Multilayer Graphene Structures Research Articles

Performance enhancement of lithium-ion battery using modified LiMn2O4 cathode followed by ultrasonic-assisted electrochemically synthesized graphene

Herein, the LiMn2O4 (LMO) cathode was modified using ultrasonic-assisted electrochemically synthesized graphene to enhance lithium-ion batteries' charging and discharging performance. Graphene was synthesized from graphite using an electrochemical exfoliation process in which 0.1 M molar (NH4)2SO4 was utilized as the electrolyte with +10 to +12V DC power, followed by ultrasonication in acetone for 2 h. The FESEM, EDX, XRD, Raman, FTIR, UV–vis, and TGA results suggested that ultrasonically treated graphene (EG1) is superior to electrochemically exfoliated graphene (EG2). Thus, EG1 was used to modify the LMO cathode to fabricate lithium-ion batteries. Afterward, the electrochemical performances of the LMO and LMO/EG1 cathode batteries were investigated. Surface morphological analysis revealed that EG1 is composed of two-dimensional, planar, brighter, and less oxidized graphene nanosheets with an average particle size of 18.02 nm. XRD results exhibited that EG1 has a smaller crystalline size and a thinner average stacking thickness of its layered structure than EG2. According to Raman analysis, the intensity ratio I2D/IG of EG2 and EG1 were 0.70 and 0.81, respectively, deduced that both are multi-layered graphene structures; however, EG1 contains a lesser number of graphene layers than EG2. The electrochemical analysis showed that LMO/EG1 cathode batteries have 89 % coulombic efficiency at 0.1C, while LMO batteries have only 81 %. The discharge capacity retention rate of the LMO batteries was 71.4 %, while it was 94.8 % for LMO/EG1 after observing 100 cycles at 0.1 C. Therefore, LMO/EG1 has excellent cycle stability and electrochemical performance and could potentially enhance the performance in hybrid automotive and electronic devices.

Multiple magnetoplasmon polaritons of magneto-optical graphene in near-field radiative heat transfer

Graphene, as a two-dimensional magneto-optical material, supports magnetoplasmon polaritons (MPP) when exposed to an applied magnetic field. Recently, MPP of a single-layer graphene has shown an excellent capability in the modulation of near-field radiative heat transfer (NFRHT). In this study, we present a comprehensive theoretical analysis of NFRHT between two multilayered graphene structures, with a particular focus on the multiple MPP effect. We reveal the physical mechanism and evolution law of the multiple MPP, and we demonstrate that the multiple MPP allow one to mediate, enhance, and tune the NFRHT by appropriately engineering the properties of graphene, the number of graphene sheets, the intensity of magnetic fields, as well as the geometric structure of systems. We show that the multiple MPP have a quite significant distinction relative to the single MPP or multiple surface plasmon polaritons (SPPs) in terms of modulating and manipulating NFRHT. We demonstrate that this remarkable behavior is attributed to the coupling between the significant contributions of surface states at multiple surfaces and Shubnikov–de Haas-like oscillations in the spectrum, indicating a transformation of intraband and interband transitions. Notably, we find that the evolution from single MPP to multiple MPP is absolutely different from that from single SPPs to multiple SPPs. Finally, a thermal magnetoresistance effect and a negative-positive transition of the relative thermal magnetoresistance ratio are predicted in the multilayered system under consideration. Our study paves the way for a flexible control of NFRHT and it offers the possibility for the thermal photon-based communication technology and a magnetically controllable thermal switch.

Ice adhesion mechanism on the patterned surface of aluminum matrix and array graphene based on molecular dynamics simulations

Solving fundamental problems in engineering application can drive rapid industrial development. The solid–ice interface adhesion mechanism on anti-icing materials has attracted strong interest from researchers. In this work, the ice adhesion mechanism at the solid–ice interface was investigated based on water molecule behavior on an aluminum matrix/array graphene (M/G) surface. We counted the number of water molecules in the gaps of the array graphene structure and measured ice and array graphene of stress changes during ice removal. The multilayer array graphene structure relies on “adhesion-type” ice removal mechanism. It was attributed to the increased horizontal displacement of ice due to the stress matching of ice/array graphene. The solid-ice interface adhesion mechanism of patterned surface is understood at the molecular-scale.

Graphene Enhances the Loading Capacity and Lubrication Performance of Ionic Liquids: A Molecular Dynamics Study.

