Browsing by Author "Li, Lei"

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    Carbon Based Nanomaterials for Electrochemical Energy Storage Applications
    (2015-04-22) Li, Lei; Tour, James M.; Ajayan, Pulickel; Martí, Angel A.
    Ever-growing energy needs, limited energy resources, and the need to decrease soaring greenhouse gas emissions have brought about an urgent demand on the pursuit of energy alternatives, includ¬ing both renewable energy sources and sustainable storage technologies. Electrochemical capacitors (ECs) and reversible lithium ion batteries (LIBs) are two promising energy storage technologies that are well positioned to satisfy this need in a green energy future. However, their large-scale deployment has been significantly hindered by several major technological barriers, such as high cost, intrinsically poor safety characteristic, limited life, and low energy density and/or power density. One promising solution is to develop advanced electrodes materials for these devices. In this thesis, various nanomaterials and nanostructures have been developed to improve the electrochemical performance of ECs and LIBs. My thesis begins with the introduction of energy storage systems of ECs and LIBs in Chapter 1. Chapter 2 to 4 discuss the synthesis of nitrogen-doped carbonized cotton, brush-like structured nanocomposites of polyaniline nanorods-graphene nanoribbons, laser induced graphene-MnO2, and laser induced graphene-polyaniline and their applications in ECs. All of them demonstrated excellent performance in energy storage, showing high potential applications as electrode materials in ECs. Chapter 5 to 8 discuss a graphene wrapping strategy designed to synthesize graphene-metal oxide/sulfide-graphene nanoribbons, including graphene-MnO2-GNRs, graphene-NiO-rGONRs, graphene-Fe3O4-GNRs, and graphene-FeS-GNRs. This sandwich structure mitigated the pulverization of these anode materials from their conversion reactions during extended cycling, leading to a large improvement in the cycling stability of anodes in LIBs. To address the volume change of SnO2-based anode materials, a facile and cost-effective approach was developed to prepare a thin layer SnO2 on reduced graphene oxide nanoribbons. Chapter 9 discusses how this nanocomposite demonstrated excellent cycling stability with high capacity. For LIBs cathode materials, a hierarchical polyaniline matrix was designed to reduce the dissolution of the intermediate lithium polysulfide into the electrolyte as shown in Chapter 10. This material showed great improvement in cycling stability with high capacity.
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    Cobalt Nanoparticles Embedded in Nitrogen-Doped Carbon for the Hydrogen Evolution Reaction
    (American Chemical Society, 2015) Fei, Huilong; Yang, Yang; Peng, Zhiwei; Ruan, Gedeng; Zhong, Qifeng; Li, Lei; Samuel, Errol L.G.; Tour, James M.; Smalley Institute for Nanoscale Science and Technology
    There is great interest in renewable and sustainable energy research to develop low-cost, highly efficient, and stable electrocatalysts as alternatives to replace Pt-based catalysts for the hydrogen evolution reaction (HER). Though nanoparticles encapsulated in carbon shells have been widely used to improve the electrode performances in energy storage devices (e.g., lithium ion batteries), they have attracted less attention in energy-related electrocatalysis. Here we report the synthesis of nitrogen-enriched core–shell structured cobalt–carbon nanoparticles dispersed on graphene sheets and we investigate their HER performances in both acidic and basic media. These catalysts exhibit excellent durability and HER activities with onset overpotentials as low as ∼70 mV in both acidic (0.5 M H2SO4) and alkaline (0.1 M NaOH) electrolytes, and the overpotentials needed to deliver 10 mA cm–2 are determined to be 265 mV in acid and 337 mV in base, further demonstrating their potential to replace Pt-based catalysts. Control experiments reveal that the active sites for HER might come from the synergistic effects between the cobalt nanoparticles and nitrogen-doped carbon.
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    Graphene-carbon nanotube hybrid materials and use as electrodes
    (2016-09-27) Tour, James M.; Zhu, Yu; Li, Lei; Yan, Zheng; Lin, Jian; Rice University; United States Patent and Trademark Office
    Provided are methods of making graphene-carbon nanotube hybrid materials. Such methods generally include: (1) associating a graphene film with a substrate; (2) applying a catalyst and a carbon source to the graphene film; and (3) growing carbon nanotubes on the graphene film. The grown carbon nanotubes become covalently linked to the graphene film through carbon-carbon bonds that are located at one or more junctions between the carbon nanotubes and the graphene film. In addition, the grown carbon nanotubes are in ohmic contact with the graphene film through the carbon-carbon bonds at the one or more junctions. The one or more junctions may include seven-membered carbon rings. Also provided are the formed graphene-carbon nanotube hybrid materials.