Ultralight and highly compressible graphene aerogels

A three-dimensional graphene aerogel containing solvent-free polyaniline fluid for high performance supercapacitors

Conducting polymer based supercapacitors usually suffer from the difficulty of achieving high specific capacitance and good long-term stability simultaneously. In this communication, a long-chain protonic acid doped solvent-free self-suspended polyaniline (S-PANI) fluid and reduced graphene oxide (RGO) were used to fabricate a three-dimensional RGO/S-PANI aerogel via a simple self-assembled hydrothermal method, which was then applied as a supercapacitor electrode. This 3D RGO/S-PANI composite exhibited a high specific capacitance of up to 480 F g^-1 at a current density of 1 A g^-1 and 334 F g^-1 even at a high discharge rate of 40 A g^-1. An outstanding cycling performance, with 96.14% of the initial capacitance remaining after 10 000 charging/discharging cycles at a rate of 10 A g^-1, was also achieved. Compared with the conventional conducting polymer materials, the 3D RGO/S-PANI composite presented more reliable rate capability and cycling stability. Moreover, S-PANI possesses excellent processability, thereby revealing its enormous potential in large scale production. We anticipate that the solvent-free fluid technique is also applicable to the preparation of other 3D graphene/polymer materials for energy storage.

Ni2 P@Carbon Core-Shell Nanoparticle-Arched 3D Interconnected Graphene Aerogel Architectures as Anodes for High-Performance Sodium-Ion Batteries

To alleviate large volume change and improve poor electrochemical reaction kinetics of metal phosphide anode for sodium-ion batteries, for the first time, an unique Ni₂ P@carbon/graphene aerogel (GA) 3D interconnected porous architecture is synthesized through a solvothermal reaction and in situ phosphorization process, where core-shell Ni₂ P@C nanoparticles are homogenously embedded in GA nanosheets. The synergistic effect between components endows Ni₂ P@C/GA electrode with high structural stability and electrochemical activity, leading to excellent electrochemical performance, retaining a specific capacity of 124.5 mA h g^-1 at a current density of 1 A g^-1 over 2000 cycles. The robust 3D GA matrix with abundant open pores and large surface area can provide unblocked channels for electrolyte storage and Na⁺ transfer and make fully close contact between the electrode and electrolyte. The carbon layers and 3D GA together build a 3D conductive matrix, which not only tolerates the volume expansion as well as prevents the aggregation and pulverization of Ni₂ P nanoparticles during Na⁺ insertion/extraction processes, but also provides a 3D conductive highway for rapid charge transfer processes. The present strategy for phosphides via in situ phosphization route and coupling phosphides with 3D GA can be extended to other novel electrodes for high-performance energy storage devices.

Stabilized Lithium-Sulfur Batteries by Covalently Binding Sulfur onto the Thiol-Terminated Polymeric Matrices

Despite the low competitive cost and high theoretical capacity of lithium-sulfur battery, its practical application is severely hindered by fast capacity fading and limited capacity retention mainly caused by the polysulfide dissolution problem. Here, this paper reports a new strategy of using thiol-terminated polymeric matrices to prevent polysulfide dissolution, which exhibits an initial capacity of 829.1 mAh g^-1 , and the exceptionally stable capacity retention of ≈84% at 1 C after 200 cycles, and excellent cycling stability with a low mean decay rate of 0.048% after 600 cycles. Significantly, in situ UV/vis spectroscopy analysis of the electrolyte upon battery cycling is performed to verify the function of preventing polysulfide dissolution by means of strongly anchoring discharge products of lithium sulphides. Moreover, density functional theory calculations reveal that the breakage of the linear sulfur chains results in the less soluble short-chain polysulfides due to the formation of the covalently crosslinked discharge products, which avoids the production of soluble long-chain polysulfide and minimizes the shuttle effect. These results exhibit an alternative for the stabilization of the electrochemical performance of lithium-sulfur batteries.

Scalable synthesis of SnS2/S-doped graphene composites for superior Li/Na-ion batteries

Tin disulfide (SnS₂) has emerged as a promising anode material for lithium/sodium ion batteries (LIBs/SIBs) due to its unique layered structure, outstanding electrochemical properties and low cost. However, its poor cycling life and time-consuming synthesis as well as low-yield production hinder the practical utilization of nanostructured SnS₂. In this work, we demonstrate a simple and reliable dissolution-regeneration strategy to construct a flexible SnS₂/sulfur-doped reduced graphene oxide (S-rGO) composite as anodes for LIBs and SIBs, highlighting its mass-production feature. In addition, the robust affinity between SnS₂ and S-rGO without interstitial volume is very beneficial for preventing the SnS₂ particles from breaking themselves away from the rGO nanosheets into free nanoparticles. As a result, the SnS₂/S-rGO composite as anodes delivers high reversible capacities of 1078 mA h g^-1 and 564 mA h g^-1 (at 0.1 A g^-1) for LIBs and SIBs, respectively, and excellent rate capabilities and cycling stability (e.g. 532 mA h g^-1 during the 600 cycles at 5.0 A g^-1 for LIBs). Our proposed strategy may also possess great potential for the practical application of other electrochemically active metal sulfide composites for energy devices.

