Density Graphite Research Articles

Determination of Thermal Properties of Carbon Materials above 2000 °C for Application in High Temperature Crystal Growth

AbstractThis work reports on the determination of the heat conductivity of high temperature stable carbon materials in the temperature range well above 2000 °C where classic material characterization methods fail. Dense graphite (DG) materials as well as rigid and soft felt isolation (RFI/SFI) components have been investigated which are used during crystal growth of SiC by the physical vapor transport method (PVT) in the temperature regime of 2000 and 2400 °C. The applied materials characterization methods include low temperature physical heat conductivity measurements using laser flash analysis (LFA) in the temperature range 25–1200 °C, data extrapolation to elevated temperatures up to 2400 °C, and a correlation of heating processes and computer simulation of the temperature field of different hot zone designs. Using this approach, the calculated temperatures and experimentally determined values with an error of less than ± 2% at 2400 °C can be merged.

Relationship between functionalization and structural defect density of graphite for application in potassium-ion batteries

Potassium-ion batteries (PIBs) have recently gained attention as an alternative to Li-ion batteries (LIBs) because Li and K belong to the same alkali metal group and are replaceable. However, the theoretical capacity of PIBs is hindered by the larger size of potassium ions compared to lithium ions. Generally, the surface treatment of graphite, an anode material in metal-ion batteries, enhances ion diffusivity and improves electrochemical performance. In this study, a straightforward approach is introduced in which graphite is treated with an acid to widen the interlayer spacing and an alkali to create pores. Acid and alkali treatments not only improve ion diffusivity but also control the surface charge of graphite in PIBs. Consequently, acid-treated graphite (AG) displays the highest specific capacity (206.2 mAh g−1 at 0.2 A g−1 after 100 cycles) with good durability. In addition, the trade-off between the physical ion pathway derived from structural defect density and functionalization-induced surface charge improves ion diffusivity.

Reactive spontaneous infiltration and spreading wetting of graphite by Cu–aTi (a = 17, 34, 68 at. %) alloys at 1100 °C

Alloying with reactive elements, such as Ti, enhances the ability of Cu melts to wet graphite. However, our understanding of the reactive wetting and kinetic mechanisms of the Cu–aTi/C system at high temperatures is still controversial. The reactive spontaneous infiltration (RSI) of Cu–aTi alloys (a = 17, 34, 68 at. %) into porous graphite and the spreading wetting (SW) on dense pyrolytic graphite were examined to elucidate the effect of the Ti content on the RSI and SW mechanisms and kinetics. The reactive wetting behaviors were investigated using a modified sessile drop method, and the interfacial microstructures, elemental distributions, and phase compositions of samples were characterized using instrumental techniques. With increasing Ti content, TiCx became depleted in carbon and experienced a morphology change. The mechanisms of RSI and SW were controlled by the synergistic effects of Ti content and TiCx. By fitting the time-dependent variation of the relevant parameters (contact angle, spreading radius, infiltration volume, and infiltration depth) for the two substrates at the same Cu–aTi alloy content using reaction- and diffusion-limited models in the reactive wetting system, we found that the kinetics of these two processes were controlled by similar mechanisms.

Expanded Graphite (EG) Stabilization of Stearic and Palmitic Acid Mixture for Thermal Management of Photovoltaic Cells

