Direct 3D Printing of Ultralight Graphene Oxide Aerogel Microlattices

Graphene aerogel microlattices (GAMs) hold great prospects for many multifunctional applications due to their low density, high porosity, designed lattice structures, good elasticity, and tunable electrical conductivity. Previous 3D printing approaches to fabricate GAMs require either high content of additives or complex processes, limiting their wide applications. Here, a facile ion‐induced gelation method is demonstrated to directly print GAMs from graphene oxide (GO) based ink. With trace addition of Ca²⁺ ions as gelators, aqueous GO sol converts to printable gel ink. Self‐standing 3D structures with programmable microlattices are directly printed just in air at room temperature. The rich hierarchical pores and high electrical conductivity of GAMs bring admirable capacitive performance for supercapacitors. The gravimetric capacitance (C_s) of GAMs is 213 F g^?1 at 0.5 A g^?1 and 183 F g^?1 at 100 A g^?1, and retains over 90% after 50 000 cycles. The facile, direct 3D printing of neat graphene oxide can promote wide applications of GAMs from energy storage to tissue engineering scaffolds.     

Prolifera‐Green‐Tide as Sustainable Source for Carbonaceous Aerogels with Hierarchical Pore to Achieve Multiple Energy Storage

The increasing demand for efficient energy storage and conversion devices has aroused great interest in designing advanced materials with high specific surface areas, multiple holes, and good conductivity. Here, we report a new method for fabricating a hierarchical porous carbonaceous aerogel (HPCA) from renewable seaweed aerogel. The HPCA possesses high specific surface area of 2200 m² g^?1 and multilevel micro/meso/macropore structures. These important features make HPCA exhibit a reversible lithium storage capacity of 827.1 mAh g^?1 at the current density of 0.1 A g^?1, which is the highest capacity for all the previously reported nonheteroatom‐doped carbon nanomaterials. It also shows high specific capacitance and excellent rate performance for electric double layer capacitors (260.6 F g^?1 at 1 A g^?1 and 190.0 F g^?1 at 50 A g^?1), and long cycle life with 91.7% capacitance retention after 10 000 cycles at 10 A g^?1. The HPCA also can be used as support to assemble Co₃O₄ nanowires (Co₃O₄@HPCA) for constructing a high performance pseudocapacitor with the maximum specific capacitance of 1167.6 F g^?1 at the current density of 1 A g^?1. The present work highlights the first example in using prolifera‐green‐tide as a sustainable source for developing advanced carbon porous aerogels to achieve multiple energy storage.     

Reconciling Mass Loading and Gravimetric Performance of MnO2 Cathodes by 3D-Printed Carbon Structures for Zinc-Ion Batteries

To promote the real application of zinc-ion batteries (ZIBs), reconciling the high mass loading and gravimetric performance of MnO₂ electrodes is of paramount importance. Herein, the rational regulation of 3D-printed carbon microlattices (3DP CMs) enabling an ultrathick MnO₂ electrode with well-maintained gravimetric capacities is demonstrated. The 3DP CMs made of graphene and carbon nanotubes (CNTs) are fabricated by direct ink 3D printing and subsequent high-temperature annealing. 3D printing enables a periodic structure of 3DP CMs, while the thermal annealing contributes to high conductivity and defective surfaces. Due to these structural merits, uniform electrical field distribution and facilitated MnO₂ deposition over the 3DP CMs are permitted. The optimal electrode with MnO₂ loaded on the 3DP CMs can achieve a record-high specific capacity of 282.8 mAh g⁻¹ even at a high mass loading of 28.4 mg cm⁻² and high ion transfer dynamics, which reconciles the loading mass and gravimetric performance. As a result, the aqueous ZIBs based on the 3DP CMs loaded MnO₂ afford an outstanding performance superior to most of the previous reports. This study reveals the essential role of interaction between active materials and current collectors, providing an alternative strategy for designing high-performance energy storage devices.     

