Constructing multi-layer heterogeneous interfaces in liquid metal graphite hybrid powder: Towards microwave absorption enhancement.

Carbon based materials are widely used in the preparation of microwave absorption materials due to their low density, high attenuation loss and large specific surface area. However, their high conductivity usually leads to high reflection loss. In this study, multi-layer heterogeneous interfaces were constructed in liquid metal graphite hybrid powder to reduce reflection loss and enhance microwave absorption performance. Gallium oxide (Ga2O3) layer was formed in Ga coated graphite powder to improve impedance matching and attenuation constant via an annealing treatment. Specifically, the hybrid particles with 50 wt% Ga and being annealed at 120 °C for 2 h have a minimum reflection loss (RLmin) value of -42.68 dB and a maximum effective absorption bandwidth (EAB) of 4.11 GHz at a thickness of 3.3 mm. The hybrid particles not only have multi-layer structures with different electrical conductivity, but also form heterojunctions between different interfaces, which can further enhance dipole and interfacial polarization.

Spatial confinement: An effective strategy to improve H2O and SO2 resistance of the expandable graphite-modified TiO2-supported Pt nanocatalysts for CO oxidation.

The expandable graphite (EG) modified TiO2 nanocomposites were prepared by the high shear method using the TiO2 nanoparticles (NPs) and EG as precursors, in which the amount of EG doped in TiO2 was 10 wt.%. Followed by the impregnation method, adjusting the pH of the solution to 10, and using the electrostatic adsorption to achieve spatial confinement, the Pt elements were mainly distributed on the exposed TiO2, thus generating the Pt/10EG-TiO2-10 catalyst. The best CO oxidation activity with the excellent resistance to H2O and SO2 was obtained over the Pt/10EG-TiO2-10 catalyst: CO conversion after 36 hr of the reaction was ca. 85% under the harsh condition of 10 vol.% H2O and 100 ppm SO2 at a high gaseous hourly space velocity (GHSV) of 400,000 hr-1. Physicochemical properties of the catalysts were characterized by various techniques. The results showed that the electrostatic adsorption, which riveted the Pt elements mainly on the exposed TiO2 of the support surface, reduced the dispersion of Pt NPs on EG and achieved the effective dispersion of Pt NPs, hence significantly improving CO oxidation activity over the Pt/10EG-TiO2-10 catalyst. The 10 wt.% EG doped in TiO2 caused the TiO2 support to form a more hydrophobic surface, which reduced the adsorption of H2O and SO2 on the catalyst, greatly inhibited deposition of the TiOSO4 and formation of the PtSO4 species as well as suppressed the oxidation of SO2, thus resulting in an improvement in the resistance to H2O and SO2 of the Pt/10EG-TiO2-10 catalyst.

Electrolyte Design Enables Stable and Energy-dense Potassium-ion Batteries.

Free from strategically important elements such as lithium, nickel, cobalt, and copper, potassium-ion batteries (PIBs) are heralded as promising low-cost and sustainable electrochemical energy storage systems that complement the existing lithium-ion batteries (LIBs). However, the reported electrochemical performance of PIBs is still suboptimal, especially under practically relevant battery manufacturing conditions. The primary challenge stems from the lack of electrolytes capable of concurrently supporting both the low-voltage anode and high-voltage cathode with satisfactory Coulombic efficiency (CE) and cycling stability. Herein, we report a promising electrolyte that facilitates the commercially mature graphite anode (> 3 mAh cm-2) to achieve an initial CE of 91.14% (with an average cycling CE around 99.94%), fast redox kinetics, and negligible capacity fading for hundreds of cycles. Meanwhile, the electrolyte also demonstrates good compatibility with the 4.4 V (vs. K+/K) high-voltage K2Mn[Fe(CN)6] (KMF) cathode. Consequently, the KMF||graphite full-cell without precycling treatment of both electrodes can provide an average discharge voltage of 3.61 V with a specific energy of 316.5 Wh kg-1-(KMF+graphite), comparable to the LiFePO4||graphite LIBs, and maintain 71.01% capacity retention after 2000 cycles.

