Thin Graphite Sheets Research Articles

Metal-free ultrathin terahertz absorber with independently tunable dual narrow bands

Abstract A technique is introduced to precisely control the resonance behaviour of a metal-free graphene-based terahertz absorber by independently tuning dual resonant peaks. The proposed ultrathin absorber features a multilayer configuration, with two isolated resonator layers of patterned graphene on dielectric (SiO2) substrates, and a thin graphite sheet at the bottom serving as a reflector. The stacked arrangement enables independent tunability of the high-absorptivity resonant peaks at 7.33THz and 9.34THz. The structure, with a thickness of just λ/15 of the free-space wavelength, offers a compact design suitable for space-constrained applications. Its symmetrical geometry ensures polarization insensitivity and stable performance for incident angles up to 60°. Simulated results, analysed via CST Studio and validated with an Equivalent Circuit Model (ECM), demonstrate excellent thermal stability. Furthermore, the narrowband response of the proposed absorber improves its sensitivity for refractive index variations induced by biomolecular interactions validating its suitability in biosensing applications. The absorber demonstrates peak absorption across both the resonant frequencies with an analyte optimised at 1.5μm thickness. Sensitivity levels of 1.1THz/RIU and 1.05THz/RIU along with figure-of-merit (FOM) values of 2.11 and 2.23. are recorded for the lower and upper bands, respectively. The absorber offers enhanced selectivity owing to low values of full-width at half maximum (FWHM). High Q-factors of 12.85 and 19.3, confirm its strong potential for refractive index sensing. 

Design and performance assessment of a solar photovoltaic panel integrated with heat pipes and bio-based phase change material: A hybrid passive cooling strategy

This study investigates the effectiveness of an indirect passive cooling solution for photovoltaic (PV) panels using flattened heat pipes (FHPs) and phase change material (PCM). An innovative passive cooling design is proposed to cool a PV panel using multiple FHPs with a thin graphite sheet between the PV panel and the FHPs. Five experimental cases are examined under varying heat flux loads. Case O serves as the baseline with no cooling system, while Cases 1 to 4 feature different configurations of FHPs and aluminum sheets, with PCM heat sinks added in Cases 2 and 4. The investigation focuses on temperature profiles, temperature reductions, and final temperatures of the PV panel, especially at the end of a 4-hour experimental period when the PCM is fully melted. The results show significant temperature reductions in Case 1 compared to the baseline, with further improvement in Case 2 due to the PCM heat sink. Temperature reductions in Cases 2 and 4 are consistently higher than in Cases 1 and 3, demonstrating the enhanced cooling potential of PCM. Case 4 achieves the highest temperature reduction of 37.0 °C, followed by Case 2 with 34.9 °C under a radiative heat flux of 1000 W/m2. Using 4 FHPs (Cases 1 and 2) is economically justified, offering comparable cooling performance to 8 FHPs (Cases 3 and 4), thus ensuring cost-effectiveness and reducing material usage by over 50 %. A maximum enhancement in PV electrical efficiency of 17.3 % is achieved in Case 2 during PCM phase change with a radiative heat flux of 1000 W/m2.

Numerical Simulation of the Transport of Gas Species in the PVT Growth of Single‐Crystal SiC

AbstractSingle‐crystal silicon carbide (SiC) is an important semiconductor material for the fabrication of power and radio frequency (RF) devices. The major technique for growing single‐crystal SiC is the so‐called physical vapor transport (PVT) method, in which not only the thermal field but also the fluid‐flow field and the distribution of gas species can be hardly measured directly. In this study, a multi‐component flow model is proposed that includes the inside and outside of a growth chamber and a joint between the seed crystal holder and crucible which allows exchanges of the gas species. The joint is simulated as a thin porous graphite sheet. The Hertz‐Knudsen equation is used to describe the sublimation and deposition. The convection and diffusion are described by the Navier–Stokes equations and mixture‐averaged diffusion model, in which the Stefan flow is taken into account. The numerical simulations are conducted by the finite element method (FEM) with a multi‐physics coupled model, which is able to predict the fluid flow field, species distribution field, crystal growth rate, and evolution of the molar concentration of dopant gas. Using this model, the effects of several experimental conditions on the transport of gas species and the growth rate of single‐crystal SiC are analyzed.

