Graphene-based Films Research Articles

Assembly of carbon nanodots in graphene-based composite for flexible electro-thermal heater with ultrahigh efficiency

A high-efficiency electro-thermal heater requires simultaneously high electrical and thermal conductivities to generate and dissipate Joule heat efficiently. A low input voltage is essential to ensure the heater’s safe applications. However, the low voltage generally leads to low saturated temperature and heating rate and hence a low thermal efficiency. How to reduce the input voltage while maintaining a high electro-thermal efficiency is still a challenge. Herein, a highly electrical and thermal conductive film was constructed using a graphene-based composite which has an internal three-dimensional (3D) conductive network. In the 3D framework, cellulose nanocrystalline (CNC) phase with chiral liquid crystal manner presents in the form of aligned helix between the graphene oxide (GO) layers. Carbon nanodots (CDs) are assembled inside the composite as conductive nanofillers. Subsequent annealing and compression results in the formation of the assembled GO-CNC-CDs film. The carbonized CNC nanorods (CNR) with the helical alignment act as in-plane and through-plane connections of neighboring reduced GO (rGO) nanosheets, forming a conductive network in the composite film. The CDs with ultrafast electrons transfer rates provide additional electrons and phonons transport paths for the composite. As a result, the obtained graphene-based composite film (rGO-CNR-CDs) exhibited a high thermal conductivity of 1,978.6 W·m−1·K−1 and electrical conductivity of 2,053.4 S·cm−1, respectively. The composite film showed an outstanding electro-thermal heating efficiency with the saturated temperature of 315 °C and maximum heating rate of 44.9 °C·s−1 at a very low input voltage of 10 V. The freestanding graphene composite film with the delicate nanostructure design has a great potential to be integrated into electro-thermal devices.

Porous shiitake mushroom carbon composite with NiCo2O4 nanorod electrochemical characteristics for efficient supercapacitor applications

Mushroom carbon based composite electrode with NiCo2O4 (m-C/NiCo2O4) nanorod arrays (NRAs), which improves the pseudocapacitive properties by effectively amplifying the electrochemical performance of supercapacitor. Carbon or graphene-based nanorod thin films have been used in supercapacitors with the low gravimetric (85–250 F g−1, and areal (5–60 mF cm−2) specific capacitance values, which is undesirable for practical applications. In the present study, shiitake mushroom was used as the carbon source. The shiitake mushroom provides higher surface area and enhanced energy storage performance when compared with other carbon materials. m-C/NiCo2O4 composite made of NiCo2O4 nanorods combined with carbon nanoparticles made from shiitake mushroom using hydrothermal method, provides a higher specific capacitance when compared with carbon and other metal oxide/carbon composite electrodes. The formation of m-C/NiCo2O4 nanorod composite attributes to the higher surface area for the ion adsorption/desorption from the electrolyte, which resulted in a high specific capacitance. Porous properties of natural carbon and non-porous NiCo2O4 metal oxides effectively amplified the capacitance behavior and enhance stability. The physico-chemical and electrochemical characteristics of the samples are examined using various techniques. Therefore, the specific capacitance and excellent cycling stability have been improved using m-C combined with NiCo2O4. m-C/NiCo2O4 symmetric coin cell showed higher stability and high specific capacitance (556 F g−1 at current density of 10 A g−1).

