Graphite Films Research Articles

In Situ S‐Doped Graphene Film using NaHSO3 as Sulfur Source for High‐Performance Flexible Supercapacitors

Herein, sulfur‐doped graphite film (SGF) is developed by a facile method. Graphene oxide (GO) film and low‐cost NaHSO3 are used for carbon and sulfur sources, respectively. A single‐step sulfur doping reaction is used to obtain SGF at 180 °C. The scanning electron microscopy (SEM) analysis of SGF reveals highly loose, highly crumpled characteristics. The SEM–energy‐dispersive spectroscopy shows that S is evenly distributed on the surface of SGF and doping amount of S is 4.6 wt%. SGF can attain high gravimetric and areal specific capacitance of 232.8 F g−1 and 672.5 mF cm−2 at 0.5 A g−1 and 1 mA cm−2 current density, respectively. The SGF shows excellent cycle stability (94.1% capacity retention after 10 000 cycles at 2.0 mA cm−2). Then, the assembled flexible SGF//SGF all‐solid‐state symmetric supercapacitor device can deliver a high energy density of 12.17 Wh kg−1 at a power density of 499.85 kW kg−1. The in situ doping method provides a simplistic and low‐cost synthesis process, which is suitable for large‐scale production of SGF. Furthermore, the well‐developed approach is applied to prepare arbitrary S‐doped matrix of carbon. Simultaneously, the fabricated SGF as the electrode material of flexible supercapacitor devices has great advantages in wearable electronics.

Thermal Response of Carbon Fiber Reinforced Polyimide Composite Laminate Coated with Highly Oriented Graphite Film Under Heating on Single Side

Thermal Response of Carbon Fiber Reinforced Polyimide Composite Laminate Coated with Highly Oriented Graphite Film Under Heating on Single Side

Tribocorrosion of stainless steel sliding against graphite in FLiNaK molten salt

The molten salt reactor (MSR) concept recently gained renewed interest in developing Generation IV nuclear reactors. One MSR design uses fluoride molten salts to cool tri-structural isotropic particle fuel encapsulated by a carbon matrix into spherical pebbles, which would inevitably contact the reactor's stainless steel container wall during salt circulation. Characterizing this interaction is crucial for reactor safety. Here we report the tribocorrosion behavior of graphite sliding against Type 316H stainless steel lubricated by a FLiNaK (LiF:NaF:KF; 46.5:11.5:42 mol %) molten salt in an argon environment. Accelerated wear loss was observed at a higher temperature because of a lower molten salt viscosity and a higher corrosion rate. The graphite had a more rapid material loss at a higher sliding speed than stainless steel because of its higher vulnerability to vibration-induced microfracture. The salt-starved condition caused more material loss than either the no-salt or the salt-flooded condition because neither a graphite transfer film nor stable boundary lubrication could be established at salt starvation. An interesting dual-layer surface film was discovered on the stainless steel worn surface: a chromium-rich top film and a nickel-accumulated but chromium-depleted interlayer. The film composition and structure provide fundamental insights to the mechanochemical interactions between stainless steel and graphite in a molten salt environment.

Pyramid-Patterned Germanium Composite Film Anode for Rechargeable Lithium-Ion Batteries Prepared Using a One-Step Physical Method

Using a top-down magnetron sputtering technique with a high deposition-rate, a one-step method for preparing germanium (Ge) hybrid film is presented. At present, graphite film is used as a current collector because it is flexible, self lubricating, and possesses a stress–strain-relieving property. In order to further suppress the volume changes of the Ge, a multilayered electrically conductive nickel film is deposited between multilayered Ge films. The cells are cycled at a current density of 200 mA g−1. An initial discharge and charge capacity of 1180.7 and 949.3 mAh g−1 are achieved by the prepared integrated pyramid patterned Ge composite film anode, respectively. The average capacity was maintained at 580 mAh g−1 after 280 cycles. In the rate capability measurement, the Ge composite demonstrated a reversible capacity of 1163.1 mAh g−1. It is easily made using magnetron sputtering, which is widely accepted in the industry. A physical approach to increase pure Ge’s specific capacity and its cycle life for LIBs is demonstrated in this work.

