Temperature Chemical Vapor Deposition Research Articles

3D Graphene Films Enable Simultaneously High Sensitivity and Large Stretchability for Strain Sensors

AbstractIntegration of 2D membranes into 3D macroscopic structures is essential to overcome the intrinsically low stretchability of graphene for the applications in flexible and wearable electronics. Herein, the synthesis of 3D graphene films (3D‐GFs) using chemical vapor deposition (CVD) is reported, in which a porous copper foil (PCF) is chosen as a template in the atmospheric‐pressure CVD preparation. When the 3D‐GF prepared at 1000 °C (noted as 3D‐GF‐1000) is transferred onto a polydimethylsiloxane (PDMS) membrane, the obtained 3D‐GF‐1000/PDMS hybrid film shows an electrical conductivity of 11.6 S cm−1 with good flexibility, indicated by small relative resistance changes (ΔR/R0) of 2.67 and 0.36 under a tensile strain of 50% and a bending radius of 1.6 mm, respectively. When the CVD temperature is reduced to 900 °C (generating a sample noted as 3D‐GF‐900), the 3D‐GF‐900/PDMS hybrid film exhibits an excellent strain‐sensing performance with a workable strain range of up to 187% and simultaneously a gauge factor of up to ≈1500. The 3D‐GF‐900/PDMS also shows a remarkable durability in resistance in repeated 5000 stretching‐releasing cycles. Kinetics studies show that the response of ΔR/R0 upon strain is related to the graphitization and conductivity of 3D‐GF which are sensitive to the CVD preparation temperature.

Perovskite oxide/carbon nanotube hybrid bifunctional electrocatalysts for overall water splitting

Perovskite oxides recently have emerged as efficient electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline solution. However, most perovskites have poor electrical conductivity at room temperature. Here, to simultaneously enhance the activity and stability towards both OER and HER, we in situ-introduce carbon nanotubes (CNTs) on the perovskite (SrTi0.1Fe0.85Ni0.05O3–δ) surface via a simple chemical vapor deposition (CVD) method. First, we evaluate the influence of the CVD temperature on the growth of the CNTs. The optimized electrocatalyst obtained at a temperature of 700 °C (denoted as STFN/CNT-700) exhibits higher OER and HER activities than the bare perovskite, which is reflected by the current density, onset potential, overpotential and Tafel slope, and thus we construct a homemade electrolyzer for overall water splitting using STFN/CNT-700 as both an anode and cathode in alkaline electrolyte. Lastly, the increased performances are mainly attributed to the improved charge transfer process, increased surface area, and synergistic effect between the perovskite phase and the CNTs phase. This work may be inspiring to adjust the performance of metal oxides and prepare highly efficient and low-cost composite electrocatalysts.

Localized growth of carbon nanotubes via lithographic fabrication of metallic deposits.

We report on the fabrication of carbon nanotubes (CNTs) at predefined positions and controlled morphology, for example, as individual nanotubes or as CNT forests. Electron beam induced deposition (EBID) with subsequent autocatalytic growth (AG) was applied to lithographically produce catalytically active seeds for the localized growth of CNTs via chemical vapor deposition (CVD). With the precursor Fe(CO)5 we were able to fabricate clean iron deposits via EBID and AG. After the proof-of-principle that these Fe deposits indeed act as seeds for the growth of CNTs, the influence of significant EBID/AG parameters on the deposit shape and finally the yield and morphology of the grown CNTs was investigated in detail. Based on these results, the parameters could be optimized such that EBID point matrixes (6 × 6) were fabricated on a silica surface whereby at each predefined site only one CNT was produced. Furthermore, the localized fabrication of CNT forests was targeted and successfully achieved on an Al2O3 layer on a silicon sample. A peculiar lift-up of the Fe seed structures as “flakes” was observed and the mechanism was discussed. Finally, a proof-of-principle was presented showing that EBID deposits from the precursor Co(CO)3NO are also very effective catalysts for the CNT growth. Even though the metal content (Co) of the latter is reduced in comparison to the Fe deposits, effective CNT growth was observed for the Co-containing deposits at lower CVD temperatures than for the corresponding Fe deposits.

