Compressible Graphene Research Articles

Preparation and electromagnetic wave absorption of compressible graphene aerogels

In this study, a developed easy-operation method was adopted to generate ultralight and compressible graphene aerogels by using graphene oxide and ammonia. By changing the process parameters, such as reduction temperature, reducing agent content and ammonia concentration, the variation laws of the density and pore size of aerogels were obtained, which aided in realizing the controllable preparation of aerogel structures. The prepared graphene aerogel has good compressive performance, and its density can reach 5.26 mg/cm3. Although it was repeatedly compressed 200 times under a load that was 4000 times as large as its own weight, it maintained its structural integrity and mechanical properties. An ideal model of three-dimensional graphene aerogel was constructed, and the electromagnetic wave absorption performance was simulated using the Computer Simulation Technology (CST) Microwave Studio software. The results showed that when the thickness, pore size and height of the sheet were 1.4, 5 and 14 mm, respectively, an optimal electromagnetic wave absorption effect of −31.08 dB could be obtained. Furthermore, the effects of thickness, pore size and height of the sheet on the electromagnetic wave absorption performance are revealed, which provide a reference for the structural design of aerogels with both compressibility and electromagnetic wave absorption performance.

Highly Compressible, Light-Weight and robust Nitrogen-Doped graphene composite aerogel for sensitive pressure sensors

The demand for compressible multifunctional carbon aerogels with reliable mechanical properties and high response sensitivity has increased in the competitive smart electronics era. This study presents a novel nitrogen-doped graphene composite aerogel that exhibits exceptional robustness, elasticity, and lightweight characteristics. The synthesis involves combining dispersions of Graphene Oxide (GO), Dopamine (DA), and Polyaniline (PANI), followed by chemical reduction, crosslinking at 90 °C, freeze-drying, and thermal annealing. The incorporation of flexible DA with the graphene sheet enhances the composite gel’s toughness, while the π-π stacking interaction between PANI and the graphene sheet strengthens the aerogel framework. The resulting composite aerogel, named GDPA demonstrates outstanding strength, toughness, and compressibility due to the combined effects of DA and PANI. Furthermore, GDPA is assembled into a pressure sensor that exhibits excellent compressive cycle stability. The sensor achieves a low detection limit of 0 Pa and a wide detection range of 0 to 25.48 kPa, surpassing the performance of most previously reported graphene-based aerogels. The remarkable properties of GDPA suggest its immense potential for application in healthcare detection, wearable electronics, and intelligent packaging.

Anisotropic Free-Standing Aerogels Based on Graphene/Silk for Pressure Sensing and Efficient Adsorption.

Compressible, conductive, ultralight, and superhydrophobic graphene aerogels (GAs) are promising for wearable electronics and adsorption applications. However, the unsatisfactory sensing performances and lack of multiscale structural regulation still impede the development of multifunctional GAs. Herein, a multifunctional aerogel based on graphene/silk is reported─a highly ordered three-dimensional (3D) reduced graphene oxide (rGO) conductive network is established by an alkali-induced hydrothermal self-assembly strategy, while silk fibroin (SF) bound to graphene oxide (GO) by electrostatic interactions is uniformly distributed throughout the network. The ultralight rGO/SF aerogel (GSA) has the property that its resistance varies with compression, so it can be used for flexible pressure sensors. A GSA-based sensor can detect compressive stresses down to 0.35 kPa and has a response time of 0.55 s and a recovery time of 0.58 s. It has a good linear response from 0.5 to 30 kPa with sensitivities of 0.54 kPa-1 (0.5-4 kPa) and 0.21 kPa-1 (4-30 kPa), respectively. The GSA-based sensor also has excellent durability, remaining stable after 12,000 cycles. As proof of concept, its applications for health monitoring, speech recognition, and motion capture are shown. Furthermore, the carbonized rGO/SF aerogels (C-GSAs) with superhydrophobicity can adsorb various organic substances (146.7-278.8 g/g) and achieve oil-water separation.

