Graphene Foam Research Articles

The effect of nitrogen species on the catalytic properties of N-doped graphene

The production of effective catalysts in the oxygen reduction reaction (ORR) continues to be a great challenge for scientists. A constant increase in demand for energy storage materials is followed by a proportionate increase in the number of reports on electrocatalyst synthesis. The scientific world focuses on environmentally friendly materials synthesized in accordance with the safest possible. In this work, we developed a facile method of obtaining heavy-metal-free electrode materials that are effective in ORR. Graphene-based catalysts were doped using azodicarbonamide (ADC) as the source of nitrogen, then carbonized at high temperatures in the range of 700–900 °C under inert gas flow. The produced materials were tested as catalysts for ORR, which is the most important reaction for Zn–air batteries and fuel cells. All obtained nitrogen-doped graphene foams showed increased catalytic activity in ORR owing to active sites created by nitrogen functional groups on the graphene surface. This paper shows that carbonization temperature has a significant impact on nitrogen content and that a small percentage of nitrogen may have a positive effect on the catalytic activity of the obtained materials. The number of transferred electrons in ORR was found to range from three to the maximal theoretical value, i.e., four.

Graphene foam as a stable anode material in lithium‐ion batteries

Graphene foam (GF) as anode material is attracting attention due to the mass-scale production and highly conductive porous three-dimensional (3D) morphology of 2D-graphene. The stable performance of lithium-ion battery (LiBs) based on GF-anode material is one of the challenges to achieve. Herein, the GF is synthesized with the help of chemical vapor deposition (CVD) method and used as anode material in coin-cell LiB. A total 250-charge and discharge cycles of LiB at 0.1 C are observed, and the highest specific capacity ~450 mAh g−1 was detected. The stable performance of LiB is observed from 100th to 250th cycle with a small capacity fading. The rate performance (0.1 C, 1 C, 2 C, 3 C, 4 C each for 10 cycles, and 0.1 C for 100 cycles) indicates a stable performance of LiB. Technologically, stable performance of LiBs is important, and present study can be used as proof of concept for future stable GF-based practical LiBs.

Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers

Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe2O4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9–13.5 mg·cm−3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached −40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites.

Thermal conductivity and energy storage capacity enhancement and bottleneck of shape-stabilized phase change composites with graphene foam and carbon nanotubes

A systematic, carbon-based composite phase change materials with substantial increase of the thermal conductivity and energy storage density was assembled by encapsulating PEG into graphene foams (GF), CNTs and hierarchical porous materials derived from GF and CNT. The influence of preparation approaches on the microstructures, thermal conductivity and thermal energy densities of composites were assessed by various characterization tools. The results obtained indicated that graphene foam-CNT hybrid structures (GCNT) composites exhibit excellent thermal conductivity, 118% higher than pure PEG and 89.5% higher relative to that of GF/PEG@CNT (GPC) composites. The content and interconnected hierarchical porous carbons enhance thermal transfer in composites during the process of phase change. Notably, GCNT@PEG (GCP) had a maximum of up to 80 wt% PCM loading. This composite has a melting latent heat of 128.7 kJ/kg, up to 39.3% and 87.5% higher than those of other composites. CNTs have significantly enhanced the thermal transport of composite PCMs, but the interfacial thermal resistance of CNTs and graphene foam is the bottleneck of heat transfer of composite PCMs. The current results create the conditions for the application of novel hierarchical porous carbon composite PCMs for high-energy density, thermal energy conversion, and shape-stabilized PCMs (ssPCMs) with improved thermal conductivity.

Theory and experiment for 3D porous graphene foam thermoacoustic transducer

Due to its excellent heat dissipation capability and high thermal conductivity, 3D porous graphene foam (3DPGF) has attracted immense attention for its potential applications in thermoacoustic devices. However, 3DPGF is usually relatively fragile, which poses a challenge to its practical application in thermoacoustic equipment. In this respect, its structural strength can be significantly improved by pasting the material onto a substrate. In this paper, the performance of thermoacoustic transducers made of 3DPGF on a substrate is investigated by theory and experiment. Both 3DPGFs on a porous anodic aluminum (AAO) substrate and on a polydimethylsiloxane (PDMS) substrate are taken into consideration. First, a theoretical model for the 3D thermoacoustic source on a substrate is proposed, and analytical solutions are obtained. The model and its corresponding solution are verified by comparing it with experiment. Subsequently, key influencing factors of 3DPGF and substrate on the acoustic field characteristics are analyzed theoretically. Finally, an experimental bending test is performed to explore the acoustic performance and flexibility of 3DPGFs on different substrates. The theoretical and experimental results reveal that 3DPGF on AAO produces a higher sound pressure level than that on PDMS substrate when the thermoacoustic transducer is undeformed, while it is easily damaged at an initial first-time bending. In contrast, 3DPGF on PDMS shows better flexibility than that on AAO substrate and it displays stable acoustic performance even after repeated and recursive bending.

