Amorphous Carbon Matrix Research Articles

Incorporation of SiC on the mechanical properties, tribological performance, and oxidation resistance of HfC-SiC/a-C:H coatings prepared by hybrid HiPIMS and pulsed-DC magnetron co-sputtering

The multiphase nanocomposite HfC-SiC/a-C:H coatings consisting of HfC and SiC grains dispersed in the amorphous carbon matrix were deposited by hybrid HiPIMS and pulsed-DC magnetron co-sputtering. The incorporation of SiC ranging from 0 to 21.3 at.% on the chemical bonding state, nanocomposite structure, mechanical and tribological properties, and oxidation resistance of the coatings were explored. Results showed that the increase of SiC content is mainly at the expense of a-C:H matrix rather than nanocrystalline HfC, and is accompanied by changes in the HfC crystallinity. Nanohardness of up to 45 GPa was obtained for the HfC-SiC/a-C:H coating with 6.6 at.% SiC content. The optimum wear rate of 6.4×10−7mm3/N and friction coefficient of 0.2 were also obtained at 6.6 at.% SiC content. The oxidation resistance is enhanced with the increase of SiC content, which delays the oxidation temperature by 100 °C with respect to the HfC/a-C:H coating.

Glucose promoted synthesis of homogeneously embedded black phosphorus carbon composite with enhanced lithium storage performance

Black phosphorus (BP) has attracted extensive attention in high-rate lithium-ion batteries due to its high theoretical capacity and moderate lithiation potential. However, the large volume expansion and the low conductivity of BP nanostructures in the electrochemical cycle have inhibited the rate performance and long-term cycle stability. In this paper, by combining the glucose-assisted ball-milling and carbonization method, a black-phosphorus/carbon (BP@C) composite anodic material is developed, in which the nano-sized BP nanoparticles are homogeneously embedded in the amorphous carbon matrix. Both the phosphorus-oxygen-carbon bonds and the phosphorus-carbon bonds improve the cross-link between BP and the surface-coated carbon matrix. The unique well-embedded structure promotes the cycling stability and the rate performance of BP@C. The composite shows a high discharge specific capacity of about 1881 mAh g−1 at 0.1 A g−1, the specific capacity at 4 A g−1 is about 63% of the low current capacity, and the discharge specific capacity retains 1130 mAh g−1 after 300 charge-discharge cycles at 0.5 A g−1. Moreover, the significant role of the active unsaturated groups for building the well-embedded composite is further revealed. These results indicate that dual regulation of surface coating and structure optimization offers great potential for further optimizing phosphorus-based anode materials.

Effect of rGO concentration on the microstructure and friction behavior of co-doped diamond-like carbon (Ni/N/rGO-DLC) films

A kind of wear-resistant and lubricated Ni/N/rGO-DLC films are deposited on the surface of Ti-6Al-4V(TC4) alloy substrate by an integrative method involving pulsed electrodeposition and liquid-phase electrodeposition with various rGO (reduced graphene oxide) concentration. The growth mechanism of the film and the formation of protrusions and gully structures on the surface of the film are investigated. Furthermore, the mechanism of the effect of rGO concentration on the dispersion stability of the electrolytic system is explored. The results reveal that the Ni/N/rGO-DLC films at 0.07 g·L−1 rGO exhibit a uniform and dense structure. rGO particles are uniformly incorporated into the carbon-based films and tend to deposit perpendicular on the substrate. Simultaneously, the highest micro-indentation hardness, the lowest coefficient of friction and wear loss are obtained as 591.88 HV, 0.072 and 1.20 × 10−4 kg·m−1 of film with 0.07 g·L−1 rGO, which are principally attributed to the synergistic effect of rGO particles and amorphous carbon matrix in improving the mechanical properties of Ni/N/rGO-DLC films.

