Graphitic Carbon Layers Research Articles

Effect of Graphite Matrix on Property of Silicon/Carbon Composite Anode Material for Lithium-Ion Battery

Nano-silicon carbon coated and combined with different graphite matrixes was synthesized by ball milling，and spray dying-pyrolysis methods. The physical properties of Si/C composites were detected by X-ray diffraction（XRD），scanning electron microscopy（SEM），and all composites were completely coated by a carbon layer. Their electrochemical performances were studied by galvanostatic cycle and electrochemical impedance spectra. These analyses show that the discharge specific capacity of composited anode based on expanded graphite exhibits the best comprehensive electrochemical performance such as cycle stability and initial charge/discharge efficiency among various composites，owing to the co-effect of expanded graphite and amorphous carbon layer as the structural stabilizer and conductive additives to prevent the volume change and enhance the electronic conductivity of the composites. The discharge specific capacity is 700.9 mAhg-1 at a current density of 100mAg-1，initial charge/discharge efficiency is 77.4%. After 30 cycles，the capacity retention rate can reach 87.7%.

C@TiO2 nanocomposites with impressive electrochemical performances as anode material for lithium-ion batteries

C@TiO2 nanocomposites as lithium-ion battery anode material have been synthesized through a typical solvothermal process. A series of characterization methods, such as scanning electron microscopy, field emission transmission electron microscopy, and X-ray photoelectron spectroscopy, has been used to determine the microstructures and chemical compositions of the C@TiO2 nanocomposites. The electrochemical performances were investigated by the LAND battery testing system and electrochemical workstation. Results showed that the size of the C@TiO2 nanoparticles is approximately 21–55 nm and the titanium dioxide (TiO2) nanoparticles are wrapped by the carbon layer containing an amount of graphitic carbon, of which the carbon source originated from the esterification reaction in the presence of KCl. An amount of graphitic carbon layers significantly ameliorated the electrical conductivity of the C@TiO2 nanocomposites and alleviated the volume expansion of TiO2 during the discharge–charge cycles, resulting in the C@TiO2 nanocomposites having a satisfactory reversible charge capacity of 237 mA h g−1 after 100 long cycles at the current density of 0.1 A g−1 and an impressive rate capability with the charge capacity of 176.5 mA h g−1 even at the high current density of 1.6 A g−1.

Unusual Formation of CoO@C “Dandelions” Derived from 2D Kagóme MOLs for Efficient Lithium Storage

AbstractDespite great breakthroughs, the search for anode materials with high performance for lithium‐ion batteries (LIBs) remains challenging. Hence, engineering advantageous structures via effective routes can bring new possibilities to the development of the LIB field. Herein, the precise synthesis of three‐dimensional (3D) hybrids of ultrathin carbon‐wrapped CoO (CoO@C) dandelions is reported by the pyrolysis of two‐dimensional (2D) Kagóme metal–organic layers (MOLs) at 400 °C under an Ar atmosphere. Due to the special coordination structure of the paternal MOLs, the resulting CoO nanowires show a small diameter of 5–10 nm and are uniformly confined within the ultrathin carbon layer. Based on the time‐dependent pyrolysis experiments, a crystal transformation mechanism of in situ self‐templated‐recrystallization‐self‐assembly accompanied by phase and morphology changes is first presented to reveal the formation of the 3D dandelion‐like spheres with assembly of nanowire arrays from a 2D Kagóme MOL. By virtue of structural and compositional features, including a 3D array structure, the small size of the primary ultrathin nanowires, and a uniform ultrathin graphitic carbon layer, these unique CoO@C dandelions display high specific capacity, good rate capability, and excellent cycling stability. Importantly, this approach can be extended to accurately synthesize other desired composite structures.

Unzipping of Single-Walled Carbon Nanotube for the Development of Electrocatalytically Active Hybrid Catalyst of Graphitic Carbon and Pd Nanoparticles.