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Si-Rich Silicon-Graphite Anodes.

Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70 wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200 mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200 mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30% Si electrode, crystalline Si amorphization at potentials <110 mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70% Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

Relationship between Capillary Wettability, Mass, and Momentum Transfer in Nanoconfined Water: The Case of Water in Nanoslits of Graphite and Hexagonal Boron Nitride.

The flow of water confined in nanosize capillaries is subject of intense research due to its relevance in the fabrication of nanofluidic devices and in the development of theories for fluid transport in porous media. Here, using molecular dynamics simulations carried out on 2D capillaries made up of graphite, hexagonal boron nitride (hBN) and a mix of the two, and of sizes from subnanometer to few nanometers, we investigate the relationship between the wettability of the wall capillary, the water diffusion, and its flow rate. We find that the water diffusion is decoupled from its flow properties as the former is not affected either by the height or chemistry of the capillary (except for the subnanometer slits), while the latter is dependent on both. The capillaries containing hBN show a reduced flow rate compared to those that are purely graphitic, likely due to the high friction coefficient between water and hBN. Such resistance to the flow is, however, at its maximum in the smallest capillary and lower for larger ones. Finally, we show that the flow rate values obtained from the Hagen-Poiseuille theory are almost always smaller than those obtained from simulations, indicating that either the slip length or the viscosity of nanoconfined water could be substantially different from the bulk values.

Artificial Electron Channels Enable Contact Prelithiation of Li-Ion Battery Anodes with Ultrahigh Li-Source Utilization.

Contact prelithiation is widely used for compensating the initial capacity loss of lithium-ion batteries (LIBs). However, the low Li-source utilization suffering from the deteriorated contact interfaces results in cycling degeneration. Herein, Li-Ag alloy-based artificial electron channels (AECs) are established in Li source/graphite anode contact interfaces to promote Li-source conversion. Due to the shielding effect of the Li-Ag alloy (50 at. % Li) on Li-ion diffusion, the dry-state corrosion of contact interfaces is restricted. The unblocked electronic conduction across the AEC-involved interface not only facilitates the Li source conversion but also accelerates the prelithiation kinetics during the wet-state process, resulting in an ultrahigh Li-source utilization (90.7%). Thereby, implementing AEC-assisted prelithiation in a LiNi0.5Co0.2Mn0.3O2 pouch cell yields a 35.8% increase in energy density and stable cycling over 600 cycles. This finding affords significant insights into the construction of an efficient prelithiation technology toward the development of high-energy LIBs.

Development of a novel method based on extraction mediated by a semipermeable membrane to determine Cd and Cr in sugar by graphite furnace atomic absorption spectrometry.

This work proposes a novel method to determine the Cd(II) and Cr(III) content in commercial sugar samples. It is based on the extraction of the analytes (as ammonium pyrrolidine dithiocarbamate complexes) into a semipermeable membrane device (SPMD) filled with CHCl3. After extraction, the SPMD was deployed and opened, and the analytes were recovered from the organic phase by back extraction with a 4.2 mol L-1 HNO3 solution. The analytes present in the acid extract were measured with graphite furnace atomic absorption spectrometry. Under optimized conditions, the limit of quantification of the method was 1.2 and 3.1 ng g-1 for Cd(II) and Cr(III), respectively. Twelve samples of different types of sugar were analyzed. In addition, a recovery test was performed to evaluate the accuracy of the method. The recovery percentage was 90 %-102 % for Cd(II) and 85.2 %-103 % for Cr(III).

Optimizing gas pressure for enhanced tribological properties of DLC-coated graphite.

