Preparation Of High-quality Graphene Research Articles

(Invited) Rapid, Large Area Preparation of Few-Layer Graphene Films Using Xenon Flash Lamp Pyrolysis for High-Performance Structural Micro-Supercapacitors

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based energy storage devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available polymers (polybenzoxazine, polyacrylonitrile and polyaniline) and a high intensity xenon flash lamp on various substrates, including carbon fibers, at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into few layer graphene upon millisecond exposures. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enabled the conversion of the polymeric material into few layer graphene in air and at room temperature, and without thermally damaging the substrate. Conversion to few-layer graphene was strongly dependent on pulse energy and the local temperature which was controlled via pulse power modulation. The obtained graphene composites at optimized conditions exhibited excellent conductivity (0.1 ohm-cm) with ID/IG ratio of 0.3 (Figure 1a). Particularly, graphene derived from polyaniline resulted in the formation of macroporous network (Figure 1b) with good adhesion to the carbon fiber, all of which facilitate the transport of ions through the material. The fabricated supercapacitor devices exhibited a very high areal capacitance of 200 mF/cm2 at 10 mV/s with retention of more than 70% of their capacitance, even at scan rates up to 100 mV/s. Moreover, mechanically, and structurally stable graphene derived from polyaniline on carbon fiber was utilized for the preparation of structural energy storage devices. We assembled symmetric structural supercapacitor comprised of carbonaceous material (carbon fiber and few-layer graphene) and polymer gel electrolyte. This resulted in the preparation of large area device (40 cm2) as shown in the Figure 1c with the capacitance exceeding 2000 mF and almost complete retention of capacitance after 5000 cycles.The preparation of high-quality graphene via photothermal pyrolysis of polymer is amenable to high throughput processing, enabling large-scale production of high performance structural electrochemical energy storage devices. Figure 1

Bioactive trans-resveratrol as dispersant of graphene in water. Molecular interactions

Currently, the preparation of high-quality graphene (G) dispersions is crucial due to the increasing demand for this nanomaterial in a wide range of industries. However, given the strong π–π stacking tendency between G sheets, dispersant agents such as surfactants or polymers are required to attain stable and homogenous dispersions in liquid media. In the present work, the effectiveness of resveratrol (RV), a fluorescent bioactive compound with antioxidant activity, as a dispersing agent for G in aqueous solutions was assessed. The interaction between G and RV was investigated via absorbance, fluorescence and Raman measurements. Dispersions were prepared via bath sonication, followed by probe ultrasonication and centrifugation, though the two last stages have little effect on the dispersion quality. The addition of G causes a quenching on RV fluorescence, and its magnitude raises with increasing G concentration, being the effect stronger up to 10 mg L-1. The change in the centrifugation speed and time have hardly influence on the RV fluorescence in the presence of G. The RV content remaining in the bulk solution after G dispersion, measured via UV–Vis absorption, decreases linearly with increasing G concentration. RV can effectively disperse all the G present in the sample up to 10 mg L-1; at higher concentrations, the dispersing ability slightly decreases, and the G content is distributed between the bulk solution and the centrifuged residue. Besides, the fluorescence of RV dispersed in G is much higher in methanol than in an aqueous medium. TEM analysis confirms the good exfoliation of G upon ultrasonication in RV solutions and indicates that the layer thickness depends on the G/RV ratio. The results of this study could open new perspectives for using natural products like resveratrolas biocompatible and efficient dispersing agents of G to be used in numerous applications, especially in biomedicine.

Rapid Fabrication of Porous Graphene Network Derived Using Photothermal Flash Lamp Processing for High Performance Electrochemical Energy Storage Devices

Graphene offers superior electrical conductivity and remarkable surface area, which holds great promise for electrochemical energy storage applications including supercapacitors and lithium-ion batteries. Current preparation methods for graphene-like materials require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based devices. Moreover, supercapacitor devices fabricated using graphene typically exhibit low areal capacitance, which limits use of the devices. We report a photothermal route to large-scale production of graphene within milliseconds from polymers using high intensity xenon flash lamp on carbon fiber at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into graphene upon millisecond exposures. This photothermally heating of polymeric material led to the formation of macroporous few layer graphene-containing network with excellent conductivity, and good adhesion to the carbon fiber all of which facilitate the transport of ions through the material. The fabricated supercapacitor devices exhibited a very high areal capacitance of 200 mF/cm2 at 10 mV/s with retention of more than 70% of its capacitance even after increasing the scan rate to 100 mV/s. Anodes for lithium-ion batteries derived from porous graphene networks on carbon fiber resulted in the device with the performance of 170 mAh/g with mass loading as high as 12 mg/cm2 (including the mass of bare CF). The preparation of high-quality graphene via photothermal pyrolysis of polyaniline is amenable to high throughput processing, enabling large-scale production of electrochemical energy storage devices.