New, 3D binder-jetted carbons with minimal periodic surface structures

This study focuses on the design, additive manufacturing, and characterization of porous carbon-based structures in the form of a triply periodic minimal surface (TPMS) with outstanding mechanical properties and oxidation resistance, combined with good electrical and thermal conductivity. Binder jetting (BJ) of graphite-carbon black powders was used to 3D print computational models of three TPMS with different topologies and geometric porosities. Infiltration and pyrolysis (PIP) with furan resin was then performed to densify the parts. Composite materials, comprising a highly disordered carbon matrix binding well-crystallized graphite grains, were obtained. The printed and pyrolyzed samples are highly porous TPMS cylinders with diameter, height and a surface thickness of ∼19 mm, ∼33 mm and 0.76 mm, respectively. The samples have a skeleton intrinsic porosity of 20%, of which 8% is open, meaning that the material could potentially be further infiltrated and densified. Nevertheless, the samples have better mechanical properties than compressed carbon-graphite composites, as well as 3D-printed carbon produced by direct ink writing and stereolithography. High-temperature tests showed that, although the amorphous carbon matrix is more prone to oxidation than the graphite grains, the overall oxidation resistance remains exceptionally high. These properties allow for applications as Joule resistors and in seasonal thermal storage.

Prussian blue microcubes-derived FeF3 cathodes for high-energy and ultra-stable lithium and lithium-ion batteries

Iron trifluoride (FeF3) is highlighted as a competitive cathode for next-generation lithium and lithium-ion batteries with higher energy densities and lower cost. However, the FeF3 cathode is typically hindered by rapid capacity fade for their poor electronic/ionic conductivity and unstable electrode/electrolyte interphase. Herein, a microcubic FeF3@C composite, where the nanosized FeF3 particles (<40 nm) are encapsulated by graphitized carbon and linked through surrounding amorphous carbon matrix, is firstly synthesized through the Prussian blue microcubes. When using as the cathode of coin-type lithium batteries, it can achieve stable and ultralong lifespan (over 1000 cycles) at FeF3 mass loading of ∼2 mg cm−2, ascribing to the compact and thick wrapping of carbon shell and stable cathode solid electrolyte interphase (CEI) during cycling. Besides, the FeF3–Li pouch cell, FeF3 full batteries with pre-lithiated Li4Ti5O12 (PLLTO) and pre-lithiated mesocarbon microbeads (PLMCMB) anodes are successfully constructed. To interpret the capacity rising of as-prepared FeF3 cathodes within initial cycles, the detailed electrochemical behaviors and electrode kinetics are investigated. The results show that the decay of the high-potential decomposition process cannot catch up with the activation of the low-potential conversion reaction The repeated electrochemical activation within initial cycles causes multiple interface and increased Li+ diffusion coefficient (resulted from the amorphization of FeF3 particle), which induce the capacity rising.

High-entropy alloy nanoparticles/biochar as an efficient catalyst for high-performance treatment of organic pollutants

High entropy alloys (HEA) have recently emerged as a new class of single-phase solid solution materials and attracted widespread attention due to their unique physical and chemical properties. In this work, high entropy alloys/biochar (HEA@BC) were successfully prepared using alkaline lignin to derive biochar in concept of waste recycling. Benefiting from the unique multi-metallic composition and entropy-stabilized structure, HEA@BC exhibited excellent catalytic activity for the degradation of organic pollutants via peroxymonosulfate (PMS) activation and showed superiority compared with pure BC-600 and monometallic catalyst. With ofloxacin (OFX) as a typical antibiotic pollutant, the HEA@BC/PMS system could achieve 98.2% degradation efficiency within 90 min. Quenching experiments and electron spin resonance (ESR) results revealed a radical/nonradical combined degradation pathway, in which 1O2 may play a dominate role. XPS characterization and mechanistic study demonstrated that the five components all participated in the catalytic process with Co and Cu considered to be the main active sites. The outstanding catalytic performance of HEA@BC could be attributed to the synergistic effects between each metallic component and amorphous carbon matrix to accelerate the electron transmission. According to the analysis of oxidation products, the major degradation pathways for OFX were proposed and the quantitative structure–activity relationship (QSAR) predictions revealed that the degradation process can reduce toxicity gradually. The study may give new insights into the design and preparation of high entropy catalysts which highlight promising applications for organic wastewater treatment.