Rapid and facile fabrication of hierarchically porous graphene aerogel for oil-water separation and piezoresistive sensing applications

Graphene aerogel (GA) holds great potentials for versatile applications, for example, oil-water separation and piezoresistive sensing. However, GA is generally prepared via time-consuming and complicated methods. Herein, a rapid and facile approach has been proposed to fabricate GA by a two-step reduction method, i.e., hydrothermal reduction by thiourea at a mild temperature of 95 °C for 30 min followed by microwave treatment for several seconds, c.a., 4–12 s. GA was partially reduced in the first step and self-assembled into a 3D scaffold which is much more receptive to microwaves and promotes the second complete reduction by microwave treatment. By tuning the microwaving time, the GA microwaved for 10 s, that is, MGA-10 exhibits hierarchically porous microstructure, ultra-low density, and super compressibility. MGA-10 can be used as a recyclable absorbent with high absorption capacities (223 ∼ 430 g/g) towards various oils and organic solvents. Meanwhile, the high sensitivity of the electric resistance to the compressive strain enables MGA-10 promising for pressure sensor applications. The MGA-10 sensor demonstrates high sensitivity (1.112 kPa−1 at a pressure range of 0 ∼ 0.3 kPa) and excellent stability (>3000 cycles). This fabrication route paves the way to efficiently prepare highly compressible graphene aerogels for versatile applications.

Three-dimensional layered porous graphene aerogel hydrogen getters

Organic getters are often introduced into sealed systems to remove the excessive reactive hydrogen gas. In this work, the formable graphene aerogel hydrogen getters are prepared by integrating the alkyne-containing molecules (e.g., DEB) into the palladium-loaded three-dimensional layered porous graphene aerogel (Pd-GA). The performance of Pd-GA/DEB composite materials in reducing reactive hydrogen gas is examined at pressures of 0.1–1 bar at a temperature of 25 °C, and the hydrogen consumption is measured as a function of time. Results suggest that the hydrogen uptake capability of Pd-GA/DEB getters increases with the loading of Pd particles on the GA and the content of Pd 0 . The highest hydrogen absorption capacity is up to 215.5 cm 3 /g, and the hydrogenation rate of DEB molecules is 89.3%. This study promotes the fundamental understanding of solid-phase catalytic hydrogenation and the applications of 3D layered porous graphene aerogel in hydrogen absorption. • A compressible and strong graphene aerogel (GA) was prepared by a gentle method. • The palladium (Pd) nanoparticles were uniformly supported on the GA. • The formable hydrogen getters were fabricated by integrating Pd-GA with DEB. • The highest hydrogen absorption capacity of Pd-GA/DEB was up to 215.5 cm 3 /g. • The GA can effectively disperse metal particles and accelerate hydrogen diffusion.

Wide range continuously tunable and fast thermal switching based on compressible graphene composite foams

Thermal switches have gained intense interest recently for enabling dynamic thermal management of electronic devices and batteries that need to function at dramatically varied ambient or operating conditions. However, current approaches have limitations such as the lack of continuous tunability, low switching ratio, low speed, and not being scalable. Here, a continuously tunable, wide-range, and fast thermal switching approach is proposed and demonstrated using compressible graphene composite foams. Large (~8x) continuous tuning of the thermal resistance is achieved from the uncompressed to the fully compressed state. Environmental chamber experiments show that our variable thermal resistor can precisely stabilize the operating temperature of a heat generating device while the ambient temperature varies continuously by ~10 °C or the heat generation rate varies by a factor of 2.7. This thermal device is promising for dynamic control of operating temperatures in battery thermal management, space conditioning, vehicle thermal comfort, and thermal energy storage.

Highly compressible graphene aerogel with high thermal conductivity along both in-plane and through-plane directions

Graphene-based thermal interface materials (TIMs), such as horizontal graphene papers and vertical graphene monoliths, commonly possess high thermal conductivity (TC) only along either in-plane or through-plane direction due to their high anisotropy structure. Three-dimensional (3D) graphene monoliths with interconnected network can extend the excellent thermal transport performances of two-dimensional graphene to macro monoliths along multi-directions. However, the high porosity of 3D graphene monoliths usually leads to low TC. Here, highly compressible graphene aerogels (HCGAs) with closely packed cell walls and regularly cellular structure were prepared. The HCGAs can be highly compressed (95% compressive strain) to reduce the porosity while maintaining the continuously thermal transport paths. Significantly increased TC along both in-plane and through-plane directions can be obtained by directly mechanical compression of the aerogels. HCGAs with initial density of 11.5 mg cm−3 at 95% compressive strain possess in-plane TC of 167.2 W m−1K−1 and through-plane TC of 46.8 W m−1K−1, which outperforms other carbon-based TIMs reported previously.