Rapid Fabrication of Graphene Derived Micro-Supercapacitors on Flexible Substrates Using Millisecond Photothermal Flash Lamp Carbonization

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available benzoxazine polymer and a high intensity xenon flash lamp on various substrates including carbon fiber, Kapton and stainless steel at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into graphene upon millisecond exposures. The absorption spectrum of the precursor overlaps well with the maxima of the xenon flash lamp emission spectrum. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enables the conversion of the polymeric material to graphene in air and at room temperature, and without thermally damaging the substrate. Characterization of these graphene composites revealed high porosity, excellent conductivity, and good adhesion. Using carbon fiber as the substrate, we prepared micro-supercapacitors exhibiting a very high areal capacitance of 3.2 mF/cm2. Furthermore, we utilized the mechanically and chemically stable graphene/carbon fiber composite as a substrate for the electrochemical deposition of MnO2 which boosted the energy storage capability of the device. The obtained pseudocapacitor has an exceptional capacitance of 300 mF/cm2 at 1mA/cm2. The device retained more than 88% of its capacitance after charging/discharging for 2000 cycles. The preparation of high-quality graphene via photothermal pyrolysis of appropriate precursors is amenable to roll-to-roll processing, and thus large-scale production of electrochemical energy storage devices can be enabled by this approach. Figure 1

H2 O-Etchant-Promoted Synthesis of High-Quality Graphene on Glass and Its Application in See-Through Thermochromic Displays.

Direct growth of graphene on glass can bring an innovative revolution by coupling the complementary properties of traditional glass and modern graphene (such as transparency and conductivity), offering brand new daily-life related applications. However, preparation of high-quality graphene on nonmetallic glass is still challenging. Herein, the direct route of low sheet resistance graphene on glass is reported by using in situ-introduced water as a mild etchant and methane as a carbon precursor via chemical vapor deposition. The derived graphene features with large domain sizes and few amorphous carbon impurities. Intriguingly, the sheet resistance of graphene on glass is dramatically lowered down to ≈1170 Ω sq-1 at the optical transmittance ≈93%, ≈20% of that derived without the water etchant. Based on the highly conductive and optical transparent graphene on glass, a see-through thermochromic display is thus fabricated with transparent graphene glass as a heater. This work can motivate further investigations of the direct synthesis of high-quality graphene on functional glass and its versatile applications in transparent electronic devices or displays.

Controlled electrophoretic deposition of electrochemically exfoliated graphene sheets on Ag nanowires network

Electrochemical exfoliation of graphite has recently attracted a big attention as a simple, fast and scalable method for the preparation of high quality graphene, but there are some drawbacks that hinder its application. Direct deposition is one of the most critical challenges that makes it difficult to deposit uniform, compact and large scale graphene thin films. This work develops a facile electrophoretic deposition route to fabricate exfoliated graphene (EG) film on Ag nanowires (NWs) networks with a controllable film thickness in nanometers scale. EG thin films are deposited with different applied potentials and times from an EG dispersion in N, N -dimethylformamide solvent. Since confirmed by light transmittance results, the increase in deposition time or applied potential lead to an increase in the number of deposited EG layers. The scanning electron microscopy results confirm the uniformity and compactness of EG films deposited on Ag NWs network. Furthermore, transparency and conductivity of Ag NWs films before and after the deposition of EG are investigated. It shows significant improvement in its performance, as a result, it leads to Ag NWs/EG hybrid films exhibiting a sheet resistance of R s = 30 Ω sq -1 , and 85% light transmittance, comparable to conventional transparent conductive oxide films.