Pulsed laser deposition of monolayer and bilayer graphene

The properties of graphene vary with the number of layers, thus determining its usefulness in different applications. Consequently, it is important to develop a method for precisely controlling the number of layers for various application demands. In this study, high quality monolayer graphene was successfully prepared using pulsed laser deposition. Meanwhile, the growth of monolayer and bilayer graphene can be controlled by adjusting the laser energy density. Raman spectra show that high quality monolayer films grew at a laser energy density of 5.66 J/cm2 and bilayer graphene films grew at a laser energy density of 8.49 J/cm2. X-ray photoelectron spectroscopy indicate that the main chemical state of carbon is the sp2 hybrid state, and the maximum atomic ratio of sp2 and sp3 results from the sample with laser energy density of 5.66 J/cm2. Scanning electron microscope images show that monolayer graphene is connected by small sheets with different sizes, and the largest graphene sheet reaches 20 μm. High resolution transmission electron microscope images and selected area electron diffraction patterns show that graphene samples are highly crystalline and yield significant layer information. UV–Vis spectra indicate that the transmittance through monolayer and bilayer graphene at 550 nm are 96.93% and 95.05%, respectively. Ultraviolet photoelectron spectroscopic measurements show that the work function of graphene ranges from 3.72 eV to 4.76 eV; the variation in the work function is related to growth defects. Finally, the relationship between the structure of the graphene films and laser energy density are investigated in detail, and these results indicate that the controllable growth of graphene can be achieved by adjusting the laser energy density. This means that a suitable laser energy density is conducive to defining an equilibrium between diffusion and condensation of carbon atoms, which is crucial to the growth of high-quality monolayer and bilayer graphene. It is expected that this study might be facilitate the preparation of graphene-based composite films and devices.

Characterization of reduced Graphene oxide films used as stripper foils in a 3.0-Mv Tandetron

Reduced graphene oxide (rGO) films can be employed as thin ion strippers in an accelerator. They show some advantages with respect to the graphite foils, due to their high thermal and electrical conductivities, low density, high mechanical resistance and high stability. The preparation method of the graphene-based films and their physical characterization are presented and discussed. Thin graphene oxide (GO) films with a thickness of from 0.5 up to 2.0 μm have been synthesized and studied to be used as an ion extractor (stripper) in the 3.0 MV Tandetron of the CANAM Laboratory at the Nuclear Physics Institute in Rez, Czech Republic. GO is transformed to rGO also by low ion beam doses. Measurements of stripper efficiency, as the ion transmission factor of films, have been carried out by accelerating different ions, from helium to carbon, having energies from 1.0 up to 16 MeV, and by using different charge states and a current density ranging between about 10 nA/cm2 and 2 μA/cm2. The ion fluence at which the so-obtained graphene oxide films can be undergone exceeds a dose of 1 × 1016 particles/cm2. Furthermore, these stripper films have demonstrated a significantly high charge production, comparable to that of the graphite films. However, the higher mechanical resistance represents an undiscussed advantage with respect to the graphite films.

Enhanced Durability of Graphene-Based Epoxy Films

Graphene-based nanoparticles are suitable to enhance toughness related to impact, fracture and fatigue of epoxy nanocomposites to make them able to meet industrial requirements. The increase in the mechanical performance of graphene-based films is well known in the literature. This paper highlights an additional beneficial effect of graphene-based nanoparticles, which is related to the increase of the photooxidative resistance of polymeric films. Graphene Nanoplatelets (GNPs) have been incorporated, at different weight percentages, in the epoxy films. Unfilled and nanofilled films (30 ± 1.5 μm thick) have been subjected to the accelerated photo-oxidative degradation by exposing them to UV-A radiation (295–380 nm). AFM-Harmonix modulus maps at the micro and nanoscale level have been detected to investigate the effect of graphene nanoparticle on the mechanical properties of untreated and UV treated unfilled and nanofilled samples. SEM analysis has been used to analyse the effect of graphene on morphological features of the film surface. UV irradiation determines relevant damages of the mechanical properties and morphological feature of the unfilled sample. The experiments carried out on the nanofilled films show that GNPs, dispersed in the epoxy-based films, determine a strong decrease in the entity of the damages of the film surfaces.

Tailorable graphene-based superconducting films via self-assembly and in-situ doping

It looks like graphene is ready for production, at least for new applications which need to use its unique properties. As doped-graphene is a typical two-dimensional (2D) superconductor, graphene has showed the possibilities for practical applications besides the significant meaning in studying relevant physical problems. We report a novel development in fabricating large-area graphene-based superconducting film (GSF) via self-assembly and in-situ calcium (Ca) intercalation. As-fabricated GSF can be tailored into puzzle-sized and arbitrary-shaped superconducting pieces, demonstrating outstanding processability. GSF shows a superconducting transition at ∼11 K and an upper critical field Hc2 at 9.85 kOe. Especially, GSF exists stably for dozens of minutes in the atmosphere. Given these advantages, GSF points out a new application direction of graphene and provides a platform for studying 2D superconductors. The self-assembly and in-situ doping method also pave a new way for the application of free-standing 2D superconductors.