In this work, passive cooling systems for the revamping of existent silicon photovoltaic (PV) cells were developed and analysed in order to mitigate the efficiency loss caused by temperature rise in the hot season. For this purpose, expanded graphite (EG) was used to stabilize a phase change material (PCM) with a melting temperature close to 53 °C in order to realize thermal management systems (TMSs) able to store heat at constant temperature during melting and releasing it in crystallization. In particular, stearic and palmitic acid mixture (PA-SA) was shape-stabilized in EG at different concentrations (10, 12 and 14 part per hundred ratio) under vacuum into a rotary evaporation apparatus followed by cold compaction; PA-SA leakage was reduced due to its intercalation between the graphite lamellae, and the thermal conductivity necessary to maximize the heat transfer to a bulk TMS was improved via powder cold compaction, which minimizes voids and creates preferential thermal conductive patterns. The composite materials, stable till 150 °C, were tested by differential scanning calorimetry (DSC) at 1 °C/min to precisely determine the phase transition temperatures and the enthalpic content, which was only slightly reduced from 196 J/g of the neat PCM to 169 J/g due to the very low EG fraction necessary for the stabilization. Despite only the 14:100 EG-to-PA-SA ratio, the system’s thermal conductivity was enhanced 40 times with respect to the neat PCM (from 0.2 to 8.3 W/(m K), value never reached in works present in the literature), with a good convergence of the values evaluated through hot disk tests and laser flash analysis (LFA), finding correlation with both graphitic content and density. In order to completely avoid leaking with the consequent dispersion of PCM in the environment during the final application, all the samples were encapsulated in a PE-made film. The mechanical properties were evaluated with compression tests at 30 °C and 80 °C simulating a possible compressive stress deriving from the contact needed to maintain the TMS position on the rear of the PV cells. Finally, the material response was simulated by imposing thermal cycles into a climatic chamber and reproducing the three hottest and coldest days of summer 2022 of two Italian locations, Verona (Veneto, 45° N, 11° E) and Gela (Sicily, 37° N, 14° E), thus highlighting the thermal management effects with delays in temperature increase and daily peak temperature smoothing. The role of EG is strategic for the processing and the properties of the resulting composites in order to realize a proper compromise between the melting enthalpy of PCM and the thermal conductivity enhancement given by EG.

Multi‐Interface Strategy for Electrode Tailoring Toward Fast‐Charging Lithium‐Ion Batteries

AbstractThick and dense graphite anodes used in lithium‐ion batteries (LIBs) suffer from sluggish reaction kinetics at the electrode level, causing Li metal plating on their surfaces and significant capacity decay at high charging currents. Thus, it is crucial to tailor electrodes based on a comprehensive understanding of the complex reaction kinetics to realize fast‐charging LIBs. A multi‐interface strategy is proposed for electrode tailoring using Al2O3 nanoparticles to enhance fast‐charging capability while suppressing Li metal plating. Molecular dynamics simulations suggest that the incorporated Al2O3 nanoparticles perturb the charge and molecule distributions in the boundary layer, forming an “interfacial highway” for facile Li+ transport at the Al2O3/electrolyte interface. This pushes Li+ deeper into the electrode and homogenizes the Li+ flux across the electrode's top surface. A full cell assembled with the Al2O3‐decorated graphite electrode (areal capacity of 4.4 mAh cm−2) exhibits excellent cyclability with a capacity retention of 83.4% over 500 cycles even at a 2C rate without any noticeable signal for undesirable Li plating. The role of interfacial highways predicted by theoretical computations is further validated using a pouch‐type full cell (500 mAh). These findings provide insights into the interfacial and microstructural design of high‐capacity graphite electrodes for fast‐charging, long‐cycling LIBs.

A critical review and meta-analysis of xenon-on-carbon sputter yield data

A systematic review and meta-analysis of sputter yield data for xenon ions normally incident on graphite at energies below 2000 eV was undertaken to identify systematic errors, determine the best model parameter values to represent yield as a function of energy, quantify uncertainty, and determine if the data support differences in yields for different types of graphite. A critical examination of the 11 published data sets for high density graphite, pyrolytic graphite, and amorphous carbon showed that, in general, they were carefully controlled to minimize errors. The most significant quantifiable systematic errors were those caused by the neglect of doubly charged ions, chemical erosion, and the impact of secondary electron emission on ion flux measurements. The effects of gas uptake and outgassing on mass loss measurements and unrepresentative surface textures may have biased other experiments, but these effects could not be quantified. The semi-empirical Eckstein model for yield as a function of energy was fit to data for the three graphite types using a hierarchical Bayesian statistical model, producing recommended fit parameters and probability distributions representing uncertainty in yields. The results showed that differences in yield for high density graphite and pyrolytic graphite were not statistically significant. Apparent differences in yield for amorphous carbon disappeared when the single data set available for energies below 150 eV was corrected for reasonable values of double ion content. Recommended procedures to avoid systematic errors and additional experiments and modeling to fill in gaps in our understanding are included.