External Fields Assisted Highly Efficient Oxygen Evolution Reaction of Confined 1T-VSe2 Ferromagnetic Nanoparticles.

As a clean and effective approach, the introduction of external magnetic fields to improve the performance of catalysts has attracted extensive attention. Owing to its room-temperature ferromagnetism, chemical stability, and earth abundance, VSe2 is expected to be a promising and cost-effective ferromagnetic electrocatalyst for the accomplishment of high-efficient spin-related OER kinetics. In this work, a facile pulsed laser deposition (PLD) method combined with rapid thermal annealing (RTA) treatment is used to successfully confine monodispersed 1T-VSe2 nanoparticles in amorphous carbon matrix. As expected, with external magnetic fields of 800 mT stimulation, the confined 1T-VSe2 nanoparticles exhibit highly efficient oxygen evolution reaction (OER) catalytic activity with an overpotential of 228mV for 10mA cm-2 and remarkable durability without deactivation after >100h OER operation. The experimental results together with theoretical calculations illustrate that magnetic fields can facilitate the surface charge transfer dynamics of 1T-VSe2 , and modify the adsorption-free energy of *OOH, thus finally improving the intrinsic activity of the catalysts. This work realizes the application of ferromagnetic VSe2 electrocatalyst in highly efficient spin-dependent OER kinetics, which is expected to promote the application of transition metal chalcogenides (TMCs) in external magnetic field-assisted electrocatalysis.

Magnetic carbon Fe3O4 nanocomposites synthesized via Magnetic Induction Heating

Magnetic Induction Heating (MIH) of magnetite nanoparticles is employed as a novel synthesis procedure of carbon based magnetic nanocomposites. Magnetic nanoparticles (Fe3O4) and fructose (1:2 weight ratio) were mechanically mixed and submitted to a RF magnetic field (305 kHz). The heat generated by the nanoparticles leads to the decomposition of the sugar and to the formation of an amorphous carbon matrix. Two sets of nanoparticles, with mean diameter sizes of 20 and 100 nm, are comparatively analysed. Structural (X-ray diffraction, Raman spectroscopy, Transmission Electron Microscopy (TEM)), electrical and magnetic (resistivity, SQUID magnetometry) characterizations confirm the nanoparticle carbon coating through the MIH procedure. The percentage of the carbonaceous fraction is suitably increased controlling the magnetic heating capacity of the magnetic nanoparticles. The procedure enables the synthesis of multifunctional nanocomposites with optimized properties to be applied in different technological fields. Particularly, Cr (VI) removal from aqueous media is presented employing the carbon nanocomposite with 20 nm Fe3O4 nanoparticles.

Heating induced self-assemble pomegranate-like Fe3C@Graphite magnetic microspheres on amorphous carbon for high-performance microwave absorption

Difficulty of multicomponent regulation and nanostructure design make it challenging to fabricate high-performance electromagnetic wave (EMW) absorption materials. Herein, pomegranate-like Fe3C@graphitic carbon embedded in amorphous carbon matrix (Fe3C@GC/AC) is successfully prepared through a viable heating induced self-assembly strategy. By adjusting carbonization temperature, controllable electromagnetic parameters and impedance matching characteristics of Fe3C@GC/AC nanocomposites could be acquired. Besides, dielectric loss and magnetic loss are offered by GC and Fe3C, while the amorphous carbon not only disperse Fe3C@GC nanoparticles well, but also strengthens interface polarization. The detailed analysis show that Fe3C@GC/AC nanocomposites exhibit excellent EMW absorption performance under the combined function of unique pomegranate-like nanostructure and various loss mechanisms of multi-components. Moreover, the strongest reflection loss value of optimal sample (RCF-700) is up to −96.3 dB (loss of EMW above 99.99999%) with a matching thickness of 2.08 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 6.38 GHz (11.62–18.0 GHz, covering Ku-band). In addition, the EAB can reach 14.08 GHz with the simulated thickness varies from 1.0 to 5.0 mm, covering 88% of the measured frequency range. The deep exploration of the bio-inspired structure of multi-component system provides a creative and effective way for high-performance EMW absorbers.