We demonstrate a new approach for the unzipping of single-walled carbon nanotube (SWCNT) in an aqueous solution using the transition metal complex PdCl42– as a sacrificial chemical scissor and the growth of graphitic-carbon-coated Pd nanoparticles for the electrocatalytic oxidation of formic acid. The chemical unzipping and the growth of Pd nanoparticles involve the spontaneous electron transfer between SWCNT and the metal complex in an aqueous solution at room temperature. The redox potential for SWCNT and PdCl42– favors the spontaneous electron transfer reaction. The metal complex, in situ generated Pd nanoparticle, and oxygen play vital role in the oxidative unzipping of SWCNT. The Pd nanoparticles have an average size of 11 nm and are coated with the graphitic carbon layer of unzipped SWCNT (UzCNT-Pd). The Pd nanoparticle of the UzCNT-Pd hybrid material has a large electrochemically active surface area of 2.14 cm2. The hybrid material exhibits excellent electrocatalytic activity toward the oxidation of formic acid. The area and mass specific activity are significantly higher than those of the traditional carbon-supported Pd nanoparticle. The synergistic effect of graphitic carbon and the metal nanoparticles controls the catalytic activity. The confinement of Pd particles inside the graphitic carbon enhances the overall performance of the catalyst.

Enhanced H2 evolution from photocatalytic cellulose conversion based on graphitic carbon layers on TiO2/NiOx

An enhanced photoreforming of biomass was achieved by loading a graphitic carbon layer on TiO2/NiOx nanoparticles.

Graphitic carbon-wrapped NiO embedded three dimensional nitrogen doped aligned carbon nanotube arrays with long cycle life for lithium ion batteries.

In this work, a three-dimensional nitrogen doped aligned carbon nanotube array (NACNTs)@NiO@graphitic carbon composite was fabricated by an effective strategy involving nebulized ethanol assisted infiltration, In this structure, the NiO nanoparticles were wrapped by graphitic carbon layers and NiO@graphitic carbon core–shell nanoparticles adhered strictly to the surface of NACNTs to form a highly ordered 3D structure. When this composite was used as an anode for lithium ion batteries, the well-ordered pore of its NACNTs can facilitate the electrolyte to penetrate and improve electronic conductivity. At the same time, the graphitic layers can promote the stability of a solid electrolyte interface film. Therefore, the NACNTs@NiO@graphitic carbon composite containing 68.1 wt% NiO delivers excellent capacity retention of 91.6% after 200 cycles at 0.2C.

Robust FeCo nanoparticles embedded in a N-doped porous carbon framework for high oxygen conversion catalytic activity in alkaline and acidic media

FeCo alloy nanoparticles were nucleated onto graphitic carbon layers through the pyrolysis of polydopamine (PDA) sub-micrometer spheres to form a highly active electrocatalytic system that exhibits excellent oxygen conversion catalytic activity in both alkaline and acidic media.

Target construction of ultrathin graphitic carbon encapsulated FeS hierarchical microspheres featuring superior low-temperature lithium/sodium storage properties

Hierarchical FeS spheres coated with ultrathin graphitic carbon layer exhibit superior low-temperature Li/Na-storage properties.

Tubular structure TiO2/C/TiO2 hybrid derived from the waste of the fluff of chinar tree

Tubular structure TiO2/C/TiO2 hybrids were successfully fabricated via impregnation-calcination method. A castoff of tubular structure FCT (the fluff of the chinar tree) was employed as template and carbon source, and economical TiCl4 was purchased as titanium source. In particular, the outer tube wall of the TiO2/C/TiO2 hybrid was constructed with interlaced and curly nanofibers. Nevertheless, the inner tube wall was assembled with spheroid-likely TiO2 nanoparticles. In addition, the graphitic carbon layer was formed between TiO2 nanofibers and nanoparticles. The FCT played a vital role in inducing and assembling the hierarchical tube structure of the TiO2/C/TiO2 hybrid. Furthermore, the design of the hydrolysis reaction during the preparation process also made contributions on building the unique structure. The hydrolysis reaction was taken place by blowing atmosphere, which could control the hydrolysis reaction at an appropriate reaction rate. Furthermore, the graphitic C layer in the TiO2/C/TiO2 hybrid could accelerate the migration and separation of the photogenerated electron during the reaction process. At appropriate carbon content, the TiO2/C/TiO2 could degrade 99% tetracycline hydrochloride (TH) under simulated sunlight irradiation within 30 min.