Joining of INCONEL-625 by microwave hybrid heating and its performance analysis

Welding is a process in joining of two or more metals which is done by using or without using of filler materials. Domestic microwave ovens have been in use since last century. Now a day’s microwave technology could be employed to process materials. The investigation is carried out to compare the performance of Joint formed by Microwave hybrid heating with respect to tungsten inert gas (TIG) welding. Radiations emitted from microwave are used to join INCONEL-625 by employing INCONEL-625 powder of grain size 40μm as interface material. Graphite, Silicon carbide (SiC) and Charcoal was used as a susceptor material. And thin graphite sheet is used as separator. Traditional TIG welding machine is used to join INCONEL625 plates with INCONEL-625 wire as filler material. Scanning electron microscope (SEM) characterization joints after welding shows complete melting of INCONEL-625 powder particles and good metallurgical bonding with surface. X-ray diffraction (XRD) reveals the formation of niobium and chromium carbides and intermetallic phases. Joining of same INCONEL-625 plates by using TIG welding has successfully conducted. The novelty of this study is to develop new material joining approach by microwave heating. The comparative study showed material diffusion in microwave hybrid heating is much greater than that of TIG welding. Weld formed by microwave heating is more effective that of TIG welding.

Effect of electrolyte circulation rate in flow-through mode on the performance of vanadium redox flow battery

Large-size redox flow battery stacks require flow channels for uniform flow circulation of electrolyte over the electrode without incurring too high a pressure drop penalty. In the present work, the use of thin graphite sheets in a flow-through mode, i.e., with the electrolyte being pumped directly into the electrode is explored. In order to reduce the pressure drop when such designs are scaled to large size cells, use of relatively thick polypropylene frames to hold carbon felt electrodes is studied. Experiments have been conducted in cells of nominal electrode areas of 120 and 440 cm2 having a 0.6 mm thick graphite sheet as the bipolar plate. Pressure drop and electrochemical characterization studies show that sufficient convection velocities of electrolyte in the carbon felt, in the range of 3–5 mm s−1, are needed to obtain high round-trip energy efficiency as well as discharge energy density. This observation is supported by estimates of mass transport limited current density for the cell. Under these conditions, use of thin graphite sheets yields a weight reduction of over 75% when compared to cells with thick graphite plates while giving comparable hydrodynamic and electrochemical performance.

Interference of Graphene Presence in Formation Mechanism of Metalloporphyrin (PtTFPP) Complex with Oxygen