Hydrophilic and Compressible Aerogel: A Novel Draw Agent in Forward Osmosis

Forward osmosis (FO) technology is an efficient route to obtain purity water for drinking from wastewater or seawater. However, there are some challenges in draw solution to limit its application. We first introduce a novel sodium alginate-graphene oxide (SA-GO) aerogel as draw agent for highly efficient FO process. The GO nanosheets covalently cross-linked to SA matrix to form a three-dimensional and highly porous aerogel to provide excellent water flux and operation stability, together with the property of compressibility served by SA-GO aerogel resulting in easy water production and regeneration process. When deionized water was used as the feed solution, the SA-GO aerogel exhibited a higher water flux (15.25 ± 0.65 L m^-2 h^-1, abbreviated as LMH) than that of 1 mol L^-1 NaCl (1 M), and there was no nonreverse osmosis phenomenon. The water fluxes were stabilized in the range of 5-6.5 LMH during recycle process of absorbing and releasing water as high as 100 times. It also had a great desalination capacity (water flux was 7.49 ± 0.61 LMH) with the seawater (Huanghai coast) as the feed solution. Moreover, the water production and regeneration process of the SA-GO aerogel can be rapidly and cost-effectively accomplished with low-strength mechanical compression (merely 1 kPa). The results present that the SA-GO aerogels as a promising, innovative draw agent can make the FO process simpler, more efficient, and lower energy consumption. It can be a potential material for hydration bags to fast and repeatable product fresh water from saline water or wastewater.

Highly Compressible Integrated Supercapacitor-Piezoresistance-Sensor System with CNT-PDMS Sponge for Health Monitoring

Rapid improvement of wearable electronics stimulates the demands for the matched functional devices and energy storage devices. Meanwhile, wearable microsystem requires every parts possessing high compressibility to accommodate large-scale mechanical deformations and complex conditions. In this work, a general carbon nanotube-polydimethylsiloxane (CNT-PDMS) sponge electrode is fabricated as the elementary component of the compressible system. CNT-PDMS sponge performs high sensitivity as a piezoresistance sensor, which is capable of detecting stress repeatedly and owns great electrochemical performance as a compressible supercapacitor which maintains stably under compressive strains, respectively. Assembled with the piezoresistance sensor and the compressible supercapacitor, such highly compressible integrated system can power and modulate the low-power electronic devices reliably. More importantly, attached to the epidermal skin or clothes, it can detect human motions, ranging from speech recognition to breathing record, thus showing feasibility in real-time health monitor and human-machine interfaces.

Ultralight, Thermally Insulating, Compressible Polyimide Fiber Assembled Sponges

Tunable density, thermally and mechanically stable, elastic, and thermally insulating sponges are required for demanding applications. Hierarchically structured sponges with bimodal interconnected pores, porosity more than 99%, and tunable densities (between 7.6 and 10.1 mg/cm³) are reported using polyimide (PI) as high temperature stable polymer. The sponges are made by freeze-drying a dispersion of short PI fibers and precursor polymer, poly(amic acid) (PAA). The concept of "self-gluing" the fibrous network skeleton of PI during sponge formation was applied to achieve mechanical stability without sacrificing the thermal properties. The sponges showed initial degradation above 400 and 500 °C in air and nitrogen, respectively. They have low thermal conductivity of 0.026 W/mK and thermal diffusivity of 1.009 mm²/s for a density of 10.1 mg/cm³. The sponges are compressible for at least 10 000 cycles and good thermal insulators even at high compressions. These fibrous PI sponges are promising candidates for potential applications in thermal insulation, lightweight construction, high-temperature filtration, sensors, and catalyst carrier for high-temperature reactions.