Low Redox Potential InN Nanowires as High-Energy-Density Anode for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have become the most predominant energy sources for various digital products and electric vehicles due to the rechargeable, high capacity, and no memory effect characteristics. Charging to 80% of the full capacity time is commonly required to be less than 30 minutes in the future as technological development. Thus, it is essential to improve the dynamics of the active material [1]. The current approach to increasing the energy density of LIBs is to increase the electrode loading mass. This has the effect of greatly increasing the thickness of the electrodes, making it difficult for Li-ions to quickly pass through the electrode. Graphite anode is the most widely used anode material due to its low cost, easy preparation, and applicable working voltage below 0.3 V (vs Li/Li+). However, its low capacity and disordered staging behavior at large currents limit the fast charging performance. Moreover, due to the low density of graphite, when designed as a high-energy density cell, its thickness increases considerably, significantly reducing the Li-ions diffusion. Therefore, new active materials with high capacity and fast Li-ions diffusion should be developed to achieve high-energy-density cells.As a well-known semiconductor, Indium Nitride (InN) has been widely used for various applications such as high-frequency terahertz and solar energy devices. When it is denoted as an anode for LIBs, the InN can deliver a theory specific capacity over 1200 mAh g-1, which is nearly four times of the conventional graphite anodes (~372 mAh g-1). Meanwhile, it shows a relatively low redox potential (below 0.7 V vs. Li+/Li), affording a wide voltage window for a full cell. Remarkably, the InN is a narrow band (0.69 eV) semiconductor showing good electron transfer properties. Thus, the InN could be considered as one of the most promising anode for the next-generation HED-LIBs. However, the inherent volume change of InN particles during the conversion and alloying/dealloying process with Li+ maybe lead to many adverse effects, including pulverization of InN particles electrode, tearing solid electrolyte interphase (SEI). The fact finally worsens the Li-storage performance, greatly hindering the commercial application of InN anode. In addition, the sluggish ion diffusion of InN particles also limits the rate capability. To address the issues, approaches like constructing micro/nano composite structures, which have been broadly explored to alleviate the volume expansion and improve ion diffusion [2]. Among these micro/nanostructures, the 1D nanostructure shows superior physicochemical properties in favor of improving Li-storage performance. Firstly, the One-dimensional (1D) nanostructures can accommodate the strain of Li-ions delidiation/lidiation along specified directions. Secondly, the gap of the 1D nanostructure is just enough to provide a buffer during the charge/discharge process. Thirdly, the 1D nanostructure is beneficial to the Li-ions diffusion leading to good rate performance [3]. Moreover, the 1D structure has the advantage of self-forming film, which greatly reduces the weight of the electrode. It is worth noting that the large ratio aspect of 1D nanostructure can lower the ion diffusion paths accelerating the rate performance.Herein, we elaborately constructed the single-crystal InN nanowires on carbon fibers (InN/Au-CFs). Firstly, the CFs are decorated with Au nanoparticles by a magnetron sputtering method, which can afford many stable growth sites for InN nanowires. And then, the InN nanowires in situ grown on the Au nanoparticle surface by chemical vapor deposition successfully improved the adhesive force active material and substrate. The structural properties and Li-storage performance of InN/Au-CFs are systematically studied. In addition, the density of state and adatom adsorption of InN nanowires are calculated by density functional theory. The ion diffusion, reactivity, and electrode stability are successfully enhanced based on the results. We also built two-terminal electrodes to decelerate the metal electrode fatigue at large rate for a full cell. Particularly, the as-prepared InN/Au-CFs anode can deliver the capacities of 624.2 mAh g-1 at 0.1 A g-1 after 500 cycles and 416 mAh g-1 at 30 A g-1 for the rate assessment, respectively. Our work suggests that the embellishment one dimentional InN nanowire and two-terminal electrodes are a successful strategy for HED-LIBs contributing excellent long cycling performance and large rate capability.[1] J. Kim et al, Nat. Rev. Mater. 8(1) (2023) 54-70.[2] A. M. Bates, et al, Joule 6(4) (2022) 742-755.[3] L. Xing et al, Nano Energy 79 (2021) 105384. Figure 1

Thermal fatigue degradation progress in SiMo ductile cast iron under oxidation conditions

