Amorphous Carbon Shell Research Articles

The rational design of hierarchical MoS2 nanosheet hollow spheres sandwiched between carbon and TiO2@graphite as an improved anode for lithium-ion batteries.

Molybdenum disulfide (MoS2) shows high capacity but suffers from poor rate capability and rapid capacity decay, which greatly limit its practical applications in lithium-ion batteries. Herein, we successfully prepared MoS2 nanosheet hollow spheres encapsulated into carbon and titanium dioxide@graphite, denoted as TiO2@G@MoS2@C, via hydrothermal and polymerization approaches. In this hierarchical architecture, the MoS2 hollow sphere was sandwiched by graphite and an amorphous carbon shell; thus, TiO2@G@MoS2@C exhibited effectively enhanced electrical conductivity and withstood the volume changes; moreover, the aggregation and diffusion of the MoS2 nanosheets were restricted; this advanced TiO2@G@MoS2@C fully combined the advantages of a three-dimensional architecture, hollow structure, carbon coating, and a mechanically robust TiO2@graphite support, achieving improved specific capacity and long-term cycling stability. In addition, it exhibited the high reversible specific capacity of 823 mA h g−1 at the current density of 0.1 A g−1 after 100 cycles, retaining almost 88% of the initial reversible capacity with the high coulombic efficiency of 99%.

Metallic CoO/Co heterostructures stabilized in an ultrathin amorphous carbon shell for high-performance electrochemical supercapacitive behaviour

A CoO based supercapacitor with high capacity and long-term storage stability is enabled by combining metallic Co-doping and a carbon shell.

Carbon-Encapsulated Metal/Metal Carbide/Metal Oxide Core–Shell Nanostructures Generated by Laser Ablation of Metals in Organic Solvents

Laser ablation of metal in organic solvents (LAMOS) has been proven to be an efficient technique for one-step synthesis of carbon-encapsulated metal/metal carbide/metal oxide core–shell nanostructures. However, the correlation between the influential factors and the final products, such as composition of the core and crystalline structure of the carbon shell, is still unclear to date; moreover, the precise control of this is full of challenges. Herein, comparative experiments of 16 transition metals (Cu, Ag, Au, Pt, Pd, Ti, V, Nb, Cr, Mo, W, Ni, Zr, Mn, Fe, and Zn) were performed to clarify the panorama of LAMOS, including metal atomization and liquid decomposition into carbon and reductive gases, subsequent metal carbonization, surface precipitation, and metal-catalyzed graphitization to form amorphous and graphitic carbon shells. Importantly, it is found that the carbon solubility in metals and the affinity of metals to oxygen are the critical factors in determining the core composition: (1) inert metal...

Core-shell Fe2N@amorphous carbon nanocomposite-filled 3D graphene framework: An additive-free anode material for lithium-ion batteries

Among various anode materials, Fe2N becomes a “shining star” owing to its high electrical conductivity and large specific capacity. However, its dramatic volume variation and air sensitive severely limit its application. To address these obstacles, herein, we synthesized a dual-carbon protected Fe2N composite (abbreviated as Fe2N@AC@rGO) by a reliable electrostatic self-assembly strategy. The amorphous carbon (AC) shell and flexible reduced graphene oxide (rGO) framework can promise stable electrode structure, reduced electrode resistance and enhanced electrochemical reaction kinetics. Benefiting from the engineered structure merits and synergistic effects between different counterparts, the resultant Fe2N@AC@rGO anode delivers a long-term cycle stability (98.9% capacity retention, 500th cycle vs. 3rd cycle, at 0.5 A g−1) and remarkable rate capability (303 mA h g−1 at 10 A g−1, retains 57% of the value at 0.2 A g−1) even totally free of any conductive additives. Supported by the detailed analysis of the recovered electrode after cycling, the superior cyclability can be largely attributed to the stable electrochemical reaction interface and robust electrode structure. The outstanding rate performance can be well-interpreted from the enhanced contributions of surface-capacitive behaviors and accelerated electrons and ions transfer kinetics.