Nickel skeleton three-dimensional nitrogen doped graphene nanosheets/nanoscrolls as promising supercapacitor electrodes

A novel nickel skeleton 3D nitrogen doped graphene (N-GR/NF) superstructure with interconnected graphene nanosheets and nanoscrolls was synthesized using a facile two-step method. By varying the precursor concentration, the assembly of a graphene aerogel can be easily regulated, yielding different micro-structures and morphologies which accelerate the fast electron/ion transportation. The N-GR/NF composites demonstrate enhanced capacitance of 250 F g^-1 at 5 A g^-1, good rate performance (237 F g^-1 at the current density of 12 A g^-1) and cycle stability (90.9% retention after 5000 cycles) in 1 M KOH electrolyte. This study provides a new strategy for the microporous engineering of graphene gel, promising for further exploitation in various other applications.

Extremely Low Density and Super-Compressible Graphene Cellular Materials

Development of extremely low density graphene elastomer (GE) holds the potential to enable new properties that traditional cellular materials cannot offer, which are promising for a range of emerging applications, ranging from flexible electronics to multifunctional scaffolds. However, existing graphene foams with extremely low density are generally found to have very poor mechanical resilience. It is scientifically intriguing but remains unresolved whether and how the density limit of this class of cellular materials can be further pushed down while their mechanical resilience is being retained. In this work, a simple annealing strategy is developed to investigate the role of intersheet interactions in the formation of extreme-low-density of graphene-based cellular materials. It is discovered that the density limit of mechanically resilient cellular GEs can be further pushed down as low as 0.16 mg cm^-3 through thermal annealing. The resultant extremely low density GEs reveal a range of unprecedented properties, including complete recovery from 98% compression in both of liquid and air, ultrahigh solvent adsorption capacity, ultrahigh pressure sensitivity, and light transmittance.

Microstructure Design of Lightweight, Flexible, and High Electromagnetic Shielding Porous Multiwalled Carbon Nanotube/Polymer Composites

Multiwalled carbon nanotube/polymer composites with aligned and isotropic micropores are constructed by a facile ice-templated freeze-drying method in a wide density range, with controllable types and contents of the nanoscale building blocks, in order to tune the shielding performance together with the considerable mechanical and electrical properties. Under the mutual promotion of the frame and porous structure, the lightweight high-performance shielding is achieved: a 2.3 mm thick sample can reach 46.7 and 21.7 dB in the microwave X-band while the density is merely 32.3 and 9.0 mg cm^-3 , respectively. The lowest density corresponds to a value of shielding effectiveness divided by both the density and thickness up to 10⁴ dB cm² g^-1 , far beyond the conductive polymer composites with other fillers ever reported. The shielding mechanism of the flexible porous materials is further demonstrated by an in situ compression experiment.

Wet-Spun Superelastic Graphene Aerogel Millispheres with Group Effect

Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high-performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost-effective scalable fabrication and miniaturization with group effect. This study shows millimeter-scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core-shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure-elastic and adsorbing materials. The GS shows a press-fly behavior with an extremely high jump velocity up to 1.2 m s^-1 . For the first time, both free and oil-adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties.

Oriented Arrangement: The Origin of Versatility for Porous Graphene Materials

Macroscopic porous graphene materials composed of graphene sheets have demonstrated their advantageous aspects in diverse application areas. It is essential to maximize their excellent performances by rationally controlling the sheet arrangement and pore structure. Bulk porous graphene materials with oriented pore structure and arrangement of graphene sheets are prepared by marrying electrolyte-assisted self-assembly and shear-force-induced alignment of graphene oxide sheets, and the super elasticity and anisotropic mechanical, electrical, and thermal properties induced by this unique structure are systematically investigated. Its application in pressure sensing exhibits ultrahigh sensitivity of 313.23 kPa^-1 for detecting ultralow pressure variation below 0.5 kPa, and it shows high retention rate for continuously intercepting dye molecules with a high flux of ≈18.7 L m^-2 h^-1 bar^-1 and a dynamic removal rate of 510 mg m^-2 h^-1 .

Rationally Incorporated MoS2/SnS2 Nanoparticles on Graphene Sheets for Lithium-Ion and Sodium-Ion Batteries

Herein, we have designed and first synthesized a unique ternary hybrid structure by simultaneously growing SnS₂ and MoS₂ particles on graphene sheets (denoted as MoS₂/SnS₂-GS) via one-pot hydrothermal route. The charge incompatibility between MoO₄^2- and graphene oxide with negative charged functional groups on surface can be compromised with the aid of Sn⁴⁺ cations, which renders the final formation of SnS₂ and MoS₂ on GS surface. This is the first report of the cohybridization of MoS₂ and SnS₂ with GS matrix from anionic and cationic precursors in the absence of premedication of graphene surface. When MoS₂/SnS₂-GS acts as anodes for lithium-ion batteries, the hybrids exhibit much better cycling stability than MoS₂-GS and SnS₂-GS counterparts. The compact adhesion of MoS₂/SnS₂ nanoparticles helps offset the undesired result of destruction of electrode materials resulting from volume expansion during repeated cycles. Furthermore, by combination with their synergetic effect on interface and the presence of discrepant asynchronous electrochemical reactions for SnS₂ and MoS₂, MoS₂/SnS₂-GS hybrids are endowed with improvement of electrochemical capabilities. Besides, they also showed outstanding Na-storage ability.