Pt supported on ordered microporous carbon as highly active catalyst for catalytic hydrodeiodination of iodinated X-ray contrast media

In this study, Pt catalysts supported on zeolite templated carbon (Pt/ZTC) were prepared by in-situ chemical vapor deposition using Pt exchanged Y zeolite as the template. For comparison, Pt catalysts supported on zeolite templated carbon (ZTC) and commercial activated carbon (AC) were prepared using the impregnation method. The liquid phase catalytic hydrodeiodination of two iodinated X-ray contrast media (ICM, i.e., diatrizoate and iopamidol) was investigated on the catalysts. The catalysts were characterized by X-ray diffraction, N2 adsorption–desorption isotherms, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy and zeta-potential measurement. The results showed that Pt/ZTC catalysts prepared by in-situ chemical vapor deposition (CVD) under varied reaction conditions were good replicas of Y zeolite in structure. Compared with the catalysts prepared by the impregnation method, Pt/ZTC had a higher Pt dispersion and more homogeneous Pt distribution. Increasing CVD temperature resulted in Pt particle growth in Pt/ZTC. The catalytic hydrodeiodination of diatrizoate and iopamidol proceeded via a sequential deiodination pathway, and followed the Langmuir-Hinshelwood model, reflecting that the conversion of adsorbed ICM was the rate-controlling step. Additionally, more effective conversion of iopamidol was observed than that of diatrizoate on Pt/ZTC. Furthermore, Pt/ZTC prepared at higher CVD temperature exhibited lower catalytic activities for the hydrodeiodination of diatrizoate and iopamidol. Solution pH markedly impacted the catalytic ICM conversion, and enhanced hydrodeiodination was observed with the increase of pH. As for catalyst reuse, Pt/ZTC remained about 80% of initial activity after 4 reuse cycles, exhibiting much higher stability than the catalyst prepared by the impregnation method. The present findings highlighted the Pt/ZTC catalysts prepared by in-situ CVD as highly active and stable catalysts for the removal of halogenated organic pollutants by catalytic hydrogenation.

Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to 50–100 °C. Our results represent a significant progress in reducing graphene synthesis temperature and understanding its mechanism.

Carbon nanotubes radially anchored on carbon fibers formed by polyacrylonitrile

We investigated a hybrid nanostructure comprised of carbon nanotubes (CNTs) directly grown on polyacrylonitrile-based carbon fibers (PAN-CFs) for three-dimensional energy materials. The optimum growth conditions, such as catalyst loading time in electroless deposition and growth temperature in chemical vapor deposition were identified. The thorn bush-like structures of the multi-walled CNTs on CFs were evaluated by field emission transmission electron microscope and field emission scanning electron microscope. Raman spectra and attenuated total reflectance Fourier transform infrared spectroscopy were used to analyze the crystal and chemical structures of CNTs on CFs. Base on the results from four-point probe measurement, the sheet resistance dropped from 40Ω/sq for PAN-CFs to less than 10Ω/sq for CNTs-grown PAN-CFs. The obtained CNTs/PAN-CFs revealed the specific surface area of 64.4m2/g with a pore volume of 0.18cm3/g. Moreover, a sulfur electrode with the CNTs/PAN-CFs current collector exhibited higher electrochemical performance than that of the electrode with planar aluminum current collector.