Nitrogen-doped amorphous carbon coated mesocarbon microbeads as excellent high rate Li storage anode materials

A composite anode material consisting of a stable inner core of mesocarbon microbeads and a porous nitrogen-doped amorphous carbon shell active for lithium storage is prepared. The thin birnessite MnO2 nanosheets hydrothermally deposited on mesocarbon microbeads are in situ replaced by polypyrrole, which is then transformed to nitrogen-doped amorphous carbon layer by calcination in nitrogen atmosphere. The surface modified mesocarbon microbeads exhibit average discharge capacities of 444 and 103 mA h g−1 at the current densities of 0.1 and 3 A g−1, respectively, obvious higher than the corresponding values of the bare sample, 371 and 60 mA h g−1. Moreover, the composite anode maintains a discharge capacity of 306 mA h g−1 after 500 cycles at 1 A g−1, suggesting an excellent cycle stability. It is believed that the nitrogen-doped amorphous carbon layer has provided additional lithium storage capacity and stabilized the structure integrity of mesocarbon microbeads. This work demonstrates that the capacity and rate performance of commercial graphitic carbons can be much improved by simply introducing a nitrogen-doped carbon coating layer active for Li storage, making them attractive for high power Li-ion batteries.

Polymer-derived Ta4HfC5 nanoscale ultrahigh-temperature ceramics: Synthesis, microstructure and properties

Nanoscale Ta4HfC5 ceramics were synthesized from curing and pyrolysis of novel polymer precursors which were synthesized by cohydrolysis and polycondensation of acetyl acetone coordinated tantalum alkoxide and hafnium alkoxide followed by blending with phenolic resin as carbon source. Pyrolysis of the polymer precursor at 1600 °C in vacuum produced Ta4HfC5 nanocrystallites with an average grain size of 21 nm and well-distributed elements, encapsulated by an amorphous carbon shell. Near full dense Ta4HfC5 monoliths can be prepared by spark plasma sintering (SPS) at 1600 °C with 10 vol% MoSi2 as an additive, of which the Vicker micro-hardness and flexural strength achieved 17.58 GPa and 466 MPa, respectively. The polymer precursor method shed light on the fabrication of ceramic matrix composites. Besides, the high electrical conductivity of 1.5 × 104 S/m entitled the ceramics to a prospective of utilization in microwave absorbing/shielding fields under harsh conditions.

Investigation of disorder in carbon encapsulated core-shell Fe/Fe3C nanoparticles synthesized by one-step pyrolysis

Fe/Fe3C (core) - graphite (shell) nanoparticles embedded in micron sized amorphous carbon globules were synthesized by pyrolysis route in a closed reactor. A large number of such nanoparticles were observed to be distributed in the inner section of each globule covered by amorphous carbon in the outer regions. The distribution of nanoparticles varies according to the reaction-temperature-profile of the furnace during the synthesis process. These particles catalyze the formation of the graphitic coating on their surface, due to metastable nature of Fe3C. The globules which contain smaller catalyst particles were found to contain defective- and less amount of graphitic carbon and large amount of amorphous carbon. We observed that for low synthesis temperature conditions the globules contain a thicker shell of amorphous carbon (without any catalyst particle). Furthermore, the amount of disorder in the graphitic layer is determined by the number and size of the (Fe/Fe3C) catalyst particles and reaction-temperature. The disorder in the graphitic layer on the particles can be potentially important for the catalytic behaviour of these particles.

Synthesis of a novel porous silicon microsphere@carbon core-shell composite via in situ MOF coating for lithium ion battery anodes

Nanostructured silicon/carbon composites with enhanced lithium storage are especially attractive for lithium-ion batteries (LIBs). The SiAl/Al-MOF core-shell precursor is prepared by the self-corrosion reaction of SiAl alloy with an organic acid in the hydrothermal condition, and the following rational annealing and etching treatments lead to the formation of the porous silicon microsphere@C (pSiMS@C) core-shell composite. The pSiMS@C composite is composed of an amorphous carbon shell and the porous silicon microsphere core consisting of interconnected nanowires, manifesting a novel core-shell structure. The as-prepared pSiMS@C electrode delivers a reversible capacity of 1027.8 mAh g−1 after 500 cycles at 1 A g−1, with a good capacity retention of 79%. The carbon shell may markedly improve the electronic conductivity, and the porous silicon microsphere core may promote the kinetics for Faradic reaction and diffusion process and alleviate the huge volume change during the charge/discharge cycling, responsible for the excellent lithium storage performance of the pSiMS@C core-shell composite.