In Situ Preparation of Sandwich MoO3/C Hybrid Nanostructures for High‐Rate and Ultralong‐Life Supercapacitors

This work presents a design of sandwich MoO₃/C hybrid nanostructure via calcination of the dodecylamine‐intercalated layered α‐MoO₃, leading to the in situ production of the interlayered graphene layer. The sample with a high degree of graphitization of graphene layer and more interlayered void region exhibits the most outstanding energy storage performance. The obtained material is capable of delivering a high specific capacitance of 331 F g^?1 at a current density of 1 A g^?1 and retained 71% capacitance at 10 A g^?1. In addition, nearly no discharge capacity decay between 1000 and 10 000 continuous charge–discharge cycles is observed at a high current density of 10 A g^?1, indicating an excellent specific capacitance retention ability. The exceptional rate capability endows the electrode with a high energy density of 41.2 W h kg^?1 and a high power density of 12.0 kW kg^?1 simultaneously. The excellent performance is attributed to the sandwich hybrid nanostructure of MoO₃/C with broad ion diffusion pathway, low charge‐transfer resistance, and robust structure at high current density for long‐time cycling. The present work provides an insight into the fabrication of novel electrode materials with both enhanced rate capability and cyclability for potential use in supercapacitor and other energy storage devices.     

Highly Elastic and Conductive N‐Doped Monolithic Graphene Aerogels for Multifunctional Applications

The simple synthesis of ultralow‐density (≈2.32 mg cm^?3) 3D reduced graphene oxide (rGO) aerogels that exhibit high electrical conductivity and excellent compressibility are described herein. Aerogels are synthesized using a combined hydrothermal and thermal annealing method in which hexamethylenetetramine is employed as a reducer, nitrogen source, and graphene dispersion stabilizer. The N‐binding configurations of rGO aerogels increase dramatically, as evidenced by the change in pyridinic‐N/quaternary‐N ratio. The conductivity of this graphene aerogel is ≈11.74 S m^?1 at zero strain, whereas the conductivity at a compressive strain of ≈80% is ≈704.23 S m^?1, which is the largest electrical conductivity reported so far in any 3D sponge‐like low‐density carbon material. In addition, the aerogel has excellent hydrophobicity (with a water contact angle of 137.4°) as well as selective absorption for organic solvents and oils. The compressive modulus (94.5 kPa; ρ ≈ 2.32 mg cm^?3) of the rGO aerogel is higher than that of other carbon‐based aerogels. The physical and chemical properties (such as high conductivity, elasticity, high surface area, open pore structure, and chemical stability) of the aerogel suggest that it is a viable candidate for the use in energy storage, electrodes for fuel cells, photocatalysis, environmental protection, energy absorption, and sensing applications.     

Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density,Excellent Rate Capability,and Long Cycle Life

The utilization of Ni(OH)₂ as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)₂ deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)₂ is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g^?1 at 5 mV s^?1 and excellent rate capability (71.9% capacitance retention at 100 mV s^?1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)₂ nanomaterials. Using the ternary Ni(OH)₂ hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg^?1 at the power density of 780 W kg^?1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)₂ can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.     

Flexible Solid‐State Supercapacitors with Enhanced Performance from Hierarchically Graphene Nanocomposite Electrodes and Ionic Liquid Incorporated Gel Polymer Electrolyte

High energy density, durability, and flexibility of supercapacitors are required urgently for the next generation of wearable and portable electronic devices. Herein, a novel strategy is introduced to boost the energy density of flexible soild‐state supercapacitors via rational design of hierarchically graphene nanocomposite (GNC) electrode material and employing an ionic liquid gel polymer electrolyte. The hierarchical graphene nanocomposite consisting of graphene and polyaniline‐derived carbon is synthesized as an electrode material via a scalable process. The meso/microporous graphene nanocomposites exhibit a high specific capacitance of 176 F g^?1 at 0.5 A g^?1 in the ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIBF₄) with a wide voltage window of 3.5 V, good rate capability of 80.7% in the range of 0.5–10 A g^?1 and excellent stability over 10 000 cycles, which is attributed to the superior conductivity (7246 S m^?1), and quite large specific surface area (2416 m² g^?1) as well as hierarchical meso/micropores distribution of the electrode materials. Furthermore, flexible solid‐state supercapacitor devices based on the GNC electrodes and gel polymer electrolyte film are assembled, which offer high specific capacitance of 180 F g^?1 at 1 A g^?1, large energy density of 75 Wh Kg^?1, and remarkable flexible performance under consecutive bending conditions.     

