favorable application pH for arsenic species adsorption, high adsorption kinetics and excellent reusability. The phosphate and silicate anions compete with the arsenic species for active adsorption sites due to the similar anionic structure. Based on FTIR spectra, arsenic species were proven to form inner sphere complex on the surface of α-FeOOH@GCA through different ligand exchanging mechanism greatly dependent on the molecular structures of arsenic species. The results show that α-FeOOH@GCA could be used as promising adsorbent for arsenic purification in water system.

(Invited) Multifunctional Graphene-Coated Carbon Nanotube Aerogels

Lightweight, superelastic foams that resist creep and fatigue over a broad temperature range are being developed as structural and functional materials for use in numerous diverse applications. Unfortunately, conventional foams display superelasticity degradation, undergo considerable creep, show fatigue under repeated usage, or fracture over large strains, particularly under significant temperature variations. We have developed lightweight (density ≈ 14 mg/mL; corresponding volume fraction ≈ 9 × 10-3) graphene-coated single-walled carbon nanotube (SWCNT) aerogels that remain superelastic, and resist fatigue and creep over a broad temperature range of -100–500 °C. We fabricate these materials by first creating a three-dimensional inelastic network of SWCNTs and then coating the junctions between SWCNTs with 2–5 layers of ≈ 3 nm long graphene nanoplatelets. Compressive stress (σ) versus compressive strain (ε) curves show that the aerogels fully recover their shapes even when strained by at least 80% over -100–300 °C and 20% at 500 °C, while the Young’s modulus remains similar over the temperature (-100–500 °C) and strain rate (0.01–0.16 1/s) ranges. The storage (E′) and loss moduli (E″) measured in the linear regime show ultralow damping ratio (tan δ = E″/E′) ≈ 0.02, and these viscoelastic properties remain constant over three decades of frequencies (0.628–628 rad/s) and across -100–500 °C. The low loss in these aerogels is corroborated by exceptional fatigue resistance for 2000 (5 × 105) cycles at ε = 60% (1%) from -100–300 °C (-100–500 °C) and creep resistance at least under σ = 20 kPa, corresponding to ε = 4%, for a minimum of 30 minutes from -100–300 °C. Interestingly, the aerogels can be readily densified while retaining the microstructure and temperature-invariant thermomechanical properties to at least a volume fraction of 0.26 that reach E′ ≈ 1 GPa. The mechanical properties, high surface area, and large porosity make these aerogels highly suitable electrodes for electrochemical applications. For example, these aerogels show a high capacitance in both aqueous and room-temperature ionic liquid (RTIL) electrolytes, achieving between 60 and100 F/g, respectively, with the performance stable over hundreds of charge/discharge cycles and at high rates exceeding 1 V/s. This performance is retained fully under 90% compression of the systems, allowing us to construct cells with high volumetric capacitances of ≈ 5−18 F/cm3 in aqueous and RTIL electrolytes, respectively. Furthermore, the aerogels can be coated with noble metals and metal oxides to fabricate electrodes for fuel cells and pseudocapacitors, respectively, without compromising the mechanical properties. The emergent thermomechanical stability of these aerogels that arises from, in part, microscopic deformations of the graphene-coated junctions, motivate junction modification as a means to generate emergent properties in CNT. For example, substituting graphene with other two-dimensional materials such as boron nitride that also impart superelasticity to SWCNT aerogels, could add other desirable properties such as chemical inertness to temperature invariance. This work has been partially supported by the NSF through Grant CMMI 1335417 and US Army Research Office through grant W911NF-14-1-0651.

Enhanced Visible Light Photocatalytic Activity of Carbon Nanotube Aerogels Decorated with Titania By Phase Selective Interface Engineering