Multiwall Carbon Nanotubes for Solid Lubrication of Highly Loaded Contacts

When lubrication of rolling bearings with oil or grease is not possible, for example because the lubricant evaporates in vacuum, solid lubrication by multiwall carbon nanotubes (MWCNT) is a viable alternative. To understand the mechanisms underlying MWCNT lubrication of highly loaded contacts, we combine an experimental approach with large-scale molecular dynamics (MD) simulations. Tribometry is performed on ground iron plates coated with two different types of MWCNTs by electrophoretic deposition. Although structural differences in the MWCNT materials result in slightly different running-in behavior, most of the tests converge to a steady-state coefficient of friction of 0.18. The resulting wear tracks and tribolayers are subjected to structural and chemical characterization and suggest a tribo-induced phase transformation resulting in tribolayers that consist of MWCNT fragments, iron oxide, and iron carbide nanoparticles embedded in an amorphous carbon matrix. Covalent bonding of the tribolayer to the iron surface and low carbon transfer to the alumina counter body indicate sliding at the tribolayer/ball interface as the dominant mechanism underlying MWCNT solid lubrication. MD simulations of nascent a-C tribofilms lubricated by MWCNT bundles and stacks of crossed MWCNTs reveal two different sliding regimes: a low-load regime that leaves the MWCNTs intact and a high-load regime with partial collapse of the tube structure and formation of a-C regions. The critical load for this transition increases with the filling ratio of the MWCNT and the packing density of the stacks. The former determines the stability of the MWCNT, while the latter controls the local stresses at the MWCNT crossings. For both MWCNT materials, the high-load regime is predicted for the experimental loads. This is confirmed by a remarkable agreement between transmission electron microscopy (TEM) and atomistic simulation images. Based on the findings of this work, a multistep lubrication mechanism is formulated for MWCNT coatings rubbing against alumina on an iron substrate.

Локализация и зарядовое состояние ионов металла в углеродных наноструктурах пиролизата дифталоцианина европия

In the experiments of Mössbauer spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM) the morphology and structurization of the carbon phase, the charge state of europium and the dynamic properties of europium bis-phthalocyanine pyrolysed derivatives, including the Debye temperature, were revealed. It was found that the pyrolysis of europium bis-pthalocyanine resulted in the amorphous carbon matrix and nanoscaled graphene clusters both forming turbostratic carbon phase. The europium ions in the charge state Eu3+/Eu2+ were detected. The data indicated that localization of Eu ions took place between layers of graphenes similar to graphite intercalation compounds. It was shown that an isomeric shift, linewidths and the magnitude of the resonant absorption are essential characteristics of structural transformations at the pyrolysis of rare earth bis-phthalocyanines.

Microstructure, mechanical and tribological properties of Ti doped ta-C films deposited by a hybrid coating system

Ti doped ta-C films were deposited by a hybrid coating system with filtered cathodic vacuum arc and pulsed DC magnetron sputtering. The microstructure, mechanical and tribological properties of ta-C: Ti films were investigated. Results showed that the Ti content in the films linearly increased from 0 to 19.9 at. % by increasing the Ti target current from 0 to 2 A. Without and with small amount of Ti doing, ta-C films presented typical amorphous characteristic. TiC phase was formed in the film at Ti content of 5.5 at. %, and as the Ti content further increased, the microstructure of the films gradually transformed to nanocomposite structure, where TiC nanocrystalls were embedded in amorphous carbon matrix. The sp3 bonding fraction was decreased with increasing Ti content, accordingly, the hardness and residual stress of films also decreased with diminishing sp3 content. In addition, the Ti doping had a positive impact on the adhesion force between films and substrates. ta-C film with Ti doping content of 5.5 at. % had the lowest friction coefficient and the lowest wear rate under different friction temperatures, corresponding to 0.09 and 3.6 × 10−8 mm3/N·m at room temperature, and 0.25 and 22.5 × 10−8 mm3/N·m at 400 °C, respectively, which was mainly attributed to the relative high hardness, lower residual stress, good adhesion of the film.