High‐Performance Supercapacitors Based on a Zwitterionic Network of Covalently Functionalized Graphene with Iron Tetraaminophthalocyanine

Graphene derivatives are promising candidates as electrode materials in supercapacitor cells, therefore, functionalization strategies are pursued to improve their performance. A scalable approach is reported for preparing a covalently and homogenously functionalized graphene with iron tetraaminophthalocyanine (FePc‐NH₂) with a high degree of functionalization. This is achieved by exploiting fluorographene's reactivity with the diethyl bromomalonate, producing graphene‐dicarboxylic acid after hydrolysis, which is conjugated with FePc‐NH₂. The material exhibits an ultrahigh gravimetric specific capacitance of 960 F g^?1 at 1 A g^?1 and zero losses upon charging–discharging cycling. The energy density of 59 Wh kg^?1 is eminent among supercapacitors operating in aqueous electrolytes with graphene‐based electrode materials. This is attributed to the structural and functional synergy of the covalently bound components, giving rise to a zwitterionic surface with extensive π–π stacking, but not graphene restacking, all being very beneficial for charge and ionic transport. The safety of the proposed system, owing to the benign Na₂SO₄ aqueous electrolyte, the high capacitance, energy density, and potential of preparing the electrode material on a large‐scale and at low cost make the reported strategy very attractive for development of supercapacitors based on the covalent attachment of suitable molecules onto graphene toward high‐synergy hybrids.     

Multilayer‐Folded Graphene Ribbon Film with Ultrahigh Areal Capacitance and High Rate Performance for Compressible Supercapacitors

Limited by 2D geometric morphology and low bulk packing density, developing graphene‐based flexible/compressible supercapacitors with high specific capacitances (gravimetric/volumetric/areal), especially at high rates, is an outstanding challenge. Here, a strategy for the synthesis of free‐standing graphene ribbon films (GRFs) for high‐performance flexible and compressible supercapacitors through blade‐coating of interconnected graphene oxide ribbons and a subsequent thermal treatment process is reported. With an ultrahigh mass loading of 21 mg cm^?2, large ion‐accessible surface area, efficient electron and ion transport pathways as well as high packing density, the compressed multilayer‐folded GRF films (F‐GRF) exhibit ultrahigh areal capacitance of 6.7 F cm^?2 at 5 mA cm^?2, high gravimetric/volumetric capacitances (318 F g^?1, 293 F cm^?3), and high rate performance (3.9 F cm^?2 at 105 mA cm^?2), as well as excellent cycling stability (109% of capacitance retention after 40 000 cycles). Furthermore, the assembled F‐GRF symmetric supercapacitor with compressible and flexible characteristics, can deliver an ultrahigh areal energy density of 0.52 mWh cm^?2 in aqueous electrolyte, almost two times higher than the values obtained from symmetric supercapacitors with comparable dimensions.     

Hierarchical Composite Electrodes of Nickel Oxide Nanoflake 3D Graphene for High‐Performance Pseudocapacitors

NiO nanoflakes are created with a simple hydrothermal method on 3D (three‐dimensional) graphene scaffolds grown on Ni foams by microwave plasma enhanced chemical vapor deposition (MPCVD). Such as‐grown NiO‐3D graphene hierarchical composites are then applied as monolithic electrodes for a pseudo‐supercapacitor application without needing binders or metal‐based current collectors. Electrochemical measurements impart that the hierarchical NiO‐3D graphene composite delivers a high specific capacitance of ≈1829 F g^?1 at a current density of 3 A g^?1 (the theoretical capacitance of NiO is 2584 F g^?1). Furthermore, a full‐cell is realized with an energy density of 138 Wh kg^?1 at a power density of 5.25 kW kg^?1, which is much superior to commercial ones as well as reported devices in asymmetric capacitors of NiO. More attractively, this asymmetric supercapacitor exhibits capacitance retention of 85% after 5000 cycles relative to the initial value of the 1^st cycle.     

Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density

Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost‐effective microwave‐assisted method. In order to achieve high energy and power densities, a high‐voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)₂/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high‐voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g^?1 and high energy density of 77.8 Wh kg^?1. Furthermore, the Ni(OH)₂/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.     

Asymmetric Supercapacitors Based on Graphene/MnO2 Nanospheres and Graphene/MoO3 Nanosheets with High Energy Density

Asymmetric supercapacitors with high energy density are fabricated using a self‐assembled reduced graphene oxide (RGO)/MnO₂ (GrMnO₂) composite as a positive electrode and a RGO/MoO₃ (GrMoO₃) composite as a negative electrode in safe aqueous Na₂SO₄ electrolyte. The operation voltage is maximized by choosing two metal oxides with the largest work function difference. Because of the synergistic effects of highly conductive graphene and highly pseudocapacitive metal oxides, the hybrid nanostructure electrodes exhibit better charge transport and cycling stability. The operation voltage is expanded to 2.0 V in spite of the use of aqueous electrolyte, revealing a high energy density of 42.6 Wh kg^?1 at a power density of 276 W kg^?1 and a maximum specific capacitance of 307 F g^?1, consequently giving rise to an excellent Ragone plot. In addition, the GrMnO₂//GrMoO₃ supercapacitor exhibits improved capacitance with cycling up to 1000 cycles, which is explained by the development of micropore structures during the repetition of ion transfer. This strategy for the choice of metal oxides provides a promising route for next‐generation supercapacitors with high energy and high power densities.     

All‐Solid‐State Asymmetric Supercapacitors with Metal Selenides Electrodes and Ionic Conductive Composites Electrolytes

All‐solid‐state flexible asymmetric supercapacitors (ASCs) are developed by utilization of graphene nanoribbon (GNR)/Co_0.85Se composites as the positive electrode, GNR/Bi₂Se₃ composites as the negative electrode, and polymer‐grafted‐graphene oxide membranes as solid‐state electrolytes. Both GNR/Co_0.85Se and GNR/Bi₂Se₃ composite electrodes are developed by a facile one‐step hydrothermal growth method from graphene oxide nanoribbons as the nucleation framework. The GNR/Co_0.85Se composite electrode exhibits a specific capacity of 76.4 mAh g^?1 at a current density of 1 A g^?1 and the GNR/Bi₂Se₃ composite electrode exhibits a specific capacity of 100.2 mAh g^?1 at a current density of 0.5 A g^?1. Moreover, the stretchable membrane solid‐state electrolytes exhibit superior ionic conductivity of 108.7 mS cm^?1. As a result, the flexible ASCs demonstrate an operating voltage of 1.6 V, an energy density of 30.9 Wh kg^?1 at the power density of 559 W kg^?1, and excellent cycling stability with 89% capacitance retention after 5000 cycles. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate high performance flexible all‐solid‐state ASCs for energy storage.     

High Electroactive Material Loading on a Carbon Nanotube@3D Graphene Aerogel for High‐Performance Flexible All‐Solid‐State Asymmetric Supercapacitors

Freestanding carbon‐based hybrids, specifically carbon nanotube@3D graphene (CNTs@3DG) hybrid, are of great interest in electrochemical energy storage. However, the large holes (about 400 µm) in the commonly used 3D graphene foams (3DGF) constitute as high as 90% of the electrode volume, resulting in a very low loading of electroactive materials that is electrically connected to the carbon, which makes it difficult for flexible supercapacitors to achieve high gravimetric and volumetric energy density. Here, a hierarchically porous carbon hybrid is fabricated by growing 1D CNTs on 3D graphene aerogel (CNTs@3DGA) using a facile one‐step chemical vapor deposition process. In this architecture, the 3DGA with ample interconnected micrometer‐sized pores (about 5 µm) dramatically enhances mass loading of electroactive materials comparing with 3DGF. An optimized all‐solid‐state asymmetric supercapacitor (AASC) based on MnO₂@CNTs@3DGA and Ppy@CNTs@3DGA electrodes exhibits high volumetric energy density of 3.85 mW h cm^?3 and superior long‐term cycle stability with 84.6% retention after 20 000 cycles, which are among the best reported for AASCs with both electrodes made of pseudocapacitive electroactive materials.     