In this study, for the first time, the optimization of applied pressure for achieving the one of the best tribological properties of diamond-like carbon (DLC) coating on graphite surface using plasma-enhanced chemical vapor deposition (PECVD) method was investigated. Raman spectroscopy and microscopy methods were used to characterize the applied coating. Additionally, the mechanical properties of the coating were investigated through nanoindentation testing. The wear resistance of coating has been tested as functional test. The results indicated that with increasing gas pressure, the sp3 hybridization percentage decreases, while the ID/IG ratio increases. The average roughness values for the uncoated sample and the coated samples at working pressures of 25, 30, and 35 mTorr were obtained as 1.6, 5.1, 3, and 2.4 nm, respectively. The results of hardness and wear tests showed that these properties were optimized by reducing the applied gas pressure. The highest hardness was 11.59 GPa, and the best sample in terms of the mechanical properties of the coating was the sample applied at a gas pressure of 25 mTorr. Results show that the optimal sample in tribological performance is the one applied at a working pressure of 25 mTorr. Because this sample demonstrates the lowest coefficient of friction, and wear depth.

Dynamic Deformation in Nuclear Graphite and Underlying Mechanisms.

Time-dependent deformation in nuclear graphite is influenced by the creation and migration of radiation-induced defects in the reactor environment. This study investigates the role of pre-existing defects such as point defect clusters and Mrozowski cracks in nuclear graphite IG-110. Separate specimens were irradiated with a 2.8 MeV Au2+ beam with a fluence of 4.38 × 1014 cm-2 and an 8 MeV C2+ beam with a fluence of 1.24 × 1016 cm-2. Microscopic specimens were either mechanically loaded inside a transmission electron microscope (TEM) or subjected to ex situ indentation-based creep loading. In situ TEM tests showed significant plasticity in regions highly localized around the Mrozowski cracks, resembling slip or ripplocation bands. Slip bands were also seen near regions without pre-existing defects but at very high stresses. Ex situ self-ion irradiation embrittled the specimens and decreased the creep displacement and rate, while heavy ion irradiation resulted in the opposite behavior. We hypothesize that the large-sized gold ions (compared to the carbon atoms) induced interplanar swelling as well as cross-plane channels for increased defect mobility. These findings illustrate the role of pre-existing defects in the dynamic relaxation of stresses during irradiation and the need for more studies into the radiation environment's impact on the mechanical response of nuclear graphite.

Carbonaceous Shape-Stabilized Octadecane/Multi-Walled Carbon Nanotube Composite Materials for Enhanced Energy Storage and Electromagnetic Interference Shielding.

Developing materials for efficient energy storage and effective electromagnetic interference (EMI) shielding is crucial in modern technology. This study explores the synthesis and characterization of carbonaceous shape-stabilized octadecane/MWCNT (multi-walled carbon nanotube) composites, utilizing activated carbon, expanded graphite or ceramic carbon foam, as shape stabilizers for phase change materials (PCMs) to enhance thermal energy storage and EMI shielding, for energy-efficient and advanced applications. The integration of octadecane, a phase change material (PCM) with carbonaceous stabilizers ensures the material's stability during phase transitions, while MWCNTs contribute to improved thermal storage properties and EMI shielding capabilities. The research aims to develop novel composites with dual functionality for thermal storage and EMI shielding, emphasizing the role of carbon matrices and their MWCNT composites. SEM and CT microtomography analyses reveal variations in MWCNT incorporation across the matrices, influenced by surface properties and porosity. Leaching tests, infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) confirm the composite's stability and high latent heat storage. The presence of nanotubes enhances the thermal properties of octadecane and ΔH values almost reached their theoretical values. EMI shielding effectiveness measurements indicate that the composites show improved electric properties in the presence of MWCNTs.

Evaluation of Shape Recovery Performance of Shape Memory Polymers with Carbon-Based Fillers.

This study focuses on enhancing the thermal properties and shape recovery performance of shape memory polymers (SMPs) through the application of carbon-based fillers. Single and mixed fillers were used to investigate their effects on the glass transition temperature (Tg), thermal conductivity, and shape recovery performance. The interaction among the three-dimensional (3D) structures of mixed fillers played a crucial role in enhancing the properties of the SMP. These interactions facilitated efficient heat transfer pathways and conserved strain energy. The application of mixed fillers resulted in substantial improvements, demonstrating a remarkable 290.37% increase in thermal conductivity for SMPCs containing 60 µm carbon fiber (CF) 10 wt% + graphite 20 wt% and a 60.99% reduction in shape recovery time for SMPCs containing CF 2.5 wt% + graphite 2.5 wt%. At a content of 15 wt%, a higher graphite content compared to CF improved the thermal conductivity by 37.42% and reduced the shape recovery time by 6.98%. The findings demonstrate that the application of mixed fillers, especially those with high graphite content, is effective in improving the thermal properties and shape recovery performance of SMPs. By using mixed fillers with high graphite content, the performance of the SMP showed significant improvement in situations where fast response times were required.