New constraints on the structure and composition of the lithospheric mantle beneath the Slave craton, NW Canada from 3-D magnetotelluric data – Origin of the Central Slave Mantle Conductor and possible evidence for lithospheric scale fluid flow

Previously collected magnetotelluric data were used to produce an improved 3-D resistivity model of the lithosphere beneath the Slave craton. A region of low resistivity (<10 Ωm) at ∼100 km depth was imaged beneath the central Slave craton, and identified as the Central Slave Mantle Conductor (CSMC) reported in previous studies. Earlier studies interpreted the CSMC as graphite films but new analysis from laboratory experiments indicates that it is unlikely that graphite films are stable/continuous at this depth. Using recent laboratory experiments we review alternative conduction mechanisms for the CSMC including (a) metasomatic phlogopite, (b) grain boundary sulphides and (c) high density fluids including hydrous carbonatite melts or brines. None of these hypotheses are without flaws requiring either unreasonably high-volume fractions or have petrological challenges. However, brines are the preferred explanation as they (1) can explain geophysical observations, (2) are observed in fibrous diamonds coincident with the CSMC and (3) require small volume fractions (<1%). We hypothesize their emplacement was related to a Mesozoic subduction event. This implies that upper mantle conductors should not be used as an indicator of carbon concentration in the mantle to prospect for diamondiferous regions. Our resistivity model indicates a lithospheric thickness of 210 ± 10 km beneath the Slave craton, consistent with seismic and xenolith studies. A water content of 10–150 ppm at 100–170 km depth in the lithospheric mantle is inferred from resistivity, broadly agreeing with estimates from mantle xenoliths from the central Slave craton lithosphere. Below 170 km the bulk lithosphere is "dry" (<10 ppm), which may explain why the cratonic root has been resistant to erosion by the underlying asthenosphere. Low resistivity fingers extend to surface in multiple locations that may represent paleo-fluid flow pathways through the lithosphere, broadly resembling those observed beneath Olympic Dam, Australia.

Laser‐Patterned Graphite‐Based Strain and Temperature Sensor on Disposable Paper Cup

Flexible sensors have versatile applications in a home environment to create better ambient intelligence, which still have high fabrication costs and disposable value. As a proof‐of‐concept example to resolve these problems, the graphite‐based sensors on a disposable paper cup by laser patterning to measure the water level and temperature are proposed. The optimal process parameters of graphitic film, sensing mechanisms, and the sensor performance are investigated in the experiments. Moreover, the paper cup with graphitic sensors is simulated by the finite element method to analyze the experimental results. This fast and low‐cost manufacturing method may open up avenues for the development of disposable flexible electronics in smart home necessities.

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

A CVD technique has been developed for the deposition of homogeneous graphitic carbon nitride films on silicon and quartz glass substrates using melamine as a precursor. Layer-by-layer deposition at low precursor loadings makes it possible to deposit a film up to 1.4 µm thick; however, it is possible to achieve large thicknesses by multiple repetition of the experimental cycle. The effect of synthesis parameters on the surface morphology of deposited layers has been studied by scanning electron microscopy. The chemical composition and structure of graphitic carbon nitride films are confirmed by a set of spectroscopic methods and X-ray diffraction. The optical properties have been studied using diffuse reflectance spectroscopy. Scanning electron microscopy and X-ray diffraction analysis have shown that films deposited at temperatures of 550–650°C have a layered microcrystalline structure. The bandgap of the obtained samples was 2.76–2.93 eV.

