Guoqing Ning

Nanographene-Constructed Carbon Nanofibers Grown on Graphene Sheets by Chemical Vapor Deposition: High-Performance Anode Materials for Lithium Ion Batteries

We report on the fabrication of 3D carbonaceous material composed of 1D carbon nanofibers (CNF) grown on 2D graphene sheets (GNS) via a CVD approach in a fluidized bed reactor. Nanographene-constructed carbon nanofibers contain many cavities, open tips, and graphene platelets with edges exposed, providing more extra space for Li(+) storage. More interestingly, nanochannels consisting of graphene platelets arrange almost perpendicularly to the fiber axis, which is favorable for lithium ion diffusion from different orientations. In addition, 3D interconnected architectures facilitate the collection and transport of electrons during the cycling process. As a result, the CNF/GNS hybrid material shows high reversible capacity (667 mAh/g), high-rate performance, and cycling stability, which is superior to those of pure graphene, natural graphite, and carbon nanotubes. The simple CVD approach offers a new pathway for large-scale production of novel hybrid carbon materials for energy storage.

Phosphorus and nitrogen dual-doped few-layered porous graphene: a high-performance anode material for lithium-ion batteries.

Few-layered graphene networks composed of phosphorus and nitrogen dual-doped porous graphene (PNG) are synthesized via a MgO-templated chemical vapor deposition (CVD) using (NH4)3PO4 as N and P source. P and N atoms have been substitutionally doped in graphene networks since the doping takes place at the same time with the graphene growth in the CVD process. Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks. The doping levels of P and N measured by X-ray photoelectron spectroscopy are 0.6 and 2.6 at %, respectively. As anodes for Li ion batteries (LIBs), the PNG electrode exhibits high reversible capacity (2250 mA h g(-1) at the current density of 50 mA g(-1)), excellent rate capability (750 mA h g(-1) at 1000 mA g(-1)), and satisfactory cycling stability (no capacity decay after 1500 cycles), showing much enhanced electrode performance as compared to the undoped few-layered porous graphene. Our results show that the PNG is a promising candidate for anode materials in high-rate LIBs.

100 mm Long, Semiconducting Triple‐Walled Carbon Nanotubes

[*] Prof. W.-Z. Qian, Prof. F. Wei, Q. Wen, J. Q. Nie, Prof. Y. Wang, L. Hu, Dr. Q. Zhang, J. Q. Huang Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University Beijing 100084 (PR China) Fax: þ86-10-6277-2051 E-mail: qianwz@mail.tsinghua.edu.cn; wf-dce@tsinghua.edu.cn Prof. A. Y. Cao Department of Advanced Materials and Nanotechnology, College of Engineering, Peking University Beijing 100871 (PR China)

Enhanced Electrode Performance of Fe2O3 Nanoparticle-Decorated Nanomesh Graphene As Anodes for Lithium-Ion Batteries

Nanostructured Fe2O3-nanomesh graphene (NMG) composites containing ∼3 nm Fe2O3 nanoparticles (NPs) uniformly distributed in the nanopores of NMG are synthesized by an adsorption-precipitation process. As anodes for Li ion batteries (LIBs), the 10%Fe2O3-NMG composite exhibits an upward trend in the capacity and delivers a reversible specific capacity of 1567 mA h g(-1) after 50 cycles at 150 mA g(-1), and 883 mA h g(-1) after 100 cycles at 1000 mA g(-1), much higher than the corresponding values for the NMG electrode. The significant capacity enhancement of the 10%Fe-NMG composite is attributed to the positive synergistic effect between NMG and Fe2O3 NPs due to the catalytic activity of Fe2O3 NPs for decomposition of the solid electrolyte interface film. Our results indicate that decoration of ultrasmall Fe2O3 NPs can significantly change the surface condition of graphene. This synthesis strategy is simple, effective, and broadly applicable for constructing other electrode materials for LIBs.

Chemical vapor deposition derived flexible graphene paper and its application as high performance anodes for lithium rechargeable batteries

We present a novel approach to fabricate flexible graphene papers using chemical vapor deposition (CVD) derived graphene. Expanded vermiculite was used as a layered template in the CVD process to produce bulk materials containing graphene sheets of the order of hundreds of microns at a gram scale. Meshes or carbon nanotubes can be introduced into the graphene sheets by template pretreating. Owing to the large sheet size, the as-obtained graphene sheets were easily fabricated into flexible graphene papers with low surface density and good conductivity, which exhibited greatly enhanced reversible capacity (1350 mA h g−1 at 50 mA g−1) and cycling performance as anodes for lithium rechargeable batteries as compared to the graphene papers fabricated using reduced graphene oxide.