3D Micro‐Extrusion of Graphene‐based Active Electrodes: Towards High‐Rate AC Line Filtering Performance Electrochemical Capacitors

A facile one‐step printing process by 3D micro‐extrusion affording binder‐free thermally reduced graphene oxide (TRGO) based electrochemical capacitors (ECs) that display high‐rate performance is presented. Key intermediates are binder‐free TRGO dispersion printing inks with concentrations up to 15 g L^?1. This versatile printing technique enables easy fabrication of EC electrodes, useful in both aqueous and non‐aqueous electrolyte systems. The as‐prepared TRGO material with high specific surface area (SSA) of 593 m² g^?1 and good electrical conductivity of ≈16 S cm^?1 exhibits impressive charge storage performances. At 100 and 120 Hz, ECs fabricated with TRGO show time constants of 2.5 ms and 2.3 ms respectively. Very high capacitance values are derived at both frequencies ranging from 3.55 mF cm^?2 to 1.76 mF cm^?2. Additionally, these TRGO electrodes can be charged and discharged at very high voltage scan rates up to 15 V s^?1 yielding 4 F cm^?3 with 50% capacitance retention. Electrochemical performance of TRGO electrodes in electrolyte containing tetraethyl ammonium tetrafluoroborate and acetonitrile (TEABF4‐ACN) yields high energy density of 4.43 mWh cm^?3 and power density up to 42.74 kW cm^?3, which is very promising for AC line filtering application and could potentially substitute state of the art electrolytic capacitor technology.     

Ultra‐High Surface Area Nitrogen‐Doped Carbon Aerogels Derived From a Schiff‐Base Porous Organic Polymer Aerogel for CO2 Storage and Supercapacitors

Nitrogen‐doped carbon aerogels (NCAs) have received great attention for a wide range of applications, from thermal electronics to waste water purification, heavy metal or gas adsorption, energy storage, and catalyst supports. Herein NCAs are developed via the synthesis of a Schiff‐base porous organic polymer aerogel followed by pyrolysis. By controlling the pyrolysis temperature, the polymer aerogel can be simply converted into porous NCAs with a low bulk density (5 mg cm^?3), high surface area (2356 m² g^?1), and high bulk porosity (70%). The NCAs containing 1.8–5.3 wt% N atoms exhibit remarkable CO₂ uptake capacities (6.1 mmol g^?1 at 273 K and 1 bar, 33.1 mmol g^?1 at 323 K and 30 bar) and high ideal adsorption solution theory selectivity (47.8) at ambient pressure. Supercapacitors fabricated with NCAs display high specific capacitance (300 F g^?1 at 0.5 A g^?1), fast rate (charge to 221 F g^?1 within only 17 s), and high stability (retained >98% capacity after 5000 cycles). Asymmetric supercapacitors assembled with NCAs also show high energy density and power density with maximal values of 30.5 Wh kg^?1 and 7088 W kg^?1, respectively. The outstanding CO₂ uptake and energy storage abilities are attributed to the ultra‐high surface area, N‐doping, conductivity, and rigidity of NCA frameworks.     

Oxygen Clusters Distributed in Graphene with “Paddy Land” Structure: Ultrahigh Capacitance and Rate Performance for Supercapacitors

The introduction of surface functional groups onto graphene can provide additional pseudocapacitance for supercapacitors. However, the compensation for the loss of electrical conductivity arising from the disruption of the conjugated system remains a big challenge. Here, a novel strategy is reported for the design of oxygen clusters distributed in graphene with “paddy land” structure via a low‐temperature annealing process. Moreover, the distribution, content, and variety of oxygen groups and the conductivity of reduced graphene oxide (RGO) can be easily adjusted by annealing temperature and time. First‐principles calculations demonstrate that “paddy land” structure exhibits conjugated carbon network, ultralow HOMO–LUMO gap, and long span of atomic charge values, which are beneficial for the enhanced pseudocapacitance and rate performance. As a result, the functionalized graphene (GO‐160‐8D) exhibits high specific capacitance of 436 F g^?1 at 0.5 A g^?1, exceeding the values of previously reported RGO materials, as well as excellent rate performance (261 F g^?1 at 50 A g^?1) and cycling stability (94% of capacitance retention after 10 000 cycles). The findings may open a door for finely controlling the location and density of functionalities on graphene for applications in energy storage and conversion fields via a green and energy‐efficient process.     