A Novel Metal–Organic Framework Route to Embed Co Nanoparticles into Multi-Walled Carbon Nanotubes for Effective Oxygen Reduction in Alkaline Media

Metal–organic framework (MOF) materials can be used as precursors to prepare non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR). Herein, we prepared a novel MOF material (denoted as Co-bpdc) and then combined it with multi-walled carbon nanotubes (MWCNTs) to form Co-bpdc/MWCNTs composites. After calcination, the cobalt ions from Co-bpdc were converted into Co nanoparticles, which were distributed in the graphite carbon layers and MWCNTs to form Co-bpdc/MWCNTs. The prepared catalysts were characterized by TEM (Transmission electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), BET (Brunauer–Emmett–Teller), and Raman spectroscopy. The electrocatalytic activity was measured by using rotating disk electrode (RDE) voltammetry. The catalysts showed higher ORR catalytic activity than the commercial Pt/C catalyst in alkaline solution. Co-bpdc/MWCNTs-100 showed the highest ORR catalytic activity, with an initial reduction potential and half-wave potential reaching 0.99 V and 0.92 V, respectively. The prepared catalysts also showed superior stability and followed the 4-electron pathway ORR process in alkaline solution.

Magnetic porous Fe3O4/carbon octahedra derived from iron-based metal-organic framework as heterogeneous Fenton-like catalyst

The synthesis of effective and recyclable Fenton-like catalyst is still a key factor for advanced oxidation processes. Herein, magnetic porous Fe3O4/carbon octahedra were constructed by a two-step controlled calcination of iron-based metal organic framework. The porous octahedra were assembled by interpenetrated Fe3O4 nanoparticles coated with graphitic carbon layer, offering abundant mesoporous channels for the solid-liquid contact. Moreover, the oxygen-containing functional groups on the surface of graphitic carbon endow the catalysts with hydrophilic nature and well-dispersion into water. The porous Fe3O4/carbon octahedra show efficiently heterogeneous Fenton-like reactions for decomposing the organic dye methylene blue (MB) with the help of H2O2, and nearly 100% removal efficiency within 60 min. Furthermore, the magnetic catalyst retains the activity after ten cycles and can be easily separated by external magnetic field, indicating the long-term catalytic durability and recyclability. The good Fenton-like catalytic performance of the as-synthesized Fe3O4/carbon octahedra is ascribed to the unique mesoporous structure derived from MOF-framework, as well as the sacrificial role and stabilizing effect of graphitic carbon layer. This work provides a facile strategy for the controllable synthesis of integrated porous octahedral structure with graphitic carbon layer, and thereby the catalyst holds significant potential for wastewater treatment.

Facile green synthesis of 3D porous glucose-based carbon aerogels for high-performance supercapacitors

As new-generation carbon materials, carbon aerogels (CAs) offer opportunities in supercapacitor application owing to their excellent properties. Herein, we present a facile, green synthesis of CAs using glucose as carbon source, one of the most important monosaccharide and abundant occurrence in the world, which can be readily available by plants photosynthesis and hydrolysis of disaccharide as well as polysaccharide. To improve the surface area and tailor the pore texture of the CAs, glucose as precursor was treated with an optional activating agent sodium hydroxide to obtain activated CA at 850 °C. SEM, TEM, XRD, XPS and Raman techniques reveal that the as-prepared CA-850 is of graphitized carbon layers and bimodal mesopores, possessing the high specific surface area of 2492.6 m2 g−1 determined by BET characterization. Impressively, as electrode material for supercapacitors, CA-850 exhibits a high specific capacitance of 299 F g−1, energy density of 41.52 Wh kg−1 as well as long-term cycling stability with 99% of the capacitance retention over 1000 cycles. This work will pave the way on the potential use of natural-abundance carbon source for green and mass production of carbon aerogels in supercapacitor applications.

