Three-dimensional Graphene Foam Research Articles

A Large-Scale and Low-Cost Thermoacoustic Loudspeaker Based on Three-Dimensional Graphene Foam.

Graphene is a promising material for thermoacoustic sources due to its extremely low heat capacity per unit area and high thermal conductivity. However, current graphene thermoacoustic devices have limited device area and relatively high cost, which limit their applications of daily use. Here, we adopt a dip-coating method to fabricate a large-scale and cost-effective graphene sound source. This sound source has the three-dimensional (3D) porous structure that can increase the contact area between graphene and air, thus assisting heat to release into the air. In this method, polyurethane (PU) is used as a support, and graphene nanoplates are attached onto the PU skeleton so that a highly flexible graphene foam (GrF) device is obtained. At a measuring distance of 1 mm, it can emit sound at up to 70 dB under the normalized input power of 1 W. Considering its unique porous structure, we establish a thermoacoustic analysis model to simulate the acoustic performance of GrF. Furthermore, the obtained GrF can be made up to 44 in. (100 cm × 50 cm) in size, and it has good flexibility and processability, which broadens the application fields of GrF loudspeakers. It can be attached to the surfaces of objects with different shapes, making it suitable to be used as a large-area speaker in automobiles, houses, and other application scenarios, such as neck mounted speaker. In addition, it can also be widely used as a fully flexible in-ear earphone.

A unified impact response analysis for FG-CNTRC and 3D-GrF sandwich composite sector- rectangular coupled plates

This paper proposes a general method for analyzing the dynamic response characteristics of sector- rectangular coupled plates subjected to external impacts. This method combines the method of reverberation-ray matrix (MRRM) with the strip transfer function method, referred to as the strip method of reverberation-ray matrix (S-MRRM). The traditional MRRM has some limitations for the dynamic modeling of the sector structure and also requires the Lévy-type exact solution, leading to simply supported boundary conditions in certain direction of the structure. The present method can not only address the aforementioned limitations but also maintain the efficiency advantage of the wave method for solution. The investigated structure consists of sandwich panels composed of functionally graded carbon nanotube reinforced (FG-CNTRC) panels and the three-dimensional graphene foam (3D-GrF) core. The structure is discretized into several strip elements by the strip transfer function method, and the whole dynamic model of the structure is obtained through matrix assembly. The motion differential equation in matrix form is derived by using Hamilton principle, followed by obtaining the matrix-form wave number equation. Upon deriving the wave solution of the structure based on this equation, the transient and steady-state responses of the structure are obtained by employing MRRM. Convergence analysis is conducted on these calculation results, followed by comparison with FEM results to validate its prediction accuracy. Finally, through a comprehensive parametric study, the impacts of various factors such as CNTs distribution form, CNTs volume fraction, 3D-GrF pore distribution form, 3D-GrF porosity, and sandwich panel thickness ratio on both transient and steady-state responses of these structures were investigated, thereby providing guidance for engineering applications.

3D interconnected porous graphene architecture as a high-performance capacitive deionization electrode

Capacitive deionization (CDI) is a promising technology for brackish water desalination because of its high efficiency, no secondary pollution and low cost. However, the ion removal capacity of CDI system for brackish water desalination is still insufficient. Herein, a new in-situ porous Cu template method is used to prepare a unique open three-dimensional mesoporous graphene foam (3DMG) with high CDI performance. The developed 3DMG material has rich mesoporous structure, interconnected pore structure, high specific surface area, good hydrophilicity and excellent electrical conductivity, which can achieve effective solution/pore contact, rapid ion migration and high electrosorption capacity. Therefore, the specific capacitance of 3DMG as high as 141.37F/g at 1 M NaCl and 10 mV/s, and the maximum salt adsorption capacity is as high as 32.08 mg/g (1000 mg/L, 1.2 V), which is significantly higher than that of graphene-based electrode materials reported in most literatures. It also shows excellent regeneration performance and stability after repeated electrosorption-desorption cycles. The developed 3DMG undoubtedly provides a promising electrode material platform for CDI devices, effectively solving the urgent problem of freshwater resource shortage.