Nanostructural study of NiTi–TiO2–C core–shell nanoparticles generated by spark discharge method

Nickel–titanium (NiTi) nanoparticles are ultrafine smart materials manifesting shape memory effect at very small scales. We have produced NiTi nanoparticles surrounded by an amorphous carbon shell using an innovative spark discharge system. The resulting nanoparticles were studied using various characterization methods to systematically study their size, morphology, size distribution, composition, structure, and thermal behavior. Field-emission scanning electron microscopy and dynamic light-scattering results indicated that the average size of the produced nanoparticles was about 13 nm. High-resolution transmission electron microscopy, energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy showed that all of the particles had a titanium oxide coating covered with a ~ 2 nm-thick carbon layer. X-ray diffraction analysis demonstrated that the carbon and titanium oxide layers were amorphous and confirmed the formation of NiTi nanoparticles. Differential scanning calorimetry demonstrated an austenite to martensite phase transformation behavior in the produced nanoparticles and further indicated the formation of NiTi phases. EDS mapping showed an incomplete oxidation for nanoparticles suggesting that the amorphous carbon and titanium oxide layers synergistically act together as a combined protective layer. These results indicate that our novel spark discharge generator is an effective system for the synthesis of NiTi nanoparticles coated with a continuous film of carbon.

Rapid activation and enhanced cycling stability of Co3O4 microspheres decorated by N-doped amorphous carbon shell for advanced LIBs

Co3O4 has been always highlighted as an anode material for lithium ion batteries (LIBs) due to its high theoretical capacity and low cost. However, its practical application is severely limited by the inherent structural pulverization and activation hysteresis during cycling. To overcome such limitation, in this work, a facile route of air-injection assisted soaking in dopamine-tris (DA-tris) solution followed by annealing in Ar atmosphere is successfully approached to decorate N-doped amorphous carbon (a-C) shells on surface of Co3O4 microspheres. The N-doped a-C shells are co-constructed by films and nanoparticles of N-doped a-C. The concentration of DA-tris plays significant roles to the structural nature of the N-doped a-C shells and the phase configuration of the Co3O4 microspheres. As an anode material for LIBs, the Co3O4 microspheres decorated by the N-doped a-C shells exhibit superior reversible capabilities of 1074 mA h g−1 under 500 mA g−1 and 830 mA h g−1 under 1000 mA g−1 after 500 cycles, respectively. Moreover, the rate capacity is impressive and the activation hysteresis is remitted effectively. Such an excellent lithium ions storage performance is firstly ascribed to the rapid activation of Co3O4 promoted by metallic Co, which is reduced by the N-doped a-C shells in situ. Secondly, the N-doped a-C shells effectively protect the structure from cracking and promote the electrochemical reactions of the Co3O4 microspheres. The present work provides an effective way to buffer the activation hysteresis of the transition metal oxides used for advanced LIBs application.

MoS2/C/C nanofiber with double-layer carbon coating for high cycling stability and rate capability in lithium-ion batteries

MoS2 has attracted a lot of interest in the field of lithium-ion storage as an anode material owing to its high capacity and two-dimensional (2D)-layer structure. However, its electrochemical properties, such as rate capability and cycling stability, are usually limited by its low conductivity, volume variation, and polysulfide dissolution during lithiation/delithiation cycling. Here, a designed two-layer carbon-coated MoS2/carbon nanofiber (MoS2/C/C fiber) hybrid electrode with a double-layer carbon coating was achieved by a facile hydrothermal and subsequent electrospinning method. The double carbon layer (inner amorphous carbon and outer carbon fiber) shells could efficiently increase the electron conductivity, prevent the aggregation of MoS2 flakes, and limit the volume change and polysulfide loss during long-term cycling. The as-prepared MoS2/C/C fiber electrode exhibited a high capacity of up to 1,275 mAh/g at a current density of 0.2 A/g, 85.0% first cycle Coulombic efficiency, and significantly increased rate capability and cycling stability. These results demonstrate the potential applications of MoS2/C/C fiber hybrid material for energy storage and may open up a new avenue for improving electrode energy storage performance by fabricating hybrid nanofiber electrode materials with double-layer carbon coatings.

Rational Design and Synthesis of Li3V2(PO4)3/C Nanocomposites As High-Performance Cathodes for Lithium-Ion Batteries

Synthesis of cathode materials with high rates and long cycle life is critical to meet the demands of high-power lithium-ion battery applications. Batteries that can work at extreme low temperature conditions are also urgently needed. Herein, we report the rational design and synthesis of a novel lithium vanadium phosphate/carbon (Li3V2(PO4)3/C) nanocomposite with a thin-layer amorphous carbon shell (∼4 nm) coating and a mesoporous KB carbon matrix. As expected, the Li3V2(PO4)3/C nanocomposite demonstrates an excellent high-rate and long-term cycling performance as well as broad temperature adaptability. Even at a high rate of 16C, a high capacity of 102 mA h g–1 can be achieved. Importantly, the capacity retention is 99% after 1000 cycles and 94% after 2000 cycles when cycled at a rate of 6 C at room temperature in a voltage range of 3–4.3 V. Importantly, this nanocomposite can cycle at −30 °C for 500 cycles with a stable capacity. The excellent rate capability, stable cycling performance, and broad temp...