Composites of photocatalysts such as titania (TiO2) and various carbon allotropes such as carbon nanotubes (CNTs) are being extensively explored because of enhanced visible light response resulting from interfacial bonding between photocatalysts and carbon that extends light absorption bandwidth and reduces recombination of photogenerated carriers through efficient interfacial charger transfer. We have developed highly visible-light photoactive composites comprised of anatase-TiO2 nanoparticles decorated on single-wall CNT (SWCNT) aerogels (TiO2/SWCNT). SWCNT aerogels are three-dimensional, highly porous network of isotropically oriented SWCNTs. We used X-ray photoelectron spectroscopy to establish interfacial bonding between TiO2 and SWCNTs mediated through Ti–C and Ti–O–C bonds, narrowing the absorption edge to ≈ 2.4eV as confirmed by absorbance spectroscopy and greatly reducing the interfacial resistance as corroborated by electrochemical impedance spectroscopy, giving rise to visible-light photoactivity. The composites rapidly degrade methylene blue dyes at a rate of 56 μmol/h/g and exhibit a high photocurrent density of 80 μA/cm2 under visible-light. In contrast, composites prepared by mechanically mixing TiO2 and SWCNTs exhibit no photoactivity in the visible-light and only slight photoactivity in the white-light. Moreover, transformation of TiO2 from anatase to rutile phase lead to a reduction in the Ti–O–C bonds, likely during crystal structure reorganization associated with anatase-to-rutile phase transformation, markedly decreasing the dye degradation rate and photocurrent density in visible-light by ≈ 50%. Our work demonstrates the impact of interfacial bonds on emergent visible-light photocatalytic response of TiO2/SWCNT heterogeneous photocatalysts and provides guidance in designing new heterocatalysts based on SWCNT aerogels for efficient solar energy conversion. This work has been partially supported by the NSF through Grant CMMI 1335417.

Freestanding Graphene-Coated Carbon Nanotube Aerogels Decorated with Metal Nanoparticles As High Performance Electrodes for Ethanol Oxidation

There has been increasing demand to develop sustainable energy sources with high energy-conversion efficiency. Direct ethanol fuel cells (DEFCs) are one type of clean power source that is promising for a variety of applications. DEFCs typically consist of an anodic chamber that oxidizes ethanol and transfers electrons via an external circuit to a cathodic chamber that reduces oxygen. Nobel metals such as platinum (Pt) and palladium (Pd) are often used as electrocatalysts for the ethanol oxidation reaction (EOR) in the DEFC anode because of their intrinsic electrochemical properties. Unfortunately, cost and poor market supply require manipulating structural features of catalysts including shapes, sizes, and compositions to achieve optimal benefit from Pt and Pd. Further, to realize the utility of DEFCs in these applications, they must be cheap, lightweight, highly efficient, and stable over long operation lifetimes. We have developed DEFCs with enhanced electrochemical performance using three different electrocatalysts (Pt, Pd, and Pd-Pt core-shell nanoparticles) supported on graphene-coated carbon nanotube aerogels. These three-dimensional, porous aerogels are lightweight, and provide easy transport pathways for fuel and ions. The ultrahigh surface area of the aerogels allows deposition of small catalyst nanoparticles, while the graphene coating hinders coarsening of the nanoparticles during operation, improving the DEFC lifetime. The catalysts are spherical nanoparticles of diameter ≈ 5 nm (Pt), ≈ 8 nm (Pd), and ≈ 9 nm (Pd-Pt core-shell). The current densities of our DEFCs in alkaline media are ≈ 118 mA/cm2 with Pt, ≈ 150 mA/cm2 with Pd, and ≈ 283 mA/cm2 with Pd-Pt core-shell electrocatalysts, which are at least an order of magnitude larger than that of DEFCs that utilize commercially available electrodes, typically comprised of Pd nanoparticles supported on carbon black. Further, the performance of our DEFCs shows minimal degradation of 30–60% over 1,000 cycles. This work has been partially supported by the NSF through Grant CMMI 1335417 and US Army Research Office through grant W911NF-14-1-0651.

Strong graphene-interlayered carbon nanotube films with high thermal conductivity

Fast growing flexible and wearable electronics and devices require thermal management materials having not only high thermal conductivity but also structural flexibility with mechanical robustness. However, most developed thermal management materials are relatively rigid and have low strength. Herein, we report a carbon nanotube/graphene hybrid film that combines high thermal conductivity (up to 1056 W/(mK)), extraordinary structural flexibility, and high mechanical strength (∼1 GPa). Such film consists of alternately stacked aligned, long and thin carbon nanotube sheets, which provide a mechanically strong and thermally conductive scaffold, and graphene sheets, which act as a highly conductive component. The hybrid film was prepared by in-situ spraying graphene oxide sheet solution onto an aligned, freestanding carbon nanotube aerogel sheet during winding the sheet on a rotating mandrel, followed by high-temperature annealing. Experimental and theoretical results suggested that the removal of defects of the hybrid films and the formation of covalent bonding between carbon nanotubes and graphene sheets resulted in improved thermal conductivities and mechanical strength. Application of such film as an orientational heat spreader has been demonstrated.