Preparation of a glassy carbon electrode modified with reduced graphene oxide and overoxidized electropolymerized polypyrrole, and its application to the determination of dopamine in the presence of ascorbic acid and uric acid.

This paper presents a method for the preparation of a graphene-based hybrid composite film by electrodeposition of reduced graphene oxide and overoxidized electropolymerized polypyrrole onto a glassy carbon electrode (GCE) using cyclic voltammetry. The morphology of the hybrid composite film was characterized by scanning electron microscopy. The electrochemical activity of the modified GCE was studied by cyclic voltammetry using the negatively charged redox probe Fe(CN)63- and the positively charged redox probe Ru(NH3)63+. The modified GCE displays excellent electrocatalytic activity for dopamine (DA) and uric acid (UA), but electrostatically repulses ascorbate anion under physiological pH conditions. The voltammetric response to DA is linear in the 2.0μM to 160μM concentration range even in the presence of 1.0mM ascorbic acid and 0.1mM of UA. The detection limit is 0.5μM. The amperometric response to DA (best measured at 0.22V vs. Ag/AgCl) extends from 0.4μM to 517μM and has a 0.2μM detection limit. Graphical abstract Schematic presentation of the fabrication of a glassy carbon electrode modified with reduced graphene oxide and overoxidized electropolymerized polypyrrole, and its application to the determination of dopamine in the presence of ascorbic acid and uric acid.

Highly Thermally Conductive Fluorinated Graphene Films with Superior Electrical Insulation and Mechanical Flexibility.

Graphene-based heat-spreading films have captured high attention in academic study and commercial applications because of their extremely high thermal conductivity and desired flexibility. However, the electrical conductivity limits their utilizations in many electronic fields. Herein, to address this problem, fluorinated graphene (F-graphene) that is exfoliated from commercial fluorinated graphite was first used to prepare the flexible free-standing composite film via vacuum filtration of uniform poly(vinyl alcohol)-assisted F-graphene suspension. The well-organized alignment of F-graphene lamellas makes the composite film show an ultrahigh in-plane thermal conductivity of 61.3 W m-1 K-1 at 93 wt % F-graphene. Despite at such high filler loading, the fabricated F-graphene film still possesses a superior electrical insulation property. Therefore, these results suggest that F-graphene, as the novel thermally conductive filler, demonstrates fascinating characters in the preparation of a thermally conductive yet electrically insulating nanocomposite.

Multifunctional Thermal Management Materials with Excellent Heat Dissipation and Generation Capability for Future Electronics.

Thermal management materials (TMMs) used in electronic devices are crucial for future electronics and technologies such as flexible electronics and artificial intelligence (AI) technologies. As future electronics will work in a more complicated circumstance, the overheating and overcooling problems can exist in the same electronics while the common TMMs cannot meet the demand of thermal management for future electronics. In this work, nacre-mimetic graphene-based films with super flexibility and durability (in over 10,000 tensile cycles), excellent capability to dissipate excess heat (20.84 W/(m·K) at only 16-22 μm thickness), and outstanding heating performance to generate urgent heat for electronics under extremely cold conditions are fabricated by a facile solution casting method, and the fabricated composites are proved to be superior multifunctional TMMs for the thermal management in electronic chips. In addition, the application of the paper-like films with high in-plane thermal conductivity to a flexible heat spreader and film heater is demonstrated by simulation using a finite volume method, which shows the high importance of the in-plane thermal conductivity in thermal management of electronics.