Preparation of high-quality graphene using triggered microwave reduction under an air atmosphere

High-quality intrinsic graphene can be prepared by a simple triggered microwave reduction method under air conditions, which provides a simple and low-cost route for large-scale production of high-quality graphene.

High-quality graphene synthesis on amorphous SiC through a rapid thermal treatment

Synthesizing high-quality graphene by catalytic transformation from amorphous silicon carbide (a-SiC) through a rapid thermal treatment (RTT) method is reported. SiO2/Si substrates are coated by a-SiC films followed by Cu and Ni films deposited sequentially. The samples are then thermally annealed by RTT for the synthesis of high-quality graphene in only 3 min. The synergistic effect of Cu and Ni catalyst is observed. We conjecture that the inserted copper film acts not only as a catalyst or substrate for graphene growth but also as a barrier for carbon diffusion to facilitate the synthesis of monolayer graphene, while the nickel film acts as another catalyst and forms Cu-Ni alloy to lower the catalytic temperature. In this paper, we present a simple and time-saving way in preparation of high-quality graphene and put forward a brief theoretical model for the growth of graphene.

Preparation of High-quality Graphene via Electrochemical Exfoliation in Acidic Electrolytes: A Review

ABSTRACTSince the discovery of graphene in 2004, graphene has already been one of the researching hotspots in the material science. As a promising method, electrochemical exfoliation has drawn great attention for producing graphene on industrial scale with high efficiency, low cost, and non-pollution. However, like other wet-chemical methods, the induced oxidation and chemical functionalization are unavoidable during the exfoliation process. Several solutions have been reported to overcome this issue and improve the graphene quality. In this review, we summarize the recent progress in preparation and potential applications of high-quality graphene via electrochemical exfoliation in acidic electrolytes, focusing on the technological innovation and related properties of obtained high-quality graphene.

Phase-field crystal modelling the nucleation processes of graphene structures on different substrates

Two-dimensional materials with unique and excellent physical and chemical properties have attracted much attention in recent years. Among the two-dimensional materials, graphene or grapheme-like materials with honeycomb structure can be mainly prepared by the chemical vapor deposition (CVD) method. The key of this method is to select the substrates and control the nucleation and growth process of honeycomb structures. Graphene prepared by CVD contains many structure defects and grain boundaries, which mainly arise from nucleation process. However, the nucleation mechanism of graphene prepared by CVD method is not very clear. In addition, more than ten kinds of metal substrates can be used as substrate materials in CVD methods, such as Cu and Ni, which have nearly always face-centered cubic (FCC) structures and similar functions in the preparation process. In order to better describe the nucleation of graphene and understand the influences of metal substrates, we introduce the structural order parameter into the three-mode phase-field crystal model to distinguish the low-density gas phase from condensed phases. Nucleation processes of graphene on substrates with different symmetries are studied at an atomic scale by using the three-mode phase-field crystal model, which can simulate transitions between highly correlated condensed phases and low-density vapor phases. Simulation results indicate that no matter whether there is a substrate in the nucleation process, firstly gaseous atoms gather to form amorphous transitional clusters, and then amorphous transitional clusters gradually transform into ordered graphene crystals, with continuous accumulation of new gaseous atoms and position adjustment of atoms. In the nucleation process, five membered ring structures act as a transitional function. When grown on the substrate with a good geometric match with the honeycomb lattice, such as (111) plane of FCC metals, the graphene island has small structural defects. However, when grown without a substrate or on the substrate with a bad geometric match, such as (100) plane of FCC metals, the graphene island contains many structural defects and grain boundaries, which are not conducive to the preparation of high quality graphene. Compared with the (100) crystal plane of the tetragonal cell, the (110) crystal plane of the rectangular cell is favorable for the preparation of graphene single crystals with less defects. Therefore, the appropriate metal substrate can promote the nucleation process of graphene and reduce the formation of distortions and defects during the nucleation and growth of graphene.