Electrochemically Derived Graphene‐Like Carbon Film as a Superb Substrate for High‐Performance Aqueous Zn‐Ion Batteries

3D graphene, as a light substrate for active loadings, is essential to achieve high energy density for aqueous Zn‐ion batteries, yet traditional synthesis routes are inefficient with high energy consumption. Reported here is a simplified procedure to transform the raw graphite paper directly into the graphene‐like carbon film (GCF). The electrochemically derived GCF contains a 2D–3D hybrid network with interconnected graphene sheets, and offers a highly porous structure. To realize high energy density, the Na:MnO₂/GCF cathode and Zn/GCF anode are fabricated by electrochemical deposition. The GCF‐based Zn‐ion batteries deliver a high initial discharge capacity of 381.8 mA h g^?1 at 100 mA g^?1 and a reversible capacity of 188.0 mA h g^?1 after 1000 cycles at 1000 mA g^?1. Moreover, a recorded energy density of 511.9 Wh kg^?1 is obtained at a power density of 137 W kg^?1. The electrochemical kinetics measurement reveals the high capacitive contribution of the GCF and a co‐insertion/desertion mechanism of H⁺ and Zn²⁺ ions. First‐principles calculations are also carried out to investigate the effect of Na⁺ doping on the electrochemical performance of layered δ‐MnO₂ cathodes. The results demonstrate the attractive potential of the GCF substrate in the application of the rechargeable batteries.     

3D Macroscopic Architectures from Self‐Assembled MXene Hydrogels

Assembly of 2D MXene sheets into a 3D macroscopic architecture is highly desirable to overcome the severe restacking problem of 2D MXene sheets and develop MXene‐based functional materials. However, unlike graphene, 3D MXene macroassembly directly from the individual 2D sheets is hard to achieve for the intrinsic property of MXene. Here a new gelation method is reported to prepare a 3D structured hydrogel from 2D MXene sheets that is assisted by graphene oxide and a suitable reductant. As a supercapacitor electrode, the hydrogel delivers a superb capacitance up to 370 F g^?1 at 5 A g^?1, and more promisingly, demonstrates an exceptionally high rate performance with the capacitance of 165 F g^?1 even at 1000 A g^?1. Moreover, using controllable drying processes, MXene hydrogels are transformed into different monoliths with structures ranging from a loosely organized porous aerogel to a dense solid. As a result, a 3D porous MXene aerogel shows excellent adsorption capacity to simultaneously remove various classes of organic liquids and heavy metal ions while the dense solid has excellent mechanical performance with a high Young's modulus and hardness.     

Gas Diffusion,Energy Transport,and Thermal Accommodation in Single‐Walled Carbon Nanotube Aerogels

The thermal conductivity of gas‐permeated single‐walled carbon nanotube (SWCNT) aerogel (8 kg m^?3 density, 0.0061 volume fraction) is measured experimentally and modeled using mesoscale and atomistic simulations. Despite the high thermal conductivity of isolated SWCNTs, the thermal conductivity of the evacuated aerogel is 0.025 ± 0.010 W m^?1 K^?1 at a temperature of 300 K. This very low value is a result of the high porosity and the low interface thermal conductance at the tube–tube junctions (estimated as 12 pW K^?1). Thermal conductivity measurements and analysis of the gas‐permeated aerogel (H₂, He, Ne, N₂, and Ar) show that gas molecules transport energy over length scales hundreds of times larger than the diameters of the pores in the aerogel. It is hypothesized that inefficient energy exchange between gas molecules and SWCNTs gives the permeating molecules a memory of their prior collisions. Low gas‐SWCNT accommodation coefficients predicted by molecular dynamics simulations support this hypothesis. Amplified energy transport length scales resulting from low gas accommodation are a general feature of CNT‐based nanoporous materials.