Ionic liquid (IL) combined with graphene additives have garnered extensive attention in the field of high-performance lubricating materials. However, the ambiguous mechanism of graphene influencing the load-carrying and anti-wear capacity of ILs needs further study. In this work, friction simulation shows that adding graphene causes friction coefficient to reduce by up to 88% compared with pure ILs, but lubrication performance is lost due to the destruction of graphene under high stress. Meanwhile, multilayer graphene has better friction-reducing performance and friction durability as compared to the monolayer structure, which is attributed to the easy-shear property and the reduction in the percentage of high tensile stress sites in multilayer graphene structure. In addition, it was found that excessively thick ILs film would form a three-body abrasive wear structure with graphene, which accelerated the structural destruction of graphene and caused a decline in its tribological properties. It is believed these findings can be valuable for designing of high-performance lubricating oil for practical engineering.

Electronic structure of graphene thin films under a perpendicular electric field

Based on density functional theory (DFT), we investigated the electronic structure of multilayer graphene under the perpendicular electric field. DFT calculations revealed that the number of layers and their stacking arrangement play a crucial role in determining the electronic structure of multilayer graphene under the perpendicular electric field. When an electric field is applied, multilayer graphene with AB stacking exhibits metallic or semi-metallic properties depending on whether the number of layers is odd or even, respectively. Multilayer graphene with ABC stacking under the electric field is a semiconductor that possesses a flat band at the valence- and conduction-band edges, irrespective of the number of layers. The electronic structure near the Fermi level of multilayer graphene with AA stacking is insensitive to the external electric field.

Electronic structure of biased alternating-twist multilayer graphene

Electronic structure of biased alternating-twist multilayer graphene

Graphene oxide- boro-phosphate glass nano-composite thin films synthesized by sol-gel spin coating method

Boro-phosphate glass-graphene oxide nanocomposites combine nanocarbon electrical properties with optical and host properties of glass with potential uses as optoelectronic, photonic materials and for bio-applications. A sol-gel glass from the zinc-boro-phosphate system was combined with graphene oxide in ethanol and further deposited by spin-coating on glass substrates at different rotation speeds. The samples were treated at 110, 250 and 500 °C. The roughness quality was studied for each sample. SEM images coupled with EDX proved the presence of graphene for all investigated samples, showing morphological changes and loss of carbon with temperature increase. Carbon-oxygen bonds, and specific borophosphate network bonds, were identified by FTIR spectroscopy. Raman spectra allowed the identification of the specific reduced graphene bands as well as the presence of multilayer graphene structures. This work paves the way to produce reduced graphene oxide-glass nanocomposites as thin layers, with potential uses in bio-to-photonic applications.

Facile preparation and properties of high nitrogen-containing Fe/Co/N co-doped three-dimensional graphene bifunctional oxygen catalysts for zinc air battery

Fe/Co/N co-doped multi-channel interpenetrating three-dimensional graphene catalyst (FeCo–N-3D-HG) with good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performances is prepared by a facile method, using poly (2,5-benzimidazole) (ABPBI), iron salt, cobalt salt and nanometer CaCO3 (template). ABPBI forms a complex with iron and cobalt ions and the complex is coated on the surface of CaCO3. The pyrolysis process is carried out in an Ar gas protection, the template is removed by acid to obtain FeCo–N-3D-HG. The results show that FeCo–N-3D-HG is three-dimensional multi-layered graphene structure with multi-channels. The catalytic performance of ORR (E1/2 = 0.860 V vs RHE) is better than 20 wt% Pt/C in O2 saturated 0.1 M KOH electrolyte. The catalyst also shows similar OER performance with the RuO2 in 1 M KOH solution. The prepared zinc-air battery exhibits outstanding peak power density (261.7 mW cm−2), preeminent specific capacity (760.1 mAh g−1), and good cycle durability (150 h).

Growth of High-Purity and High-Quality Turbostratic Graphene with Different Interlayer Spacings.

Turbostratic graphene is a multilayer graphene, which has exotic electrical properties similar to those of monolayer graphene due to the low interlayer interaction. Additionally, the stacking structure of the turbostratic multilayer graphene can decrease the effect of attachment of charge impurities and surface roughness. This paper explores the growth of high-purity and high-quality turbostratic graphene with different interlayer spacings by calcining ferric chloride and sucrose at 1000 °C for 1 h under an argon atmosphere. X-ray diffraction patterns and Raman results imply that the turbostratic graphene contains two different interlayer spacings: 3.435 and 3.55 Å. The 3.55 Å turbostratic graphene is on top of the 3.435 Å turbostratic graphene, and there is an AB stacking pattern between the topmost graphene layer of 3.435 Å turbostratic graphene and the first graphene layer of the 3.55 Å turbostratic graphene, with an interlayer spacing of 3.35 Å. The two different interlayer spacings of turbostratic graphene arise from different cooling rates between the higher temperature ranges (>700 °C) and lower temperatures (<700 °C).