Ultralight Interconnected Graphene-Amorphous Carbon Hierarchical Foam with Mechanical Resiliency for High Sensitivity and Durable Strain Sensors

Ultralight graphene-amorphous carbon (AC) hierarchical foam (G-ACHF) was synthesized by chemical vapor deposition at 1065 °C, close to the melting point of copper. The high temperature leads to the hierarchical structure with an inner layer of graphene and an outer layer of AC. The inner graphene layer with high conductivity and integrity provides high sensitivity. The outer AC layer helps to enhance its durability and mechanical resiliency. The hierarchical structure recovers without damaging the structural integrity after a large strain of 90%. The electrical resistance of G-ACHF remains stable after 200 cycles of compression to a strain level of 50%. The fluctuation of the resistance value remains within ±3%, showing its stability in sensing performance. The pressure sensitivity of G-ACHF reaches as high as ∼11.47 Pa^-1. Finite element simulation reveals that the stress borne by the key position of G-ACHF is 47% lower than that of graphene foam without the AC layer, proving that the AC layer can disperse the stress effectively. With a very low density of 1.17 × 10^-3 g cm^-1, the reversibly compressible G-ACHF strain sensor material exhibits its promising application potential in lightweight and wearable devices.

Highly reusable and superhydrophobic spongy graphene aerogels for efficient oil/water separation

Graphene aerogels (GAs) are three-dimensional (3D) graphene sponges with unique wettability and have demonstrated the potential for reducing contamination from oil spills and chemical accidents. Herein, we report new polyurethane (PU) sponge-reinforced GAs with low surface energy, high sorption capacity and excellent recyclability for use as efficient oil sorbents. Spongy graphene aerogels (SGAs) with a hierarchical porous morphology were produced by simply freeze-casting reduced graphene oxide (rGO) to form compacted macroscale sponges. This novel micro-structure benefits from the advantages of embedded graphene and presents reversible large-strain deformation (90%), high compressive strength (63 kpa) and viscoelastic stability. These superior properties, in addition to super-hydrophobicity, endow the aerogels with excellent recyclability without deteriorating the oil absorption performance. Furthermore, SGA has selective and high-volume absorbability (>100%) and can efficiently separate oil from water under continuous pumping action. The excellent absorption performance and robust mechanical properties make this graphene material promising for the large-scale recovery of spilled oil.

High performance electrochemical glucose sensor based on three-dimensional MoS2/graphene aerogel

Two-dimensional (2D) nanosheets have been extensively explored as electrode materials for the development of high-performance electrochemical biosensors due to their unique structural characteristics. Nevertheless, 2D nanosheets suffer from sheet aggregation issues limiting the electrical conductivity of layered metal sulfides or hydroxides. Here, we report high-performance glucose biosensors based on a three-dimensional (3D) aerogel composed of interconnected 2D MoS₂ and graphene sheet. 3D MoS₂/graphene aerogel (MGA) provides a large surface area for the effective immobilization of enzymes, and continuous framework of electrically conductive graphene sheets. Flow-injection amperometric evaluation of the glucose biosensor using a 3D MGA electrode exhibits a rapid response (∼4s), a linear detection range from 2 to 20mM, a sensitivity of 3.36μA/mM, and a low limit of detection of 0.29mM. Moreover, the interference response from oxidizable species, such as ascorbic acid, uric acid and dopamine is negligible at an operating potential of -0.45V.

Ultrasensitive Pressure Sensor Based on an Ultralight Sparkling Graphene Block

Herein, we develop a supersensitive pressure sensor based on a fully air-bubbled ultralight graphene block through a simple sparkling strategy. The obtained sparkling graphene block (SGB) exhibits excellent elasticity even at 95% compressive strain and rebounds a steel ball with an ultrafast recovery speed (∼1085 mm s^-1). Particularly, the SGB-based sensor reveals a record pressure sensitivity of 229.8 kPa^-1, much higher than other graphene materials, because of the highly cavity-branched internal structure. Impressively, the pressure sensor can detect the extremely gentle pressures even beyond the real human skin and hence are promising for ultrasensitive sensing applications.

