Pyrolytic Graphite Research Articles

Biopolymer-Derived Carbon Materials for Wearable Electronics.

Advanced carbon materials are widely utilized in wearable electronics. Nevertheless, the production of carbon materials from fossil-based sources raised concerns regarding their non-renewability, high energy consumption, and the consequent greenhouse gas emissions. Biopolymers, readily available in nature, offer a promising and eco-friendly alternative as a carbon source, enabling the sustainable production of carbon materials for wearable electronics. This review aims to discuss the carbonization mechanisms, carbonization techniques, and processes, as well as the diverse applications of biopolymer-derived carbon materials (BioCMs) in wearable electronics. First, the characteristics of four representative biopolymers, including cellulose, lignin, chitin, and silk fibroin, and their carbonization processes are discussed. Then, typical carbonization techniques, including pyrolysis carbonization, laser-induced carbonization, Joule heating carbonization, hydrothermal transformation, and salt encapsulation carbonization are discussed. The influence of the processes on the morphology and properties of the resultant BioCMs are summarized. Subsequently, applications of BioCMs in wearable devices, including physical sensors, chemical sensors, energy devices, and display devices are discussed. Finally, the challenges currently facing the field and the future opportunities are discussed.

Intrinsic Mechanical Effects on the Activation of Carbon Catalysts.

The mechanical effects on carbon-based metal-free catalysts (C-MFCs) have rarely been explored, despite the global interest in C-MFCs as substitutes for noble metal catalysts. Stress is ubiquitous, whereas its dedicated study is severely restricted due to its frequent entanglement with other structural variables, such as dopants, defects, and interfaces in catalysis. Herein, we report a proof-of-concept study by establishing a platform to continuously apply strain to a highly oriented pyrolytic graphite (HOPG) lamina, simultaneously collecting electrochemical signals. Notably, we establish, for the first time, the correlation between the surface strain of graphitic carbon and its activation effect on the oxygen reduction reaction (ORR). Our results indicate that while in-plane and edge carbon sites in HOPG could not be further activated by applying tensile strain, a strong and repeatable dependence of catalytic activity on tensile strain was observed when the structure incorporated in-plane defects, leading to a significant ∼35.0% improvement in ORR current density with the application of ∼0.6% tensile strain. Density functional theory (DFT) simulations reveal that appropriate strain on specific defects can optimize the adsorption of reaction intermediates, and the Stone-Wales defect on graphene is correlated with the observed mechanical effect. This work elucidates fundamental principles of strain effects on the catalytic activity of graphitic carbon toward ORR and may lay the groundwork for the development of carbon-based mechano-electrocatalysis.

Ni Single Atoms/Fe3N Nanoparticles Supported by N-Doped Carbon Hollow Nanododecahedras with Nanotubes on the Surface for Efficient Electro-Reduction of CO2 to CO.

The transition metal single atoms (SAs)-based catalysts with M-NX coordination environment have shown excellent performance in electrocatalytic reduction of CO2, and they have received extensive attention in recent years. However, the presence of SAs makes it very difficult to efficiently improve the coordination environment. In this paper, a method of direct high-temperature pyrolysis carbonization of ZIF-8 adsorbed with Ni2+ and Fe2+ ions is reported for the synthesis of Ni SAs and Fe3N nanoparticles (NPs) supported by the N-doped carbon (NC) hollow nanododecahedras (HNDs) with nanotubes (NTs) on the surface (Ni SAs/Fe3N NPs@NC-HNDs-NTs). The synergistic effect between Ni SAs and Fe3N NPs can obviously improve the proton-coupled electron transfer step of CO2 reduction reaction and promotes the process of electrocatalytic reduction of CO2 to CO. The fabricated Ni SAs/Fe3N NPs@NC-HNDs-NTs exhibits a high CO selectivity of up to 94% in the potential range of -0.41--0.81 V versus Reversible Hydrogen Electrode (vs RHE), and an optimal CO Faraday efficiency (FECO) of ≈97.31% at -0.68 V (vs RHE) in the reduction reaction CO2 to CO. In the theoretical calculation results, due to the non-bonding synergy effect between Ni SAs and Fe3N NPs, the free energy of *COOH formation is greatly reduced and the adsorption of *CO is obviously improved, which will efficiently promote the conversion between the intermediates in the reaction step and accelerate electro-reduction process of CO2. This work will provide a new method for constructing a mutually optimized coordination environment between Ni SAs and Fe3N NPs to improve the catalytic performance of CO2RR by synergistic complementarity between the dual active sites.