Introduction Pressure sensitive Paints (PSP) are widely applied in aerodynamic surface tests, as they allow fast data acquisition and pressure mapping across the entire surface during flight simulation [1]. The PSP used in this work is mainly composed of Fluoro-Isopropyl-Butyl (FIB) (Figure 1.A), a polymer that allows oxygen permeability in the paint and platinum tetra(pentafluorophenyl)porphyrin (PtTFPP), responsible for pressure sensitivity (Figure 1.B) [2]. Considering the PSP unique properties, it is possible to obtain an electrical response that enables the use of this paint in airplanes pressure sensors, during flight. For this, an electrical charge of graphene derivative is added to the PSP.Graphene has properties that make it interesting for several applications. Its final application is related to its production method. Electrochemical exfoliation of graphite was used to produce the carbonaceous electrical charge, which has advantages such as ecofriendly reagents, simple product purification and ease of subsequent steps [3, 4]. Seeking to reach the PSP application potential as an oxygen sensitive material that generates an electrical response on pressure, it is necessary that the added electrical charge is compatible with the paint, producing a homogeneous material, high electrical conductivity and mechanical properties suitable for aerospace applications. Thus, the interaction of graphene derivatives with paint and how this influence on its sensitivity to oxygen was studied. This sensitive material can be used in an aeronautical sensor redundant to the Pitot Tube. Therefore, the main objective of the proposed research is to increase the safety of air navigation using a graphene-derived composite with a pressure-sensitive metalloporphyrin paint (PSP).Materials and methods Initially, the production of graphene derivatives was carried out by electrochemical exfoliation of graphite, in which plates of thin graphite sheets pressed were used as working electrode and counter electrode. As an electrolyte solution, a mixture of salts (NH4)2SO4 and (NH4)2HPO4 was used at a concentration of 0.1 mol.L-1 and a proportion of 70/30 v/v%. Exfoliation took place at a fixed potential of 10 V, applied by an electrical power supply. At the end of this process, two drying methodologies were tested: kiln at 70°C (Graphene A) and lyophilization (Graphene B). The composite production consists of mixing the graphene derivative and PSP, at a concentration of 1 mg.mL-1, with the aid of an ultrasound tip for 30 minutes. In addition to the carbonaceous material, a commercial graphene (Graphene C) was also used. After mixing, the material is dripped onto an aluminum surface. The characterizations performed were Raman Spectroscopy and X-Ray Diffraction Spectroscopy to analyze the morphology of the graphene used and Stereo Microscopy, XRD and electrical impedance for the composites.Results and discussion Analyzing the Raman spectra, Graphene A has a more disorder in the carbon chain, higher degree of stacking between planes and a greater association of defects (D4, 2D1 bands, respectively). The lyophilized material showed less interactions between the edges (D1+D4 band) configuring smaller and less agglomerated particles. Graphene C also showed a certain degree of defects and functionalization by oxygenated groups. The diffractogram of Graphene B and C indicates greater disorder in the bonds of the carbon rings with sp2 hybridization than that presented in Graphene A, with A being the material with the highest number of layers and the smallest lamellar distance. Stereo microscopy (Figure 2) images of the composites showed that the mixture is not homogeneous, especially after drying and presents roughness, being these characteristics that can be a problem for the final application. The composite diffractograms show the same peaks only for the paint, with a difference in intensity. The amorphous peak at 16.4°, referring to the polymer, becomes more intense and crystalline with Graphene A and C indicating possible interaction and intercalation of graphene layers with the polymer. The Electrical Impedance of the composites was performed in variable vacuum without flow. Composites with Graphene A and B are resistive, without variation in the presence of different amounts of oxygen. With Graphene C, the response was capacitive-resistive, and was sensitive to pressure changes, but still needs calibration (Figure 3).[1] PUKLIN, E. et al. Ideality of pressure-sensitive paint. I. Platinum tetra(pentafluorophenyl)porphine in fluoroacrylic polymer. Journal of Applied Polymer Science, v. 77, n. 13, p.2795-2804, 2000.[2] GAMAL, E.; et. al. Oxygen pressure measurement using singlet oxygen emission. Review of Scientific Instruments 76, 054101, 2005.[3] KARIMOV, K. S.; et. al. Development of pressure-sensitive thermo-electric cell using graphene and n-Bi2Te3. Emergent Materials 2, pages 387–390, 2019.[4] ANJU, M.; et. al. Graphene-dye hybrid optical sensors. Vol 17, 194 – 217, 2019. Figure 1

Fabrication of Bipolar Plates from Thermoplastic Elastomer Composites for Vanadium Redox Flow Battery.