Low-Density, Mechanical Compressible, Water-Induced Self-Recoverable Graphene Aerogels for Water Treatment

Graphene aerogels (GAs) have demonstrated great promise in water treatment, acting as separation and sorbent materials, because of their high porosity, large surface area, and high hydrophobicity. In this work, we have fabricated a new series of compressible, lightweight (3.3 mg cm^-3) GAs through simple cross-linking of graphene oxide (GO) and poly(vinyl alcohol) (PVA) with glutaraldehyde. It is found that the cross-linked GAs (xGAs) show an interesting water-induced self-recovery ability, which can recover to their original volume even under extremely high compression strain or after vacuum-/air drying. Importantly, the amphiphilicity of xGAs can be adjusted facilely by changing the feeding ratio of GO and PVA and it exhibits affinity from polar water to nonpolar organic liquids depended on its amphiphilicity. The hydrophobic xGAs with low feeding ratio of PVA and GO can be used as adsorbent for organic liquid, while the hydrophilic xGAs with high feeding ratio of PVA and GO can be used as the filter material to remove some water-soluble dye in the wastewater. Because of the convenience of our approach in adjusting the amphiphilicity by simply changing the PVA/GO ratio and excellent properties of the resulting xGAs, such as low density, compressive, and water-induced self-recovery, this work suggests a promising technique to prepare GAs-based materials for the water treatment in different environment with high recyclability and long life.

Carbon Nanoparticle Hybrid Aerogels: 3D Double-Interconnected Network Porous Microstructure, Thermoelectric, and Solvent-Removal Functions

We report reduced graphene oxide (rGO)/single-walled carbon nanotube (SWCNT) hybrid aerogels with enhanced thermoelectric (TE) performance and removal of organic solvents by designing 3D double-interconnected network porous microstructures. A convenient, cost-effective, and scalable preparation procedure is proposed compared with conventional high-temperature pyrolysis and supercritical drying techniques. The obtained hybrid aerogels are systematically characterized by apparent density, scanning electron microscopy, X-ray photoemission spectroscopy, Raman spectroscopy, and porosity. An enhanced TE performance of ZT ≈ ∼8.03 × 10^-3 has been achieved due to the 3D double-interconnected network porous microstructure, the energy-filtering effect, and the phonon scattering at the abundant interfaces and joints. In addition, upon a large axial compression deformation, a high degree of retention of the Seebeck coefficient and a simultaneously significant enhancement of the electrical conductivity are observed. Finally, the hybrid aerogels display high capability for the removal of diverse organic solvents and good recyclability. These findings open a new avenue for exploiting aerogels with multifunctions and widening the applications of TE materials by judicious microstructure design.

Ultralight Multifunctional Carbon-Based Aerogels by Combining Graphene Oxide and Bacterial Cellulose

Nanostructured carbon aerogels with outstanding physicochemical properties have exhibited great application potentials in widespread fields and therefore attracted extensive attentions recently. It is still a challenge so far to develop flexible and economical routes to fabricate high-performance nanocarbon aerogels, preferably based on renewable resources. Here, ultralight and multifunctional reduced graphene oxide/carbon nanofiber (RGO/CNF) aerogels are fabricated from graphene oxide and low-cost, industrially produced bacterial cellulose by a three-step process of freeze-casting, freeze-drying, and pyrolysis. The prepared RGO/CNF aerogel possesses a very low apparent density in the range of 0.7-10.2 mg cm^-3 and a high porosity up to 99%, as well as a mechanically robust and electrically conductive 3D network structure, which makes it to be an excellent candidate as absorber for oil clean-up and an ideal platform for constructing flexible and stretchable conductors.

Spongy Structures Coated with Carbon Nanomaterials for Efficient Oil/Water Separation

Rapid progress of processing and transportation of oil and petroleum products may cause disaster for environment like oil spill. Oil booms, combustion, and oil skimmer vessels are usually used to clean up the oil spill, but often with poor efficiency and even with undesirable environmental side effects. With obtaining of carbon nanomaterials (CNMs) (graphene, carbon nanotubes) and developing inexpensive technologies for their synthesis it has become perspective to use them for creation of 3D structures which may serve as a hydrophobic sorbents for oil and petroleum products. In this study, sponges coated with carbon nanomaterials were obtained using “dip-coating” method. Walls of commercially available polyurethane (PU) and melamine sponges were coated with reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs). The resulting sponges are characterized by excellent mechanical properties, they are superhydprophobic, and they fully repel water and at the same time selectively absorb oil and organic liquids of different densities. We believe that superhydrophobic and superoleophilic sponges, the walls of which are coated with CNMs, are perspective candidates for reusable sorbents for collection of oil and petroleum products from the surface of water and moreover due to its excellent mechanical properties they can serve as a hydrophobic filtering materials for separation of oil from the surface of water.