Low-Cycle Fatigue Damage Mechanism and Life Prediction of High-Strength Compacted Graphite Cast Iron at Different Temperatures.

Tensile and low-cycle fatigue tests of high-strength compacted graphite cast iron (CGI, RuT450) were carried out at 25 °C, 400 °C, and 500 °C, respectively. The results show that with the increase in temperature, the tensile strength decreases slowly and then decreases rapidly. The fatigue life decreases, and the life reduction increases at high temperature and high strain amplitude. The oxide layer appears around the graphite and cracks at high temperature, and the dependence of crack propagation on ferrite gradually decreases. With the increase in strain amplitude, the initial cyclic stress of compacted graphite cast iron increases at three temperatures, and the cyclic hardening phenomenon is obvious. The fatigue life prediction method based on the energy method and damage mechanism for compacted graphite cast iron is summarized and proposed after comparing and analyzing a large amount of fatigue data.

Adsorption Performance of Modified Graphite from Synthetic Dyes Solutions.

Due to the severe harmful impacts of industrial dyeing wastewater on ecosystems and human health, proper treatment is crucial. Herein, the use of modified graphite as an adsorbent for dyeing wastewater treatment was investigated in this study. The graphite was oxidized and intercalated using a phosphoric acid-nitric acid-potassium permanganate system and then thermally treated at high temperatures to optimize its structure. By adjusting the thermal treatment temperature, the graphite adsorbent with varying porosity was obtained. The optimized graphite demonstrated significant improvement in adsorption performance for dyes and organic compounds, achieving a removal rate of over 85% for methylene blue (MB) dye. The optimal adsorption performance is achieved with a 1.6 mg modified graphite adsorbent at 60 °C under alkaline conditions for adsorbing 10 ppm MB. Adsorption kinetics and isotherm models were applied to elucidate the adsorption mechanisms. The results fit the Langmuir model, suggesting that monolayer homogeneous adsorption is favorable. Importantly, the results demonstrate that high-temperature treatment can significantly enhance the adsorption properties of coal-based graphite, supporting its application in dyeing wastewater treatment.

Si/Graphite@C Composite Fabricated by Electrostatic Self-Assembly and Following Thermal Treatment as an Anode Material for Lithium-Ion Battery.

Commercial graphite anode has advantages such as low potential platform, high electronic conductivity, and abundant reserves. However, its theoretical capacity is only 372 mA h g-1. High-energy lithium-ion batteries have been a research hotspot. The Si anode has an extremely high specific capacity, but its application is hindered by defects such as large volume changes, poor electronic conductivity, and a small lithium-ion diffusion coefficient. Here, the Si/thermally reduced graphite oxide@carbon (Si/RGtO@C) composite was fabricated by electrostatic self-assembly followed by thermal treatment. The RGtO synergistic carbon coating layer can effectively compensate for the low electronic conductivity and buffer the volume expansion effect of the Si nanoparticles during charge/discharge cycles. The Si/RGtO@C anode demonstrated a significantly increased capacity compared to the RGtO. After 300 cycles, Si/RGtO@C kept a discharged capacity of 367.6 mA h g-1 at a high current density of 1.0 A g-1. The Si/RGtO@C anode shows an application potential for commercial high-energy lithium-ion batteries.

Influence of carbon content and irradiation modes on the antibiotic removal from water using VIS-activated TiO2/expanded graphite composite photocatalysts.