A vanadium redox flow battery (VRFB) is a promising large-scale energy storage device, due to its safety, durability, and scalability. The utilization of bipolar plates (BPs), made of thermoplastic vulcanizates (TPVs), synthetic graphite, woven-carbon-fiber fabric (WCFF), and a very thin pyrolytic graphite sheet (GS), is investigated in this study. To boost volumetric electrical conductivity, WCFF was introduced into the TPV composite, and the plate was covered with GS to increase surface electrical conductivity. Created composite BPs acquire the desired electrical conductivity, mechanical strength, and deformation characteristics. Those properties were assessed by a series of characterization experiments, and the morphology was examined using an optical microscope, a scanning electron microscope, and atomic force microscopy. Electrochemical testing was used to confirm the possibility of using the suggested BP in a working VRFB. The laminated BP was utilized in a flow cell to electrolytically convert V(IV) to V(V) and V(II), which achieved comparable results to a commercial graphite bipolar plate. Following these experiments, the laminated bipolar plates’ surfaces were examined using X-ray photoelectron spectroscopy, and no evidence of corrosion was found, indicating good durability in the hostile acidic environment.

Graphite sheets in study of radiation dosimetry and associated investigations of damage

Present work builds upon prior investigations concerning the novel use of graphite-rich polymer pencil-lead for passive radiation dosimetry. Working with photon-mediated interactions at levels of dose familiar in radiotherapy, exploratory investigations have now been made using graphite produced commercially in the form of 50 μm thick sheets. Focusing on the relationship between absorbed radiation energy and induced material changes, investigations have been made of thermo- and photoluminescence dose dependence, also of alterations in Raman spectroscopic features. Photoluminescence studies have focused on the degree of structural order of the samples when exposed to incident MeV energy gamma-radiation, supported by crystallite size evaluations. The results are consistent and evident of structural alterations, radiation-driven thermal annealing also being observed. The results, supportive of previous TL, Raman and photoluminescence studies, are readily understood to arise from irradiation changes occurring at the microscopic level. Notwithstanding the non-linearities observed in the conduct of Raman and photoluminescence studies there is clear potential for applications in use of the defect-dependent methods herein, providing sensitive detection of radiation damage in graphite and from it dose determination. Most specifically, the readily available thin graphite sheets can provide the basis of a low-cost yet highly effective system for studies of radiation-driven changes in carbon (and/or carbon based composites), also as a dosimetric probe of skin dose, its atomic number closely matching with the effective atomic number of soft tissues.

Graphite-based lithium ion battery with ultrafast charging and discharging and excellent low temperature performance

Lithium-ion (Li+) batteries are widely used in portable electronics and vehicles. However, fast charging and discharging at room temperature and charging at subzero temperature are still great challenges. Graphite is presently the most common anode material for lithium-ion batteries, but the long diffusion distance of Li+ limits its rate performance. Herein, to shorten the diffusion path, we develop a favorable electrode consisting of thin graphite sheets with through-holes and carbon nanotube. The carbon nanotube can effectively prevent the restack of graphite sheets. Combining with low desolvation energy electrolyte, which facilitates Li+ transport through electrode/electrolyte interface, the fabricated battery exhibits not only an excellent rate performance (almost be fully charged and discharged at 8 C-rate) at room temperature but also an improved low-temperature performance. These findings pave a way for the design of robust graphite-based lithium-ion batteries with high performance at both room and low temperatures.

Polymer Stamp-Based Mechanical Exfoliation of Thin High-Quality Pyrolytic Graphite Sheets

This paper reports on a polymer stamp-based mechanical exfoliation method for producing thin (<1 μm) graphite sheets from a highly ordered pyrolytic graphite (HOPG) source by tailoring key exfoliation process parameters, utilizing in-plane shear oscillation during exfoliation, and controlling the thickness of a polydimethylsiloxane (PDMS) stamp. Experiments on the effect of high frequency in-plane shear oscillation and the effect of PDMS stamp thickness are designed to reduce the thickness of exfoliated layers and to minimize surface morphological variations. Results show that the exfoliated sheets consist of a range of layer thicknesses, surface areas, and surface morphological features. The exfoliated HOPG sheets are also found to be thinner, more electrically and thermally conductive, and of higher quality than commercially available pyrolytic graphite sheets.