Pressure-Sensitive and Conductive Carbon Aerogels from Poplars Catkins for Selective Oil Absorption and Oil/Water Separation

Multifunctional carbon aerogels that are both highly compressible and conductive have broad potential applications in the range of sound insulator, sensor, oil absorption, and electronics. However, the preparation of such carbon aerogels has been proven to be very challenging. Here, we report fabrication of pressure-sensitive and conductive (PSC) carbon aerogels by pyrolysis of cellulose aerogels composed of poplars catkin (PC) microfibers with a tubular structure. The wet PC gels can be dried directly in an oven without any deformation, in marked contrast to the brittle nature of traditional carbon aerogels. The resultant PSC aerogels exhibit ultralow density (4.3 mg cm^-3), high compressibility (80%), high electrical conductivity (0.47 S cm^-1), and high absorbency (80-161 g g^-1) for oils and organic liquids. The PSC aerogels have potential applications in various fields such as elastomeric conductors, absorption of oils from water and oil/water separation, as the PSC aerogels feature simple preparation process with low-cost biomass as the precursor.

Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries

Ultrafine SnS₂ nanocrystals-reduced graphene oxide nanoribbon paper (SnS₂-RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and sulfuration. The as-formed SnS₂ nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm^-3. The as-prepared SnS₂-RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS₂ nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508-244 mAh cm^-3 was obtained at current densities in the range of 0.1-10 A g^-1. Discharge capacities of 334 and 255 mAh cm^-3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g^-1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.

Highly Compressible Nitrogen-Doped Carbon Foam Electrode with Excellent Rate Capability via a Smart Etching and Catalytic Process

Freestanding three-dimensional nitrogen-doped carbon foam with large pores is proposed as a promising electrode configuration for elastic electronics. Although it exhibits excellent mechanical performance, the capacitive performances (especially its rate capability) are still unsatisfactory. By using KMnO₄, we demonstrate a smart etching and catalytic process to form highly graphitized and etched nitrogen-doped carbon foam (ENCF) with an exfoliated carbon-shell architecture. These compositional and structural features endow the ENCF electrodes with excellent electron conductivity as well as more ion-accessible electrochemical active sites. Significantly, all-solid-state symmetric supercapacitor devices based on the ENCF electrodes exhibit enhanced specific capacitance and marked high-rate capability. Furthermore, the integrated device has no significant capacity loss under 60% compressive strain.

Enhanced mechanical, thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-temperature thermal reduction

Graphene aerogels with high surface areas, ultra-low densities and thermal conductivities have been prepared to exploit their wide applications from pollution adsorption to energy storage, supercapacitor, and thermal insulation. However, the low mechanical properties, poor thermal stability and electric conductivity restrict these aerogels' applications. In this paper, we prepared mechanically strong graphene aerogels with large BET surface areas, low thermal conductivities, high thermal stability and electric conductivities via hydrothermal reduction and supercritical ethanol drying. Annealing at 1500 °C resulted in slightly increased thermal conductivity and further improvement in mechanical properties, oxidation temperature and electric conductivity of the graphene aerogel. The large BET surface areas, together with strong mechanical properties, low thermal conductivities, high thermal stability and electrical conductivities made these graphene aerogels feasible candidates for use in a number of fields covering from batteries to sensors, electrodes, lightweight conductor and insulation materials.

Flyweight 3D Graphene Scaffolds with Microinterface Barrier-Derived Tunable Thermal Insulation and Flame Retardancy

In this article, flyweight three-dimensional (3D) graphene scaffolds (GSs) have been demonstrated with a microinterface barrier-derived thermal insulation and flame retardancy characteristics. Such 3D GSs were fabricated by a modified hydrothermal method and a unidirectional freeze-casting process with hierarchical porous microstructures. Because of high porosity (99.9%), significant phonon scattering, and strong π-π interaction at the interface barriers of multilayer graphene cellular walls, the GSs demonstrate a sequence of multifunctional properties simultaneously, such as lightweight density, thermal insulating characteristics, and outstanding mechanical robustness. At 100 °C, oxidized GSs exhibit a thermal conductivity of 0.0126 ± 0.0010 W/(m K) in vacuum. The thermal conductivity of oxidized GSs remains relatively unaffected despite large-scale deformation-induced densification of the microstructures, as compared to the behavior of reduced GSs (rGSs) whose thermal conductivity increases dramatically under compression. The contrasting behavior of oxidized GSs and rGSs appears to derive from large differences in the intersheet contact resistance and varying intrinsic thermal conductivity between reduced and oxidized graphene sheets. The oxidized GSs also exhibit excellent flame retardant behavior and mechanical robustness, with only 2% strength decay after flame treatment. In a broader context, this work demonstrates a useful strategy to design porous nanomaterials with a tunable heat conduction behavior through interface engineering at the nanoscale.