Thermal fatigue tests were conducted on a high Si low Mo ductile cast iron (DCI) under oxidation conditions at 600 °C. The study aimed to understand the evolution of surface degradation, focusing on complex composed graphite nodules, pearlite islets, and their impact on crack initiation and growth in relation to oxidation processes, etc. Degenerated graphite nodules, that include ferrite particles, and areas of increased graphite nodule density, along with pearlite islets, were examined for their oxidation behavior. At lower thermal cycles numbers cracks primarily initiated of at the graphite-matrix interface and grew faster in the case of successively arranged graphite nodules and their higher local number density. Graphite degradation involved debonding between graphite and matrix, followed by complex oxidation processes. Degenerated nodules exhibited higher oxidation rates due to the presence of ferrite which acts as oxidation pathways. Areas with increased graphite density and larger sizes facilitated accelerated oxidation via crack formation. Additionally, pearlite degradation started with cracked cementite lamellae, followed by oxidation. Strategies to enhance thermal fatigue resistance included reducing graphite nodule diameter, ensuring their uniform distribution, preventing of formation of degenerated nodules and eliminating porosity. These findings improve understanding of thermal fatigue behavior in DCI that has proven to be even more complex than previously thought. The findings will guide the development of advanced materials for demanding applications.

The influence of graphite moderator density on the neutronic performance and fuel economy of a Molten Salt Reactor

Typical thermal molten salt reactor (MSR) employs graphite as its neutron moderator, due to its chemical compatibility and low neutron absorption. It is not without issues, however, since graphite provides positive temperature feedback when the MSR is fueled with U-233. Reducing the graphite density can possibly ameliorate this issue, but at the cost of other neutronic parameters, such as fertile conversion into fissile nuclide, and fuel economy, such as fissile makeup cost. This study evaluates the influence of graphite moderator density on the neutronic performance and fuel economy of an MSR. Passive Compact Molten Salt Reactor (PCMSR) design was used as the MSR model. To evaluate the neutronic parameters, MCNP6.2 radiation transport code with ENDF/B-VII.0 neutron cross section library were used. The evaluated neutronic parameters were temperature coefficient of reactivity (TCR), kinetic parameters, and conversion ratio (CR). Meanwhile, the fuel economy evaluation comprised the initial fuel inventory cost and fissile makeup cost. From the calculation results, lowering graphite density remarkably improves TCR, but also decreased CR in a notable amount. While effective delayed neutron fraction (βeff) was not particularly affected, mean neutron generation time (Λ) was reduced in lower graphite density. Considering the fuel economy, initial fuel cost is not significantly affected, but the fissile makeup cost can be sensitive of graphite density.

Rate capability and Ragone plots for designing battery thermal management system based on phase change material

Phase change material (PCM), as a passive thermal regulation technology, is anticipated to mitigate the thermal challenges associated with anomalous temperature in lithium-ion batteries (LIBs). Nevertheless, the examination of its performance, i.e., energy and power density, has received limited attention in applications of battery thermal management system (BTMS). The primary aim of this work is to concentrate on the parametric optimization and performance assessment of BTMS utilizing PCM. Initially, a numerical model integrated paraffin/expanded composite and pouch battery is built and validated. Subsequently, a series of parametric studies are conducted to explore several aspects, including PCM type, expanded graphite loading, packing density, and PCM thickness. The thermal rate capability and Ragone plots are used to describe the specific energy and specific power of PCM. Based on that, the effects of PCM properties, geometry, and operating conditions can be effectively clarified. Furthermore, a multi-attribute decision making (MADM) method is introduced to aid variable selection. From analysis, the composite with PCM type of RT28, expanded graphite loading of 1–5 wt%, packing density of 700 kg m−3, and thickness of 3 mm is regarded as a suitable choice to achieve good performance. The present framework is helpful to provide guidance for PCM-based BTMS design.

Astonishing performance improvements of dry-film graphite anode for reliable lithium-ion batteries

The electric vehicle (EV) market now requires advanced graphite anodes that can enable both high loading and quick charging. However, meeting these requirements simultaneously is challenging because of uneven electrochemical reactions and Li-plating on the surface of graphite anodes during fast-charging. In this study, high current density graphite anodes (≈6 mA cm−2) were fabricated through a solvent-free dry-electrode process using homogeneously dispersed polytetrafluoroethylene fibrils (2.0 wt% in electrode). This approach significantly improved the mechanical properties and electrochemical performance of graphite anodes during charge/discharge cycles. Dry-processed graphite anodes outperformed conventional wet-processed electrodes in terms of rate performance and capacity retention. Furthermore, LiNi0.6Co0.2Mn0.2O2 (NCM)/graphite coin-type full cells are rapidly charged at a 3C-rate to induce Li-plating on the graphite surface. Thus, dry-processed graphite anodes exhibited less Li-plating than wet-processed anodes, implying that dry-processed electrodes are capable of fast-charging even under high-loading conditions. In addition, dry-processed graphite anodes retain 88.2 % capacity retention after 300 cycles, indicating a stable full-cell operation. Consequently, this research highlights the dry-electrode process as an innovative technique for electrode manufacturing, with the potential to reduce battery production costs while improving electrochemical performance during fast-charging.