Growth Dynamics of Single-Layer Graphene on Epitaxial Cu Surfaces

The growth of single-layer graphene on Cu metal by chemical vapor deposition (CVD) is a versatile method for synthesizing high-quality, large-area graphene. It is known that high CVD temperatures, close to the Cu melting temperature (1083 °C), are effective for the growth of large graphene domains, but the growth dynamics of graphene over the high-temperature Cu surface is not clearly understood. We investigated the surface dynamics of the single-layer graphene growth by using heteroepitaxial Cu(111) and Cu(100) films. At relatively lower temperatures, 900–1030 °C, the as-grown graphene showed the identical orientation with the underlying Cu(111) lattice. However, when the graphene was grown above 1040 °C, a new stable configuration of graphene with 3.4° rotation became dominant. This slight rotation is interpreted by the enhanced graphene–Cu interaction due to the formation of long-range ordered structure. Further increase of the CVD temperature resulted in graphene which is rotated with wide angle distr...

Quantum Chemical Simulation of Carbon Nanotube Nucleation on Al2O3 Catalysts via CH4 Chemical Vapor Deposition.

We present quantum chemical simulations demonstrating how single-walled carbon nanotubes (SWCNTs) form, or "nucleate", on the surface of Al2O3 nanoparticles during chemical vapor deposition (CVD) using CH4. SWCNT nucleation proceeds via the formation of extended polyyne chains that only interact with the catalyst surface at one or both ends. Consequently, SWCNT nucleation is not a surface-mediated process. We demonstrate that this unusual nucleation sequence is due to two factors. First, the π interaction between graphitic carbon and Al2O3 is extremely weak, such that graphitic carbon is expected to desorb at typical CVD temperatures. Second, hydrogen present at the catalyst surface actively passivates dangling carbon bonds, preventing a surface-mediated nucleation mechanism. The simulations reveal hydrogen's reactive chemical pathways during SWCNT nucleation and that the manner in which SWCNTs form on Al2O3 is fundamentally different from that observed using "traditional" transition metal catalysts.

Controlling Grain Size and Continuous Layer Growth in Two-Dimensional MoS<sub>2</sub> Films for Nanoelectronic Device Application

We report that control over the grain size and lateral growth of monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film, yielding a uniform large-area monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film, can be achieved by submitting the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surfaces of the substrates to oxygen plasma treatment and modulating substrate temperature in chemical vapor deposition (CVD) process. Scanning electron microscopy and atomic force microscopy images and Raman spectra revealed that the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> lateral growth could be controlled by the surface treatment conditions and process temperatures. Moreover, the obtained monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films showed excellent scalable uniformity covering a centimeter-scale SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si substrates, which was confirmed with Raman and photoluminescence mapping studies. Transmission electron microscopy measurements revealed that the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film of the monolayer was largely single crystalline in nature. Back-gate field effect transistors based on a CVD-grown uniform monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film showed a good current on/off ratio of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and a field effect mobility of 7.23 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s. Our new approach to growing MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films is anticipated to advance studies of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or other transition metal dichalcogenide material growth mechanisms and to facilitate the mass production of uniform high-quality MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films for the commercialization of a variety of applications.

Research Progress in Diamond Cutting Tool Materials and Preparation Technology

High temperature and high pressure (HTHP) and chemical vapor deposition (CVD) are two important methods of preparing diamond. This article briefly introduced the kinds of diamond cutting tool materials and the two technologies of synthesizing diamond. And in the end, the developing trends of diamond cutting tool materials and the preparation technologies were forecasted.

A CVD route for the preparation of templated and activated carbons for gas storage applications using zeolitic imidazolate frameworks (ZIFs) as template

Templated porous carbon materials were prepared via a chemical vapour deposition (CVD) method using zeolitic imidazolate framework (ZIF) templates impregnated with furfuryl alcohol (FA). ZIF-templated carbons prepared at CVD temperature of between 700 and 850°C are highly microporous and exhibit surface area in the 350–970m2/g range (with up to 96% from micropores) and pore volume of between 0.28 and 0.66cm3/g. After chemical activation (with KOH) the surface area and pore volume increase significantly to as high as 2400m2/g and 1.6cm3/g, respectively. This increase in porosity is accompanied by a broadening of the micropore size distribution and formation of larger pores, although the activated carbons remain predominantly microporous. The increase in textural properties after activation is reflected in enhancement of hydrogen storage capacity; activated ZIF-templated carbons prepared at CVD temperature of 700 and 850°C achieve high hydrogen uptake (at 20bar and −196°C) of 6.2 and 5.1wt%, respectively. Activation also improves the CO2 uptake; the CO2 storage capacity (at 25°C and 1bar under flow conditions) increases from ca. 1.8mmol/g for ZIF-templated carbons to as high as 2.4mmol/g after activation. The best porosity and gas uptake properties were achieved by a sample whose preparation required temperatures no higher than 700°C. Our findings show that incorporation of a CVD step not only simplifies the templating process by reducing the temperature required but also removes the need for a washing step prior to activation.