Electrical energy generation by squeezing a graphene-based aerogel in an electrolyte

Mechanical energy harvesters are widely studied because of their diverse applications, such as harvesting ocean wave energy, self-powered wireless sensors, portable power supplies and so on. To be feasible, an energy harvester needs to provide a high output current and voltage, in addition to being environmentally friendly. Hence, in this study, a new energy harvester is developed via reversible deformation of a three-dimensional graphene aerogel which was immersed in a salt solution. The movement of solvated ions in the diffusion layer during the squeezing of the electrode induced the transmission of electrons out of graphene, resulting in electrical energy. The developed harvester can supply a power density of 11.7 W kg-1 and an energy density of 14.3 J kg-1, in addition to achieving a high energy conversion efficiency of approximately 43.2%. The device can also generate a high open-circuit voltage and short-circuit current when an external compression strain is applied. Moreover, it can be easily scaled up by being connected in series with multiple harvesters. Thus, the proposed energy harvester can not only be widely used for harvesting ocean wave energy, but also for adsorbing pollutants to prevent the pollution of ocean environments.

Fabrication of graphene aerogel and graphene/carbon nanotube composite aerogel by freeze casting under ambient pressure and comparison of their properties

Graphene aerogels are super lightweight and highly compressible 3D graphene structure. In this research, graphene aerogels and graphene/single-walled carbon nanotubes (G/SWCNTs) nanocomposite aerogels were produced by freeze casting under ambient pressure without the need for vacuum apparatus. The mechanical experiments showed that both aerogels can withstand a strain of up to 90%, but in general, G/SWCNTs aerogels have greater elasticity than the pure graphene aerogels. It was found that graphene aerogels had better electrical conductivity than G/SWCNTs aerogels and there was a threshold voltage of approximately 2 V, below which no electrical current could be established but by applying stress, the electrical current increased almost linearly by increasing the stress. Adsorption capacity of diesel oil, petroleum, edible oil and ethanol by graphene and G/SWCNTs aerogels were measured and found that among them, the diesel oil uptake by the aerogels was the highest. The highest adsorption capacity of graphene and G/SWCNTs aerogels were measured 85.5 gg−1 and 30.5 gg−1, respectively.

Ultralight, Highly Compressible Graphene Cellular Materials with Enhanced Mechanical and Electrical Performance

AbstractConventional three‐dimensional graphene cellular materials (GCMs) from chemically derived graphene oxide undergo low mechanical strength, severe plastic deformation and poor electrical conductivity. Herein, ultralight, ultraelastic, excellent mechanical and electrically conductive GCMs have been successfully prepared by the self‐assembly of graphene nanosheets by extensive hydrogen bonds generated from a glycolic acid crosslinker. Meanwhile, ethanol‐water solution is used to dramatically restrict the volume expansion of water converting into ice crystal during the freeze process. Eventually, the GCMs exhibit ultralow densities of about 4.3 mg cm−3, and can be fabricated on a large scale (volume of ∼350 cm3). The GCMs have a maximum reversible strain of ca. 90% in the whole density range from 4.3 mg cm−3 to 25.3 mg cm−3. Young's moduli (E) are from 13.7 kPa (ρ=4.3 mg cm−3) to 125.1 kPa (ρ=25.3 mg cm−3), with the scale of E∼ρ2.1, and the exponent n is less than the GCMs previously reported. The GCMs also have high electrical conductivities of about 98.1 S/m (ρ=25.3 mg cm−3). Our work provides a facile method for the fabrication of ultralight, highly compressible and conductive GCMs, paving the way towards future potential applications in energy storage and conversions, adsorbents for the environment, etc.