A study of Co‐Mn phosphate supported with graphene foam as promising electrode materials for future electrochemical capacitors

Mn and Co are known for their redox storage mechanism depending on the kinetics of their ions, which is required to boost capacity values of the material electrodes for energy storage applications. However, to the best of our knowledge, Co-Mn phosphate material-based electrochemical capacitors have been rarely investigated. In this work, CoMn(PO4)2 synergized with graphene foam (GF) was synthesized following an easy, direct and low-temperature hydrothermal method. The study investigated the synergy between Co, Mn and GF-supported composite, with a strong P-O covalent tie occurring at the surface of the material, leading to a high degree of polarization and very low relaxation time. The CoMn(PO4)2/GF material tested as a half-cell could achieve a specific capacity of 58.15 mAh g−1 at 0.5 A g−1. A CoMn(PO4)2/GF//activated carbon (AC) hybrid device was made up considering CoMn(PO4)2/GF and an AC material as positive and negative electrodes, respectively. The CoMn(PO4)2/GF//AC hybrid device achieved a specific capacity of 45.89 mAh g−1, specific energy of 51.53 Wh kg−1 and a corresponding specific power of 561.52 W kg−1 at 0.5 A g−1. Furthermore, the device displayed a 95% capacity retention after 10 000 GCD cycles at 12 A g−1 and showed improved performance over its initial specific capacity after a voltage holding test for over 110 hours at 2 A g−1.

Controllable synthesis and electrochemical performance of Fe2O3@ graphene foam composite as anode materials for sodium-ion batteries

Controllable synthesis and electrochemical performance of Fe2O3@ graphene foam composite as anode materials for sodium-ion batteries

Graphene Particles Interfere with Pro-Inflammatory Polarization of Human Macrophages: Functional and Electrophysiological Evidence.

The interaction of two types of fragmented graphene particles (30-160nm) with human macrophages is studied. Since macrophages have significant phagocytic activity, the incorporation of graphene particles into cells has an effect on the response to functional polarization stimuli, favoring an anti-inflammatory profile. Incubation of macrophages with graphene foam particles, prepared by chemical vapor deposition, and commercially available graphene nanoplatelet particles does not affect cell viability when added at concentrations up to 100µg mL-1 ; macrophages exhibit differential quantitative responses to each type of graphene particles. Although both materials elicit similar increases in the release of reactive oxygen species, the impact on the transcriptional regulation associated with the polarization profile is different; graphene nanoplatelets significantly modify this transcriptomic profile. Moreover, these graphene particles differentially affect the motility and phagocytosis of macrophages. After the incorporation of both graphene types into the macrophages, they exhibit specific responses in terms of the mitochondrial oxygen consumption and electrophysiological potassium currents at the cell plasma membrane. These data support the view that the physical structure of the graphene particles has an impact on human macrophage responses, paving the way for the development of new mechanisms to modulate the activity of the immune system.

Mechanical Properties and Deformation Mechanisms of Graphene Foams with Bi-Modal Sheet Thickness by Coarse-Grained Molecular Dynamics Simulations.

Graphene foams (GrFs) have been widely used as structural and/or functional materials in many practical applications. They are always assembled by thin and thick graphene sheets with multiple thicknesses; however, the effect of this basic structural feature has been poorly understood by existing theoretical models. Here, we propose a coarse-grained bi-modal GrF model composed of a mixture of 1-layer flexible and 8-layer stiff sheets to study the mechanical properties and deformation mechanisms based on the mesoscopic model of graphene sheets (Model. Simul. Mater. Sci. Eng. 2011, 19, 54003). It is found that the modulus increases almost linearly with an increased proportion of 8-layer sheets, which is well explained by the mixture rule; the strength decreases first and reaches the minimum value at a critical proportion of stiff sheets ~30%, which is well explained by the analysis of structural connectivity and deformation energy of bi-modal GrFs. Furthermore, high-stress regions are mainly dispersed in thick sheets, while large-strain areas mainly locate in thin ones. Both of them have a highly uneven distribution in GrFs due to the intrinsic heterogeneity in both structures and the mechanical properties of sheets. Moreover, the elastic recovery ability of GrFs can be enhanced by adding more thick sheets. These results should be helpful for us to understand and further guide the design of advanced GrF-based materials.