Growth of silicon/carbon microrods on graphite microspheres as improved anodes for lithium-ion batteries

We report a facile chemical vapor deposition (CVD) method to grow silicon/carbon (Si/C) microrods on the surface of commercial graphite microspheres (GMs) to prepare Si/C/GM composite materials as Li-ion battery anodes. Dimethyldichlorosilane and toluene were used as Si and C precursors, respectively. The CVD temperature and time, as well as the mechanism of materials growth were investigated. The samples were characterized by using X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. It was found that the obtained Si/C/GM composites with an urchin-like morphology are composed of Si particles, amorphous carbon, and graphite. The CVD conditions have a significant impact on the morphology and electrochemical performance of the composite materials. The composite prepared under the optimum CVD conditions, namely at 900 degrees C for 5 h, displayed the best anode properties with a specific capacity of 562.0 mA h g(-1) at a current density of 50 mA g(-1), much higher than that of GMs (361.0 mA h g(-1)), and a good cycling performance (i. e., a reversible capacity of 590.5 mA h g(-1) after 50 cycles). The improved electrochemical performance is attributed to the incorporation of Si, together with the formation of a Si/C microrod network, which connects the GMs and buffers the volume change of Si during lithium ion insertion/extraction. The work provides a simple and low-cost route to enhance the performance of commercial graphite anode materials for Li-ion batteries.

A facile low-temperature growth of large-scale uniform two-end-open Ge nanotubes with hierarchical branches

We present a facile approach for the controlled fabrication of well-aligned arrays of Ge nanotubes (GeNTs) with tunable sizes and hierarchical branches inside the pre-designed nanochannels of porous anodic aluminum oxide (AAO) templates. Metal salts, such as nickel nitrate, silver nitrate, cobalt nitrate and copper sulphate are pre-decorated on the inner wall of the AAO nanochannels as catalyst precursors, where they are reduced into nickel, silver, cobalt, and copper clusters, and provide nucleation sites for subsequent Ge growth. GeNTs are formed by confining the Ge growth on the inner walls of the porous AAO template in a low temperature (300–380 °C) chemical vapor deposition process. The as-grown GeNTs have open ends with tailored wall thickness (between 10 and 26 nm), diameter (between 80 and 248 nm), and geometrical configuration (e.g., linear, Y-branching, multi-branching, and various multiple-generation branching). The GeNT formation process is sensitive to the choice of the catalyst precursor. Nickel salts lead to a uniform wall thickness of GeNTs compared with copper, silver, and cobalt salts. And GeNTs grown with copper salts as catalysts are polycrystalline, while nickel, silver and cobalt salts assisted GeNTs are amorphous though they can crystallize via post-annealing at 400 °C in Ar/H2 atmosphere. These open-end hollow nanotubes with tunable sizes and hierarchical branches can serve as nanoscale containers or pipes to deliver fluids and molecular species, and are excellent building blocks for the construction of large-scale nanofluidic systems.