Origami system for efficient solar driven distillation in emergency water supply

Facing lack of infrastructure and no access of electricity, insuring drinking water for people during an emergency in remote area is becoming a great challenge. Here, we develop an origami as photothermal material based on daily pencil and paper for solar driven water purification in emergency. The drawn process destroyed the Van der Waals’ force between graphite layers, making pencil cartridge exfoliated into thin graphite sheets. The paper fibers combined with graphite sheets were demonstrated with broadband absorption for solar energy harvesting and excellent hydrophilicity for water transportation. The origami structure effectively promoted the utilization of solar energy attributing to the increased solar absorption area and decreased solar reflection loss compared with planar system. In particular, the solar vapor efficiency and vapor evaporation rate of as-prepared origami system were reached to 80% and 1.16 kg m−2 h−1, respectively. In addition, the analog calculation results of COMSOL Multiphysics indicated that the origami structure was free from the dynamic solar motion. Herein, this nearly free cost, facile fabricated and high efficiency design would unlock a new generation of efficient water purification for water supply in emergency.

Characterization of Pyrolytic Graphite Sheet: A New Type of Adsorption Substrate for Studies of Superfluid Thin Films

We have measured surface morphology and gas adsorption characteristics of uncompressed pyrolytic graphite sheet (uPGS) which is a candidate substrate for AC and DC superflow experiments on monolayers of 4He below T = 1 K. The PGS is a mass-produced thin graphite sheet with various thicknesses between 10 and 100 {\mu}m. We employed a variety of measuring techniques such as imagings with optical microscope, SEM and STM, Raman spectroscopy, and adsorption isotherm. PGS has smooth and atomically-flat external surfaces with high crystallinity. Although the specific surface area (<0.1 m$^2$/g) is rather small, by making use of its smooth external surface, the thinnest uPGS of 10 {\mu}m thick is found to be suitable for the superflow experiments on the strictly two-dimensional helium systems.

A carbon cloth-based lithium composite anode for high-performance lithium metal batteries

The two most challenging issues for Li metal based battery are infinite volume change during uneven deposition/dissolution process and the growth of Li dendrite. Therefore, the Li metal battery exhibits poor cycling life span and even the safety issue. Here we developed a facile method to prepare dendrite-mitigation Li composite electrode (Li@CC) using commercial carbon cloth as the interfacial layer between Li metal anode and the electrolyte without pre-stored Li process in carbonate-based electrolyte. The Li@CC symmetrical cells exhibit highly reduced polarization (150 mV) and stable cycling performance (>200 cycles) at a high current density of 5 mA cm−2. Furthermore, the Li@CC composite anode based full cell with limited Li and moderately high loading cathode exhibits longer cycling life span, better rate performance, lower and more stable polarization than that of bare Li anode. Especially, the Li@CC-Li4Ti5O12 full cell delivers an excellent cycling performance of 700 cycles with capacity retention of over 80%, which shows dozens of times’ improvement than that of full cell based on bare Li. We believe that the high performance are due to the unique characteristics of carbon cloth such as the high conductivity, enlarged surface area and intrinsic pore structure consisted of thin crystalline graphite sheets. The high performance results with the commercial available carbon cloth can not only offer a competitive approach for industry application of Li metal battery, but also be used for other metal based energy devices.

High Performance Poly(viologen)-Graphene Nanocomposite Battery Materials with Puff Paste Architecture.

Four linear poly(viologens) (PV1, PV2: phenylic, PV3: benzylic, and PV4: aliphatic) in tight molecular contact with reduced graphene oxide (rGO), that is, PV@rGO, were prepared and used as anodic battery materials. These composites show exceptionally high, areal, volumetric, and current densities, for example, PV1@rGO composites (with 15 wt % rGO, corresponding to 137 mAh g-1) show 13.3 mAh cm-2 at 460 μm and 288 mAh cm-3 with 98% Coulombic efficiency at current densities up to 1000 A g-1, better than any reported organic materials. These remarkable performances are based on (i) molecular self-assembling of PVs on individual GO sheets yielding colloidal PV@GO and (ii) efficient GO/rGO transformation electrocatalyzed by PVs. Ion breathing during charging/discharging was studied by electrochemical quartz crystal microbalance and electrochemical atomic force microscopy revealing an absolute reversible and strongly anisotropic thickness oscillation of PV1@rGO at a right angle to the macroscopic current collector. It is proposed that such stress-free breathing is the key property for good cyclability of the battery material. The anisotropy is related to a puff paste architecture of rGO sheets parallel to the macroscopic current collector. A thin graphite sheet electrode with an areal capacity of 1.23 mAh cm-2 is stable over 200 bending cycles, making the material applicable for wearable electronics. The polymer acts as a lubricant between the rGO layers if shearing forces are active.