Exploring the Influence of Temperature on Anode Degradation in Cycling-Aged Commercial Cylindrical Graphite-Si|NCA Cells

The degradation mechanisms of commercial graphite–SiOx/NCA battery related to the aging process in full cell under cycling conditions at three different temperatures, namely, 10 °C, 25 °C, and 45 °C, have been studied via post-mortem analysis, emphasizing the high energy density graphite–SiOx anode behaviour. The aging process of the full battery has been studied by non-destructive electrochemical methods. Then, to gain more understanding on the mechanisms that govern the graphite–SiOx degradation, full cells are disassembled, and the anodes are studied by physicochemical analysis techniques, electron microscopy techniques, and electrochemical characterizations. The battery cycled at 25 °C, between 2.5 and 4.2 V, shows higher cyclability than those cycled at 45 °C and 10 °C, at SoH 80%. Under these conditions, the structural and morphological changes undergo by graphite–SiOx and SiOx particles, respectively, and the loss of active material, together with the SEI growth explain the anode degradation.

Hybrid Machine Learning-Enabled Potential Energy Model for Atomistic Simulation of Lithium Intercalation into Graphite from Plating to Overlithiation.

Graphite is one of the most widely used negative electrode materials for lithium ion batteries (LIBs). However, because of the rapid growth of demands pursuing higher energy density and charging rates, comprehensive insights into the lithium intercalation and plating processes are critical for further boosting the potential of graphite electrodes. Herein, by utilizing the dihedral-angle-corrected registry-dependent potential (DRIP) (Wen et al., Phys. Rev. B 2018, 98, 235404), the Ziegler-Biersack-Littmark (ZBL) potential (Ziegler and Biersack, Astrophysics, Chemistry, and Condensed Matter; 1985, pp 93-129), and the machine learning-based spectral neighbor analysis (SNAP) potential (Thompson et al., J. Comput, Phys. 2015, 285, 316-330), we have successfully trained a hybrid machine learning-enabled potential energy model capable of simulating a wide spectrum of lithium intercalation scenario from plating to overlithiation. Our extensive atomistic simulations reveal the trapping of intercalated lithium atoms close to the graphite edges due to high hopping barriers, resulting in lithium plating. Furthermore, we report a stable dense graphite intercalation compound (GIC) LiC4 with a theoretical capacity of 558 mAh/g, wherein lithium atoms occupy alternating upper/lower graphene hollow sites with a nearest Li-Li distance of 2.8 Å. Surprisingly, following the same lithium insertion manner would allow the nearest Li-Li distance to be retained until the capacity reaches 845.2 mAh/g, corresponding to a GIC of LiC2.6. Hence, the present study demonstrates that the hybrid machine learning approach could further extend the scope of machine learning energy models, allowing us to investigate the lithium intercalation into graphite over a wide range of intercalation capacity to unveil the underlying mechanisms of lithium plating, diffusion, and discovery of new dense GICs for advanced LIBs with high charging rates and high energy densities.

Carbon nanotubes – PEI – Formate dehydrogenase nano-biointerface for the specific bioelectrochemical reduction of CO2 to formate

Reduction of extensive CO2 emissions is one of the key challenges that our society must overcome in order to minimize the effects of global warming and climate change. In this respect, electrochemical reduction of CO2 via redox enzymes is believed to be a promising route to minimize global CO2 concentrations, as they specifically catalyze the selective CO2 reduction in a reversible way at low potentials and mild conditions. In this work, we describe the effective anchoring of the enzyme Desulfovibrio vulgaris Hildenborough FdhAB formate dehydrogenase using electrostatic interactions favoring oriented immobilization, to the surface of MWCNTs-modified low density graphite electrodes with subsequent protection of the enzyme with polyethyleneimine (PEI) polymer. The synergistic effect of MWCNTs and PEI has been studied. High catalytic current densities, up to −230 μA cm−2, as well as a high operational stability of 11 h of continuous long-term measurements, were achieved.