Unfolding of von Willebrand Factor Type D Like Domains Promotes Mucin Adhesion.

Mucins are the macromolecular key components of mucus. On wet epithelia of mammals, mucin solutions and gels act as powerful biolubricants and reduce friction and wear by generating a sacrificial layer and establishing hydration lubrication. Yet the structure-function relationship of mucin adhesion and lubrication remains elusive. We study the adhesion behavior of mucin using atomic force microscopy-based single molecule force spectroscopy with covalently attached, lab-purified salivary MUC5B and gastric MUC5AC. We can resolve the structural motifs mediating adhesion on chemically distinct substrates, such as highly oriented pyrolytic graphite and steel. We report on force-induced partial unfolding of the von Willebrand factor type D like domains and deliver their unfolding rates and free energy barriers. These domains serve to dissipate energy during the desorption process of mucins. Partial mucin unfolding might significantly contribute to the stability of a sacrificial mucin layer during shearing processes, enhancing the lubrication potential of mucin solutions.

Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling

Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) architectured pyrolytic carbon (PyC) structures with ultrahigh specific strength and energy absorption capabilities. However, their scalability is limited by reduced strength at larger sizes. Here we introduce a modular assembling approach to scale up PyC lattice structures while retaining strength. Three assembling mechanisms—adhesive, Lego-adhesive, and mechanical interlocking—are explored, demonstrating notably increased specific compressive strength and modulus as size increases, driven by energy release from assembly joint fractures. Practical application is demonstrated by using assembled PyC lattices as the core of an aerospace sandwich structure, significantly enhancing indentation resistance compared to conventional aramid paper honeycomb core. The method also enables versatile designs, including curved structures for space debris protection and bio-scaffold applications. This scalable approach offers a promising pathway for integrating PyC structures into large-scale engineering applications requiring superior mechanical properties and programmability in complicated shape design.

An Energy Level Alignment Study of 2PACz Molecule on Perovskite Device‐Related Interfaces by Vacuum Deposition

Self‐assembling molecules (SAM) have been widely used in inverted perovskite solar cells (PSC) as a hole transfer layer due to nearly lossless charge transfer giving excellent device performance. However, the energy level alignment between SAM‐ and PSC‐related interfaces has not been systematically studied. Herein, the 2PACz, a typical SAM with the largest dipole moment, is chosen as the model system and is studied by vacuum deposition. It is found that the energy level alignment is determined by the orientation of 2PACz molecules on a different substrate. The molecules are lying down on highly oriented pyrolytic graphite and giving nearly zero interface dipole. On solvent‐cleaned and plasma‐treated indium tin oxide (ITO) substrates, the SAM is vertically assembled with 0.22 and 0.13 eV work function increases, respectively. However, on sputtered ITO, SAM is assembled with upside down orientation, with 0.51 eV work function decrease. The change of orientation is due to strong interaction between oxygen vacancies in ITO substrate and carbazole head group of 2PACz. On perovskite film, SAM also shows a slightly upward orientation with additional passivation of free MA+ ions. Herein, it is confirmed that the energy level alignment of SAM plays an important role in hole extraction.

Orchestrating a Controllable Engineering of Dual‐Model Carbon Structure in Si/C Anodes