Graphene transparent conductive films directly grown on quartz substrates by assisted catalysis of Cu nanoparticles

Graphene-based transparent conductive films (TCFs) are promising alternative to indium tin oxide owing to their high transmittance and conductivity. Graphene films were directly deposited on quartz substrates by assisted catalysis of Cu nanoparticles in ambient pressure chemical vapor deposition. Growth conditions, including the concentration of Cu nanoparticles as catalyst, flow rate of CH4, temperature and growth time, were systematically investigated to optimize the quality and performance of graphene TCFs. With the optimized growth conditions, the obtained graphene TCFs exhibit good performance with sheet resistance of 2.48 kΩ sq−1 at transmittance of 82.83%. With this method, graphene TCFs with good performance were obtained without the need of a complex transfer process of graphene, opening a considerable route toward fabricating graphene TCFs on dielectric substrates.

CVD-graphene/graphene flakes dual-films as advanced DSSC counter electrodes

The use of graphene‐based electrodes is burgeoning in a wide range of applications, including solar cells, light emitting diodes, touch screens, field‐effect transistors, photodetectors, sensors and energy storage systems. The success of such electrodes strongly depends on the implementation of effective production and processing methods for graphene. In this work, we take advantage of two different graphene production methods to design an advanced, conductive oxide- and platinum-free, graphene-based counter electrode for dye-sensitized solar cells (DSSCs). In particular, we exploit the combination of a graphene film, produced by chemical vapor deposition (CVD) (CVD-graphene), with few-layer graphene (FLG) flakes, produced by liquid phase exfoliation. The CVD-graphene is used as charge collector, while the FLG flakes, deposited atop by spray coating, act as catalyst for the reduction of the electrolyte redox couple (i.e. - and Co+2/+3). The as-produced counter electrodes are tested in both - and Co+2/+3-based semitransparent DSSCs, showing power conversion efficiencies of 2.1% and 5.09%, respectively, under 1 SUN illumination. At 0.1 SUN, Co+2/+3-based DSSCs achieve a power conversion efficiency as high as 6.87%. Our results demonstrate that the electrical, optical, chemical and catalytic properties of graphene-based dual films, designed by combining CVD-graphene and FLG flakes, are effective alternatives to FTO/Pt counter electrodes for DSSCs for both outdoor and indoor applications.

Self-assembled free-standing graphene oxide hybrid films modified by silane functionalized TiO2 nanotubes to increase their final Young's modulus

Free-standing hybrid films of graphene oxide (GO) and titanium dioxide nanotubes (TNT) were prepared trough a bar coating and drying method from GO-based dispersions. Successful chemical functionalization of the nanotubes with allyltriethoxysilane as a linker is confirmed by XPS and Raman spectroscopy. These resulting functionalized nanotubes were then used to prepare self-assembled hybrid films with GO in aqueous suspension. These hybrid films exhibit outstanding mechanical properties. The Young's modulus was as high as ∼10 GPa (38% higher than the pristine graphene oxide film) and an ultimate tensile strength around ∼40 MPa. The method presented here is versatile, and it can be easily coupled to fabricate other graphene-based hybrid films for applications, such as fuel-cells, photocatalysis, filters, amongst others.

Efficient Conversion of Lignin Waste to High Value Bio-Graphene Oxide Nanomaterials.

Lignin graphene oxide was oxidized after Kraft lignin was graphitized by thermal catalytic conversion. The reduced lignin graphene oxide was derived from lignin graphene oxide through thermal reduction treatment. These Kraft lignin, lignin graphite, lignin graphene oxide, and reduced lignin graphene oxide were characterized by scanning electron microscopy, raman microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and thermogravimetric analysis. The results showed lignin graphite converted from Kraft lignin had fewer layers with smaller lateral size than natural graphite. Moreover, lignin graphene oxide was successfully produced from lignin graphite by an oxidation reaction with an hour-long reaction time, which has remarkably shorter reaction time than that of graphene oxide made from natural graphite. Meanwhile, this lignin-derived graphene oxide had the same XRD, FTIR and Raman peaks as graphene oxide oxidized from natural graphite. The SEM, TEM, and AFM images showed that this lignin graphene oxide with 1–3 average layers has a smaller lateral size than that of graphene oxide made from natural graphite. Moreover, the lignin graphene oxide can be reduced to reduced lignin graphene oxide to fabricate graphene-based aerogel, wire, and film for some potential applications.