Effective decontamination of 99TcO4−/ReO4− from Hanford low-activity waste by functionalized graphene oxide–chitosan sponges

Treatment and recycling of radioactive waste are major challenges for the nuclear energy sector. Pertechnetate anions, 99TcO4−, occur in nuclear waste and are formed mainly during nuclear fission. 99TcO4− is a very hazardous contaminant due to its long half-life and high solubility and mobility in water. The effective capture of 99Tc contamination at legacy nuclear sites remains a serious and unsolved environmental issue. In this work, 99TcO4−/ReO4− was adsorbed by compressible graphene–chitosan sponges with grafted tertiary amine groups. Moreover, the hydrophobic branched chains strongly reduced the interference of competitive anions during adsorption. Results show that 99TcO4−/ReO4− can be effectively removed even under highly acidic conditions and in the presence of competing anions. More than 98% of 99TcO4−/ReO4− was removed using simulated nuclear wastes.

Ultralight and highly compressible coal oxide-modified graphene aerogels for organic solvent absorption and light-to-heat conversion

Ultralight, hydrophobic, highly compressible and low-cost coal oxide-modified graphene aerogels exhibit high absorption capacity and high solar thermal conversion efficiency.

Hydrophobic, blocky silica-reduced graphene oxide hybrid sponges as highly efficient and recyclable sorbents

Silica aerogels are prone to be destroyed due to their brittleness and low mechanical properties, which limits their applications. To break the unfavorable situation, we presented a scalable and facile approach to assemble blocky silica-reduced graphene oxide (SiO2-rGO) hybrid sponges by atmospheric pressure drying technique. Briefly, ungelled silica solution from two-step sol-gel of tetraethoxysilane (TEOS), was incorporated into compressible graphene sponge (CGS). Different silicon concentration ratios had great influence on the performance of hybrid sponges. When VTEOS: Vethanol was fixed at 1:15, the sample had good flexibility and could absorb 8.5–10.2 times its own mass of solvents, but the adsorption efficiency slightly decreased with the increase of the number of experiments. When VTEOS: Vethanol was fixed at 4:7, the SiO2-rGO hybrid sponges exhibited unbroken shape, low volume shrinkage (24%), large specific surface area (803.351 m2/g), and high mass retention (83.64%) at 790 °C of thermal treatment. Moreover, they could support approximately 146 times their weight without structural damage, and possess excellent hydrophobicity with 129 ± 1° of water contact angle. These superior properties enable SiO2-rGO hybrid sponges to exhibit highly efficient absorption of oils and toxic solvents, to be regenerated (10 times) with the full release of adsorbates by heat treatment.

Ultralight, highly compressible and fire-retardant graphene aerogel with self-adjustable electromagnetic wave absorption

Macroscopic three-dimensional (3D) free-standing porous all-graphene aerogel with ultralight density and high compressibility is successfully fabricated through a mild in-situ self-assembly and thermal annealing processes. The formed interconnected 3D porous graphene network, high thermal stable all-graphene composition and large porosity of aerogels made it possible to remove heat quickly during combustion, exhibiting a conspicuous fire-retardancy. Meanwhile, excellent recoverable compressibility with high strain levels of up to 75% endowed the aerogel with high sensitive strain-responsive characteristic in volume electrical conductivity, thereby opening a new way for realizing the adjustment of internal free space and electrical conductivity of 3D architecture. Based on the results, the microwave absorption performance of the graphene aerogel was effectively self-adjusted via a simple mechanical compression. The optimal absorbing value was up to 61.09 dB with a broad qualified bandwidth of 6.30 GHz at the thickness of 4.81 mm when the compression strain ratio of the sample was controlled to be 30%.

Highly compressible three-dimensional graphene hydrogel for foldable all-solid-state supercapacitor

The fabrication of three-dimensional (3D) graphene-based macroscopic materials with superior mechanical and electrical properties for flexible energy storage devices is still extremely challenging. Here, we report a novel 3D graphene hydrogel decorated by the biomass phytic acid (PAGH) with developed porosity and strengthen mechanical property via hydrothermal and freeze-drying methods. The phytic acid molecules are intercalated into the graphene sheets, enabling robust network structure. This induces the formation of materials with larger specific surface area, lower density and enhanced compressive strength compared with pure GH. When directly employed as an electrode, the PAGH exhibits a high specific capacitance of 248.8 F g−1 at 1 A g−1 and excellent rate performance of 67.9% as current density increasing to 20 A g−1. Furthermore, the all-solid-state supercapacitor based PAGH can deliver outstanding cycle life (86.2% after cycling 10,000 times), glorious energy density (26.5 Wh kg−1) and power density (5135.1 W kg−1). The prepared device shows stable electrochemical behaviors at random bending angles. Therefore, the present work will open a new avenue to design and fabricate new flexible and portable graphene-based electrodes for future applications in energy storage devices.