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

Heat Dissipation Performance Research of Power Lithium Battery Based on High Thermal Conductivity Graphite Film

Heat will be generated inside the power lithium-ion battery during operation, if heat dissipation is not carried out in time, its temperature will rise continuously, causing thermal safety accidents once the temperature exceeds its normal work temperature range. In addition, the uniformity of the battery temperature will affect its performance, life, and even safety. Therefore, research on the heat dissipation performance of lithium battery can effectively improve its safety characteristics and working performance. To improve the temperature uniformity of single battery, different high thermal conductivity graphite films are used as the thermal conductivity enhanced scheme, the heat production and heat generation rate model of single battery was established, and its temperature simulation model was built by Ansys software to simulate heat dissipation performance. The results show that the high thermal conductivity graphite film can significantly enhance the battery heat dissipation performance, and its thickness, specific heat capacity and density have important effects on its performance.

Diamond-like carbon graphene nanoplatelet nanocomposites for lubricated environments

The tribological behaviour of diamond-like carbon (DLC) and graphene nanoplatelets (GNP) nanocomposite has not been previously explored in a lubricated environment, with some previous studies reporting only on graphene materials on the surface of the DLC. In this study DLC-GNP nanocomposite films with various GNP coverages were synthesised by a 3 step process: spin coating a GNP suspension, heat treatment, and DLC deposition. In this study, the effect of the GNP coverage on the mechanical properties, and tribological response of the DLC-GNP nanocomposite film were studied at elevated temperatures against a cast iron pin in a base-oil lubricated environment. The study shows decrease in friction and wear of the DLC-GNP nanocomposites as the GNP coverage increased, with the lowest friction (COF ∼0.03) and wear (∼1.6 × 10−19 m3/Nm−1) achieved with a 4.5% coverage. This study reports the addition of GNP into the DLC matrix reduced both friction and wear by creating a highly graphitic transfer film on the counter-body, but for higher GNP coverages agglomeration during the spin coating of GNP islands were recorded, leading to removal of the GNP during sliding wear negating the friction reduction effect of the GNP.

Star-shaped furoate-PCL: An effective compound for the development of graphite nanoplatelets-based films

The aim of this study was to improve the dispersibility of graphite nanoplatelets (GNP) in films based on poly(ε-caprolactone) (PCL). To this end, a star-shaped PCL with furoate-like end groups (PCL-Fur), potentially capable of interacting/reacting with the surface of the graphene layers through Diels-Alder reactions, was synthesized by enzymatic catalysis. PCL-Fur was applied for film development by blending it with a commercial high molecular weight PCL (PCL-L) and GNP. The reactivity of GNP with respect to furoate groups was demonstrated by studying the thermal behavior of the GNP/methyl 2-furoate system, while the dispersibility of graphite in the solution containing PCL-Fur was studied by UV–Vis measurements. GNP proved to be well dispersed and adhered to the polymer matrix in the PCL-L/PCL-Fur/GNP composite films prepared by casting, in contrast to the films based on the neat PCL-L. This fine GNP dispersion resulted in films characterized by high electrical conductivity.

Operando formation of multiphase heterostructure for achieving macroscale superlubricity with ultra-long lifetime under high contact stress

Pressure-induced reactions in situ at the sliding interface for carbon-based or disulfide-based films are well-known to yield structural evolution or chemical modifications for obtaining low friction. However, the underlying lubrication mechanisms between them remain poorly understood, and it poses indeterminacy in realizing the long-lasting heterointerface superlubricity. Here, we achieve the macroscale superlubricity (∼0.0055) with an ultra-long lifetime of at least 340,000 cycles and the ultra-mild wear (∼1.2 × 10−8 mm3/N·m) by sliding of diamond-like a-C:H (DLCH) against MoS2 under a high pressure of 1.28 GPa in nitrogen. Detailed studies reveal that a composite shear band based on tribo-induced graphitized nano-carbon films (GNCF) with disordered or local sp2 ordering structure and the layered MoS2 transfer film is formed on DLCH ball surface. Meanwhile, the slip interface of MoS2 disc encounters structural transformation to form a harder and smoother tribolayer parallel to sliding direction by stress-motivated tribochemical reactions. At micro-contact areas, in-situ formation of sliding heterostructure between the GNCF/MoS2 shear band and the reoriented MoS2 tribolayer is speculated to mainly provide the easy-shearing interface as well as incommensurate contact for the occurrence of microscale superlow friction. Macroscale superlubricity is then established as a result of the combination effect of numberless micro-asperities superlubricity. The findings provide fundamental insights into heterointerface friction and design pathway for long-term superlubricity.