AbstractSilicon‐carbon composites (Si/C) with multistage structures enable structural integrity during cycling. However, the lack of controllable structure preparation on a large scale hinders the stability improvement in practical applications. Herein, a new strategy is proposed to synthesize kilogram‐scale Si/C (PySi/C) featuring a dual‐model carbon structure in one step. The controllable combination of an onion‐like carbon coating on the Si surface with independent pyrolytic carbon is accomplished through the precise adjustment of the pyrolysis temperature. The dual‐model carbon formation mechanism is unraveled, detailing the cooperative coupling of the nucleation laws of carbon compositions as well as the changes trends in morphology and crystallinity. This density functional theory and finite element analysis highlight the dual‐model structure's essential contribution to the electrochemical behavior and structural stability. As expected, PySi/Cs anodes deliver stable cycling performance with retention of 91.5% after 800 cycles at 2 A g−1. Its comprehensive electrochemical performance surpasses that of the state‐of‐the‐art kilogram‐scale Si‐based anode reported. Moreover, the assembled pouch cell exhibits actual competitiveness, showing a capacity of 1.97 Ah and a retention of 88.9% after 300 cycles at 1 C. This work provides valuable design concepts to further advance the development of Si/C anodes.

Anion-Responsive π-Conjugated Macrocycles That Form Ordered Structures.

In this study, anion-responsive π-conjugated macrocycles were synthesized to demonstrate anion-binding and ion-pairing properties along with the ordered structures. Ion-pairing charge-by-charge assembly of a [1+2]-type complex of a macrocycle as a pseudo π-electronic anion and a countercation was revealed by single-crystal X-ray analysis. Further, two-dimensional (2D) arrays of the macrocycles bearing alkoxy chains, exhibiting anion-driven disordered structures, were constructed on a highly oriented pyrolytic graphite (HOPG) substrate as observed by scanning tunneling microscopy (STM).

Application of products derived from pyrolysis and hydrothermal carbonization as conditioners for aerobic composting produced multiple beneficial effects: Evaluation based on 10-ton pilot scale trials

Application of products derived from pyrolysis and hydrothermal carbonization as conditioners for aerobic composting produced multiple beneficial effects: Evaluation based on 10-ton pilot scale trials

Enhanced Thermal and Structural Performance of Mesophase Pitch-based C/C-SiC Composites via Pyrolytic Graphite Matrix Modification

Enhanced Thermal and Structural Performance of Mesophase Pitch-based C/C-SiC Composites via Pyrolytic Graphite Matrix Modification

Performance characterization of x-ray crystal spectroscopy highly oriented pyrolytic graphite reflectors based on x-ray diffractometry experiments.

The use of Highly Oriented Pyrolytic Graphite (HOPG) reflectors is often proposed in the design of X-ray Crystal Spectroscopy (XCS) diagnostic systems for the next-generation tokamak devices, including the ITER project. This study introduces an experimental study based on the X-Ray Diffractometry (XRD) method to evaluate the performance of HOPG reflectors. The experimental method provides both the angular responses and the reflectivities of the HOPG reflectors. A demonstrative XRD experiment is conducted, and the details of the experiment are introduced. This method enables precise studies on HOPG reflectors, facilitating the design of XCS diagnostic systems for future tokamaks.

Quasi-1D, rectangular-like and hexagonal moiré superlattices in exfoliated highly oriented pyrolytic graphite

Understanding the dynamics of structural collapse in hexagonal moiré superlattices is of importance towards the stabilization of exotic superconductive phenomena in quasi-1D superlattices. Here we investigate unusual exfoliation-induced structural transformations of hexagonal moiré superlattices, in a μm-thin lamella of highly oriented pyrolytic graphite (HOPG). By employing a combination of experimental techniques, namely transmission electron microscopy (TEM), high resolution TEM (HRTEM) and selective area electron diffraction (SAED) we systematically investigate the collapse of hexagonal moiré superlattices into rectangular-like and quasi-1D superlattices in an exfoliated lamella. Interestingly, the rectangular-like lattice reveals perpendicular super-periodicities D1 ~ 17 nm and D2 ~ 9 nm. The width of the quasi-1D channels was found to vary from ~5 nm to ~13 nm, with a super-periodicity D ~ 3 nm. Most importantly, systematic SAED acquisitions reveal a splitting of the electron diffraction signals into multiple components, consisting of doubled and tripled diffraction rings. We interpret these as a clear indicator of structural disorder which results from an interplay of exfoliation-induced structural transitions, namely interlayer-sliding, local layer-rotation (twisting) and significant wrinkling (strain) effects.

Frequency-domain thermoreflectance with beam offset without the spot distortion for accurate thermal conductivity measurement of anisotropic materials.