Chinese knot-like bimetallic NiCo2S4 grew on 3D graphene foam as high-performance electrode for Na+ storage

Bimetallic NixCo3−xS4 (x = 1 or 2) with synergistic effect is a promising candidate material for sodium-ion battery (SIB) anodes because of its higher electrical conductivity than monometallic sulfides owing to its lower bandgap. In this study, samples of bimetallic sulfide NixCo3−xS4 with tunable chemical Ni/Co components are successfully grown on graphene foam (GF), forming free-standing Chinese knot-like nanowires (NiCo2S4 NWs/GF) and Chinese lantern-like nanoarrays (CoNi2S4 NAs/GF). When evaluate as anodes for SIBs at 0.3–3.0 V in ether-based electrolytes, the NiCo2S4 NWs/GF electrodes offer superior rate performance and cycling stability than the CoNi2S4 NAs/GF electrodes. More specifically, the NiCo2S4 NWs/GF electrode has a high capacity of 650–556 mAh g−1 at 0.1–2.0 A g−1 and 457 mAh g−1 after 200 cycles at 0.5 A g−1 with a high initial coulombic efficiency (ICE) of 95.6%. And its rate performance outperforms most existing electrodes those contain NiSx, CoSx, or NiCo2S4. The excellent electrochemical performance of the NiCo2S4 NWs/GF electrode is attributed to its unique composition, smaller size, and porous nanowires that can reduce the diffusion length of e- and Na+, and enhance reaction kinetics.

Zeolite-templated mesocellular graphene foam with adjustable defects as highly efficient catalysts for oxygen reduction reaction

Zeolite-templated mesocellular graphene foam with adjustable defects as highly efficient catalysts for oxygen reduction reaction

An analytical solution for vibro-acoustic characteristics of sandwich panel with 3DGrF core and FG-CNT reinforced polymer composite face sheets

This paper presents the analytical solution on vibro-acoustic characteristics of three-dimensional graphene foam core and functionally graded carbon nanotube-reinforced polymer face sheet (3DGrFC-CNTRPFS) sandwich panel. Stress resultants of functionally graded carbon nanotube reinforced composite face sheets and 3D graphene foam core are determined by integrating their relevant stress expressions over the thickness of the face sheet and core, respectively. Further, this stress resultants are used in the equation based on Hamilton's principle to develop the governing equation. The third-order shear deformation theory is used to capture the effect of transverse shear in dynamic response. Based on mode superposition principle, the vibration response is calculated. This vibration response is given as an input to the Rayleigh integral to calculate the sound radiation characteristics. The study focuses on capturing the acoustic characteristics by varying the porosity coefficient of 3D graphene foam in the core while the carbon nanotubes are varied along with the thickness of the face sheets. The detailed analysis of the effect of the various functionally graded pattern of carbon nanotube and porosity coefficient of 3D graphene foam on acoustic characteristics is studied and the results are discussed.

Compressive modulus and deformation mechanisms of 3DG foams: experimental investigation and multiscale modeling

Due to the wide applications of three-dimensional graphene (3DG) foam in bio-sensors, stretchable electronics, and conductive polymer composites, predicting its mechanical behavior is of paramount importance. In this paper, a novel multiscale finite element model is proposed to predict the compressive modulus of 3DG foams with various densities. It considers the effects of pore size and structure and the thickness of graphene walls on 3DG foams’ overall behavior. According to the scanning electron microscope images, a unit cell is selected in the microscale step to represent the incidental arrangement of graphene sheets in 3DG foams. After derivation of equivalent elastic constants of the unit cell by six individual load cases, the whole unit cell is considered an equivalent element. The macroscale model is prepared by defining a representative volume element (RVE), containing a sufficient number of the equivalent elements. Assigning a stochastic local coordinate system for each equivalent element in the macro RVE provides a model that could be utilized for elastic modulus estimation of 3DG foams in macroscale. To investigate the correspondence between the theoretical results and experimental data, 3DG foams were synthesized with four densities, and their compressive behavior were evaluated. The mass densities of the prepared foams were 5.36, 8.50, 9.37, and 11.5 mg cm−3, and the corresponding measured elastic modulus for each were 6.4, 10.7, 16.9, and 29.1 kPa, respectively. The predicted modulus by the proposed model for the synthesized foams were 6.1, 13.1, 15.6 and 21.7 kPa, respectively. The results show that the maximum divergence between estimated values and experimental data is less than 25%, confirming the high capability of the model in the estimation of 3DG foams’ properties.