Low temperature transport properties of pyrolytic graphite sheet

We have made thermal and electrical transport measurements of uncompressed pyrolytic graphite sheet (uPGS), a mass-produced thin graphite sheet with various thicknesses between 10 and 100μm, at temperatures between 2 and 300K. Compared to exfoliated graphite sheets like Grafoil, uPGS has much higher conductivities by an order of magnitude because of its high crystallinity confirmed by X-ray diffraction and Raman spectroscopy. This material is advantageous as a thermal link of light weight in a wide temperature range particularly above 60K where the thermal conductivity is much higher than common thermal conductors such as copper and aluminum alloys. We also found a general relationship between thermal and electrical conductivities in graphite-based materials which have highly anisotropic conductivities. This would be useful to estimate thermal conductance of a cryogenic part made of these materials from its electrical conductance more easily measurable at low temperature.

Electrochemical Performance of Activated Carbon Based Electric Double Layer Capacitors Using 1-Ethyl-3-Methylimidazolium Dicyanamide Ionic Liquid and Its Gel Polymer Electrolyte

The supercapacitors have emerged as an important energy storage device as they can deliver a high specific power, long cycle life, and much higher charge-discharge rates than a battery. In particular, solid-state supercapacitors have gained worldwide attention as an emerging candidate for smart and efficient energy storage devices due to the increasing demand for miniaturized electronics. Electric double layer capacitors (EDLCs) are the most widely studied class of supercapacitors which physically stores charge by forming an electric double layer at the interfaces between the high surface area carbon electrode and the electrolyte. The conventional EDLCs using high surface area activated carbon electrodes and non-aqueous liquid electrolytes represent the current state of the art. The most common cause of failure of such devices is related to the electrolyte leakage. Most of the past work on EDLCs have been carried out using the liquid electrolytes (aqueous, organic and pure ionic liquid). The gel polymer electrolytes with high ionic mobility and good dimensional/mechanical stability, offer a viable substitute for the liquid electrolytes and they are being used for flexible and solid-state electrochemical energy storage devices. Here, we report the electrochemical performance of high surface area activated carbon based EDLCs using 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA) ionic liquid and its poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) gel counterpart as electrolytes. The gel electrolyte films were prepared by immobilizing the EMImDCA ionic liquid in PVdF-HFP copolymer matrix by solution casting method. The activated carbon electrodes were prepared by mixing the activated carbon powder with conductive additive (Super C65) and PVdF-HFP binder in a ratio of 8:1:1 (w/w/w), and then the mixture was drop-casted onto a flexible thin graphite sheet which serves as current collector. The solid-state EDLC cells were fabricated by sandwiching the gel electrolyte film between two identical activated carbon electrodes whereas EDLC cells with pure IL were fabricated by using fiberglass separator soaked with IL. The EDLC cells show highly capacitive behavior as evident from the cyclic voltammogram of the cells measured at a scan rate of 20 mV s-1 which is rectangular in shape (Fig 1a). However, gel electrolyte based solid-state cell shows slightly higher resistance, obvious from slight deviation from rectangular shape at both turning potential. Typical galvanostatic charge-discharge characteristic of the EDLC cells at current density of 5 mA cm-2is shown in Fig. 1b. The linear discharge characteristics of the cell further confirms the capacitive behavior of the cells due to formation of an electric double layer at the interfaces. The EDLC cell with pure IL shows specific capacitance of ~98 F g-1 whereas IL-gel based EDLC cell shows specific capacitance of ~86 F g-1, derived from charge-discharge curves at 5 mA cm-2. A comparative performance of the EDLC cells was carried our using the impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. This paper discusses the results of these comparative studies with pure IL and its PVdF-HFP gel electrolytes. Figure 1

Graphite exfoliation in cellulose solutions.