Facile synthesis of N-doped carbon layer encapsulated Fe2N as an efficient catalyst for oxygen reduction reaction

Development of non-noble metal catalysts for oxygen reduction reaction (ORR) is of significant importance for the commercialization of fuel cells and metal-air batteries. Here we provide an efficient method to produce core-shell structured FeNC catalyst via a facile in-situ chelating strategy by introducing ammonia iron citrate during the polymerization process of dopamine. The influence of calcination temperature and atmosphere on the physicochemical property and the activity of the catalyst are systematically evaluated. By calcination at 800 °C with NH3 atmosphere, Fe2N encapsulated with N doped carbon layers shows excellent activity with close onset and half wave potential (E1/2) while better methanol crossover resistance than the Pt/C catalyst. The high activity could be due to the synergistic effect of Fe2N with the N-doped graphitic carbon layers and the mesoporous structure facilitating the mass transfer. Moreover, the simple synthesis process could provide a versatile routine to construct core-shell structured metal-NC composite for a wild catalytic application.

Coaxial Carbon/MnO2 Hollow Nanofibers as Sulfur Hosts for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have recently attracted a large amount of attention as promising candidates for next-generation high-power energy storage devices because of their high theoretical capacity and energy density. However, the shuttle effect of polysulfides and poor conductivity of sulfur are still vital issues that constrain their specific capacity and cyclic stability. Here, we design coaxial MnO2 -graphitic carbon hollow nanofibers as sulfur hosts for high-performance lithium-sulfur batteries. The hollow C/MnO2 coaxial nanofibers are synthesized via electrospinning and carbonization of the carbon nanofibers (CNFs), followed by an in situ redox reaction to grow MnO2 nanosheets on the surface of CNFs. The inner graphitic carbon layer not only maintains intimate contact with sulfur and outer MnO2 shell to significantly increase the overall electrical conductivity but also acts as a protective layer to prevent dissolution of polysulfides. The outer MnO2 nanosheets restrain the shuttle effect greatly through chemisorption and redox reaction. Therefore, the robust S@C/MnO2 nanofiber cathode delivers an extraordinary rate capability and excellent cycling stability with a capacity decay rate of 0.044 and 0.051 % per cycle after 1000 cycles at 1.0 C and 2.0 C, respectively. Our present work brings forward a new facile and efficient strategy for the functionalization of inorganic metal oxide on graphitic carbons as sulfur hosts for high performance Li-S batteries.

Structural and electrochemical studies of tungsten carbide/carbon composites for hydrogen evolution

In an attempt to develop high-activity and earth-abundant electrocatalysts for hydrogen evolution reaction (HER), tungsten carbide/carbon composites are prepared readily via annealing a polyaniline/tungstic acid hybrid precursor under vacuum condition. By simply changing the mass ratio of polyaniline and tungstic acid, a variety of products with different structures can be obtained. The varying mass ratio causes the change of crystalline sizes of carbides, existential state of carbon and carbides/carbon content of final products. The composite produced at mass ratio of 1/1 shows the worst HER activity among all the catalysts due to its minimal content of active ingredients and the lowest degree of graphitization. In the case of the mass ratio of 1/3, an excess of tungsten source results in increasing graphitic carbon layers and decreasing electrochemical active surface area, which leads to the limited charge transfer process and less exposed active sites for HER. The composite fabricated at the mass ratio of 1/2 presents favorable electrocatalytic activity and excellent stability in both acidic and alkaline solutions, indicating its great potential to serve as a HER catalyst for water splitting.

In situ observation of phase transformation in iron carbide nanocrystals

This paper reports on the in situ observation of phase transformation in an iron carbide nanocrystal encapsulated in a graphitic shell by means of high resolution transmission electron microscopy (HR-TEM). A Fe7C3 nanocrystal in orthorhombic (o-Fe7C3) structure with carbon graphitic cover is captured at the initial time of the experiment. Under the projection of a high-energy electron beam (200kV), the graphitic carbon layer evaporates gradually and structural changes in orthorhombic (o-Fe7C3) crystal manifests simultaneously. Specifically, changes in crystal direction happens first and then the crystal structure switching between orthorhombic and hexagonal (h-Fe7C3) follows. Details analysis and conclusive evidences of the phase structure and transformation are presented and discussed. The appearance of o-Fe7C3 structure is captured for about 92min over 100min of observation, indicating the preference of o-Fe7C3 form over h-Fe7C3 form.