Flat Bands for Electrons in Rhombohedral Graphene Multilayers with a Twin Boundary

AbstractTopologically protected flat surface bands make thin films of rhombohedral graphite an appealing platform for searching for strongly correlated states of 2D electrons. In this work, rhombohedral graphite is studied with a twin boundary stacking fault and the semimetallic and topological properties of low‐energy bands, localized at the surfaces and at the twinned interface, are analyzed. An effective 4‐band low energy model is derived, where the full set of Slonczewski–Weiss–McClure (SWMcC) parameters is implemented, and the conditions for the bands are found to be localized at the twin boundary, protected from the environment‐induced disorder. This protection together with a high density of states at the charge neutrality point, in some cases—due to a Lifshitz transition, makes this system a promising candidate for hosting strongly‐correlated effects.

Effect of Graphitization Degree of Mesocarbon Microbeads (MCMBs) on the Microstructure and Properties of MCMB-SiC Composites.

Mesocarbon microbead-silicon carbide (MCMB-SiC) composites were prepared by hot-press sintering (2100 °C/40 MPa/1 h) with two different graphitized MCMBs as the second phase, which exhibited good self-lubricating properties. The effects of the graphitization degree of the MCMBs on the microstructure and properties of the composites were investigated contrastively. The results showed that the composites that added raw MCMBs with a low degree of graphitization had excellent self-sintering properties, higher densities, and better mechanical properties; by comparison, the composites that added mature MCMBs with a high degree of graphitization, which has regular and orderly lamellar structures, not only had good mechanical properties but also exhibited a lower and more stable dry friction coefficient (0.35), despite the higher wear rate (2.66 × 10-6 mm3·N-1·m-1). Large amounts of mature MCMBs were peeled off during the friction process to form a uniform and flat graphite lubricating film, which was the main reason for reducing the dry friction coefficient of the self-lubricating composites and making the friction coefficient more stable.

Ultrahigh thermal conductive graphite film via the in-situ construction of aligned nanographene skeleton using chemical vapor deposition

Both high thermal conductivity (K) and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability. However, the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications. In this work, graphite film with both large thickness and high K value is produced based on an in-situ composition strategy between nanographene (G) and pyrocarbon (PyC) via chemical vapor deposition (CVD) using CH3OH/C2H5OH mixed precursors. It's found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites. Such G/PyC composites can be completely graphitized at a lower temperature than the existing products. After 2400 °C annealing, dense, thick, and highly aligned graphite films were prepared. Their K values reach 1350 and 1010 W m–1 K–1 at the thickness of 40 and 120 μm, respectively, surpassing the existing records with similar thicknesses. More importantly, the proposed method is insensitive to the deposition substrates, and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials. Besides, the G/PyC also exhibits better mechanical and electromagnetic shielding performances than the existing products, indicating a promising multifunctional application prospect.