TiO2/expanded graphite (TiO2/EG) composite films were applied to water treatment for sulfadiazine (SDZ) degradation in a continuous flat plate photochemical reactor. The films were synthesized by sol-gel method and deposited on borosilicate glass by airbrush spray coating technique, forming a TiO2/C heterojunction. Increasing the amount of carbon promoted more efficient photocatalytic removal of SDZ under simulated sunlight, which increased from 9.1% in the absence of carbon to 49.8% for the material containing 7.5% C. From the formation of the TiO2/C heterojunction, morphological modifications, changes in the electronic structure and reduction of the band gap energy were observed. Type-II heterojunction formation was observed. Foreground and background irradiation modes were investigated, and a possible photocatalytic mechanism was proposed. TiO2/7.5 %-EG exhibited the best photocatalytic performance, with the possibility of reuse. The films showed good reusability in the SDZ degradation over 4 photocatalytic cycles. The influence of irradiation modes and the role of oxidizing species were discussed. The results showed that TiO2/EG hybrid films are a promising alternative for practical photocatalytic applications under sunlight.

Hybridization of Sulfur-Defective MoS2 and Holey Expanded Graphite for a Long Cycling Lithium Oxygen Battery Cathode.

The development of MoS2 as a cathode electrocatalyst for lithium-oxygen batteries (LOBs) has attracted considerable attention due to its natural abundance, excellent catalytic activity, and chemical stability. However, the sluggish and complicated kinetic of insulating and bulk discharge products on the electrode surface is one of major factors for MoS2 as a cathode for high performance LOBs. Defect engineering of an electrocatalyst and its hybridization with highly conductive frameworks are effective strategies to address this critical issue. Herein, we report a hybrid of rich sulfur-defective MoS2 (MoS2-x) nanosheets grown on highly conductive holey expanded graphite (hEG) with well-defined "worm-like" and holey structures (MoS2-x/hEG). Benefiting from rich sulfur defects of MoS2-x and the highly conductive nature and holey structures of hEG, the MoS2-x/hEG hybrid as a cathode for LOBs displays outstanding electrochemical performance with an extremely high discharge capacity of 19000.3 mAh g-1 at 500 mA g-1 and an ultralong cycling life of over 500 cycles at 1000 mA g-1 with a controlled specific capacity of 1000 mAh g-1.

Electrochemical biosensing of Acinetobacter baumannii gene using chitosan-gold composite modified electrode.

In this study, a novel electrochemical biosensor was developed for the sensitive and selective detection of the Acinetobacter baumannii gene sequence. The biosensor was created by immobilizing a capture probe specific to the A. baumannii gene on the surface of chitosan-gold modified pencil graphite electrodes. Following solid-state hybridization on the Chit-Au/PGE surface, the target DNA sequence of the A. baumannii was detected by measuring the guanine signal using square wave voltammetry (SWV). All experimental parameters impacting sensor response are examined in order to improve hybridization efficacy, and the electrochemical biosensor's performance. The limit of detection (LOD) for the A. baumannii gene sequence was calculated and found to be 1.93 nM. Three different non-complementary DNA sequences were used to evaluate the assay selectivity, but no interference effect was obtained. Additionally, the potential applicability of the biosensor to real samples was tested in artificial serum media. The suggested electrochemical test procedure is simple, approachable, and quick, making it a convenient approach for the screening of DNA sequence.

Tribological Properties of Nitrate Graphite Foils.