Nanostructuring Ultra-thin Co Films to Active Catalyst Particles for Vertically Aligned Single-walled CNT Growth

In the field of material synthesis using chemically-derived technique, nanostructuring metal catalyst particles towards high quality production of carbon nanotubes (CNTs) has been very attractive. In this work, cobalt (Co) which used as catalyst for vertical growth of CNTs were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Aluminum (Al) films (20 nm) were thermally-oxidized to form aluminum oxide (Al-O) to support 0.5 nm Co catalyst during CNT growth. In growing CNTs by using chemical vapor deposition (CVD) technique, the role and characters of all involving materials are crucial to the growth result. From the Co/Al-O substrate and at 650°C of CVD temperature, 33-μm thick of vertically aligned single-walled CNT (VA-SWCNT) forest has been grown. TEM particle analysis revealed that the Co particles have an average of 3.50 nm experimentally and in principle favored the growth of highly demanded VA-SWCNTs. The as-prepared Co particles are suggested chemically active for the CNT growth. In addition, XPS analysis confirmed the surface chemical state of Co particles prior to the VA-SWCNT growth using ethanol based CVD system.

Production of Carbon Nanotubes over Fe-FSM-16 Catalytic Material: Effect of Acetylene Flow Rate and CVD Temperature

In this article, a high-yield synthesis of high-quality carbon nanotubes (CNTs) using Fe catalysts trapped within channels of Folded Sheet Mesoporous Materials, FSM-16, by chemical vapor deposition (CVD), using acetylene as a hydrocarbon source, is reported. The effect of reaction temperature and acetylene flow rate on the formation of CNTs was investigated. It was found that the yield, diameter and quality of CNTs synthesized strongly depend on reaction temperature during CVD. The resulting materials were characterized by scanning electron microscopy, Raman spectroscopy and thermogravimetric analysis. Our research found that carbon deposition, diameter and quality of the CNTs strongly depend on CVD temperature. However, the acetylene flow rate did not have any significant effect on diameter distribution. Raman measurement indicated that the synthesized products were multi-walled carbon nanotubes (MWCNTs). High-resolution transmission electron micrographs of samples reveal the multi-layer sidewalls of individual MWCNTs with a diameter of 40 nm, in which hollow and tubal structures were observed.

The use of aliphatic alcohol chain length to control the nitrogen type and content in nitrogen doped carbon nanotubes

Nitrogen doped carbon nanotubes (N-CNTs) were synthesized using acetonitrile/alcohol mixtures as the nitrogen, carbon and oxygen sources using the chemical vapor deposition (CVD) method. XPS analysis of the CNTs produced from an acetonitrile/ethanol mixture using different CVD temperatures (700–1000°C), revealed that nitrogen incorporation in N-CNTs decreased with an increase in CVD temperature and that the type of nitrogen species incorporated also varied. Molecular nitrogen and a low content of pyridinic nitrogen was obtained in N-CNTs grown at 700 and 800°C, while quaternary nitrogen was noted in all N-CNTs grown. Use of 20% acetonitrile/ROH (R=CH3, C2H5, C4H9, C5H11, C7H15 and C8H17) mixtures allowed the C/O ratio to be changed whilst the N content in the precursor mixture was kept constant. The N content in the N-CNTs grown at 850°C increased with the alcohol chain length and also controlled the nitrogen species incorporated, an effect related to the oxygen content of the reactant mixtures.

A CFD study on a vertical chemical vapor deposition reactor for growing carbon nanofibers

A computational fluid dynamic (CFD) study has been carried out to simulate velocity, temperature, and concentration profiles in a vertical chemical vapor deposition (CVD) reactor used for growing carbon nanofibers (CNFs). CNFs were grown over activated carbon fibers (ACFs) wrapped over an especially designed perforated tube which was vertically mounted in the reactor. The numerical model analysis incorporated the conservation equations of momentum, energy, and species. Natural convection effects on the heat-transfer and the exothermic heat generation due to the decomposition of benzene were included. The model simulation results revealed that approximately uniform temperature and concentration profiles existed in the ACF-packed bed. In addition, multiple combinations of the heating length and the wall temperature of the reactor were possible to achieve the prescribed CVD temperature. Under the simulated CVD conditions, the present model predicted an average carbon deposition rate of 5×10−13kg/m2s, which corresponded to the yield of ∼0.005g of CNFs per g of ACFs. The simulation results of this study are important for the optimization of the CVD operating conditions to achieve a high and uniform CNF growth in the vertical reactor.

