Carbon Allotropes Research Articles

Electrochemical investigation of phosphorous and boron heteroatoms incorporated reduced graphene oxide electrode material for supercapacitor applications

Graphene-based nanomaterials are becoming common components for consumer products due to their outstanding charge carrier ability, high surface area, high thermal stability, and great potential for environmental decontamination. Nowadays, heteroatoms added carbon allotropes are providing better electrochemical performances in the field of supercapacitors as an electrode material. In this present work, boron and phosphorus heteroatoms were introduced in the network of reduced graphene oxide to increase the capacitance of the supercapacitor. The B and P incorporated rGO (PB-rGO) electrode material was prepared by the hydrothermal method. The properties of the electrode material were analyzed using structural, morphological, and elemental analysis. The prepared electrode material was used as a working electrode material in supercapacitors. In 1 M H2SO4 aqueous electrolyte medium, a maximum specific capacitance of 436 F g−1 was found for PB-rGO in a three-electrode configuration. In a symmetric configuration, a power density of 394 W kg−1 and an energy density of 12.48 Wh kg−1 were observed for the PB-rGO electrode. The cyclic stability analysis showed 97.6 % retention after 10,000 cycles at the current density of 3 A g−1.

Stability of 2D Crystals from Tessellation

AbstractReticular chemistry has been a cornerstone in the design of novel 2D materials. Despite numerous possibilities for topological arrangements, only a few with high symmetry can form stable networks. Here, starting from 2D carbons, four types of highly stable tessellations are discovered, which consist of chains of non‐hexagonal rings separated by hexagonal ribbons. A modified Read–Shockley model is established to perfectly describe the stability of these highly stable frameworks, which is based on the interaction between non‐hexagonal rings. Moreover, these four types of tessellations and the modified Read–Shockley model are found to be of general validity in designing highly stable 2D materials, which is verified by the calculations on polymorphs of boron nitride and molybdenum disulfide. Besides, among the studied 2D carbon allotropes, two semi‐metallic structures with highly anisotropic Dirac cones and one semimetal with a Dirac nodal line at the Fermi level are discovered, as protected by their D2h symmetry. Spin‐orbital coupling is further found to open small bandgaps for these three Dirac structures, making them nontrivial topological insulators. The in‐depth understanding of the stability of 2D crystals in this study provides a new way for rational design of 2D crystals that may show peculiar electronic structures.

An effective microwave absorber using multi-layer Design of carbon allotrope based Co2Z hexaferrite-Polymer nanocomposite film for EMI shielding applications

This report shows impressive electromagnetic interference (EMI) shielding efficiency of laminated nanocomposites of PVDF containing binary nanofillers of rGO and Co2Z hexaferrite. These rGO layers in the PVDF matrix in association with magnetic nanofillers have been considered to improve interfacial polarization by accumulating charges at the interfaces of rGO-Co2Z hexaferrite-PVDF system. The crystallographic phase, chemical composition, and successful incorporation of the binary nanofillers into PVDF have been verified using XRD, XPS, RAMAN, and FESEM analysis. The J-E analysis of rGO-Co2Z hexaferrite-PVDF nanocomposite films confirm that the current density of all the nanocomposite films is very less and found in the order of 10-5 A/m2 under the maximum electric field of 70 kV/m. This indicates the emergence of polarization effect in the nanocomposite films when subjected to high external electric field without having electrical breakdown. The significant magnetization of ∼8.9 emu/g for nanocomposite films, at room temperature is beneficial for boosting the EMI shielding effectiveness due to absorption (SEA). The combination of magnetization and electrical polarization in nanocomposite film helps to attain significantly high total shielding effectiveness (SET) in the frequency range of 12–18 GHz. The shielding effectiveness study of both mono-layer and multi-layer nanocomposite films have been investigated. Improvement of SEA has also been achieved by the elevation of the thickness of the nanocomposite film within the range of 0.8 to 1.0 mm, which in turn improves SET to a value of −54.09 dB at 15.70 GHz for multi-layer system of thickness 0.861 mm with >99.999 % of attenuation whereas the mono-layer film of thickness 0.180 mm shows the SET of −47.03 dB at 14.76 GHz with an attenuation of >99.99 %.

Methane-H2S Reforming Catalyzed by Carbon and Metal Sulfide Stabilized Sulfur Dimers.