Graphene-Coated Carbon Nanotube Aerogels Remain Superelastic while Resisting Fatigue and Creep over −100 to +500 °C

Lightweight, superelastic foams that resist creep and fatigue over a broad temperature range are being developed as structural and functional materials for use in numerous diverse applications. Unfortunately, conventional foams display superelasticity degradation, undergo considerable creep, show fatigue under repeated usage, or fracture over large strains, particularly under significant temperature variations. We report that graphene-coated single-walled carbon nanotube (SWCNT) aerogels remain superelastic, and resist fatigue and creep over a broad temperature range of −100–500 °C. The microstructure of these ultralow density (≈14 mg/mL; corresponding volume fraction ≈9 × 10–3) aerogels is composed of a three-dimensional network of randomly oriented SWCNTs with junctions between SWCNTs coated with 2–5 layers of ≈3 nm long graphene nanoplatelets. Compressive stress (σ) versus compressive strain (e) curves show that the aerogels fully recover their shapes even when strained by at least 80% over −100–300 °C...

Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts.

Self-assembled M-N-doped carbon nanotube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe-N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.

Electroconductive properties of zirconia/carbon nanotube aerogel composite

Electroconductive properties of zirconia/multiwalled carbon nanotube aerogel composite are investigated. The composite exhibits bulk percolation cluster-like conductivity at wide range of spatial scales. Conductive atomic force microscopy reveals the localized nature of conductive properties of the composite on the micro(nano)scopic scale and the uniformity of current distribution in all conductive areas independently of their size. The presence of unlinked conductive chains and the possibility of their linking by dissociating ions are demonstrated in experiments on registration of I–V curves during the evacuation of the composite impregnated with distilled water. The experimental data make it possible to describe the electrical properties of the composite as the properties of a circuit formed by the parallel connections of numerous voltage dividers arranged in a bulk porous structure. These features make the synthesized composite a promising candidate for use in catalysis and water vapor sensors.

Three-Dimensional Graphene/Single-Walled Carbon Nanotube Aerogel Anchored with SnO2 Nanoparticles for High Performance Lithium Storage

A unique 3D graphene-single walled carbon nanotube (G-SWNT) aerogel anchored with SnO2 nanoparticles (SnO2@G-SWCNT) is fabricated by the hydrothermal self-assembly process. The influences of mass ratio of SWCNT to graphene on structure and electrochemical properties of SnO2@G-SWCNT are investigated systematically. The SnO2@G-SWCNT composites show excellent electrochemical performance in Li-ion batteries; for instance, at a current density of 100 mA g-1, a specific capacity of 758 mAh g-1 was obtained for the SnO2@G-SWCNT with 50% SWCNT in G-SWCNT and the Coulombic efficiency is close to 100% after 200 cycles; even at current density of 1 A g-1, it can still maintain a stable specific capacity of 537 mAh g-1 after 300 cycles. It is believed that the 3D G-SWNT architecture provides a flexible conductive matrix for loading the SnO2, facilitating the electronic and ionic transportation and mitigating the volume variation of the SnO2 during lithiation/delithiation. This work also provides a facile and reasonable strategy to solve the pulverization and agglomeration problem of other transition metal oxides as electrode materials.

Nanospherical solid electrolyte interface layer formation in binder-free carbon nanotube aerogel/Si nanohybrids to provide lithium-ion battery anodes with a long-cycle life and high capacity.

Silicon anodes for lithium ion batteries (LiBs) have been attracting considerable attention due to a theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle causes cracks in the silicon, resulting in the degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and an unstable solid electrolyte interface (SEI) layer resulting from repeated changes in volume still block the next step forward for the commercialization of the silicon material. Herein we demonstrate the carbon nanotube (CNT) aerogel/Si nanohybrid structure for anode materials of LiBs via freeze casting followed by an RF magnetron sputtering process, exhibiting improved capacity retention compared to Si only samples during 1000 electrochemical cycles. The CNT aerogels as 3D porous scaffold structures could provide buffer volume for the expansion/shrinkage of Si lattices upon cycling and increase electrical conductivity. In addition, the nanospherical and relatively thin SEI layers of the CNT aerogel/Si nanohybrid structure show better lithium ion diffusion characteristics during cycling. For this reason, the Si@CNT aerogel anode still yielded a high specific capacity of 1439 mA h g-1 after 1000 charge/discharge cycles with low capacity fading. Our approach could be applied to other group IV LiB materials that undergo large volume changes, and also has promising potential for high performance energy applications.