Zincophilic multilayer graphene structures leveraging fast and ultrastable Zn-ion storage

Zincophilic multilayer graphene structurein situconstructed to glue more electroactive sites and opposite charge-carrier uptake entails alternate binding of Zn2+/CF3SO3−at active sites.

Effect of graphene-based additives on mechanical strength and microstructure of gypsum plaster

In this study, graphene-based materials such as graphene oxide, reduced graphene oxide, and boron-doped reduced graphene oxide were synthesized, and their effects on the microstructure and mechanical properties of gypsum plaster were investigated. The graphene oxide (GO) sample was synthesized by modified Hummers’ method, and reduced graphene oxide (rGO) was obtained with the thermal reduction of GO. Boron doped reduced graphene oxide (B-rGO) was prepared via the impregnation method. The synthesized graphene-based materials were characterized using H 2 -TPR, TGA-DTA, XRD, FT-IR, SEM-EDS, TEM, Raman, and N 2 adsorption-desorption analysis. Analysis results confirmed that 450 o C was a sufficient temperature under an H 2 atmosphere to reduce GO and preserve rGO structure. XRD results revealed the presence of multilayer graphene structure in the rGO and B 2 O 3 crystals in the B-rGO sample. Multilayer graphene formation was also determined from the I 2D /I G ratio (0.1) of Raman analysis. Mechanical strength studies showed that while GO had a negative effect on both bending and compressive strength of gypsum plaster, rGO enhanced its bending and compressive strength. The addition of 0.1 wt% rGO added gypsum plaster increased the bending strength by 15.1% and compressive strength by 3.70%. SEM, He Pycnometry, and N 2 adsorption-desorption analyses revealed that rGO addition significantly changed the microstructure of gypsum plaster. The addition of B-rGO positively affected the compressive strength of the plaster and the highest increase was obtained as 8.6%; however, no significant change was observed in the microstructure of gypsum. • Electron microscopy images represented graphene nanosheets and graphene layers • X-ray diffraction results revealed the B 2 O 3 crystals in the boron-doped sample • Reduced graphene oxide increased the bending and compressive strength • Boron doped reduced graphene oxide enhanced the compressive strength • Reduced graphene oxide decreased the porosity of the gypsum

Graphene multilayers for coherent perfect absorption: effects of interlayer separation.

We present a model study to estimate the sensitivity of the optical absorption of multilayered graphene structure to the subnanometer interlayer separation. Starting from a transfer-matrix formalism we derive semi-analytical expressions for the far-field observables. Neglecting the interlayer separation, results in upper bounds to the absorption of 50% for real-valued sheet conductivities, exactly the value needed for coherent perfect absorption (CPA), while for complex-valued conductivities we identify upper bounds that are always lower. For pristine graphene the number of layers required to attain this maximum is found to be fixed by the fine structure constant. For finite interlayer separations we find that this upper bound of absorption only exists until a particular value of interlayer separation (Dlim) which is less than the realistic interlayer separation in graphene multilayers. Beyond this value, we find a strong dependence of absorption with the interlayer separation. For an infinite number of graphene layers a closed-form analytical expression for the absorption is derived, based on a continued-fraction analysis that also leads to a simple expression for Dlim. Our comparison with experiments illustrates that multilayer Van der Waals crystals suitable for CPA can be more accurately modelled as electronically independent layers and more reliable predictions of their optical properties can be obtained if their subnanometer interlayer separations are carefully accounted for.

Fabrication of multi-layer graphene by repeated transfer

Multi-layer graphene was formed by repeated transfer onto a silicon oxide substrate, and changes in its doping characteristics were observed. The structure of multi-layer graphene was investigated in comparison with pyrolytic graphite with a turbostratic structure. Single-layer graphene is doped due to the influence of the silicon oxide substrate, and the influence of poly(methyl methacrylate) and water residue, which are used for the transfer, is small. Graphene in the first layer suppresses the influence of the silicon oxide substrate, and the second and subsequent layers are almost unaffected. By repeating the transfer and stacking, multi-layer graphene approaches ideal turbostratic graphite.