CVD Growth Graphene Foam Functionalized with Platinum for Fuel Cells Applications

The development of catalysts with high activity for the ORR is essential to proton exchange membrane fuel cells (PEMFCs), since the majority of activation losses occur at the cathode and it turns into an interesting research area. In the present study, it is investigated the hydrothermal platinum functionalization of the CVD grown three-dimensional graphene foam (3D-GrFoam) using three concentrations of dihydrogen hexachloroplatinate (IV) hydrate [1]. The platinum functionalized graphene foam determined from XPS was 0.2at %, 0.3 at % and 0.4 at %, respectively.The catalytic activity towards ORR was analyzed from linear sweep voltammetry (LSV) plots recorded with a scan rate of 5 mV s-1 in oxygen saturated 0.5 M H2SO4. From the LSV curves and the Koutecky-Levich (K-L) plots for 0.4PtGrFoam as current density (mA-1 cm2 geo) vs. w-1/2 (rad s-1)-1/2), for various rotation speeds (among 250–1500 rpm) and different potentials (0.1 V-0.8 V). From the fitted K-L plots it is noticed a fair linear relationship at all potentials, that confirms the electroreduction of platinum. The number of transferred electrons is between 3.22 to 3.59 indicating the preponderance of the four-electron transfer mechanism in the ORR corresponding to the directly reduction of O2 to H2O.1. Ion-Ebrasu, R.D. Andrei, S. Enache, S. Caprarescu, C. C. Negrila, C. Jianu, A. Enache, I. Boerasu, E. Carcadea, M. Varlam, B. S. Vasile, J. Ren, Materials 2021, 14, 4952.

A stretchable wearable sensor with dual working electrodes for reliable detection of uric acid in sweat

Wearable sweat sensors with stretch capabilities and robust performances are desired for continuous monitoring of human health, and it remains a challenge for sweat sensors to detect targets reliably in both static and dynamic states. Herein, a flexible sweat sensor was created using a cost-effective approach involving the utilization of three-dimensional graphene foam and polydimethylsiloxane (PDMS). The flexible electrochemical sensor was fabricated based on PDMS and Pt/Pd nanoparticles modified 3D graphene foam for the detection of uric acid in sweat. Pt/Pd nanoparticles were electrodeposited on the graphene foam to markedly enhance the electrocatalytic activity for uric acid detection. The graphene foam with excellent electrical property and high porosity, and PDMS with an ideal mechanical property endow the sensing device with high stretchability (tolerable strain up to 110 %), high sensitivity (0.87 μA μM−1 cm−2), and stability (remaining unchanged for more than 5000 cycles) for daily wear. To eliminate possible interferences, the wearable sensor was designed with dual working electrodes, and their response difference ensured reliable and accurate detection of targets. This strategy of constructing sweat sensors with dual working electrodes based on the flexible composite material represents a promising way for the development of robust wearable sensing devices.

A flexible supercapacitor with high energy density and wide range of temperature tolerance using a high-concentration aqueous gel electrolyte

As the demand for a wide range of wearable devices increases, extensive effort is devoted to developing high-performance flexible energy storage devices such as batteries and supercapacitors. Of particular interest, flexible supercapacitors using aqueous electrolytes have high application potential owing to their many advantages including low cost, harmlessness to the human, and environmental safety compared to others using electrolytes such as ionic liquids and organic electrolytes. However, poor temperature tolerance and narrow operation voltage window have hindered the practical application of aqueous supercapacitors. In this study, we report on a wide temperature-tolerant flexible aqueous supercapacitor featuring high electrochemical performance designed by a deliberate selection of electrode materials and electrolytes. As a flexible electrode, three-dimensional microporous graphene foam coated with conducting polymer Polypyrrole (PPy) is used to enhance capacitance up -to 90.0 F/g by increasing the surface area and inducing the pseudo-capacitance of PPy. As a gel-type electrolyte, a high-concentration NaClO4 is mixed with Polyvinyl alcohol to enlarge the voltage window to 1.8 V and a stable temperature range from -25 to 80°C, even under repetitive bending deformation. The fabricated supercapacitor exhibits a superior energy density of 37.4 Wh kg−1 and maintains 92.0% of initial capacitance at room temperature after three repeated cycles of cooling/heating across a wide temperature range over 100°C. This work suggests a high potential application of the fabricated supercapacitor as an eco-friendly and stable energy storage system for powering diverse wearable devices under various conditions.