Vapor and Pressure Sensors Based on Cellulose Nanofibers and Carbon Nanotubes Aerogel with Thermoelectric Properties

Vapor and Pressure Sensors Based on Cellulose Nanofibers and Carbon Nanotubes Aerogel with Thermoelectric Properties

Carbon Nanotube and Graphene Aerogels – The World’s 3D Lightest Materials for Environment Applications: A Review

Carbon Nanotube and Graphene Aerogels (CNTAs & GAs)- the world’s lightest 3D materials (GA isseven times lighter than air - a cubic meter weighs just 160 grams) attracted widespread attention due to their excellent mechanical compressible properties, high temperature and thermal stability, recyclable and highly efficient organic pollutants adsorption capability (GA can absorb up to 900 times its own weight in oil and do so quickly, with one gram of Aerogel able to absorb up to 68.8 grams of organics per second). In this review, we present briefly recent progress in synthesis methods for fabrication of 3D CNTAs andGAs and their emerging applications in the field of environmental protection such as removingoil, organic pollutants, arsenic ions and other toxic metalsfrom water. Furthermore, to assist advanced research for practical applications of these 3D materials, the technical challenges are discussed, and future research directions are proposed.

Ag@Pd nanoparticles immobilized on a nitrogen-doped graphene carbon nanotube aerogel as a superb catalyst for the dehydrogenation of formic acid

Catalytic dehydrogenation of formic acid by silver palladium supported on a nitrogen-doped graphene carbon nanotube aerogel.

Creep- and fatigue-resistant, rapid piezoresistive responses of elastomeric graphene-coated carbon nanotube aerogels over a wide pressure range.

Lightweight, flexible piezoresistive materials with wide operational pressure ranges are in demand for applications such as human physical activity and health monitoring, robotics, and for functional interfacing between living systems and wearable electronics. Piezoresistivity of many elastomeric foams of polymers and carbon allotropes satisfies much of the required characteristics for these applications except creep and fatigue resistance due to their viscoelasticity, critically limiting the reliability and lifetime of integrated devices. We report the piezoresistive responses from aerogels of graphene-coated single-walled carbon nanotubes (SWCNTs), made using a facile and versatile sol-gel method. Graphene crosslinks the junctions of the underlying random network of SWCNTs, generating lightweight elastomeric aerogels with a mass density of ≈11 mg mL-1 (volume fraction ≈7.7 × 10-3) and a Young's modulus of ≈0.4 MPa. The piezoresistivity of these aerogels spans wide compressive pressures up to at least 120 kPa with sensitivity that exhibit ultrafast temporal responses of <27 ms and <3% delay ratio over 104 compressive loading-unloading cycles at rates between 0.1-10 Hz. Most importantly, the piezoresistive responses do not show any creep at least for 1 hour and 80 kPa of compressive static loading. We suggest that the fatigue- and creep-resistant, ultrafast piezoresistive responses of these elastomeric aerogels are highly attractive for use in dynamic and static lightweight, pressure sensing applications such as human activity monitoring and soft robotics.

Utilization of carboxylic functional groups generated during purification of carbon nanotube fiber for its strength improvement

One of the most promising method to produce carbon nanotube (CNT) fiber is directly spinning CNT fiber from CNT aerogel. Despite the advantage of this method in terms of productivity, the CNTs thus produced include impurities such as amorphous carbon and residual catalysts. To remove these unwanted materials, the CNT fiber is usually subjected to acid treatment. At the same time, however, the acid treatment damages the CNT wall, creating functional groups on it. In this work, specific tensile strength of CNT fibers was increased by introducing cross-links between the individual CNTs using carboxylic functional groups which were inevitably generated during the acid treatment of CNT fibers. The esterification of the carboxylic acid with 1,5-pentanediol as a linker resulted in cross-links in between the CNTs, thereby increasing the specific strength of the CNT fiber from 0.43 to 1.12N/tex and Young’s modulus from 30.70 to 47.57N/tex. Supporting weak shear interactions of untreated CNT fiber by adding covalent bonding through the cross-linking reaction led to the improvement of mechanical properties of the CNT fiber. Elimination of impurities and narrowed interspacing between CNT bundles caused by acid treatment was also confirmed, which additionally contributed to enhancing the mechanical properties of CNT fiber.