Synthesis and characterizations of graphene-based composite film for thermal dissipation

In this study, we develop a series of graphene nanosheets(GNs)/carbon nanotubes(CNTs)/copper(Cu) composite film for heat dissipation. Scanning electronic microscopy (SEM), Raman spectroscopy, X-ray photo spectroscopy (XPS), Laser flash and infrared thermal images of composite film are carried out in this study. We discovered that the content of CNTs in composite film plays an important role on heat dissipation performance. Optimized ratio of GNs to CNTs were found to be 6:4. Raman spectra showed that ID/IG ratio of GNs was 0.23, and the ID/IG ratio would increase to 0.84 by adding CNTs with the ratio of 6:4. Laser flash analysis shows that the thermal conductivity (K) could be enhanced from 520 W/m⋅K of GNs film to 687 W/m⋅K of GNs/CNTs composite film. Infrared thermal images also relative the relationship between the microstructure of composite film and heat dissipation performance. These data indicate that as-synthesized graphene nanosheets/CNTs/Cu composite film is a potential candidate for heat dissipation applications.

Heat dissipation study of graphene-based film in single tube IGBT devices

The insulated gate bipolar transistor (IGBT) devices often work under significantly high voltage and current, and how to reduce loss within them and prevent damage to them, caused by excessive heating must be considered in their operation. In this paper, a three-dimensional model of a single-tube IGBT device is constructed to simulate the temperature field distribution. The influence of different nanometer and micrometer thicknesses of graphene-based film (GBF) on the heat dissipation performance of IGBT devices is studied. The simulation results show that GBF placed on a chip surface, as a heat spreader, can improve the lateral heat dissipation of local hot spots, with a high heat flux, and GBF can greatly reduce the highest temperature on the chip surface. Moreover, graphene-based film of micrometer thickness provides better heat dissipation than that of nanometer thickness.

Experimental Demonstration of Ultrafast THz Modulation in a Graphene-Based Thin Film Absorber through Negative Photoinduced Conductivity.

We present an experimental demonstration and interpretation of an ultrafast optically tunable, graphene-based thin film absorption modulator for operation in the THz regime. The graphene-based component consists of a uniform CVD-grown graphene sheet stacked on an SU-8 dielectric substrate that is grounded by a metallic ground plate. The structure shows enhanced absorption originating from constructive interference of the impinging and reflected waves at the absorbing graphene sheet. The modulation of this absorption, which is demonstrated via a THz time-domain spectroscopy setup, is achieved by applying an optical pump signal, which modifies the conductivity of the graphene sheet. We report an ultrafast (on the order of few ps) absorption modulation on the order of 40% upon photoexcitation. Our results provide evidence that the optical pump excitation results in the degradation of the graphene THz conductivity, which is connected with the generation of hot carriers, the increase of the electronic temperature, and the dominant increase of the scattering rate over the carrier concentration as found in highly doped samples.

High-performance graphene-based heaters fabricated using maskless ultraviolet laser patterning

Graphene-based film heaters (GFHs) with laser-patterned electrode structures can be used in microheaters, thermal sensors, and thermostatic apparatuses for various high-value-added medical devices and creative products. To obtain uniform and higher temperatures, this study aims to design, fabricate, and measure GFHs with net-like electrode structures using ANSYS Workbench software, an ultraviolet laser processing system, and an infrared thermal imaging camera, respectively. The electric heating experiments (which were measured with an infrared thermal imaging camera) demonstrated that the temperatures of GFHs with net-like electrode structures were significantly higher than those of devices without patterned graphene films. Moreover, the temperatures of GFHs with net-like electrode structures increased rapidly with time when DC voltages higher than 12 V were applied for at least 10 s. A maximum temperature of 91.5 °C was obtained at 200 s when a DC voltage of 18 V was applied. Besides, minimal and maximal deviations of steady-state temperatures between experimental and simulated values were 6.9 °C and 10 °C under each corresponding DC voltage, respectively.