H2S reforming of methane (HRM) provides a potential strategy to directly utilize sour natural gas for the production of COx-free H2 and sulfur chemicals. Several carbon allotropes were found to be active and selective for HRM, while the additional presence of transition metals led to further rate enhancements and outstanding stability (e.g., Ru supported on carbon black). Most metals are transformed to sulfides, but the carbon supports prevent sintering under the harsh reaction conditions. Supported by theoretical calculations, kinetic and isotopic investigations with representative catalysts showed that H2S decomposition and the recombination of surface H atoms are quasi-equilibrated, while the first C-H bond scission is the kinetically relevant step. Theory and experiments jointly establish that dynamically formed surface sulfur dimers are responsible for methane activation and catalytic turnovers on sulfide and carbon surfaces that are otherwise inert without reaction-derived active sites.

Proposing TODD-graphene as a novel porous 2D carbon allotrope designed for superior lithium-ion battery efficiency.

The category of 2D carbon allotropes has gained considerable interest due to its outstanding optoelectronic and mechanical characteristics, which are crucial for various device applications, including energy storage. This study uses density functional theory calculations, ab initio molecular dynamics (AIMD), and classical reactive molecular dynamics (MD) simulations to introduce TODD-Graphene, an innovative 2D planar carbon allotrope with a distinctive porous arrangement comprising 3-8-10-12 carbon rings. TODD-G exhibits intrinsic metallic properties with a low formation energy and stability in thermal and mechanical behavior. Calculations indicate a substantial theoretical capacity for adsorbing Li atoms, revealing a low average diffusion barrier of 0.83eV. The metallic framework boasts excellent conductivity and positioning TODD-G as an active layer for superior lithium-ion battery efficiency. Charge carrier mobility calculations for electrons and holes in TODD-G surpass those of graphene. Classical reactive MD simulation results affirm its structural integrity, maintaining stability without bond reconstructions at 2200K.

Enhanced non-metal catalyzed CO2 reduction on doped biphenylene

– Using non-metals to replace the rare or precious transition metals as active component in catalyst in electrocatalysts is highly desirable in renewable energy applications. The diverse structures of carbon allotropes make it possible to support emerging non-metallic catalysts. Biphenylene is a recently discovered two-dimensional layered carbon allotrope, which outperforms graphene in terms of catalytic activity. Employing density functional theory calculations, we explore the possibility of non-metal doped biphenylene as promising catalyst for CO2 reduction. In aqueous environment, the active sites on the biphenylene surface are partially occupied by H* under reduction potential. On pure biphenylene, the coverage of H* leads to an large onset potential of U > 1.1 V. On boron-doped biphenylene, part of active sites is covered by H*. The remaining unoccupied sites still have activity for CO2 reduction, and the onset potential is significantly reduced to U = 0.2 V. By contrast, nitrogen-doping does not have obvious effect on reducing the onset potential of CO2 reduction (U = 0.9 V). The reason of influencing catalytic activity is then studied. This work reveals provides guidance for the future application of biphenylene in renewable energy.

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

A superhard orthorhombic carbon allotrope: Cmca-C16

A novel three-dimensional sp3 hybrid carbon allotrope, namely Cmca-C16, is predicted through structure searching within density functional theory (DFT) calculations. The structural, electronic, relative formation enthalpy and mechanical properties including bulk, shear, Young's modulus, ideal strength and Vickers' hardness are systematically investigated. The obtained results demonstrated that Cmca-C16 exhibiting excellent mechanical and dynamic stability. The calculations of ideal strength indicate that the failure mode occurs along the [100] direction, with the lowest peak stress of 80.8 GPa. The theoretical hardness of Cmca-C16 is calculated to be 88.6 GPa, which is comparable to that lonsdaleite (90.5 GPa) and C14-carbon (89.7 GPa), but higher than most other known carbon phases.