Facile synthesis and wide-band electromagnetic wave absorption properties of carbon-coated ZnO nanorods

ABSTRACTIn this work, a facile and scalable acetylene decomposition method was employed to synthesize carbon-coated ZnO (ZnO@C) nanorods. The characterization of morphology and structure analysis demonstrate that ZnO nanorod was well coated by an amorphous carbon shell with a thickness of about 20 nm. Comparted with ZnO, ZnO@C exhibit significantly enhanced microwave absorption properties. The effective absorption bandwidth with RL values exceeding –10 dB can reach 5.3 GHz for ZnO@C with a matching thickness of 2.5 mm. The excellent microwave absorption arose from enhanced dielectric loss caused by interfacial polarization, dipole polarization and the formation of conductive network.

Synthesis of Fe5C2@SiO2 core@shell nanoparticles as a potential candidate for biomedical application

A new strategy for water-dispersibility of hydrophobic carbide nanostructures was proposed. In this regard, hydrophobic Fe5C2 nanoparticles (NPs) with size ranging 25–40 nm were synthesized and coated with 12–15 nm silica shell for biomedical applications. X-ray diffraction (XRD) results revealed that Fe5C2 NPs with monoclinic structure were successfully prepared. The crystalline structure of Fe5C2 NPs was remained unchanged and saturation magnetization of core remained nearly constant after coating with silica shell. Moreover, Raman spectroscopy identified D-band of amorphous carbon shells which was also confirmed by transmission electron microscopy (TEM). Finally, Fe5C2@SiO2 core@shell NPs demonstrated no significant cytotoxicity and appropriate heat generating which makes them a promising candidate for magnetic fluid hyperthermia applications.

A high-performance ternary Si composite anode material with crystal graphite core and amorphous carbon shell

Si is a promising anode material for lithium-ion batteries, but suffers from sophisticated engineering structures and complex fabrication processes that pose challenges for commercial application. Herein, a ternary Si/graphite/pyrolytic carbon (SiGC) anode material with a structure of crystal core and amorphous shell using low-cost raw materials is developed. In this ternary SiGC composite, Si component exists as nanoparticles and is spread on the surface of the core graphite flakes while the sucrose-derived pyrolytic carbon further covers the graphite/Si components as the amorphous shell. With this structure, Si together with the graphite contributes to the high specific capacity of this Si ternary material. Also the graphite serves as the supporting and conducting matrix and the amorphous shell carbon could accommodate the volume change effect of Si, reinforces the integrity of the composite architecture, and prevents the graphite and Si from direct exposing to the electrolyte. The optimized ternary SiGC composite displays high reversible specific capacity of 818 mAh g−1 at 0.1 A g−1, initial Coulombic efficiency (CE) over 80%, and excellent cycling stability at 0.5 A g−1 with 83.6% capacity retention (∼610 mAh g−1) after 300 cycles.

MOF-Derived Hierarchical MnO-Doped Fe3O4@C Composite Nanospheres with Enhanced Lithium Storage.

Hierarchically nanostructured binary/multiple transition-metal oxides with electrically conductive coatings are very attractive for lithium-ion batteries owing to their excellent electrochemical properties induced by their unique compositions and microstructures. Herein, hierarchical MnO-doped Fe3O4@C composite nanospheres are prepared by a simple one-step annealing in Ar atmosphere, using Mn-doped Fe-based metal-organic frameworks (Mn-doped MIL-53(Fe)) as precursor. The MnO-doped Fe3O4@C composite particles have a uniform nanosphere structure with a diameter of ∼100 nm, and each nanosphere is composed of clustered primary nanoparticles with an amorphous carbon shell, forming a unique hierarchical nanoarchitecture. The as-prepared hierarchical MnO-doped Fe3O4@C composite nanospheres exhibit markedly enhanced lithium-storage performance, with a large capacity of 1297.5 mAh g-1 after 200 cycles at 200 mA g-1. The cycling performance is clarified through analyzing the galvanostatic discharge/charge voltage profiles and electrochemical impedance spectra at different cycles. The unique microstructures and Mn element doping of the hierarchical MnO-doped Fe3O4@C composite nanospheres lead to their enhanced lithium-storage performance.