Three-Dimensional Graphene Promotes the Proliferation of Cholinergic Neurons

Introduction: An early substantial loss of basal forebrain cholinergic neurons (BFCNs) is a common property of Alzheimer’s disease and the degeneration of functional BFCNs is related to learning and memory deficits. As a biocompatible and conductive scaffold for growth of neural stem cells, three-dimensional graphene foam (3D-GF) supports applications in tissue engineering and regenerative medicine. Although its effects on differentiation have been demonstrated, the effect of 3D-GF scaffold on the generation of BFCNs still remains unknown. Methods: In this study, we used 3D-GF as a culture substrate for neural progenitor cells (NPCs) and demonstrated that this scaffold material promotes the differentiation of BFCNs while maintaining excellent cell viability and proliferation. Results: Immunofluorescence analysis, real-time polymerase chain reaction, Western blotting, and ELISA revealed that the proportion of BFCNs at 21 days of differentiation reached approximately 30.5% on 3D-GF compared with TCPS group that only presented 9.7%. Furthermore, a cell adhesion study suggested that 3D-GF scaffold enhances the expression of adhesion proteins including vinculin, integrin, and N-cadherin. These findings indicate that 3D-GF scaffold materials are preferable candidates for the differentiation of BFCNs from NPCs. Conclusions: These results suggest new opportunities for the application of 3D-GF scaffold as a neural scaffold for cholinergic neurons therapies based on NPCs.

Buckling analysis of multi-span non-uniform beams with functionally graded graphene-reinforced foams

This paper conducts the buckling analysis of multi-span functionally graded (FG) beams reinforced by three-dimensional graphene foams (3D-GFs) restrained by elastic supports. The graphene foams are considered as graded variation in the thickness direction according to four different porosity distributions. The width and height of the non-uniform beams vary in the longitudinal direction in accordance with the power-law principle, and the multi-span beams consist of two types of optional beams. The governing equations of buckling behavior are derived based on the Timoshenko beam theory and the principle of virtual displacements, and solved by the discrete singular convolution (DSC) method. The purpose of this paper is to obtain the critical buckling load of FG 3D-GFs reinforced beams under the consideration of variable cross-section and multi-span beams with 2–4 spans. The effect of porosity coefficients, slenderness ratio, and spring constants on the buckling characteristic also are studied. The results suggest that the taper ratio of beams and the configuration of multi-span beams lead to remarkable changes in the critical buckling load of beams.

Electrically and Thermally Triggered Three-Dimensional Graphene-Foam-Reinforced Shape Memory Epoxy Composites.

Shape memory polymer (SMP) epoxy composites have attracted significant attention due to their easy processing, lightweight nature, and ability to recover strain. However, their limited recovery rate and inferior mechanical properties have hindered their functional applications. This research explores the potential of three-dimensional (3D) graphene foam (GrF) as a highly efficient reinforcement for SMP epoxy composites. We demonstrated that the incorporation of a mere 0.13 wt.% GrF into mold-cast SMP epoxy leads to a 19% increase in the glass transition temperature (Tg). To elucidate the reinforcing mechanism, we fabricated and extensively analyzed composites with varying weight percentages of GrF. The GrF-based SMP epoxy composite exhibits a 57% increase in thermal conductivity, measuring 0.296 W mK-1 at 70 °C, due to the interconnected 3D graphene network within the matrix. Notably, this composite also demonstrates remarkable electrical conductivity, making it suitable for dual-triggering applications. The GrF-SMP epoxy composite achieves a maximum shape recovery ratio and a significant 23% improvement in the recovery rate, effectively addressing the issue of slow recovery associated with SMPs. We investigated the effect of switching temperatures on the shape recovery rate. We identified the optimal triggering temperature to initiate shape recovery for epoxy SMP and GrF-epoxy SMP as thermal energy equivalent to Tg + 20 °C. Additionally, we fabricated a bird-shaped composite using GrF reinforcement, which showcases self-healing capabilities through the crack opening and closure and serves as a tangible demonstration of the transformative potential of the composite. These GrF-epoxy SMP composites, responsive to stimuli, hold immense promise for diverse applications, such as mechanical systems, wearable sensors, morphing wings, foldable robots, and antennas.