Improving stability, mechanical and electronic properties of pentadiamond by doping with alkali or alkaline-earth metals: A first-principles investigation

Pentadiamond (PD), a recently proposed carbon allotrope, has garnered considerable attention owing to its unique covalent framework comprising both sp2 and sp3 carbon atoms. Despite its intriguing structure with potentially useful thermal, electronic and optical properties, PD is supposed to be thermodynamically very unstable, due to the strain imposed by adjacent pentagonal rings in the carbon framework, which poses a major concern for its practical production. Here, we employ first-principles simulations to demonstrate that inserting alkali or alkaline-earth metals into the bigger cavities of PD significantly enhances its thermodynamic stability. Moreover, the resulting doped materials exhibit high kinetic stability at high temperatures typical for synthesis of fullerenes and metallofullerenes. We systematically investigate the structures and the modulation of mechanical properties and electronic structures of metal-doped PDs. Most remarkably, beryllium is revealed to be the energetically most favorable dopant among the metals considered. Be-doped PD exhibits an increased shear and Young's moduli (by about 55.6 % and 44.4 %, respectively), along with a substantially reduced Poisson's ratio (from 0.23 to 0.14). Furthermore, doping with Be transforms PD from an indirect-gap material to a direct-gap semiconductor, narrowing the band gap from 3.58 eV to 2.67 eV. We hope these findings may stimulate the experimental endeavors to synthesize metal-doped PD materials and unlock their potential applications.

Prediction of highly stable 2D carbon allotropes based on azulenoid kekulene

Despite enormous interest in two-dimensional (2D) carbon allotropes, discovering stable 2D carbon structures with practically useful electronic properties presents a significant challenge. Computational modeling in this work shows that fusing azulene-derived macrocycles – azulenoid kekulenes (AK) – into graphene leads to the most stable 2D carbon allotropes reported to date, excluding graphene. Density functional theory predicts that placing the AK units in appropriate relative positions in the graphene lattice opens the 0.54 eV electronic bandgap and leads to the appearance of the remarkable 0.80 eV secondary gap between conduction bands – a feature that is rare in 2D carbon allotropes but is known to enhance light absorption and emission in 3D semiconductors. Among porous AK structures, one material stands out as a stable narrow-multigap (0.36 and 0.56 eV) semiconductor with light charge carriers (me = 0.17 m0, mh = 0.19 m0), whereas its boron nitride analog is a wide-multigap (1.51 and 0.82 eV) semiconductor with light carriers (me = 0.39 m0, mh = 0.32 m0). The multigap engineering strategy proposed here can be applied to other carbon nanostructures creating novel 2D materials for electronic and optoelectronic applications.

A novel two-dimensional all-carbon Dirac node-line semimetal

Carbon allotropes have vast potential in various applications, including superconductivity, energy storage, catalysis, and photoelectric semiconductor devices. Recently, there has been significant research interest in exploring new carbon materials that exhibit unique electronic structures. Here, we propose a novel two-dimensional (2D) carbon allotrope called TCH-SSH-2D, which possesses a Dirac node-line (DNL) semimetallic state. The structure of TCH-SSH-2D is derived from the TCH-type Archimedean polyhedral carbon cluster units, combined with the SSH lattice model, possessing a space group of tetragonal P4/mmm. Using first-principles calculations, we demonstrate that the system is dynamically, thermodynamically, and mechanically stable. It exhibits an energetically favorable structure with no imaginary frequency in the phonon dispersion curves and elastic constants satisfying the Born-Huang stability criterion. Our findings not only contribute to a deeper understanding of the carbon allotrope family but also provide an opportunity to explore unique Dirac states in two-dimensional pure carbon systems.

Carbon Material-Reinforced Polymer Composites for Bipolar Plates in Polymer Electrolyte Membrane Fuel Cells.

Bipolar plates (BPs) are one of the most important components of polymer electrolyte membrane fuel cells (PEMFCs) because of their important role in gas and water management, electrical performance, and mechanical stability. Therefore, promising materials for use as BPs should meet several technical targets established by the United States Department of Energy (DOE). Thus far, in the literature, many materials have been reported for possible applications in BPs. Of these, polymer composites reinforced with carbon allotropes are one of the most prominent. Therefore, in this review article, we present the progress and critical analysis on the use of carbon material-reinforced polymer composites as BPs materials in PEMFCs. Based on this review, it is observed that numerous polymer composites reinforced with carbon allotropes have been produced in the literature, and most of the composites synthesized and characterized for their possible application in BPs meet the DOE requirements. However, these composites can still be improved before their use for BPs in PEMFCs.