Deposition Rate, Texture, and Mechanical Properties of SiC Coatings Produced by Chemical Vapor Deposition at Different Temperatures

Silicon carbide (SiC) coatings were produced on carbon/carbon (C/C) composites substrates using chemical vapor deposition (CVD) at different temperatures (1100°C, 1200°C, and 1300°C). The deposition rate was found to increase with deposition temperature from 1100°C to 1200°C. From 1200°C to 1300°C, the deposition rate decreased. SiC coating produced at 1200°C exhibited a strong (111) texture compared with the coatings produced at other temperatures. Both hardness and Young's modulus were also found to be higher in the coating produced at 1200°C. The variation in mechanical properties with the increase in temperature from 1100°C to 1300°C showed a direct correlation with the change in deposition rate and (111) texture. Microstructure analysis shows that the change in CVD temperature leads to the change in grain size, crystallinity, and density of stacking faults of SiC coatings, which appears to have no significant effect on mechanical properties of SiC compared with the texture observed in SiC coating. For the coating deposited at 1200°C, both the hardness and Young's modulus increased gradually from the substrate/coating interface to the top surface. The nonuniformity of mechanical properties along the cross‐section of the coating is attributed to the nonuniform microstructure.

Ordered Mesoporous Platinum@Graphitic Carbon Embedded Nanophase as a Highly Active, Stable, and Methanol-Tolerant Oxygen Reduction Electrocatalyst

Highly ordered mesoporous platinum@graphitic carbon (Pt@GC) composites with well-graphitized carbon frameworks and uniformly dispersed Pt nanoparticles embedded within the carbon pore walls have been rationally designed and synthesized. In this facile method, ordered mesoporous silica impregnated with a variable amount of Pt precursor is adopted as the hard template, followed by carbon deposition through a chemical vapor deposition (CVD) process with methane as a carbon precursor. During the CVD process, in situ reduction of Pt precursor, deposition of carbon, and graphitization can be integrated into a single step. The mesostructure, porosity and Pt content in the final mesoporous Pt@GC composites can be conveniently adjusted over a wide range by controlling the initial loading amount of Pt precursor and the CVD temperature and duration. The integration of high surface area, regular mesopores, graphitic nature of the carbon walls as well as highly dispersed and spatially embedded Pt nanoparticles in the mesoporous Pt@GC composites make them excellent as highly active, extremely stable, and methanol-tolerant electrocatalysts toward the oxygen reduction reaction (ORR). A systematic study by comparing the ORR performance among several carbon supported Pt electrocatalysts suggests the overwhelmingly better performance of the mesoporous Pt@GC composites. The structural, textural, and framework properties of the mesoporous Pt@GC composites are extensively studied and strongly related to their excellent ORR performance. These materials are highly promising for fuel cell applications and the synthesis method is quite applicable for constructing mesoporous graphitized carbon materials with various embedded nanophases.

On the nucleation of graphene by chemical vapor deposition

We demonstrate that homogeneous single-layer graphene can be grown by simply annealing crystalline Cu(111)/c-plane sapphire (α-Al2O3) at 900 and 1000 °C without additional carbon supply. The resulting graphene film shows a high carrier mobility of 1210 cm2 V−1 s−1. However, the annealing at a lower temperature of 800 °C gives an amorphous carbon film. Further investigations indicate that graphitization of amorphous carbon and/or adsorbed carbon atoms during chemical vapour deposition (CVD) is not simply a consequence of carbon supersaturation, it is also affected by CVD temperature, and crystallographic plane of the underlying metal, which are essentially correlated to the energy barrier of nucleation. Our results provide the direct experimental evidence to elucidate the influencing factors of graphitization of amorphous carbon, and contribute fundamental insight into the nucleation and growth of graphene to improve its quality for applications.