Carbon最新文献

In the marine sector, hydraulic machinery suffers severe damage from cavitation erosion. Although amorphous carbon (a-C) coatings are an effective measure to enhance the cavitation erosion resistance (CER), their widespread application is hindered by their metastable nature characterized by internal stress. In this study, a planification strategy was employed via different sp²/sp³ distributions (including uniform ones with different sp²/sp³ levels and periodically transitional ones with different periods), aiming to construct a pure a-C coating that enhances CER on 316L stainless steel by modulating the bias during magnetron sputtering. The effects of the sp²/sp³ distributions on the microstructure, chemical bonding, adhesion strength, fracture toughness, corrosion resistance and CER was investigated and compared with the coatings featuring uniform sp²/sp³ distributions. The results show that the periodic-mode coatings exhibit much higher CER due to their lower internal stress, excellent adhesion strength, enhanced fracture toughness and high corrosion resistance. After the cavitation erosion test for 4 h, the periodic-mode coatings only show striped structures without any coating delamination, along with less graphitization tendency during cavitation erosion. Hence, the design approach of periodic sp²/sp³ carbon bonds provides a promising new direction for marine equipment with improved CER and potential applications in various other environments.

The rapid development of spacecraft thermal control systems necessitates high-performance phase change materials (PCMs) with low density, high thermal conductivity and high enthalpy. Graphene aerogels (GAs) prepared by unidirectional freezing are ideal candidates as thermal conductive networks for PCMs due to the anisotropic porous structures. However, constructing anisotropic thermal conductive composite PCMs with low graphene aerogel loading while employing environmentally friendly cross-linking agents remains challenging. To fulfill the research gap, this study explores the synthesis of poly(vinyl alcohol) (PVA)/graphene aerogels (PGAs) by hydrothermal reaction and conventional freeze-drying. Anisotropic PGAs with oriented porous structures were fabricated by unidirectional freezing. After annealing and impregnation with paraffin wax, composite PCMs with excellent shape stability were obtained. The prepared composite exhibits low density (0.82 g cm⁻³) and high enthalpy (165 J g⁻¹). The combination of PVA and graphene enables the composite to achieve an ultralow graphene aerogel loading (0.85 wt%) while maintaining high thermal conductivity (1.37 W m⁻¹ K⁻¹), leading to a high specific thermal conductivity enhancement up to 477. This work sheds light on the potential of combing PVA and graphene to construct thermal conductive aerogels, intending to provide feasible means to develop high-performance PCMs for spacecraft thermal management.

Defect modulation strategies have been shown to be an effective way to design efficient EMW absorbing materials, but the coexistence of multiple loss mechanisms due to the complexity of the existing models makes it difficult to elucidate the mechanism by which defect-induced dielectric losses dominate. In this work, p(C₃O₂)_x is applied for the first time in the field of EMW absorption and the concentration of defects in the sample is controlled by changing the pyrolysis temperature. In addition, the unique molecular structure of p(C₃O₂)_x enables the prepared samples to completely eliminate the interference of interfacial polarization and magnetic loss on EMW dissipation. The results show that the dielectric loss induced by defects significantly enhances the EMW absorption performance as the concentration of defects increases, but excessive defects lead to a sudden drop in the conductivity of the sample and reduce the EMW absorption performance. In which, the RL_min of OC-800 can reach −51.0 dB, and the EAB of OC-900 can go up to 5.6 GHz at only 1.6 mm. Finally, CST simulation verified the potential application of the prepared absorber in real scenarios. This work has improved the theoretical basis of the effect of defect-induced dielectric loss on EMW absorbing properties, and the simple synthetic raw materials and routes have made the industrialized production of highly efficient EMW absorbing materials possible.

MoS₂ boasts high capacity but often encounters issues such as poor electrical conductivity, limited cycling stability due to volume expansion, and polysulfide shuttling when applied as the anode in sodium-ion batteries (SIBs). To this end researchers have developed MoS₂/carbon composites, which enhance electronic conductivity, ion diffusion, and structural stability. Herein, we develop a new synthesis method using a KSCN molten salt to produce hierarchical MoS₂ on nitrogen and phosphorus co-doped carbon (NPC). The molten KSCN acts both as the sulfur source and the reaction medium, facilitating the creation of hierarchical MoS₂ structures with a high loading of 85.8 wt%. These structures optimize ion diffusion channels and enhance electrochemical reaction kinetics. Additionally, the NPC framework improves electron transport and reduces polysulfide shuttling. With its superior structural stability and accelerated electrode kinetics, MoS₂/NPC exhibits an impressive rate capacity of 468 mAh g⁻¹ at 10 A g⁻¹ and maintains a long lifespan of 1300 cycles at 2 A g⁻¹. Moreover, full cells equipped with a NaNi_1/3Fe_1/3Mn_1/3O₂ cathode retain 98 % capacity retention after 400 cycles. This study presents a promising approach for fabricating advanced MoS₂/carbon anodes with dedicate nanostructures for SIBs.