A stretchable array of high-performance electrochromic devices for displaying skin-attached multi-sensor signals

We report on the fabrication of an interactive display system consisting of a stretchable array of electrochromic devices (ECDs) and temperature and strain sensors for visual display of skin temperature and wrist movement. The electrochromic device is prepared by coating poly(3-hexylthiophene) and tungsten trioxide as electrochromic materials on a flexible and transparent electrode of indium-tin-oxide-coated polyethylene terephthalate, and the subsequent assembly of the prepared electrodes using a gel-type electrolyte of Li-mixed 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(methyl methacrylate). The fabricated ECD exhibits three different colors due to the redox reactions of the electrochromic materials at the corresponding potentials: magenta, violet, and blue at −1.5 V, 0.5 V, and 1.5 V, respectively. By using patterned liquid metal Galinstan interconnections, a stretchable array of the ECDs is fabricated based on a strain relieving mechanism with an island-bridge design, resulting in mechanical stability to repeated stretching of up to 30%. A high-performance strain sensor is fabricated by embedding fragmentized graphene foams inside poly(demithylsiloxane) thin film, and a temperature sensor is prepared by embedding multi-walled carbon nanotubes/polyaniline composite in poly(vinyl alcohol) film. With the integrated system, the strain due to wrist bending and the skin temperature measured by the sensors are displayed as changes in the color pattern of the ECD array aided by an Arduino circuit. This work demonstrates the high potential of our system for application to wearable healthcare devices providing real-time visual display of varied bio-signals.

Advanced Engineering for Cathode in Lithium–Oxygen Batteries: Flexible 3D Hierarchical Porous Architecture Design and Its Functional Modification

AbstractModern technology constantly requires smaller, more efficient lithium–oxygen batteries (LOBs). To meet this need, a chemical vapor deposition (CVD) method is used to create an innovative cathode design with both a hierarchical porous nanostructure and a 3D flexible macroscopical morphology. This method employs architectural optimization to further improve cathodic ORR and OER performance via heteroatom doping, surface‐sprouted carbon nanofibers (CNFs) grafting, and boundary exposing. The cathode consists of a 3D hierarchical porous graphene foam (PGF), along with RuO2 nanoparticles impregnated and nitrogen doped CNFs (RuO2@NCNFs), where the PGF serves as a structural support and cathodic current collector, and the RuO2@NCNFs work as a superior bi‐functional catalyst. The cathode delivers an outstanding discharge capacity of 8440 mAh gcathode−1 while maintaining a recharge plateau at ≈4.0 V, and can cycle for over 700 rounds without obvious degeneration under a fixed capacity. Notably, this free‐standing cathode can be directly used in LOBs without the need for additional substrates or current collectors. Therefore, the current densities and capacities herein are calculated based on the total weight of the cathodes. These results demonstrate the RuO2@NCNFs‐PGF cathode's remarkable potential for LOB applications, and this rational cathodic structure may be extended to other highly efficient catalyst applications.

Research and Preparation of Graphene Foam Based on Passive Ultra-Low Energy Consumption Building New Ultra-Thin External Wall Insulation Material

As an advanced upgrade form of green buildings, passive ultra-low energy consumption building is an inevitable trend of future building development. Therefore, it is of great significance to develop new fireretardant and ultra-thin thermal insulation materials for exterior wall. In this paper, we focus on graphene foams with excellent thermal insulation, and the microstructure of graphene hydrogel was studied as an intermediate to prepare graphene foam. The microstructure of graphene hydrogel as an intermediate to prepare graphene foam was studied. This study was proposed based on two problems: (1) Graphene hydrogels change from hydrophilic/lipophobic to hydrophobic/lipophilic after freeze-drying. (2) Compared with the poor mechanical properties of graphene hydrogels, graphene-based nanocomposite hydrogels have highly extensible and resilient properties. We studied the microstructures of both graphene and graphene hydrogel. Notably, many stomatas were distributed in graphene hydrogel, and the proportion could be adjusted by changing the quantity and type of reducing agent. This property can be applied to adjust the microstructure and properties of graphene foams. Based on the practice of passive ultra-low energy consumption buildings, the heat insulation mechanism of graphene foam insulation material and the preparation process of graphene foam were studied through theoretical analysis and experimental research. The results of this study provide a theoretical basis and scientific basis for the development and application of graphene foam insulation materials, and promote the industrial production of graphene foam insulation materials, with important research value and application prospect to solve the problems of high quality and large-scale development of passive ultra-low energy consumption building restricted by conventional exterior wall insulation materials.

Nitrogen Functionalization of CVD Grown Three-Dimensional Graphene Foam for Hydrogen Evolution Reactions in Alkaline Media.