The measurement of thermal conductivities of anisotropic materials and atomically thin films is pivotal for the thermal design of next-generation electronic devices. Frequency-domain thermoreflectance (FDTR) is a pump-probe technique that is known for its accurate and straightforward approach to determining thermal conductivity and stands out as one of the most effective methodologies. Existing research has focused on advancing a measurement system that incorporates beam-offset FDTR. In this approach, the irradiation positions of the pump and probe lasers are spatially offset to enhance sensitivity to in-plane thermal conductivity. Previous implementations primarily adjusted the laser positions by modifying the mirror angle, which inadvertently distorted the laser spot. Such distortion significantly compromises measurement accuracy, which is especially critical in beam-offset FDTR, where the spot radius has a crucial impact on measured values. This study introduces an advanced FDTR measurement system that realizes probe laser offset without inducing spot distortion, utilizing a relay optical system. The system was applied to measure the thermal conductivities of both isotropic standard materials and anisotropic samples, including highly oriented pyrolytic graphite and graphene. The findings corroborate those of prior studies, validating the measurement's reliability in terms of sensitivity. This development of a beam-offset FDTR system without laser spot distortion establishes a robust basis for accurate thermal conductivity values of anisotropic materials via thermoreflectance methods.

Fabrication of SiCw reinforced SiC ceramics by binder jetting combined with particulate pyrolytic carbon (PyC) encapsulated SiCw modification method

Fabrication of SiCw reinforced SiC ceramics by binder jetting combined with particulate pyrolytic carbon (PyC) encapsulated SiCw modification method

Co-Hydrothermal Carbonization of Goose Feather and Pine Sawdust: A Promising Strategy for Disposal of Sports Waste and the Robust Improvement of the Supercapacitor Characteristics of Pyrolytic Nanoporous Carbon

Discarded sports waste faces bottlenecks in application due to inadequate disposal measures, and there is often a neglect of enhancing resource utilization efficiency and minimizing environmental impact. In this study, nanoporous biochar was prepared through co-hydrothermal carbonization (co-HTC) and pyrolytic activation by using mixed goose feathers and heavy-metals-contaminated pine sawdust. Comprehensive characterization demonstrated that the prepared M-3-25 (Biochar derived from mixed feedstocks (25 mg/g Cu in pine sawdust) at 700 °C with activator ratios of 3) possesses a high specific surface area 2501.08 m2 g−1 and abundant heteroatomic (N, O, and Cu), exhibiting an outstanding physicochemical structure and ultrahigh electrochemical performance. Compared to nanocarbon from a single feedstock, M-3-25 showed an ultrahigh capacitance of 587.14 F g−1 at 1 A g−1, high energy density of 42.16 Wh kg−1, and only 8.61% capacitance loss after enduring 10,000 cycles at a current density of 10 A g−1, positioning M-3-25 at the forefront of previously known biomass-derived nanoporous carbon supercapacitors. This research not only introduces a promising countermeasure for the disposal of sports waste but also provides superior biochar electrode materials with robust supercapacitor characteristics.

Investigating pyrolytic carbon black in natural rubber compounds: rheological, mechanical and dynamic effects

Investigating pyrolytic carbon black in natural rubber compounds: rheological, mechanical and dynamic effects

Effects of Temperature and Water Vapor Content on Microstructure, Mechanical Properties and Corrosion Behavior of C/C-SiC Composites.

Carbon-fiber-reinforced carbon and silicon carbide (C/C-SiC) composites were prepared using chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI). The microstructure and flexural properties of C/C-SiC composites after oxidation in different temperature water vapor environments were studied. The results indicate that the difficulty of oxidation in water vapor can be ranked from easy to difficult in the following order: carbon fiber (CF), pyrolytic carbon (PyC), and ceramic phase. The surface CFs become cone-shaped under corrosion. PyC has a slower oxidation rate and lower degree of oxidation compared to CF. The SiO2 layer formed by the oxidation of SiC and residual Si was insufficient to fully cover the surface of CFs and PyC. As the temperature increased, the oxide film thickened, but the corrosion degree of CF and PyC intensified, and the flexural performance continuously deteriorated. The flexural strength of C/C-SiC composites was 271.86 MPa at room temperature. Their strength retention rates were all higher than 92.19% after water vapor corrosion at 1000 °C, still maintaining the "pseudoplastic" fracture characteristics. After water vapor corrosion at 1200 °C, the CFs inside the composites sustained more severe damage, with a strength retention rate as low as 48.75%. The fracture mode was also more inclined towards brittle fracture.

