Browsing by Author "Fei, Huilong"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Atomic cobalt on nitrogen-doped graphene for hydrogen generation
    (Nature Publishing Group, 2015) Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M. Josefina; Ye, Gonglan; Kim, Nam Dong; Samuel, Errol L.G.; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M.; Chen, Dongliang; Tour, James M.
    Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Synthesis and design of nanostructured materials for electrochemical energy storage and conversion
    (2015-09-18) Fei, Huilong; Tour, James M.; Ajayan, Pulickel M; Martí, Angel A
    The finite nature of fossil fuels and environmental problems caused by traditional energy sources call for renewable and sustainable energy strategies, including energy storage and conversion. The synthesis and design of nanostructured materials play an important role in the advances of alternative energy systems and devices. Lithium-ion batteries (LIBs) are one of the most important energy storage devices that have been commercially used in daily life. LIBs consist of one positive electrode and one negative electrode, which are separated by a lithium-ion conducting electrolyte. The development of LIBs with high energy density and power density mainly relies on the use of advanced nanomaterials in the two electrodes. For energy conversion, water splitting and the fuel cell are two important clean and renewable techniques to interconvert electrical energy and chemical energy. Water splitting, by applying external electrical energy, generates hydrogen gas on one electrode (hydrogen evolution reaction, HER) and oxygen gas on the other electrode (oxygen evolution reaction, OER). By this process, electrical energy is converted to chemical energy stored in hydrogen fuels. Fuel cells, on the other hand, convert chemical energy into electrical energy by combining hydrogen and oxygen gas into water. The two half-reactions involved are the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR). Due to the presence of kinetic barriers, all of the above four reactions need electrocatalysts to improve their efficiency. This thesis begins with an introduction of energy storage system of LIBs and energy conversion systems of fuel cells and water splitting in Chapter 1. Chapter 2 discusses three different nanomateirals with core-shelled structures and their applications in LIBs and HER. The graphitic carbon shell is demonstrated to improve the cycling stability and rate capability of Fe2O3 as an anode and LiFePO4 as a cathode. In addition, the graphitic carbon shell with a nitrogen dopant can interact with cobalt nanoparticles at the core to give high HER catalytic activity. Chapter 3 describes two different heteroatom-doped nanocarbons for ORR application. One is B, N-doped graphene nanoribbon and the other is B, N-doped graphene quantum dots/graphene hybrid. The edge abundance in the nanoribbon and quantum dots is demonstrated to have a critical role in enhancing the catalytic activity. In Chapter 4, various porous films, including MoS2, WS2, WC, NiCoOx and CoP/CoPO4, are used as binder-free electrodes for water splitting applications. The porous structure is created by the use of anodization technique. Benefited from the high porosity and high surface area, these films show excellent catalytic activity for HER and/or OER. Chapter 5 describes a new type of electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and exceptionally active in aqueous media. A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centers coordinated to nitrogen.