Benchmark of Neutron Thermalization in Graphite Using a Pulsed Slowing-Down-Time Experiment

A benchmark has been developed using a pulsed slowing-down-time experiment to isolate the thermalization process in graphite. The experiment was conducted at the Oak Ridge Electron Linear Accelerator facility at Oak Ridge National Laboratory, and it measured the time spectrum of neutrons leaking from a graphite pile during slowing down and thermalization within graphite. Simulations of the benchmark experiment were performed using the MCNP6.1 Monte Carlo code and the ENDF/B-VII.1 and ENDF/B-VIII.0 cross-section databases. The benchmark provides a time spectrum (i.e., time-dependent counts in a detector) that allows for validation of the graphite thermal scattering libraries (TSLs). The impact on the simulations using a suite of graphite TSLs was compared with the experimental results. Given the density of nuclear graphite, the TSL corresponding to graphite with 30% porosity, as implemented in ENDF/B-VIII.0, was found to most accurately represent the measured time spectrum corresponding to the thermal energy range with an average deviation of ±1.7%.

In English

In the work, carbon nanostructures (CNS) were synthesized on a plasma chemical plant using graphite electrodes SIGE (Special Impregnated Graphite Electrodes) and FGDG-7 (Fine-grained dense graphite) in a helium environment. In the experiments, it was established that graphite electrodes of the SIGE brand are suitable for the synthesis of CNS by the electric arc plasma chemical method. In addition, the experiments indicate that SIGE graphite in electric arc synthesis in a gas environment allows the creation of centimeter composite rods (deposits), where the core consists of graphene sheets rolled into nanotubes that can withstand extremely high temperatures (>4000 K). Studies using scanning microscopy have shown that the synthetic deposit of SIGE graphite can be divided into blocks, which is important for its use in high voltage stations because it is possible to prepare deposits of the required length without mechanical impact and without violating the integrity of its structure. The structure of the synthesized carbon materials was studied by scanning and transmission electron microscopy and it was shown that carbon nanotubes are formed during the evaporation of SIGE brand graphite even without the use of a catalyst. Experiments have confirmed that the mass yield of wall fullerene-containing carbon black during the evaporation of SIGE grade graphite significantly exceeds the results obtained during the evaporation of FGDG-7 grade graphite electrodes. Such results make SIGE graphite more productive for the synthesis of expensive carbon nanoproducts (fullerenes and fullerene-like structures) by the electric arc method. It was also recorded that during the synthesis of carbon nanostructures, single-walled carbon nanotubes are formed, which have a positive charge and are deposited in the form of a core on the surface of the cathode electrode under the action of an electromagnetic field.

Rapid Preparation of Patterned Conductive Films Based on In Situ Voltaic Cell Templated 3D Controllable Metal Deposition

AbstractThe fabrication of patterned metal films is essential for a wide range of applications. Here, a novel solution‐processing method is presented to achieve the area‐selective deposition of copper on aluminum substrates via an in situ Al/CuSO4/Graphite voltaic cell template. And the copper ions preferentially deposit in the graphite‐covered area due to the formed latent image of the potential difference between the graphite‐covered area and the blank area on the aluminum surface. Benefiting from the low adhesive force of graphite, the formed copper layer can be easily peeled off and transferred to a flexible substrate to obtain the patterned conductive metal films. By studying the electrochemical properties of different surfaces and the in situ microscopic observation, four stages of electroplating process are proposed. More importantly, a positive correlation between the deposition speed and graphite coverage density is confirmed. This further enables a regional control of deposition thickness in addition to area‐selective deposition, which means a 3D controllable metal deposition. Other forms of electroactive carbon are also demonstrated to replace graphite in this method, which offers a versatile and accessible technique to fabricate large‐area flexible patterned metal films with defined feature size and controlled resolution from microscale to macroscale.