Sacrificial-template-free synthesis of core-shell C@Bi2S3 heterostructures for efficient supercapacitor and H2 production applications

Core-shell heterostructures have attracted considerable attention owing to their unique properties and broad range of applications in lithium ion batteries, supercapacitors, and catalysis. Conversely, the effective synthesis of Bi2S3 nanorod core@ amorphous carbon shell heterostructure remains an important challenge. In this study, C@Bi2S3 core-shell heterostructures with enhanced supercapacitor performance were synthesized via sacrificial- template-free one-pot-synthesis method. The highest specific capacities of the C@Bi2S3 core shell was 333.43 F g−1 at a current density of 1 A g−1. Core-shell-structured C@Bi2S3 exhibits 1.86 times higher photocatalytic H2 production than the pristine Bi2S3 under simulated solar light irradiation. This core-shell feature of C@Bi2S3 provides efficient charge separation and transfer owing to the formed heterojunction and a short radial transfer path, thus efficiently diminishing the charge recombination; it also facilitates plenty of active sites for the hydrogen evolution reaction owing to its mesoporous nature. These outcomes will open opportunities for developing low-cost and noble-metal-free efficient electrode materials for water splitting and supercapacitor applications.

Influence of carbon coating with phenolic resin in natural graphite on the microstructures and properties of graphite/copper composites

Carbon-coated graphite/copper composites were fabricated by using electrolytic copper powder and phenolic resin-coated graphite as raw materials via powder metallurgy method. The effect of natural graphite with phenolic resin coating on the microstructures and properties of graphite/copper composites was investigated. The results indicated that the surface of natural graphite was modified by phenolic resin. Smooth amorphous carbon shell with the thickness of 40 nm to 1 μm was formed on the surface of natural graphite after carbonizing at 900 °C for 2 h under hydrogen atmosphere. The sintering of Cu particles was accelerated by phenolic resin coating, and a continuous network-shaped Cu matrix with isolated graphite phase was formed in carbon-coated graphite/copper composites. The electrical conductivity, flexural strength, and tribological properties of graphite/copper composites were improved.

Designed Synthesis and Supercapacitor Electrode of V2O3@C Core‐shell Structured Nanorods with Excellent Pseudo‐capacitance in Na2SO4 Neutral Electrolyte

AbstractV2O3@C core‐shell structured nanorods (VCNR) were successfully prepared using V2O5 nanowires and glucose via a facile hydrothermal route combination of calcination. VCNR comprised of core‐shell structures with V2O3 cores and amorphous carbon shells. Electrochemical properties of VCNR as supercapacitor electrodes were studied in Na2SO4 neutral electrolyte. Results demonstrated that VCNR featured capacitive behavior originating from pseudocapacitance. Specific capacitances of VCNR at 0.5, 1, 2, 5 and 10 A⋅g−1 were achieved to 219, 192, 148, 127 and 119 F⋅g−1, respectively, and VCNR displayed higher specific capacitance than the values of carbon spheres and V2O3 particles. Maximum specific capacitance of VCNR reached 219 F⋅g−1 at 0.5 A⋅g−1 in present study, which was superior to the reported values of V2O3‐based materials and VO2‐based materials. Capacitance retention of VCNR was 100% after 700 cycles and 66% after 1000 cycles. Findings in present study proved that VCNR could be promising candidate as an ideal material for supercapacitors’ electrode.

Low temperature oxidation synthesis of carbon encapsulated Cr2O3 nanocrystals and its lithium storage performance

A highly efficient and convenient strategy is developed for the one-step in-situ synthesis of carbon encapsulated Cr2O3 nanocrystals with core-shell structure (Cr2O3@C). The explosive reaction of chromocene with ammonium persulfate in an autoclave at 200[Formula: see text]C is crucial for the formation of this nanostructure. The Cr2O3 nanocrystals have a diameter of 5 to 20[Formula: see text]nm, which are entirely encapsulated by the amorphous carbon shell. The Cr2O3@C anode can retain a stable reversible capacity of 397[Formula: see text]mAh[Formula: see text]g[Formula: see text] after 50 cycles at a current density of 119[Formula: see text]mA g[Formula: see text].