Detecting Subtle Vibrations Using Graphene-Based Cellular Elastomers

Ultralight graphene elastomer-based flexible sensors are developed to detect subtle vibrations within a broad frequency range. The same device can be employed as an accelerometer, tested within the experimental bandwidth of 20-300 Hz as well as a microphone, monitoring sound pressures from 300 to 20 000 Hz. The sensing element does not contain any metal parts, making them undetectable by external sources and can provide an acceleration sensitivity of 2.6 mV/g, which is higher than or comparable to those of rigid Si-based piezoresistive microelectromechanical systems (MEMS).

Bacterial cellulose-based sheet-like carbon aerogels for the in situ growth of nickel sulfide as high performance electrode materials for asymmetric supercapacitors

Electroactive materials, such as nickel sulfide (NiS), with high theoretical capacities have attracted broad interest to fabricate highly efficient supercapacitors. Preventing aggregation and increasing the conductivity of NiS particles are key challenging tasks to fully achieve excellent electrochemical properties of NiS. One effective approach to solve these problems is to combine NiS with highly porous and conductive carbon materials such as carbon aerogels. In this study, a green and facile method for the in situ growth of NiS particles on bacterial cellulose (BC)-derived sheet-like carbon aerogels (CAs) has been reported. CA prepared by the dissolution-gelation-carbonization process was used as a framework to construct NiS/CA composite aerogels with NiS uniformly decorated on the pore walls of CA. It was found that the NiS/CA composite aerogel electrodes exhibit excellent capacitive performance with high specific capacitance (1606 F g^-1), good rate capacitance retention (69% at 10 A g^-1), and enhanced cycling stability (91.2% retention after 10 000 continuous cyclic voltammetry cycles at 100 mV s^-1). Furthermore, asymmetric supercapacitors (ASCs) were constructed utilizing NiS/CA composite and CA as the positive and negative electrode materials, respectively. Through the synergistic effect of three-dimensional porous structures and conductive networks derived from CA and the high capacitive performance offered by NiS, the ASC device exhibited an energy density of ∼21.5 Wh kg^-1 and a power density of 700 W kg^-1 at the working voltage of 1.4 V in 2 M KOH aqueous solution. The ASC device also showed excellent long-term cycle stability with ∼87.1% specific capacitance retention after 10 000 cycles of cyclic voltammetry scans. Therefore, the NiS/CA composite shows great potential as a promising alternative to high-performance electrode materials for supercapacitors.

Compressible, Dense, Three-Dimensional Holey Graphene Monolithic Architecture

By creating holes in 2D nanosheets, tortuosity and porosity can be greatly tunable, which enables a fast manufacturing process (i.e., fast removal of gas and solvent) toward various nanostructures. We demonstrated outstanding compressibility of holey graphene nanosheets, which is impossible for pristine graphene. Holey graphene powder can be easily compressed into dense and strong monoliths with different shapes at room temperature without using any solvents or binders. The remarkable compressibility of holey graphene, which is in sharp contrast with pristine graphene, not only enables the fabrication of robust, dense graphene products that exhibit high density (1.4 g/cm³), excellent specific mechanical strength [18 MPa/(g/cm³)], and good electrical (130 S/cm) and thermal (20 W/mK) conductivities, but also provides a binder-free dry process that overcomes the disadvantages of wet processes required for fabrication of three-dimensional graphene products. Fundamentally different from graphite, the holey graphene products are both dense and porous, which can enable possible broader applications such as energy storage and gas separation membranes.