Three-dimensional graphene foam based triboelectric nanogenerators for energy systems and autonomous sensors

In this work we investigate the potential of three-dimensional graphene (3DG) foam as an active layer in triboelectric nanogenerators (TENGs) and as an energy harvesting power source for autonomous sensors. A series of comprehensive measurements have been carried out to test the output characteristics of 3DG-TENG under cyclic mechanical stimulus, capable of operating TENG in contact-separation mode at different frequencies, gap distances between electrodes, and applied pressures. The triboelectric response of 3DG-TENG (with an effective surface of 16 cm2) showed maximum open-circuit voltage (Voc) and short-circuit current (Isc) of 400 V and 105.7 μA respectively when stimulated at 3 Hz (contact-separation frequency) and 70 mm (optimum gap distance). Under the same conditions, a maximum output power (Pout) of around 10.37 W/m2 is produced using an external load resistance of 40 MΩ; this is an order of magnitude lower resistance than that needed with other graphene based TENG variants. 3DG-TENG exhibited great stability in the output characteristics with 15,000 cyclic mechanical stimuli and a retention percentage in Pout above 95%. This is a significant improvement with respect to other carbon based TENG`s, which show enhanced deterioration of TENG performance due to material transfer between electrodes and plastic deformation of triboelectric materials. Simulations of TENG Voc using distance dependent model determined high triboelectric charge densities in the range of mC/m2. Here, we also demonstrate the potential of 3DG-TENG as an energy supply for energy storage devices, and as an active layer in an autonomous pressure sensing platform for anonymous room occupancy monitoring in smart buildings.

Study of Viscoelastic Properties of Graphene Foams Using Dynamic Mechanical Analysis and Coarse-Grained Molecular Dynamics Simulations

As a promising nano-porous material for energy dissipation, the viscoelastic properties of three-dimensional (3D) graphene foams (GrFs) are investigated by combining a dynamic mechanical analysis (DMA) and coarse-grained molecular dynamic (CGMD) simulations. The effects of the different factors, such as the density of the GrFs, temperature, loading frequency, oscillatory amplitude, the pre-strain on the storage and loss modulus of the GrFs as well as the micro-mechanical mechanisms are mainly focused upon. Not only the storage modulus but also the loss modulus are found to be independent of the temperature and the frequency. The storage modulus can be weakened slightly by bond-breaking with an increasing loading amplitude. Furthermore, the tensile/compressive pre-strain and density of the GrFs can be used to effectively tune the viscoelastic properties of the GrFs. These results should be helpful not only for understanding the mechanical mechanism of GrFs but also for optimal designs of advanced damping materials.

Far-field blast responses of sandwich arbitrary polygonal reinforced plate system

This paper presents a spectral element model for investigating the dynamic response characteristics of the arbitrary polygonal built-up reinforced plate system subjected to far-field blast load. In the researched system, the plate elements are made of sandwich materials with functionally graded carbon nanotube reinforced (FG-CNTRC) panels and three-dimensional graphene foam (3D-GrF) core. The stiffness matrix assembly method is incorporated into the spectral element method (SEM) for establishing the overall dynamic formulas of arbitrary assembled plates. Thereinto, the governing equations of motion of plate elements are derived by the Hamilton's principle based on the simple first-order shear deformation theory (S-FSDT) retaining only four displacement variables, which provides an advantage to maintain interelement continuity conditions completely. After that, the natural frequencies and transient responses of the systems with different built-up forms are solved by introducing a golden section search algorithm and Fourier series expansion of the blast load. The admirable predictive accuracy of the present model is verified by comparing the obtained results and the reference solution from finite element method (FEM). Moreover, the effects of the CNT distribution form, CNT volume fraction, 3D-GrF pore distribution form, 3D-GrF porosity, the thickness ratio of the sandwich panel, TNT mass and explosion radius on the transient vibration properties of the system are revealed through a detailed parametric study.