Shaking graphite powder dispersed in an aqueous alkaline cellulose solution produces stable dispersions of hydrophilic, thin graphite sheets with lateral dimensions reaching many micrometers. The X-ray diffractogram and Raman spectrum of the exfoliated graphite differ from the well-known graphite patterns. Analytical transmission electron micrographs show cellulose bound to the surface of thin lamellae and this is confirmed by scanning probe micrographs. The dispersant properties of dissolved cellulose are assigned to its adsorption on graphite by juxtaposition of the hydrophobic planes on both substances, forming hydrophilic particles. This method uses only simple and easily accessible chemicals, processed under mild conditions. The resulting nanographite-cellulose dispersions are suitable for making conductive lignocellulosic nanocomposites and coatings.

Carbon Nanotube Synthesis via the Calciothermic Reduction of Carbon Dioxide with Iron Additives

The novel fabrication of multi-walled carbon nanotube (MWCNT)/cementite (Fe3C) nanocomposites was demonstrated via the calciothermic reduction of carbon dioxide (CO2) through electrolysis in molten CaCl2/CaO with iron additives at 1173 K. In this technique, CO2 generated from a graphite anode is reduced to carbon with a metallic calcium reductant formed on a graphite cathode via electrolysis in molten salt. Calciothermic reduction without iron additives resulted in the formation of onion-like carbons (OLCs) with spherical graphite layers and thin graphite sheets. In contrast, MWCNT/Fe3C nanocomposites and OLCs were successfully fabricated via calciothermic reduction with iron additives through their catalytic activities. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0031509ssl] All rights reserved.

High-Performance Solid-State Supercapacitors Fabricated by Pencil Drawing and Polypyrrole Depositing on Paper Substrate.

A solid-state powerful supercapacitor (SC) is fabricated with a substrate of Xerox paper. Its current collector based on a foldable electronic circuit is developed by simply pencil drawing. Thin graphite sheets on paper provide effective channels for electron transmission with a low resistance of 95 Ω sq−1. The conductive organic material of polypyrrole coated on thin graphite sheets acts as the electrode material of the device. The as-fabricated SC exhibits a high specific capacitance of 52.9 F cm−3 at a scan rate of 1 mV s−1. An energy storage unit fabricated by three full-charged series SCs can drive a commercial light-emitting diode robustly. This work demonstrated a simple, versatile and cost-effective method for paper-based devices.Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-015-0039-3) contains supplementary material, which is available to authorized users.

Thick Graphene Embedded Metal Heat Spreader with Enhanced Thermal Conductivity

In this paper, a copper foil-thick grapheme (thin graphite sheet)-copper foil structure is reported to achieve mechanically strong and high thermal conductive layer suitable for heat spreading components. Since graphene provides much higher thermal conductivity than copper, thick graphene embedded copper layer can achieve higher effective thermal conductivity which is proportional to graphene/copper thickness ratio. Since copper is nonreactive with carbon material which is graphene, chromium is used as adhesion layer to achieve copper-thick graphene-copper bonding for graphene embedded copper layer. Both sides of thick graphene were coated with chromium as an adhesion layer followed by copper by sputtering. The copper foil was bonded to sputtered copper layer on thick graphene. Angstrom's method was used to measure the thermal conductivity of fabricated copper-thick graphene-copper structure. The thermal conductivity of the copper-thick graphene-copper structures is measured as <TEX>$686W/m{\cdot}K$</TEX> which is 1.6 times higher than thermal conductivity of pure copper.