Investigation on thermal conduction of graphite film enhanced carbon fiber polymer composite by laser flash analysis

Laser flash analysis (LFA) is an advantageous transient method, widely used for measuring thermal diffusivity of solid materials nowadays. In this paper, the thermal conductivity of graphite film enhanced carbon fiber composite was measured by LFA and the results show an unusual size-dependent effect which was considered to be due to violation of homogeneous assumptions. To investigate the size effect, numerical analyses based on the representative volume element (RVE) models were implemented to evaluate the thermal conductivities of composites with periodic microstructures. Transient periodic boundary conditions (PBCs) were proposed and applied to the RVEs for simulating the LFA. Transient simulative results obtained by applying PBCs verify the size effect and are in better agreement with the experimental data than those obtained by applying conventional adiabatic conditions. Moreover, the classical steady-state analyses on RVEs were performed for comparison. The reason for size effect was discussed in details. The present work expands the application scope of LFA to measuring thermal conductivity of complex composite and provides a perception of discreetly selecting specimen size and modifying the general LFA technique.

Flexible graphite films with high cross-plane thermal conductivity prepared by graphitization of polyimide catalyzed by Ni-coated-CNTs

Graphite films are widely used in microelectronic devices as heat-dissipation materials due to their high thermal conductivity, low thermal expansion coefficient and lightweight.

Recent progress of graphitic carbon nitride films and their application in photoelectrochemical water splitting

This review summarizes the progress in the synthesis of CN electrodes spanning from top-down and bottom-up categories, carrier dynamics modulation, and surface water oxidation reaction kinetics.

An SECM-Based Spot Analysis for Redoxmer-Electrode Kinetics: Identifying Redox Asymmetries on Model Graphitic Carbon Interfaces.

The fundamental process in non-aqueous redox flow battery (NRFB) operation revolves around electron transfer (ET) between a current collector electrode and redox-active organic molecules (redoxmers) in solution. Here, we present an approach utilizing scanning electrochemical microscopy (SECM) to evaluate interfacial ET kinetics between redoxmers and various electrode materials of interest at desired locations. This spot-analysis method relies on the measurement of heterogeneous electron transfer rate constants (kf or kb ) as a function of applied potential (E-E0 '). As demonstrated by COMSOL simulations, this method enables the quantification of Butler-Volmer kinetic parameters, the standard heterogeneous rate constant, k0 , and the transfer coefficient, α. Our method enabled the identification of inherent asymmetries in the ET kinetics arising during the reduction of ferrocene-based redoxmers, compared to their oxidation which displayed faster rate constants. Similar behavior was observed on a wide variety of carbon electrodes such as multi-layer graphene, highly ordered pyrolytic graphite, glassy carbon, and chemical vapor deposition-grown graphite films. However, aqueous systems and Pt do not exhibit such kinetic effects. Our analysis suggests that differential adsorption of the redoxmers is insufficient to account for our observations. Displaying a greater versatility than conventional electroanalytical methods, we demonstrate the operation of our spot analysis at concentrations up to 100 mM of redoxmer over graphite films. Looking forward, our method can be used to assess non-idealities in a variety of redoxmer/electrode/solvent systems with quantitative evaluation of kinetics for applications in redox-flow battery research.

Structural Modeling and Thermal Conductivity of Graphite Film Reinforced Aluminum Matrix Laminated Composites

Abstract: Excellent thermal conductivities of thermal management materials are expected to ensure the timely heat dissipation in lots of engineering applications and electronic devices. High in-plane thermal conductivity of laminated composites has become increasing significant for high energy and power density electronic devices. In this study, the continuous graphite film/aluminum (Gr film/Al) laminated composites were fabricated by vacuum hot pressing. In-plane and out-of-plane thermal conductivity of Gr film/Al laminated composites are tested. Two-dimensional structural models of Gr film/Al laminated composites are established, in which volume fraction, interfacial property, punching zone and orientation angle of Gr films can be controlled according to their actual composite microstructures. The effects of volume fraction and interfacial property on the thermal conductivity of Gr film/Al laminated composites are investigated. Two ways to reduce anisotropy of thermal conductivity are introduction of punching zones and control of Gr orientation, which are verified to be effective. On basis of the analysis above, a good understanding can be brought out for extensive thermal management applications of Gr/Al composites.