Preparation of high-quality graphene via electrochemical exfoliation & spark plasma sintering and its applications

In this paper, we report a simple and fast approach for producing high-quality graphene (HQG) by electrochemical exfoliation and spark plasma sintering (SPS). Via a pressureless sintering at 1500°C for 10min, the oxygen-containing groups of electrochemically exfoliated graphene can be effectively eliminated and its intrinsic structures and properties are restored. The experimental results show that: 1) the HQG exhibits very low defect density (ID/IG=0.16), extremely high carbon to oxygen (C/O) ratio of 25.3 and good processability in various solvents; 2) When the HQG is applied to fabricate a free-standing graphene paper (G-paper), its conductivity reaches to as high as 38460S/m; 3) The G-paper without any binders, which is used as supercapacitor electrodes, delivers a specific capacitance of 129.0F/g at 1A/g, and retains 97% capacitance even after 1000 cycles.

Preparation of high quality graphene using high gravity technology

In this paper, the preparation of graphene from graphite oxide (GO) by high gravity technology in Rotating Packed Bed (RPB) was studied. It was verified that the surface area of graphene oxide exfoliated by high gravity technology was about 7–8 times of that obtained by ultrasonic technology and the layer numbers could be reduced to about two layers with high gravity technology. After reduction, the electric conductivity and specific capacitance of graphene prepared by high gravity technology increased 12.5% and 15.0% compared to that prepared by common method respectively. This technology has obvious advantages in sufficient exfoliation and reduction besides better product qualities and application properties. Moreover, it is easily scaled up.

ChemInform Abstract: Direct Preparation of High Quality Graphene on Dielectric Substrates

AbstractReview: 50 refs.

Direct preparation of high quality graphene on dielectric substrates.

Graphene, an amazing two-dimensional material with excellent physical properties, has attracted great attention in various disciplines. Both fundamental studies and applications require graphene samples with controlled parameters including their quality, size, crystallinity, layer number and so on. While graphene can be prepared by direct exfoliation from mother materials or growth on transition metals, the uncontrolled production or the additional complex transfer process has been challenging for graphene applications. Direct preparation on a desired dielectric substrate is an important research direction that potentially addresses these problems. Many advances have been made in the past few years, and this tutorial review provides a brief summary of ways of preparing graphene on dielectric substrates. Various methods including the annealing method, direct chemical vapor deposition graphene synthesis on conventional dielectric substrates and hexagonal boron nitride layers are systematically reviewed and discussed. The main problems and further directions in this field are also presented.

Free-Green Synthesis and Dynamics of Reduced Graphene Sheets via Sun Light Irradiation

It is universally known that the preparation of high quality graphene on a large scale and in a cost-effective manner is essential for many technological applications. Graphene oxide (GO) has emerged as the precursor of choice for bulk production of graphene-based materials, as it can be synthesized from inexpensive graphite powders. In this paper, a simple method is described for reduction of GO solution by a free and green irradiation based technique. The majority of oxygen-containing functional groups of GO are removed by sun light. This methodology provides an effective way to quantitatively produce high quality graphene sheets. This paper presents irradiation by sun light of synthesized graphene oxide nano-flakes prepared by Hummer’s method. These nano-flakes have been successfully reduced while the dynamic of this irradiation process is discussed. The irradiated nano-flakes of graphene oxide have been investigated using X-Ray diffraction, ATR-FTIR and UV-Vis-NIR.

Promising alternative routes for graphene production and functionalization

Strategies often ignored could become very important for the preparation of high quality graphene and its functionalization.

“Unrolling” multi-walled carbon nanotubes with ionic liquids: application as fillers in epoxy-based nanocomposites

Ionic liquid enables a straightforward procedure for the preparation of high quality graphene by opening multi-walled carbon nanotubes.

Preparation of Quasi-Free-Standing Graphene with a Super Large Interlayer Distance by Methane Intercalation

Preparation of high quality graphene with uniform layers currently remains a bottleneck. In particular, graphene with only one large-sized monolayer is very difficult to obtain. With epitaxial growth of graphene under a hydrogen atmosphere and high temperature, even as high as 1550 °C, the obtained graphene was intercalated by methane and methyl group (−CH3) species. Spontaneously, this intercalation makes the coupling of adjacent layers weak and leads to each layer behaving like free-standing graphene. X-ray diffraction spectra demonstrate that the interdistance of adjacent layers is abnormally large, disclosing each layer suspended by the intercalation, regardless of the layer number. Our findings have opened a possible route to prepare free-standing, high quality graphene effectively in large-scale, behaving like one monolayer free-standing graphene. The Raman spectra also support this conclusion.