Controlled construction of three-dimensional graphene foam with FeSe2 as anode for high-performance sodium-ion batteries

Controlled construction of three-dimensional graphene foam with FeSe2 as anode for high-performance sodium-ion batteries

Heteroatom dopant strategy triggered high-potential plateau to non-graphitized carbon with highly disordered microstructure for high-performance sodium ion storage

Non-graphitized carbon (NGC) has been extensively utilized as carbonaceous anode in sodium-ion batteries (SIBs). However, more optimization to achieve competitive capacity and stability is still challenging for SIBs. In the study, the dopant strategy is utilized to construct nitrogen/sulfur-doped non-graphitized carbon (N-NGC or S-NGC) shell decorated on three-dimensional graphene foam (GF) as a self-support electrode. The highly disordered microstructures of heteroatom doped carbons are produced by applying a low-temperature pyrolysis treatment to precursors containing nitrogen and sulfur. The DFT calculations of Na-ion adsorption energies at diverse heteroatom sites show marginal-S, pyrrolic N and pyridinic N with more intensive Na-ion adsorption ability than middle-S, CO and pristine carbon. The N-NGC with dominant small graphitic regions delivers adsorption ability to Na-ion, while the S-NGC with significant single carbon lattice stripes demonstrates redox reaction with Na-ion. Evidently, in comparison with only adsorption-driven slope regions at high potential for N-NGC, the redox reaction-generated potential-plateau enables non-graphitized S-NGC superior discharge/charge capacity and cycle-stability in the slope region. This work could provide deep insight into the rational design of non-graphitized carbon with rich microstructure and composition.

Three-dimensional graphene foams with two hierarchical pore structures for metal-free electrochemical assays of dopamine and uric acid from high concentration of ascorbic acid

Three-dimensional graphene foams with two hierarchical pore structures for metal-free electrochemical assays of dopamine and uric acid from high concentration of ascorbic acid

A Fast-Responding Electro-Activated Shape Memory Polymer Composite with Embedded 3D Interconnected Graphene Foam.

Shape memory polymers (SMPs) have gained increasing attention as intelligent morphing materials. However, due to the inherent electrical insulation and poor thermal conductivity of polymers, deformation and temperature control of SMPs usually require external heating devices, bringing about design inconveniences and fragility of interfaces. Herein, we report a shape memory composite that integrates reliable temperature and shape control functions into the interior. The composite is comprised of resin-based SMP and three-dimensional interconnected graphene foam (3DGF), exhibiting a high recovery rate and thermal/electrical conductivity. With only 0.26 wt% of graphene foam, the composite can improve electrical conductivity by 15 orders of magnitude, thermal conductivity by 180%, tensile strength by 64.8%, and shape recovery speed by 154%. Using a very simple Joule heating scheme, decimeter-sized samples of the composite deformed to their preset shapes in less than 10 s.

Highly sensitive flexible strain sensor based on GSB-enhanced three-dimensional graphene composite

High-sensitive flexible strain sensor is a key device for artificial intelligence and wearable electronics. Specifically, the aim of this work is to investigate the design of graphene-SiO2 balls enhanced (GSB-enhanced) three-dimensional (3D) graphene foam (GSBF) electrode structure, which is combined with flexible material polydimethylsiloxane (PDMS) for a highly sensitive strain sensor. The GSBF/PDMS strain sensor presents excellent performances: stretching ratio of 50%, response time of less than 128 ms and high sensitivity (the strain coefficient GF = 103, in variation range of 0–13% strain), due to its unique mechanical and conductive properties. Moreover, a high stability of more than 300 loading-unloading cycles is achieved without dramatic resistance increment. Our sensors could be used in several wearable applications including monitoring finger movement, the pulse ratio, the strain of the knee joint in patellar reflex and the movements of elbow, wrist, sole etc. Our research illustrates the potential abilities in the fields of robotic systems, healthcare and flexible electronics applications with less cost and more accessible.