Knitted Carbon-Nanotube-Sheath/Spandex-Core Elastomeric Yarns for Artificial Muscles and Strain Sensing.

Highly stretchable, actuatable, electrically conductive knitted textiles based on Spandex (SPX)/CNT (carbon nanotube) composite yarns were prepared by an integrated knitting procedure. SPX filaments were continuously wrapped with CNT aerogel sheets and supplied directly to an interlocking circular knitting machine to form three-dimensional electrically conductive and stretchable textiles. By adjusting the SPX/CNT feed ratio, the fabric electrical conductivities could be tailored in the range of 870 to 7092 S/m. The electrical conductivity depended on tensile strain, with a linear and largely hysteresis-free resistance change occurring on loading and unloading between 0% and 80% strain. Electrothermal heating of the stretched fabric caused large tensile contractions of up to 33% and generated a gravimetric mechanical work capacity during contraction of up to 0.64 kJ/kg and a maximum specific power output of 1.28 kW/kg, which far exceeds that of mammalian skeletal muscle. The knitted textile provides the combination of strain sensing and the ability to control dimensions required for smart clothing that simultaneously monitors the wearer's movements and adjusts the garment fit or exerts forces or pressures on the wearer, according to needs. The developed processing method is scalable for the fabrication of industrial quantities of strain sensing and actuating smart textiles.

Aerogels based on carbon nanomaterials

Carbon nanomaterial-based aerogels have attracted significant interests from both academia and industry due to their extremely low bulk density, tunable surface functionality, high specific surface area, dielectric strength and thermal and electrical properties, and diverse applications. There is currently a lack of understanding of how processing factors would determine the structure–property relationships important to the wide applications of these aerogels. The present work thoroughly examines the preparation, structure, properties and applications of three types of aerogels. Firstly, we briefly review carbon aerogels prepared from the sol–gel of certain organic monomers, where the synthesis and processing conditions determine the structural features, such as pore volume and pore size distribution. Secondly, carbon nanotube (CNT) aerogels made by three methods are discussed to identify their relative advantageous over carbon aerogels in terms of electrical conductivity and mechanical robustness. Finally, graphene aerogels are reviewed, which can be prepared by four routes—template-directed CVD, in situ reduction assembly, template-directing assembly and cross-linking. In comparison with CNT aerogels, graphene aerogels can be made at lower manufacturing costs to achieve appropriate properties meeting various needs. The major applications of these aerogels include flexible energy storage devices and environmental applications, both of which exploit the key characteristics of carbon aerogels such as low density and high porosity, deformability, mechanical robustness, electrical conductivity, adsorption and electro-sorption. Challenges, research opportunities and future applications are also discussed.

Carbon Nanotube Sponges, Aerogels, and Hierarchical Composites: Synthesis, Properties, and Energy Applications

Carbon nanotube (CNT) aerogels and sponges are macroscopic porous materials with a unique isotropic structure. CNTs make an interconnected 3D scaffold, therefore the resulting aerogels are robust, highly conductive, and flexible, enabling a much broader range of applications than aligned arrays and thin films, especially in energy and environmental areas. A comprehensive overview of the recent progress in isotropic CNT‐based macroscopic structures is provided, including their synthesis methods, structural characteristics, mechanical properties, and deformation mechanism, as well as potential applications in energy and environmental fields. In particular, this study focuses on the CNT sponges developed, which are high‐performance porous materials with many distinct properties such as their versatile deformations and shape recovery. Importantly, the CNT sponges provide a universal platform for designing and manufacturing a variety of hierarchical functional composites by introducing polymers or inorganic guests, thus greatly extend application areas from highly compressible electrodes for supercapacitors and batteries, catalysis, to environmental cleanup. Future research directions and associated challenges in this field are proposed.