In-situ synthesis of graphene encapsulated Fe/Fe2O3 nanoparticles for possible biomedical applications

This paper reports on the in-situ synthesis, optimization, characterization and cytotoxicity tests of multi-layer graphene (MLG) encapsulated Fe/Fe2O3 nanoparticles (Fe/Fe2O3@C core–shell nanostructures) by spray drying-assisted chemical vapor deposition (CVD) using iron-nitrate/silica-based precursors. The influences of CVD reaction temperature, holding time, CH4/H2 gas flows and pressure on the synthesis of MLG encapsulated Fe/Fe2O3 nanoparticles were investigated. CVD-synthesized powders were purified using acid leaching to remove residual silica and probable uncoated Fe/Fe-oxide phases. XRD analyses revealed the presence of FCC (Fe,C), BCC Fe, graphite/graphene and trace amount of Fe2O3 phases. Raman spectra confirmed the existence of MLG shells. TEM indicated that MLG (from at least 3 to maximum of 35 layers) wrapped around the metallic cores ranged between 4 and 85 nm. Purification of nanoparticles did not degrade, dissolve or create discontinuity on the MLG structure. VSM measurements showed that nanoparticles obtained from the optimized conditions (900 °C, 100 ml/min CH4/H2, 50 mbar) had a soft ferromagnetic behavior with low saturation magnetization (∼85 emu/g) and coercivity (∼552 Oe) values. Optimized MLG encapsulated Fe/Fe2O3 nanoparticles were successfully suspended in water using a poly(acrylic acid) coating. Aqueous MLG encapsulated Fe/Fe2O3 nanoparticles were cytocompatible below 100 μg/ml at short incubation times, and showed the potential to be used in biomedical applications.

Graphene electronic tattoos 2.0 with enhanced performance, breathability and robustness

Graphene electronic tattoos (GETs) have recently emerged as unique tools for personalized healthcare. The monolayer GETs have been used to monitor human electrophysiological signals, including brain, heart, and muscle activities, skin temperature, and hydration level. However, a few drawbacks of the earlier GETs hindered their perception by clinical and biomedical experts: they were not permeable to sweat, and the tattoo performance varied greatly. In this work, we introduce GETs 2.0: the skin wearable tattoo sensors with superior electrical properties, permeability to sweat, and robustness. We report on the categorical analysis of the graphene tattoos of different layer constitutions. When stacking the graphene monolayers within a single tattoo, we see a drastic enhancement in their electronic properties. The older monolayer GETs were susceptive to minor growth- or transfer-related discrepancies, resulting in highly scattered electrical properties. In this work, the GETs 2.0 with the addition of graphene nanoscrolls (GNS) or multilayer (2 L and 3 L) graphene structures exhibit 3.5-fold decreased sheet resistance, 2.5-fold lower skin impedance, and 5-fold reduced standard deviations of these values. In addition, we introduced holes into the tattoo, enabling healthy sweat evaporation without a substantial decrease in electrical properties. Furthermore, we show that microholes allow for advanced biplanar contact with graphene tattoos. Finally, we show that multilayer GETs 2.0 can be used as efficient skin-wearable electronic heaters, exhibiting heating efficiency of ~6 mW/°C.

In situ constructed multilayer graphene structure enabling improved supercapacitive charge storage

Designing controllable multilayer graphene (MLG) structure in amorphous carbons is crucial but still challenging to deliver durable supercapacitive energy storage. Herein, the lead is taken in in-situ nanoarchitecturing a 2–10 layered graphene structure within the amorphous carbon skeleton by the cobalt salt/sodium metal-assisted carbonization of starch. The rearrangement of graphite crystallites forms MLG structure, which shows a large specific surface area of 1917 m2 g−1 and a mesopore volume of 0.71 cm3 g−1. These two parameters are 1.64 and 1.46 times of the corresponding amorphous carbon. Such profitable structures promise a high specific capacitance of 312 F g−1 at 1 A g−1 and a durable cycle-life with 98.5% capacitance retention at 10 A g−1 over 100,000 cycles. The designed MLG structure in amorphous carbons matrix also exhibits an increased electrochemically active surface area from 392.5 to 599.5 m2 g−1, and a low ion-transport resistance (0.59 Ω s–0.5) as well as an ultrafast ion-response time (0.37 s), endowing the fabricated carbon supercapacitor with 67.7% capacitive contribution from fast-kinetics response at 10 mV s–1. Experiment characterization unravels the formation mechanism of MLG in amorphous carbons via the synergy of coalt salt and sodium metal. The elaborate design of MLG structure within amorphous carbon matrix provides an effective strategy to boost the electrochemical energy storage performances.