This study investigates the tribological properties of graphite foils (GF) with densities of 1.0, 1.3, and 1.6 g/cm3, produced from purified natural graphite of different particle sizes (40-80 µm, 160-200 µm, >500 µm). Surface roughness was measured after cold rolling and friction testing at static (0.001 mm/s) and dynamic conditions (0.1 Hz and 1 Hz). Results showed that static friction tests yielded similar roughness values (Sa ≈ 0.5-0.7 µm, Sq ≈ 0.5-1.0 µm) across all densities and particle sizes. Dynamic friction tests revealed increased roughness (Sa from 0.7 to 3.5 µm, Sq from 1.0 to 6.0-7.0 µm). Friction coefficients (µ) decreased with higher sliding speeds, ranging from 0.22 to 0.13. GF with 40-80 µm particles had the lowest friction coefficient (µ = 0.13-0.15), while 160-200 µm particles had the highest (µ = 0.15-0.22). Density changes had minimal impact on friction for the 40-80 µm fraction but reduced friction for the 160-200 µm fraction. Young's modulus increased with density and decreased with particle size, showing values from 127-274 MPa for 40-80 µm, 104-212 MPa for 160-200 µm, and 82-184 MPa for >500 µm. The stress-strain state in the graphite foil samples was simulated under normal and tangential loads. This makes it possible to investigate the effect of the anisotropy of the material on the stress concentration inside the sample, as well as to estimate the elasticity modulus under normal compression. Structural analyses indicated greater plastic deformation in GF with 40-80 µm particles, reducing coherent-scattering region size from 28 nm to 24 nm. GF samples from 160-200 µm and >500 µm fractions showed similar changes, expanding with density increase from 18 nm to 22 nm. Misorientation angles of GF nanocrystallites decreased from 30° to 27° along the rolling direction (RD). The coherent scattering regions of GF with 40-80 µm particles increased, but no significant changes in the coherent scattering regions were observed for the 160-200 µm and >500 µm fractions during dynamic friction tests. Microstrains and residual macrostresses in GF increased with density for all fractions, expanding under higher friction-induced loads. Higher values of both stresses indicate a higher level of accumulated deformation, which appears to be an additional factor affecting the samples during friction testing. This is reflected in the correlation of the results with the roughness and friction coefficient data of the tested samples.

A Novel Structured Si-Based Composite with 2D Structured Graphite for High-Performance Lithium-Ion Batteries.

Silicon is a promising alternative to graphite anodes for achieving high-energy-density in lithium-ion batteries (LIBs) because of its high theoretical capacity (3579 mAh g-1). However, silicon anode must be developed to address its disadvantages, such as volume expansion and low electronic conductivity. Therefore, the use of silicon as composed with graphite and carbon anode materials is investigated, which requires properties such as a spherical morphology for high density and encapsulation of silicon particles in the composite. Herein, a graphite@silicon@carbon (Gr@Si@C) micro-sized spherical anode composite is synthesized by mechanofusion process. This composite comprises an outer surface, middle layer, and core pore, which are formed by the capillary force arising from 2D structured graphite and pitch properties. This structure effectively addresses the intrinsic issues associated with Si. Gr@Si@C exhibits a high capacity of 1622 mAh g-1 and capacity retention of 72.2% after 100 cycles, with a high areal capacity 4.2 mAh cm-2. When Gr@Si@C is blended with commercial graphite, the composite exhibits high capacity retention and average Coulombic efficiency after cycling. The Gr@Si@C blended electrode exhibits a high energy density of 820 Wh L-1 with ≈16% metallic Si in the electrode (40 wt.% composite), enabling the realization of practical commercial LIBs.

Weakly Solvating Ether-Based Electrolyte Constructing Anion-Derived Solid Electrolyte Interface in Graphite Anode toward High-Stable Potassium-Ion Batteries.

Low-cost graphite has emerged as the most promising anode material for potassium-ion batteries (PIBs). Constructing the inorganic-rich solid electrolyte interface (SEI) on the surface of graphite anode is crucial for achieving superior electrochemical performance of PIBs. However, the compositions of SEI formed by conventional strongly solvating electrolytes are mainly organic, leading to the SEI structure being thick and causing the co-intercalation behavior of ions with the solvent. Herein, a weakly solvating electrolyte is applied to weaken the cation-solvent interaction and alter the cation solvation sheath structures, conducing to the inorganic composition derived from anions also participating in the formation of SEI, together with forming a uniformly shaped SEI with superior mechanical properties, and thus improving the overall performance of PIBs. The electrolyte solvation structure rich in aggregated ion pairs (AGGs) (69%) enables remarkable potassium-ion intercalation behavior at the graphite anode (reversible capacity of 269 mAh g-1) and highly stable plating/stripping of potassium metal anode (96.5%). As a practical device application, the assembled potassium-ion full-battery (PTCDA//Graphite) displays superior cycle stability. The optimizing strategy of cation solvation sheath structures offers a promising approach for developing high-performance electrolytes and beyond.