Highly compressible graphene/polypyrrole aerogel for superelastic pseudocapacitors

ABSTRACTHighly compressible graphene aerogel are proposed as the promising electrode materials for compression-tolerant electrochemical capacitors. Herein, the polypyrrole (PPy) was introduced into the compressible graphene aerogel to further improve its specific capacitance and compression-tolerant ability. As-prepared graphene/PPy aerogel withstands 95% repeated compression cycling without any structure collapse. The gravimetric capacitance of the superelastic pseudocapacitors based on graphene/PPy aerogel electrodes reaches 335 F g−1 and can retain 97% even under 95% compressive strain. And a volumetric capacitance of 108 F cm−3 is achieved due to the significantly increased density of the electrodes under 95% strain. This value of the volumetric capacitance can be preserved by 85% after 3500 charge/discharge cycles with various compression conditions. This work will pave the way for advanced applications in the area of compressible energy-storage devices.

Fabrication of an arbitrary-shaped and nitrogen-doped graphene aerogel for highly compressible all solid-state supercapacitors

Herein, we report a new template method for fabricating an arbitrary-shaped compressible nitrogen-doped graphene aerogel (GA).

Sulfur and nitrogen co-doped holey graphene aerogel for structurally resilient solid-state supercapacitors under high compressions

A highly compressible, conductive nitrogen and sulfur co-doped holey graphene aerogel (NS-HGA) is developed for structurally resilient solid-state supercapacitors under high compressions.

Highly Compressible and Conductive N-Doped Graphene Foam for Lithium Batteries

Over almost five years, 3-dimensional graphene and graphene-based nanostructured foams have been widely progressed. These materials have potential for use in next-generation energy-related technology for energy storage and generation as well as use in sensors and actuators. Among graphene-based materials, graphene oxides (GOs) can be described as rising material candidates because they show multiple advantage of ultra-light, strong, flexible, elastic, and porous. In addition, they have excellent properties such as high surface area, robust mechanical strength, resistive chemical behavior, and scaffolds with high conducivity. In this presentation, we describe the simple synthesis of ultralow-density 3-dimensional reduced graphene oxide (rGO) foams that show high electrical conductivity and excellent compressibility for the applicaion of lithium batteries. The rGO foams are synthesized using the combination of hydrothermal and thermal annealing method in which hexamethylenetetramine is employed. We confirm that the N-binding configurations of rGO foams increase as evidenced by the change in pyridinic-N/quaternary-N ratio. The conductivity of this graphene foam is almost 12 S/m at 0 strain, whereas the conductivity is ≈704 S/m at the compressive strain (≈80%), which is comparable to previous reported any 3D sponge-like low-density carbon materials. The foam also has excellent hydrophobicity (contact angle on water surface: ≈137°) and shows selective absorption for organic solvents and oils. The compressive modulus of the rGO foam is higher than that of other carbon-based foams. This graphene foam is the simplified, light-weight architecture allowing for large mass loading of guest materials. Our graphen foam has unique electrical and mechanical properties due to the presence of N-doped monolithic graphene, and can be suitable for the use in electrodes for lithium batteries, fuel cells, energy absorption, energy storage, and sensing applications. * K.-Y. Chun & J. Oh are equally contributed as corresponding authors in this study .

Morphology and Mechanical Property of Compressible Graphene Aerogel

Compressible graphene aerogel (CGA) was prepared via one-step reduction and self-assembly of graphene oxide with urea as reducing agent and then freeze-drying. The morphology and mechanical property of CGA were characterized by scanning electron microscope (SEM) and mechanical testing. The results revealed 3D honeycomb-shaped porous structure was built and ultra-light CGA with density of 6.3 mg·cm-3 was achieved. The CGAs showed exceptional compression performance, which could be compressed to more than 50% of its own height and recover to original state immediately after released. The maximum stress reached to 8.1kPa with 50% strain and decreased quite little after compression up to 100 cycles.