From quartz (qtz) to diamond (dia) carbon topologies: Stepwise rationale from crystal chemistry and DFT investigations

From crystal chemistry and density functional theory DFT calculations, a stepwise rationale is proposed for the transformation from standalone distorted tetrahedron α-C5favored over standalone regular tetrahedron β-C5to high density – ultra hard orthorhombic α-C6and β-C6withqtz(quartz-based) topology characterized by 3D arrangements of distorted tetrahedra to lower densitydia-C topology (diamond-like, with regular C4 tetrahedra). Progressive C insertions into orthorhombic α-C5, α-C6, and lastly into C7were operated leading to ultimate C8stoichiometry identified as diamond-like. C7was also used as template to devise C3N4carbonitride with exceptional mechanical properties. The induced structural and physical changes are supported with elastic properties pointing to ultra-hardness, larger forqtzα,β-C6thandiaC8and inferred dynamic stability for all stoichiometries from the phonons band structures. The thermodynamic quantities as the specific heat were compared with diamond experimental CV. The electronic band structures reveal semi-conducting C6, metallic C7characterized by diamond-defect structure, and insulating C8. The results are meant to help further systemic understanding of tetrahedral carbon allotropes.

En route to superhard and 1D conductive carbon allotropes via unusual sp 2–sp 3 bonding configuration

Carbon structures with sp 2–sp 3 hybrid bonds were expected to exhibit both excellent mechanical and electronic properties. Here, we theoretically design several unique carbon structures, which contain unusual sp 2–sp 3 hybrid bonds. We found that the introduction of sp 2 bonding units into carbon structure with sp 3 bonding can tune the electronic densities of state at Fermi level, especially resulting in 1D conductive channels in 3D structures. Further simulations indicate that Vickers hardness of these structures is close to diamond via the increase in sp 3 building blocks. Our current work provides insights into the design of carbon structures with both excellent superhard and remarkably metallic properties.

Fullertubes inhibit mycobacterial viability and prevent biofilm formation by disrupting the cell wall.

Mycobacterium tuberculosis and nontuberculous mycobacteria such as Mycobacterium abscessus cause diseases that are becoming increasingly difficult to treat due to emerging antibiotic resistance. The development of new antimicrobial molecules is vital for combating these pathogens. Carbon nanomaterials (CNMs) are a class of carbon-containing nanoparticles with promising antimicrobial effects. Fullertubes (C90 ) are novel carbon allotropes with a structure unique among CNMs. The effects of fullertubes on any living cell have not been studied. In this study, we demonstrate that pristine fullertube dispersions show antimicrobial effects on Mycobacterium smegmatis and M. abscessus. Using scanning electron microscopy, light microscopy, and molecular probes, we investigated the effects of these CNMs on mycobacterial cell viability, cellular integrity, and biofilm formation. C90 fullertubes at 1 µM inhibited mycobacterial viability by 97%. Scanning electron microscopy revealed that the cell wall structure of M. smegmatis and M. abscessus was severely damaged within 24 h of exposure to fullertubes. Additionally, exposure to fullertubes nearly abrogated the acid-fast staining property of M. smegmatis. Using SYTO-9 and propidium iodide, we show that exposure to the novel fullertubes compromises the integrity of the mycobacterial cell. We also show that the permeability of the mycobacterial cell wall was increased after exposure to fullertubes from our assays utilizing the molecular probe dichlorofluorescein and ethidium bromide transport. C90 fullertubes at 0.37 µM and C60 fullerenes at 0.56 µM inhibited pellicle biofilm formation by 70% and 90%, respectively. This is the first report on the antimycobacterial activities of fullertubes and fullerenes.

Effect of graphite filler on the physiochemical properties of graphite reinforced thermoset rooflite – unsaturated polyester resin composites

It is well known that many polymers are insulators with poor mechanical properties, which limit their use in fuel cell applications. Physicochemical properties of the polymers can be improved by adding conductive fillers. Carbon-based materials like graphite, which provides excellent mechanical strength and thermal conductivity to the polymer matrices, is of special interest because of its abundance, low cost and light weight when compared to other carbon allotropes. In the present work we describe the physicochemical properties of rooflite unsaturated polyester resin/graphite composites. Rooflite resin and three of its composites containing 1%, 3% and 5% of graphite by weight (C-2, C-3, and C-4, respectively) were synthesized and characterized by FTIR spectral data. XRD showed two peaks at 2q = 27.37°and 55.40° with d spacing value of 3.2559 nm and 1.6571 nm, respectively, indicating the change in degree of crystallinity of the composite. The calculated crystallinity for the resin is 7.3%, and for C-2, C-3 and C-4 its values are 12.1%, 14.3%, 17.1%, respectively, evidencing the interactions between the graphite and polymer matrix. The composites showed fractured surfaces and porous rough structure with randomly distributed vascularized cavities. Agglomeration occurs, when the concentration of graphite increases. The glass transition temperature for the pure resin is 65.9 °C and increases when the resin is filled with graphite. Thermogravimetric analysis (TGA) of the composites showed no marked difference between Tmax and Tfinal, and LOI values of C-3 and C-4 are above 21%, making them self-extinguishable materials that could be used for making bipolar plates. The chemical resistance investigation against water, NaCl, NaOH, acetic acid, and toluene showed more resistance to acid than alkali solutions. These rooflite resin/graphite composites could be further studied to explore the possibility of making bipolar plates, which are an essential component of fuel cells.