Electrochemical Reconstruction of NiFe/NiFeOOH Superparamagnetic Core/Catalytic Shell Heterostructure for Magnetic Heating Enhancement of Oxygen Evolution Reaction (Small 3/2023)

Superparamagnetic Core/Catalytic Shell Heterostructures In article number 2205665, Cailei Yuan and co-workers design and successfully prepare electrochemical-reconstructed NiFe/NiFeOOH core/shell nanoparticles confined in highly conductive amorphous carbon matrix. Benefiting from the unique superparamagnetic NiFe/catalytic NiFeOOH core/shell heterostructure, their oxygen evolution reaction performance is improved significantly with an alternating magnetic field stimulation as the consequence of magnetic heating effect.

Poly-adamantane as precursor for low temperature chemical vapor deposition of nanocrystalline diamond films

Nanocrystalline diamond (NCD) films are technologically important tribological coatings and their large area, uniform growth is needed for a wide range of applications. The conventional growth of NCD requires the seeding of the foreign substrates by detonation nanodiamond particles. In terms of diamond seeds for subsequent NCD film deposition, the use of chemical precursor offers advantages in producing higher purity and higher crystallinity nanodiamond particles than that by detonation method. However, the easy sublimation of chemical precursor in plasma is a serious drawback. Here we report that the poly-adamantane layer formed by the photochemically induced polymerization of adamantane serves as a promising precursor for the growth of wafer scale NCD film using linear antenna plasma-assisted chemical vapor deposition at 500 °C. TEM cross-section analysis of the interface reveals the formation of well-faceted diamond nuclei within the amorphous carbon matrix (sp 3 % ~ 40 %) decomposed from poly-adamantane. The influence of plasma chemistry on the nucleation process was also discussed. Our work provides guidance for low-temperature deposition of high-quality NCD film by chemical nucleation. • Deposition of 4-in. nanocrystalline diamond wafer using 230 nm-thick poly-adamantane precursor layer • Cross-sectional TEM study of diamond nuclei derived from poly-adamantane precursor • Study of plasma chemistry on nucleation process by poly-adamantane precursor • Film quality control by poly-adamantane precursor at low temperature

Effect of substrate rotational speed during deposition on the microstructure, mechanical and tribological properties of a-C:Ta coatings

Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C–Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating.

Enhancing hydrogen evolution reaction of confined monodispersed NiSe2−X nanoparticles by high-frequency alternating magnetic fields

Introduction of alternating magnetic field (AMF) to electrocatalytic process has been proved an effective strategy for significantly enhancing catalytic performance of magnetic nanoparticles (NPs) electrocatalysts. Coupling AMF with currently highly promising monodispersed NPs electrocatalysts could be an interesting tactics. However, magnetic heating effect under AMF may cause agglomeration and even falloff of NPs, and how to efficiently and stably utilize AMF in monodispersed NPs electrocatalysts to enhance the catalytic performance is an urgent issue. In this work, room-temperature ferromagnetism is introduced into NiSe2−X nanoparticle by vacancy engineering, and proposes a feasible design to confine monodispersed ultra-small NiSe2−X NPs in an amorphous carbon matrix. Under AMF, the spin flips of the magnetic domains in confined NiSe2−X NPs generate magnetic heating related to Néel relaxation, which achieve rapid local heating of NiSe2−X NPs electrocatalyst and greatly improves hydrogen evolution reaction performance (a significantly increase of current density by ∼400 %). This work provides new ideas for the preparation of ultra-small monodispersed NPs electrocatalysts that can utilize AMF to enhance catalytic performance, and has an important significance in accelerating clean energy production.

Zero-Strain Insertion Anode Material of Lithium-Ion Batteries.