Inhomogeneous Nanoscale Conductivity and Friction on Graphite Terraces Explored via Atomic Force Microscopy

The interplay of conductivity and friction in layered materials such as graphite is an open area of investigation. Here, we measure local conductivity and friction on terraces of freshly cleaved highly oriented pyrolytic graphite via atomic force microscopy under ambient conditions. The graphite surface is found to exhibit a rich electrical landscape, with different terraces exhibiting different levels of conductivity. A peculiar dependency of conductivity on scan direction is observed on some terraces. The terraces that exhibit this dependency are also found to show enhanced friction values. A hypothesis based on tip asymmetry and the puckering effect is proposed to explain the findings. Our results highlight the non-triviality of the electrical and tribological properties of graphite on the nanoscale, as well as their interplay.

INVESTIGATION OF THE DENSITY OF CCCM AND ITS INFLUENCE ON SPECIFIC VOLUME ELECTRICAL RESISTIVITY

This article investigates the structure and properties of carbon-carbon composite materials (CCCM), where the carbon matrix is formed by the deposition of pyrolytic carbon in the porous volume of a carbon fiber preform using thermogradient gas-phase pyrolysis densification technologies. The results of studying the apparent density of CCCM by hydrostatic methods and its influence on the specific volume electrical resistivity of the material are presented. The conducted study established that the specific volume electrical resistivity of CCCM significantly depends on a number of factors, one of which is the material density. An increase in the apparent density of the material leads to a decrease in its porosity, which, in turn, affects the decrease in electrical resistance. It is emphasized that density control becomes a key factor in ensuring optimal electrical conductivity of carbon-carbon composite materials. It is shown that the densification of CCCM significantly improves the structure of blanks and crucibles, increasing their physical and operational characteristics. This makes them more suitable for use in high-temperature conditions, aggressive environments, in the production of heat-resistant components and other high-tech areas. Repeated densification of CCCM revealed a significant impact on the quality of the material. It is shown that an increase in density after additional densification leads to a decrease in porosity, improvement of mechanical properties and a change in the pore distribution in the material, which positively affects its porosity and strength. Bench tests of model samples made of CCCM showed that an increase in the apparent density of the material leads to a decrease in its electrical resistance. To ensure control in industrial practice, an effective and affordable method for assessing the degree of completion of crystalline transformations and determining the degree of graphitization during high-temperature treatment of carbon materials is recommended to compare the specific volume electrical resistivity of the working sample with the reference one. The importance of controlling the parameters of density, porosity, and electrical resistance to optimize technological processes and ensure high quality of final products is emphasized. The obtained data can be useful for applications in various industries.

MODEL OF INTERNAL STRESS IN BLANKS OF CARBON-CARBON COMPOSITE MATERIALS BASED ON NEEDLE-PUNCHED FRAMEWORKS MANUFACTURED BY THE FABRIC WINDING METHOD

This paper presents the results of constructing a model of internal residual stresses arising during the manufacture of blanks of carbon-carbon composite materials based on needle-punched axisymmetric reinforcing frames, obtained by the method of winding fabric with simultaneous needle-punching, compacted with a pyrolytic carbon matrix using a thermogradient method. Calculations were carried out for changes in the stress-strain state of a material workpiece that arise during its manufacture during heating and cooling. The main dependencies of the stress level on the technological parameters of blank manufacturing are obtained, the magnitude and danger from the point of view of occurrence of defects of various stresses are estimated. The main dependencies of the stress level on the technological parameters of blank manufacturing are obtained, the magnitude and danger from the point of view of occurrence of defects of various stresses are estimated. The result of the calculations shows that radial stresses are directly proportional to the temperature difference during cooling of the blank. It is shown that the greater the thickness of the material blank, the higher the radial stresses in it. The results obtained can be useful in optimizing the parameters of the manufacturing technology of this class of materials.