Kinetic study of graphene oxide synthesis by electrochemical exfoliation of graphite

A kinetic study of graphene oxide (GO) synthesis using electrochemical exfoliation of graphite in the acidic and alkaline electrolyte has been carried out. The effects of temperature (301–333 K), sulfuric acid concentration (0.3–0.6 M), pH (0.3–11.2), current density (12–40 mA/cm2), and graphite density (1.72–1.92 g/cc) on the rate of GO formation have been examined. The GO exfoliation rate was found to be unaffected by graphite density; therefore, all the kinetic was studied with the graphite density of 1.82 g/cc. The GO exfoliation rate increased with a sulfuric acid concentration in the electrolyte. The temperature was seen to enhance the rate of GO synthesis. The activation energy of GO exfoliation was found to be 33.53 kJ/mol in a temperature range of 301–333 K. Based on the findings the mechanism was proposed and the rate law was deduced.. The surface reaction of anions during intercalation and de-intercalation in the interstices of graphite has been found to be the rate-controlling step. Synthesized GO was characterized with transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The kinetic model has been developed to fit the GO exfoliation rate within a pH range of 0.3–1.1.

Emerging dual carbon fiber batteries

Dual graphite battery emerges as a promising renewable energy storage system with merits of a high working voltage, low cost and environment-friendliness. However, energy density is limited because of a low packing density of graphite. We propose for the first time dual carbon fiber batteries (DCFBs) in which carbon fiber functions as both cathode and anode. With a graphite mass loading of ∼30 mg cm−2 at pitch-based carbon fiber (PCF) cloth, the reversible discharge capacity of PCF-PCF type DCFBs (with PCF cloth cathodes/anodes) can reach 72 mAh g−1 at 0.1 C (1 C corresponding to 80 mAh g−1), resulting in an unprecedentedly high areal capacity of ∼2.2 mAh cm−2. Unlike the general applicability of commercialized carbon fiber as DCFBs anode, only PCF out of five kinds of commercialized carbon fibers can function as DCFBs cathode. Meanwhile, PCF-PCF type DCFB enables investigation into distinct electrochemical behaviors of Li+/PF6−intercalation/deintercalation in PCF. Morphological difference of PCF brought about by Li+/PF6− ions, as found out by ex-situ X-ray diffraction (XRD) and ex-situ scanning electronic microscopy/energy dispersive spectroscopy (SEM/EDS) characterizations, facilitates comprehensive understanding of electrochemical behavior of graphite. This work lays good foundations for future exploration into a new arena of dual ion batteries.

In English

Carbon nanostructures (CNS) were synthesized by the electric arc plasma chemical method during the evaporation of a high-quality graphite electrode of the brand “fine-grained dense graphite” (FGDG-7) filled with a catalyst (Pt), which was evaporated in a helium environment. In the synthesis process, the following were synthesized: multi-walled (MWCNT) and single-walled carbon nanotubes (SWCNT), fullerenes, graphene packets and nanocomposites. A deposit in the form of growth on the cathode electrode was also synthesized. All synthesis products were analyzed at the micro- and nanolevels, which made it possible to analyze the influence of platinum vapors on the formation of carbon nanomaterials (CNM). The non-uniform distribution of catalyst atoms (platinum) in the products of electrochemical synthesis in a gas medium using FGDG-7 graphite was investigated. During the analysis, it was found that platinum is in the state of the face-centered cubic (FCC) lattice and is distributed in the synthesis products as follows: the core of the deposit is less than < 0.001 %, the shell of the deposit is less than < 1 %, the wall soot is more than > 1 %. The morphology and composition of the platinum deposit, which has a hexagonal graphite structure with an admixture of a rhombohedral graphite phase, was studied. In the studies, differential thermal analysis in air (TG, DTG, DTA) was carried out, which made it possible to identify the composition of the synthesis products. It is an established fact that the parts of the deposit with platinum are more heat-resistant compared to the deposit components that do not contain Pt. The resulting carbon nanotubes (CNTs) in diameter (5–25 nm) and length (1.5–2 μm) do not differ from those obtained without the participation of platinum, except for some anomalies. When studying the suitability of platinum-containing carbon nanostructures for 3D printing of CJP (ceramic printing) technology, it was found that for the use of platinum-containing carbon black, it is necessary to carry out a preliminary short-term treatment, namely, grinding in special “ball mills” or rubbing through a fine sieve with minimal effort to create uniformity product. Previous studies have shown that such platinum-containing carbon nanostructures can already be used in 3D printing of CJP technology, or to create new composites for 3D printing technologies of FDM, SLA.