Three-dimensional self-folding assembly of multi-layer graphene at the interface with a polymeric film

Three-dimensional (3D) architectures of graphene are of great interest for applications in flexible electronics, supercapacitors, and biointerfaces. Here, we demonstrate that multi-layer graphene (MLG), like single-layer graphene (SLG), can self-fold to form 3D architectures at the interface with a polymeric film. Bilayers composed of graphene and polymeric film tightly adhere to each other and possess a sloped internal strain, which leads to spontaneous rolling to predetermined 3D microscale architectures. The curvature radii of self-folding films can be controlled by changing the thicknesses of the polymeric film and the stacking order. In contrast to single-layer graphene, multi-layer graphene shows no strain in most of the outer graphene layers and linear ohmic current characteristics after self-folding. Throughout the self-folding process, the conductance of MLG decreases but remains higher than that of SLG. This versatile way of forming a 3D multi-layer graphene structure is potentially applicable for fabrication of practical carbon devices without the changes in their conductive properties.

Impact of molecular components on performance of multilayer graphene-based infrared emissivity modulator

Actively controlling the infrared emissivity of materials is critical for many applications, such as radiative cooling and thermal camouflage. Multilayer graphene (MLG) has shown great potential as a functional material with a tunable infrared emissivity. However, the spatial homogeneity in adjusting MLG's emissivity through ion intercalation is rather poor, which limits its practical applications. Here, we study how mixing various molecular components (e.g., ethanol) with ionic liquids affects the performance of MLG-based infrared emissivity modulators. The results indicate that introducing a moderate concentration of molecular components not only significantly improves spatial homogeneity in tuning emissivity but also enhances modulation depth, dynamic response, and the stability of the modulators. This is likely due to the increasing conductivity of the mixture and the improved wetting properties between the mixture and the separator, which leads to more effective charge transfer from ions in ionic liquids to carbons in graphene. The microscopic structure of MLG, revealed by Raman spectroscopy, confirms that the improvement in modulator performance is mostly due to homogeneous transportation of ions in the modulators. This not only sheds light on the underlying physics of the modulator but also greatly expands the options when selecting ionic liquids, thereby opening a new route for the modulator design.

Temperature and inhomogeneity combination effects on collective excitations in three-layer graphene structures

Temperature and the inhomogeneity of background dielectric combination effects on the collective excitations in a multilayer graphene structure consisting of three monolayer graphene sheets are investigated, within the random-phase approximation. Numerical calculations present that three weakly damped plasmon modes exist and continue in inter single-particle excitation region. Our investigations show that as temperature increases, the acoustic plasmon frequencies slightly decrease and then increase after getting the lowest peak. Dissimilarly, the optical plasmon frequency increases with the increasing temperature in the large wave vector regions. Besides, temperature effects cause the energy loss to plasmon modes even nearby the Dirac points, outside the single-particle excitation region of the system. We also observe that the inhomogeneity of background dielectric declines the plasmon energy, the damping rate of plasma oscillations , and the effects of temperature and interlayer separation on the collective excitations in the system. • Three plasmon modes exist and continue in SPE region of the system. • Acoustic modes decrease and then increase with increasing temperature. • Optical mode increases as temperature increases. • Temperature causes the energy loss to plasmon modes outside the SPE region. • The inhomogeneity declines the plasmon energy, the damping rate and the effects of temperature and separation on the collective excitations.

Fe3O4/MnO2 co-doping phenolic resin porous carbon for high performance supercapacitors

BackgroundThus, the excellent electrochemical property of PR-Fe@MnO2 composite made it an encouraging electrode material for practical applications like charge storage and in other pseudocapacitors. MethodsUsing phenolic resin (PR) as a carbon source, potassium ferrate (K2FeO4) and manganese acetate (Mn(CH3COO)2·4H2O) as the dopants, a one-step carbonization method was used to prepare a series of Fe3O4 and MnO2 co-doped composites, which are denoted as PR-Fe@MnO2. During high-temperature carbonization (800 °C), partially amorphous carbon forms a multi-layer graphene structure, making PR-Fe@MnO2 exhibit a high degree of graphitization. After doping, the transition metal Mn was investigated theoretically by performing density functional theory calculations. Significant FindingsThe results confirmed that doping of moderate Mn ions in the PR-Fe lattice improved the interactions between OH− in the electrolyte and Mn metal center, consequently, the electrical conductivity (19%) of the electrode according to the equivalent series resistance (Rs). The Mn composition also increased the specific area for more electroactive sites and reduced the charge transfer resistance (decreased by 27.7%). As a result, PR-Fe@MnO2–1.5 had the highest specific capacitance of 601 F/g at 1.0 A/g and superior cycling stability (capacitance retention of 97.8% after 10,000 cycles). Furthermore, the assembled PR-Fe@MnO2–1.5//PR-Fe@MnO2–1.5 symmetric supercapacitor provided a specific energy density of 25.7 Wh/kg at a power density of 384.9 W/kg.