Carbon fiber enhanced mechanical and electromagnetic absorption properties of magnetic graphene-based film

Graphene-based films have attracted much attention as possible candidates for lightweight, wide absorption frequency, high thermal stability, and mechanically strong electromagnetic (EM) absorbers. In this study, colloidal solutions of carbon fiber (CF), Fe3O4 nanoparticles (FeNPs), and reduced graphene oxide (rGO) were used for synthesizing composite films that were first cast and then gradually heated in vacuum for thermal reduction. Compared with FeNPs/rGO film, the as-prepared CF/FeNPs/rGO film with 10 wt% CF exhibited 125% and 100% enhancement in tensile strength and EM interference shielding efficiency, respectively. A minimum reflection loss of −22.18 dB at 10.64 GHz with a matching thickness of 2.0 mm has been attained in the composite containing 50 wt% loading in the wax matrix, and the effective absorption bandwidth with reflection loss values less than −10 dB covered 9.2–12.32 GHz. The results indicated that CF can be considered as promising filler for improving the mechanical properties and microwave absorption capabilities of magnetic graphene-based system and the magnetic graphene-based composites may be used as high-performance EM absorbing materials.

A low-friction graphene nanoplatelets film from suspension high velocity oxy-fuel thermal spray

The addition of graphene-based nanomaterials is known to improve the tribology properties of materials by lowering the coefficient of friction and reducing wear. The covering of small areas with thin graphene-based films is routinely carried out; however, a fast and efficient way of covering large areas represents an outstanding challenge. Here we present a method for the deposition of graphene nanoplatelets (GNPs) on stainless steel substrates based on suspension high-velocity oxy fuel thermal spray. GNPs were radially injected into the combustion jet, providing sufficient momentum and moderate heat transfer to facilitate effective bonding with the substrate. Upon unlubricated ball-on-disc wear testing against an alumina counterbody, GNPs undergo gradual exfoliation, covering the substrate and thus lowering the friction coefficient (<0.1). We have reported the formation of a thin layer, composed of GNPs having different amounts of disorder, which protects the underlying substrate from wear. GNP structural ordering is studied throughout deposition and wear tests, showing an increase of inter- and intralayer disorder at the nanoscale, whilst largely preserving the GNP microstructure.

Strong and Highly Conductive Graphene Composite Film Based on the Nanocellulose-Assisted Dispersion of Expanded Graphite and Incorporation of Poly(ethylene oxide)

Graphene films promise great application potential in modern electronic devices due to their superior electrical and thermal conductivities. However, the green manufacturing of graphene films is still faced with challenges. Also, graphene films prepared by the oxidation and exfoliation method are expensive and exhibit poor mechanical properties. In this work, the highly conductive graphene-based film with reinforced mechanical strength is fabricated by employing cellulose nanofiber (CNF) to help expandable graphite (EG) exfoliate directly in aqueous solution and poly(ethylene oxide) (PEO) to construct a nacre-like structure. Herein, we succeeded in addressing the issue of the graphene films’ unsatisfactory cost and mechanical properties by using very cheap EG as the raw material and taking advantage of the synergistic performance of the two-dimensional EG nanoplatelet, one-dimensional CNF, and flexible PEO. When the mass ratio of EG, CNF, and PEO reaches 95:5:3, the graphene-based film displays a relatively high tensile strength (about 63.3 MPa), which shows a 587% increase over that of EG film (9.2 MPa) and is much higher than those of the reported graphene films prepared through physical exfoliation to our knowledge. Moreover, it shows extraordinary electrical conductivity (1226 S cm–1), thermal conductivity (302.3 W m–1 K–1), and electromagnetic interference shielding effectiveness (44 dB with a thickness of 12 μm). In summary, the manufacturing route of the EG/CNF/PEO composite film is efficient, economical, and promising for commercial applications in the contemporary electronic industry.