Three-dimensional graphene foam (3D-GrFoam) is a highly porous structure and sustained lattice formed by graphene layers with sp2 and sp3 hybridized carbon. In this work, chemical vapor deposition (CVD)—grown 3D-GrFoam was nitrogen-doped and platinum functionalized using hydrothermal treatment with different reducing agents (i.e., urea, hydrazine, ammonia, and dihydrogen hexachloroplatinate (IV) hydrate, respectively). X-ray photoelectron spectroscopy (XPS) survey showed that the most electrochemically active nitrogen-doped sample (GrFoam3N) contained 1.8 at % of N, and it exhibited a 172 mV dec−1 Tafel plot associated with the Volmer–Heyrovsky hydrogen evolution (HER) mechanism in 0.1 M KOH. By the hydrothermal process, 0.2 at % of platinum was anchored to the graphene foam surface, and the resultant sample of GrFoamPt yielded a value of 80 mV dec−1 Tafel associated with the Volmer–Tafel HER mechanism. Furthermore, Raman and infrared spectroscopy analysis, as well as scanning electron microscopy (SEM) were carried out to understand the structure of the samples.

Highly sensitive piezoresistive pressure sensors based on laser-induced graphene with molybdenum disulfide nanoparticles

Wearable pressure sensors have drawn significant attention because of their extensive applications in motion detection, tactile sensing, and health monitoring. However, the complex manufacturing process and high cost of active materials make low-cost, large-scale production elusive. In this work, we report a flexible piezoresistive pressure sensor assembled with two 3D laser-induced graphene (LIG) foam electrodes on a polyimide thin film from a simple laser scribing process in the ambient environment. The design of the air gap between the two foam electrodes allows the sensor to showcase a low limit of detection of 0.274 Pa, which provides favorable sensing performance in motion detection and wrist pulse monitoring. The addition of spherical MoS2 nanoparticles between the two foam electrodes further enhances the sensitivity to 88 kPa−1 and increases the sensing range to significantly outperform the previous literature reports. The demonstrated LIG pressure sensors also exhibit fast response/recovery rates and excellent durability/repeatability.

Strain Hardening in Graphene Foams under Shear.

Strain hardening is an important issue for the design and application of materials. The strain hardening of graphene foams has been widely observed but poorly understood. Here, by adopting the coarse-grained molecular dynamics method, we systematically investigated the microscopic mechanism and influencing factors of strain hardening and related mechanical properties of graphene foams under shear loading. We found that the strain hardening is induced by cumulative nonlocalized bond-breakings and rearrangements of microstructures. Furthermore, it can be effectively tuned by the number of graphene layers and cross-link densities, i.e., the strain hardening would emerge at a smaller shear strain for the graphene foams with thicker sheets and/or more cross-links. In addition, the shear stiffness G of graphene foams increases linearly with the cross-link density and exponentially with the number of graphene layers n by G ∼ n1.95. These findings not only improve our understanding of the promising bulk materials but also pave the way for optimizing structural design in wide applications based on their mechanical properties.

Co1-xS/N-doped graphene foam composite as efficient bifunctional electrocatalysts for the evolution reaction of oxygen and hydrogen

As an environment-friendly and sustainable energy conversion technology, water electrolysis is strongly dependent on the efficiency and cost of the electrocatalysts. Herein, nanosheet-constructed cobalt sulfide microspheres incorporated with nitrogen-doped graphene foam (Co1-xS/NGF), a highly efficient bifunctional electrocatalyst for overall water splitting, was obtained by controlled two-step synthesis. The nitrogen-doped graphene foam (NGF) underlying the Co1-xS microspheres provides an electrically conducting support for the catalysts, contributes small size and homogeneous distribution of the in-situ grown Co1-xS microspheres, and affords abundant active sites for fast and sufficient transport of mass and electrons and, therefore, highly enhanced catalytic activity through the strong synergistic effect of Co1-xS microspheres and the NGF substrate. In 1 M KOH, the Co1-xS/NGF hybrid catalyst exhibits remarkable OER and HER catalytic performance, with overpotentials of 233.6 mV for the OER and 163.7 mV for the HER at 10 mA cm−2, and the corresponding Tafel slopes of 138 and 95 mV dec−1, respectively. The hybrid material of Co1-xS/NGF even exhibits a lower overpotential (η20) to reach 20 mA cm−2 towards OER than that of RuO2, and its performance matches the best cobalt sulfide bifunctional electrocatalysts reported to date. Besides, the Co1-xS/NGF is highly stable for long-term water electrolysis in the 1 M KOH. These findings support that the current Co1-xS/NGF is a competitive candidate of transition metal-based catalysts for cost-efficient and large-scale overall water electrolysis in the alkaline environment.