Boosting Potassium Adsorption and Diffusion Performance of Carbon Anodes for Potassium-Ion Batteries via Topology and Curvature Engineering: From KT-Graphene to KT-CNTs.

We propose a two-dimensional carbon allotrope (named KT-graphene) by incorporating kagome and tetragonal lattices consisting of trigonal, quadrilateral, octagonal, and dodecagonal rings. The introduction of non-hexagonal rings can give rise to the localized electronic states that improve the chemical reactivity toward potassium, making KT-graphene a high-performance anode material for potassium-ion batteries. It shows a high theoretical capacity (892 mAh g-1), a low diffusion barrier (0.33 eV), and a low average open-circuit voltage (0.51 V). The presence of electrolyte solvents is propitious to boost the K-ion adsorption and diffusion capabilities. Moreover, one-dimensional nanotubes (KT-CNTs), rolled up by the KT-graphene sheet, are metallic regardless of the tube diameter. As the curvature increases, KT-CNTs exhibit significantly increased surface activity, which can promote the electron-donating ability of K. Furthermore, the curvature effect greatly enhances the efficiency of K diffusion on the inner surface compared to that on the outer surface.

Accelerate the design of new superhard carbon allotropes in Pca21 space group: High-throughput screening and machine learning strategies

As an efficient calculation and screening method, high-throughput can discover and optimize new materials, shorten the development cycle and cost of new materials. However, using high throughput for material screening and computation, a large amount of computing resources and storage space are indispensable. To accelerate the design of novel superhard carbon materials, we combined machine learning methods with high-throughput computing to construct three machine learning models: support vector machine regression, random forests, and artificial neural networks, and mined data from existing material databases to select 1276 structures as datasets for the model to predict the volume modulus and shear modulus. Through comparative analysis, the optimal model was selected to predict the bulk modulus and shear modulus of the structures obtained by high-throughput calculations, and the prediction results of the model were verified by density functional theory (DFT) calculations, and 8 superhard carbon allotropes in the Pca21 space group were eventually found.

Topological electronic states in holey graphyne

We unveil that the holey graphyne (HGY), a two-dimensional carbon allotrope where benzene rings are connected by two −C≡C− bonds fabricated recently in a bottom-up way, exhibits topological electronic states. Using first-principles calculations and Wannier tight-binding modeling, we discover a higher-order topological invariant associated with C 2 symmetry of the material, and show that the resultant corner modes appear in nanoflakes matching to the structure of precursor reported previously, which are ready for direct experimental observations. In addition, we find that a band inversion between emergent g-like and h-like orbitals gives rise to a nontrivial topology characterized by Z2 invariant protected by an energy gap as large as 0.52 eV, manifesting helical edge states mimicking those in the prominent quantum spin Hall effect, which can be accessed experimentally after hydrogenation in HGY. We hope these findings trigger interests towards exploring the topological electronic states in HGY and related future electronics applications.

First-principles calculations to investigate structural, mechanical and electronic properties of carbon (tP8) allotrope under high-pressure

The structural stability, electronic and mechanical attributes of the tetragonal carbon (tP8) allotrope at high-pressure are examined in the proposed research. The crystal structure of tP8 carbon is different and possesses unusual properties owing to electron localisation. Moreover, tP8 carbon allotrope exhibits remarkable mechanical stability and resilience, making it a strong contender for various applications owing to its plastic deformation and resistance to fracture. Furthermore, the results of the current work show that the band gap of tP8 carbon increases under high pressures, making it a useful material for nanoelectronic device applications. The present report on high-pressure studies of tP8 carbon will pave the way for novel applications in semiconductor technology and high-pressure material applications.