Efficiency of Carbon-Based Electrodes on a Microbial Electrolysis System for the Treatment of Bilge Water

A coupled Microbial Electrolysis Cell (MEC) – Anaerobic Granular Sludge (AGS) system was settled to investigate for the first time the ability of various carbon-based electrodes to enhance biodegradation of real bilge water (BW) and increase methane generation as an emerging technology for converting organic matter into value-added products. Results revealed that the performance of the three types of electrodes named carbon foam (CF), carbon cloth (CC) and three-dimensional graphene foam (3DG), was both time and organic load content dependent during the experimental cycles. Cumulative CH4 generation reached 235 mL in just 13 days after feeding the AGS with 50% of BW and application of 1.0 V at 3DG electrodes, followed by CC electrodes (148.3 mL). CF proved to be more resistant in higher BW concentration showing a sufficient performance of 1 month. However, in the third cycle, the performances of MECs containing 3DG and CC were higher compared to the CF and the control. Over the first cycle, the soluble Chemical Oxygen Demand (sCOD) removal was found to be around 70% to all MECs, and this value was around 10% higher than the control. Among the different Volatile Fatty Acids (VFAs), acetic acid was identified in the highest concentration in the first cycle, whereas propionic acid was detected in the second and third cycles. Microbial profile analysis showed that Methanobacterium and Desulfovibrio had substantially higher abundances in the cathodes than in the suspended anaerobic sludge. An X-ray diffraction (XRD) investigation of the used electrodes pointed out the formation of various crystalline compounds on their surface, which were different for the anode and cathode.

Structure–property relations of three-dimensional nanoporous template-based graphene foams

Recently, much attention has been directed to 3D graphene structures due to their potential of retaining intrinsic 2D graphene properties, in combination with structural flexibility and tunable porosity. From a theoretical point of view, however, it is challenging to build 3D graphene foam structures that accurately represent experimental topological configurations. Here, we generate open-cell 3D graphene structures that closely reflect template-based manufacturing techniques and investigate their mechanical properties. We use all-atom molecular dynamics simulations to relate the overall stiffness, collapse stress and fracture properties to the underlying graphene microstructure represented by the graphene relative density, template relative density and number of graphene layers. We do so for four different template morphologies: gyroids, regular foam (BCC), random foam and nanoporous gold. The overall mechanical properties as a function of graphene relative density are analyzed in terms of power law relations to probe the microstructural deformation modes. Our results show that the open-cell 3D graphene structures feature bending as the dominant deformation mode, with regular graphene foams having the highest stiffness and strength and random foams the lowest. For gyroids we found that a higher template relative density leads to reduced mechanical properties but improved ductility. A similar trend was observed when the number of graphene layers was increased: enhanced ductility but at the expense of a reduced strength. Interestingly, we found that for low graphene density, the gyroids feature a strong self-stiffening response, leading to improvements in both strength as well as ductility. Our findings can be used as a guideline for the experimental design of innovate and lightweight graphene structures with strongly enhanced mechanical properties.

Synthesis, experimental testing and multi-scale modelling of graphene foam/epoxy composite

In this work, randomly three-dimensional graphene foam (RGF) is synthesized from the chemical reduction of graphene oxide solution in the self-assembly method. RGF/epoxy composite is then obtained by the RTM method. Tensile testing highlights the effect of RGF drying percentage on the composite and shows a 138% and 48% increase in the Young modulus and tensile strength compared to epoxy. Also, by considering representative unit cell (RUC), a multi-scale numerical method using finite element analysis based on Carrera Unified Formulation (CUF), and molecular dynamics (MD), are performed to obtain the mechanical properties of the RGF/epoxy composite material.