Although metallic lithium is one of the most potential anode candidates for next-generation batteries, its applications are still restricted by several problems, especially the formation of lithium dendrites. However, insufficient emphasis has been placed on dealing with the incipient lithium dendrites. Herein, a three-dimensional insulating glass-fiber skeleton with gradient-distributed trigger-type carbonized ZIF-8 (GF-cZIF8) was developed. In this structure, plentiful conductive cZIF-8 on the collector/skeleton interface guided uniform lithium nucleation, while highly conductive and lithophilic cZIF-8 on the skeleton passivated and reversed lithium dendrites to a stable part of lithium anode when trigged by lithium dendrites. In addition, insulating glass fibers improved the homogeneity of Li ions. As a consequence, the GF-cZIF8/Cu collector exhibited a high and stable coulombic efficiency of 98 % after 280 cycles, and the GF-cZIF8-Li anode exhibited a low voltage hysteresis of 17 mV and a long cycling life up to 1100 h.

We developed a new graph theory rooted in Clar's sextet rule to unravel the bulk-boundary correspondence of graphene. This methodology is specifically focused on the topological invariant and the chiral winding number, which enables the chemical rationalization of edge and boundary states in one-dimensional graphene nanoribbon (GNR) materials. The Clar structure derived from facile Lewis structures facilitates direct prediction of free radical distribution along edges and boundaries of GNRs across various geometric configurations. We then extend this graph theoretical framework to include metallic GNRs, demonstrating its power in several paradigms where conventional topological theories show limitations. Upon reducing the topological parameters and hence the complexity, the new approach provides a visual comprehension for the electronic topology and hence conductivity of GNR, greatly simplifying the formulation of design principles for future application of graphene interconnects.

The development of electromagnetic wave-absorbing materials (EWAMs) with good environmental adaptability has emerged as a focal point of research in the realm of electromagnetic protection. Herein, a core-shell structure composite EWAMs, in which flake carbonyl iron powders and O, N co-doped single-walled carbon nanohorns are respectively a core and a shell (F–CIP@O/N-SWCNHs), has been prepared by a simple electrostatic adsorption method. The high-shape anisotropy of the F–CIP core exhibits strong specific saturation magnetization (160.47 emu/g) and excellent magnetic loss capacity. The tunable O/N-SWCNHs shell effectively enhances the dielectric properties and improves impedance matching, while the oxygen and nitrogen doping strengthens the dipole polarization. The surface protection provided by O/N-SWCNHs imparts favorable corrosion resistance and anti-oxidation properties to the F-CIP@O/N-SWCNHs. Moreover, F–CIP@O/N-SWCNHs exhibit excellent wave absorption performance. When the sample thickness is 1.53 mm, the minimum reflection loss reaches −74.8 dB. This study provides a feasible approach for the preparation of efficient EWAMs with strong environmental adaptability for the practical application of composite-absorbing materials.

The increasing proliferation of modern communications, radar systems, and military equipment operating in the X and Ku bands (8–18 GHz) has exacerbated the issue of electromagnetic wave (EMW) pollution, highlighting the urgent need for lightweight, broadband EMW-absorbing materials. In this paper, the lightweight carbon fiber aerogel@hollow carbon/Co₃O₄ microsphere (CFA@H–C/Co₃O₄) were composed by ZIF-67 derived hollow carbon/Co₃O₄ microsphere and bamboo cellulose fiber derived carbon fiber aerogels and constructed by in-situ chemical deposition, dopamine treatment and pyrolysis. Carbon fiber aerogels form a lightweight three-dimensional (3D) interconnected conductive network, which expands the multiple reflection and absorption paths of EMW and increases the dielectric loss. The hollow carbon/Co₃O₄ microsphere inhibits the collapse of the structure by forming a polydopamine shell through the self-polymerization effect of dopamine on the surface of ZIF-67 during pyrolysis, showing dipole polarization loss, interface polarization loss and magnetic loss, which plays an important role in improving EMW polarization loss and optimizing impedance matching. The minimum reflection loss (RL_min) of CFA@H–C/Co₃O₄ reaches −43.5 dB at frequency of 12.88 GHz with thickness of 3.0 mm and the effective absorption bandwidth (EAB) of CFA@H–C/Co₃O₄ reaches 7.84 GHz (10.08–17.92 GHz) with thickness of 3.0 mm, covering most of X and Ku bands at a low filling ratio of 15 wt%. The radar cross-section (RCS) value of CFA@H–C/Co₃O₄ is 22.68 dB m² lower than the perfect electrical conductor (PEC). This study provides valuable insights into materials that can improve the absorption bandwidth of electromagnetic waves in the X and KU bands.