Biocompatible, Ultralight, Strong Hydroxyapatite Networks Based on Hydroxyapatite Microtubes with Excellent Permeability and Ultralow Thermal Conductivity

In the past decade, ultralight materials such as aerogels have become one of the hottest research topics owing to their unique properties. However, most reported ultralight materials are bioinert. In this work, by using biocompatible, monodisperse, single-crystalline hydroxyapatite (HAP) microtubes as the building blocks, ultralight, strong, highly porous, three-dimensional (3-D) HAP networks have been successfully fabricated through a facile freeze-drying method and subsequent sintering at 1300 °C for 2 h. The as-prepared ultralight, strong, highly porous 3-D HAP microtube networks exhibit superior properties, such as ultrahigh porosity (89% to 96%), low density (94.1 to 347.1 mg/cm³), high compressive strength that can withstand more than 6400 times of their own weight without any fracture and is higher than aerogels with similar densities, and ultralow thermal conductivity (0.05 W/mK). Owing to their high porosity, ultralight, and good mechanical properties and high biocompatibility, the HAP microtube networks reported herein are promising for applications in various fields.

The extraction of uranium using graphene aerogel loading organic solution

A new approach for uranium extraction employing graphene aerogel (GA) as a skeleton loading organic solution (GA-LOS) is proposed and investigated. Firstly, the GA with super-hydrophobicity and high organic solution absorption capacity was fabricated by one-step reduction and self-assembly of graphene oxide with ethylenediamine. By adsorbing Tri-n-butyl phosphate (TBP)/n-dodecane solution to prepare GA-LOS, the extraction of U(VI) from nitric acid medium using GA-LOS was investigated and compared with conventional solvent extraction. It is found that the GA-LOS method can provide several advantages over conventional solvent extraction and adsorption due to the elimination of aqueous-organic mixing-separation procedures and easy solid-liquid separation. Furthermore, it also possesses higher extraction capacity (the saturated extraction capacity of GA loading TBP for U(VI) was 316.3mgg^-1 ) and lower consumption of organic diluents, leading to less organic waste. Moreover, the stability of GA-LOS in aqueous solution and cycling test were also studied, and it shows a remarkable regeneration capability, making it an ideal candidate for metal extraction from aqueous solution.

Greatly Suppressed Shuttle Effect for Improved Lithium Sulfur Battery Performance through Short Chain Intermediates

The high solubility of long-chain lithium polysulfides and their infamous shuttle effect in lithium sulfur battery lead to rapid capacity fading along with low Coulombic efficiency. To address above issues, we propose a new strategy to suppress the shuttle effect for greatly enhanced lithium sulfur battery performance mainly through the formation of short-chain intermediates during discharging, which allows significant improvements including high capacity retention of 1022 mAh/g with 87% retention for 450 cycles. Without LiNO₃-containing electrolytes, the excellent Coulombic efficiency of ∼99.5% for more than 500 cycles is obtained, suggesting the greatly suppressed shuttle effect. In situ UV/vis analysis of electrolyte during cycling reveals that the short-chain Li₂S₂ and Li₂S₃ polysulfides are detected as main intermediates, which are theoretically verified by density functional theory (DFT) calculations. Our strategy may open up a new avenue for practical application of lithium sulfur battery.

CNT-enhanced amino-functionalized graphene aerogel adsorbent for highly efficient removal of formaldehyde

Graphene aerogels modified using two different methods were investigated for their capacities to adsorb gaseous formaldehyde.

3D nitrogen-doped graphene gels as robust and sustainable adsorbents for dyes

Herein, a series of 3D nitrogen-doped graphene gels (NG) were synthesized for the removal of dyes from wastewater.

Graphene/MnO2 aerogel with both high compression-tolerance ability and high capacitance, for compressible all-solid-state supercapacitors

Graphene/MnO₂ electrodes for compressible all-solid-state supercapacitors show good compression-tolerance ability and achieve high volumetric capacitance under 90% compressive strain.

Robust ambient pressure dried polyimide aerogels and their graphene oxide directed growth of 1D–2D nanohybrid aerogels using water as the only solvent

Through soft/hard template directed hydrothermal polymerization, we reported the first green approach to the morpho-controlled synthesis of monolithic polyimide aerogels and their graphene nanohybrid aerogel using nothing but water.

Moldable clay-like unit for synthesis of highly elastic polydimethylsiloxane sponge with nanofiller modification

A clay-like unit is beneficial for the moldable synthesis of a superelastic polydimethylsiloxane sponge with nanofiller modification via an ultrasound-assisted in situ polymerization approach.

Three-dimensional nitrogen and boron codoped graphene for carbon dioxide and oils adsorption

Three-dimensional heteroatom-doped graphene macroporous structures possess superior features, such as the large pore volume, numerous surface active sites and the high specific surface area.

Effect of flake size on the mechanical properties of graphene aerogels prepared by freeze casting

Graphene flake size has a profound effect on the mechanical performance of the assembled graphene aerogels, particularly their strength, modulus and fatigue resistance under compression.