High density Co3O4 nanoparticles confined in a porous graphene nanomesh network driven by an electrochemical process: ultra-high capacity and rate performance for lithium ion batteries

Here, we report a novel Co3O4–graphene hybrid electrode material with high density Co3O4 nanoparticles (NPs) in a size range of 2–3 nm confined in a few-layered porous graphene nanomesh (PGN) framework driven by an electrochemical process. Raman spectra indicate that Co species preferentially anchor on the defective sites of the PGN, which results in markedly reduced irreversible Li storage and therefore significantly enhanced coulombic efficiency. The ultra-small Co3O4 NPs provide a large surface area and a short solid-state diffusion length, which is propitious to achieving a high Li ion capacity at high rate. Also, the few-layered graphene network with high electronic conductivity not only permits easy access to the high surface area of the Co3O4 NPs for the electrolyte ions, but also serves as a reservoir for high capacity Li storage. As a result, the Co3O4–PGN composite layers deliver an ultra-high capacity (1543 mA h g−1 at 150 mA g−1) and excellent rate capability (1075 mA h g−1 at 1000 mA g−1) with good cycling stability.

Facile and rapid synthesis of highly crumpled graphene sheets as high-performance electrodes for supercapacitors

Highly crumpled graphene sheets (HCGSs) have been prepared by a facile and rapid route through freezing a chemically reduced graphene oxide aqueous suspension with liquid nitrogen. The porous and highly crumpled graphene structure with a large surface area and pore volume facilitates fast ionic transport within the electrode while preserving excellent electrical conductivity and thus endows HCGSs with excellent electrochemical properties. As the electrodes for supercapacitors, the HCGSs exhibit high specific capacitance (259 F g−1), excellent rate capability and cycling stability (93% retention after 5000 cycles).

Enhancing the Li Storage Capacity and Initial Coulombic Efficiency for Porous Carbons by Sulfur Doping

Here, we report a new approach to synthesizing S-doped porous carbons and achieving both a high capacity and a high Coulombic efficiency in the first cycle for carbon nanostructures as anodes for Li ion batteries. S-doped porous carbons (S-PCs) were synthesized by carbonization of pitch using magnesium sulfate whiskers as both templates and S source, and a S doping up to 10.1 atom % (corresponding to 22.5 wt %) was obtained via a S doping reaction. Removal of functional groups or highly active C atoms during the S doping has led to formation of much thinner solid-electrolyte interface layer and hence significantly enhanced the Coulombic efficiency in the first cycle from 39.6% (for the undoped porous carbon) to 81.0%. The Li storage capacity of the S-PCs is up to 1781 mA h g(-1) at the current density of 50 mA g(-1), more than doubling that of the undoped porous carbon. Due to the enhanced conductivity, the hierarchically porous structure and the excellent stability, the S-PC anodes exhibit excellent rate capability and reliable cycling stability. Our results indicate that S doping can efficiently promote the Li storage capacity and reduce the irreversible Li combination for carbon nanostructures.

Plasma synthesis of nitrogen-doped porous graphene supporting Pd nanoparticles as a new catalyst for C–C coupling reactions

We report an environmentally-friendly approach to the synthesis of hybrids based on porous graphene and metal nanoparticles. The nitrogen-doped porous graphene (N-PG) and Pd nanoparticles decorated N-PG (Pd/N-PG) was synthesized by a plasma method. The N-PG was characterized by X-ray photoelectron spectroscopy and Raman spectroscopy, and the results clearly indicate that the amount of nitrogen doping was 6.65 wt%. The synthesized Pd/N-PG hybrid materials were confirmed by transmission electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy mapping. The hybrid material based on Pd/N-PG as a new catalyst was applied in Suzuki reaction. This catalyst offers a number of advantages such as high stability, easy removal from the reaction mixture and reusability with minimal loss of activity, showing better performance than the well-known commercial Pd/C catalyst.

Oxygen-assisted synthesis of SWNTs from methane decomposition

Single-walled carbon nanotubes (SWNTs) were prepared from CH4 decomposition by an Fe–Mo/MgO catalyst. A small amount of O2 (about 0.04%–0.20%) was introduced into the process to tailor the activity of the catalyst. By comparing the effect of adding O2 at different stages of SWNT growth, the online BET and gas chromatography detection indicated the effective regeneration of the catalyst at the early stage of SWNT growth. In addition, TEM, Raman and TGA characterizations revealed that the effect of O2 was to remove the amorphous carbon and other carbon impurities to increase the purity and yield of the SWNTs. Furthermore, detailed characterization of the TGA and Raman spectra indicated that a slight increase in the O2 concentration was effective for preparing SWNTs with a narrower diameter distribution without decreasing their total yield. The mechanism was attributed to the cycle of oxidation and reduction of iron nanocrystallites on the MgO lattice, in the presence of O2. This in situ oxidation, regeneration and purification method with O2 is useful for the controlled mass production of SWNTs at low cost.