Ultrathin Carbon-Coated Pt/Carbon Nanotubes: A Highly Durable Electrocatalyst for Oxygen Reduction

Nanostructures constituted of Pt nanoparticles (NPs) supported on carbon materials are considered to be among the most active oxygen reduction reaction (ORR) catalysts for fuel cells. However, in practice, the usage of such ORR catalysts is limited by their insufficient durability caused by the low physical and chemical stability of Pt NPs during the reaction. We herein present a strategy to synthesize highly durable and active electrocatalysts composed of Pt NPs supported on carbon nanotubes (CNTs) and covered with an ultrathin layer of graphitic carbon. Such hybrid ORR catalysts were obtained by an interfacial in situ polymer encapsulation–graphitization method, where a glucose-containing polymer was grown directly on the surface of Pt/CNTs. The thickness of the carbon-coating layer can be precisely tuned between 0.5 nm and several nanometers by simply programming the polymer growth on Pt/CNTs. The resulting Pt/CNTs@C with a carbon layer thickness of ∼0.8 nm (corresponding to ∼2–3 graphene layers) showe...

Non-noble metal catalyst on carbon ribbon for fuel cell cathode

A non-noble metal Fe/N/C catalyst is prepared by pyrolyzing the ball-milled mixture of graphitized carbon ribbon, iron precursor, and nitrogen precursor in ammonia. The Fe/N/C catalyst shows high ORR activity in alkaline solution, together with much improved stability compared with Pt/C catalyst. In the catalyst, FeN particles are covered by graphitic carbon layers. The activity is proposed to originate from the FeN and Fe/N/C sites. The stability is explained by the protecting effect of the carbon layers surrounding the FeN particles. The ORR mechanism on the Fe/N/C catalyst is proposed to be similar with Pt/C catalyst based on the Tafel plots. The Fe/N/C catalyst shows great potential in ORR in alkaline solution, while the performance in acid still needs improvement.

Nanodiamonds in sp2/sp3 configuration for radical to nonradical oxidation: Core-shell layer dependence

Nanocarbons in molecular configurations of sp2/sp3 present versatile structural and electronic properties, exhibiting a complexity in the structure-activity chemistry. In this work, we employed detonation nanodiamonds constructed as a characteristic core/shell structure in the sp2/sp3 configuration to demonstrate the intrinsic correlation between the structure and catalysis. Annealed detonation nanodiamonds were found to show a superb activity for catalytic peroxymonosulfate activation and organic oxidation. A synergistic effect of charge transport was discovered at the interface to construct an electron-enriched carbon surface that further promoted the catalytic activity evidenced by the density functional theory (DFT) calculations. More importantly, both experimental results and theoretical predictions revealed that the catalytic oxidation via peroxymonosulfate (PMS) activation was intimately dependent on the proportion of graphitic carbon layer in the sp2/sp3 configurations. The increase of graphitic layers on nanodiamonds would alter the PMS activation from a radical-based reaction to a nonradical pathway for catalytic oxidation. The novel catalytic properties of tunable oxidative potentials from carbocatalysis may simulate fascinating prospects for environmental catalysis and organic synthesis.

Facile synthesis of NiS anchored carbon nanofibers for high-performance supercapacitors

Transition metal sulfide compounds with carbon materials are promising for high-performance supercapacitors. Carbon nanofibers (CNFs) wrapped with NiS nanoparticles were herein obtained through electrospinning and calcination. NiS nanoparticles in composite nanofibers are covered by a layer of graphitic carbon, which not only increase the conductivity but also provide active regions for nanoparticle growth to prevent aggregation. The CNFs-NiS electrode has high specific capacity of 177.1mAhg−1 at 1Ag−1 (0.41mAhcm−2 at a current density of 2.3mAcm−2) and long-term cycling stability, with 88.7% capacitance retention after 5000 cycles. The excellent electrochemical activity may be attributed to the accessible specific surface, unique porous structure of CNFs and high specific capacitance of NiS. In addition, the asymmetric supercapacitor has an enhanced volumetric energy density of 13.32 mWh cm−3 at a volumetric power density of 180mWcm−3 and high cycling stability, with 89.5% capacitance retention after 5000 cycles. It also successfully lights up a light-emitting diode. The CNFs-NiS composite has significant potential applications in supercapacitor.