The insertion type materials are the most important anode materials for lithium-ion batteries, but their insufficient capacity is the bottleneck of practical application. Here, LiAl5 O8 nanowires with high theoretical capacity and Li-ions diffusion coefficient are prepared and studied as an insertion anode material, which exhibits zero-strain properties upon electrochemical cycling. However, the poor electronic conductivity of LiAl5 O8 definitely sacrifices the capacity and limits the rate performance. Therefore, compact LiAl5 O8 and carbon composite are further synthesized, in which nanosized LiAl5 O8 particles are uniformly embedded in an amorphous carbon matrix. It displays a reversible capacity of 490.9 mAh g-1 at 1 A g-1 , and the capacity rises continuously to 996.8 mAh g-1 after 1000 cycles due to the interfacial storage mechanism, that the excess Li+ ions can be accommodated in the grain boundaries and C/LiAl5 O8 interfaces.

Utilizing the cross-linked effect and reconstruction strategy of phytic acid to build Fe-Co-Ni trimetallic amorphous carbon-matrix compounds as efficient oxygen evolution catalyst

Developing low-cost electrocatalysts with excellent activity is significant for accelerating the slow oxygen evolution reaction (OER). In this work, an effective electrocatalyst is prepared via the cross-linked effect and reconstruction strategy based on inexpensive transition metals (Fe, Co, and Ni) and phytic acid (PA). The feasibility of utilizing the cross-linked effect and reconstruction strategy is due to that PA molecules with strongly electronegative phosphoric acid groups possess a great deal of complexing sites, which can facilitate the formation of large cross-linked network by randomly complexing Fe, Co and Ni ions. And the carboatomic rings in PA molecules will reconstructed as carbon-matrix when PA molecules decompose. The above structural evolution of large cross-linked network and reconstructing process is rigorously analyzed through the characterization methods such as XPS. These analysis results indicate that FeCoNi-PA-300 possesses a high degree of amorphization, an abundant nanoporous structure, and a small nanoparticle size, resulting in a large electrochemically active area. Consequently, FeCoNi-PA-300 just needs low overpotentials of about 271 mV and 286 mV to obtain the current densities of 50 and 100 mA cm−2, respectively. Meaningfully, this synthetic method is a general strategy to meliorate the OER activity and electrical conductivity of other catalysts.

Comparison of magnetic anisotropy and structural properties in chemically ordered CoPt and FePt nanoparticles

The intrinsic magnetic properties of nanoparticles (NPs) can be accurately determined using highly dispersed NPs in a matrix. In this paper, we study chemically ordered CoPt and FePt NPs with a diameter of 3 nm embedded in an amorphous carbon matrix. Although both alloys exhibit almost the same magnetic and crystallographic properties in the bulk materials, they are completely different as NPs. We show that their magnetic anisotropy differs greatly. To understand the origin of such a difference, a fine crystallographic structure study has been performed using extended x-ray absorption fine structure. In that respect, the atomic relaxations appear to be different in both nanoalloys. Ab initio calculations of the atomic relaxation shed light on these experimental results, showing that the wide distance distribution in Co sublattice should strongly alter the magnetic anisotropy of CoPt NPs.

Electrodeposition, microstructure and tribological performance of Ni/(N) incorporated diamond-like carbon films

Modified diamond-like carbon (DLC) films doped with nickel and nitrogen and coated with nickel interlayer were synthesized by a combined method of pulsed and direct-current electrodeposition. The growth mechanisms of the co-doped film and the influences of different nitrogen concentrations on the microstructure and friction performance of the films were explored. The results illustrated that the smallest grain size and the densest binding of the film were achieved when the carbamide concentration was 0.12 g/L. Raman and XPS analysis revealed that the appropriate addition of nitrogen is conducive to the generation of sp3-C. Meanwhile, most of the nickel exists in the amorphous carbon matrix as crystalline clusters, while the nitrogen is preferentially bonded with the carbon matrix at the cluster interface in the form of low-energy double bonds. Furthermore, Ni/ (0.12 g/L) N-DLC films demonstrated the maximum microhardness (461.50 HV) and excellent wear resistance, which benefits from the compact structure, high sp3-C content and formation of the proper amount of CN groups.