Browsing by Author "Yacaman, Miguel Jose"

Now showing 1 - 5 of 5
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    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.
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    High-Performance Hydrogen Evolution from MoS2(1–x)P x Solid Solution
    (Wiley, 2016) Ye, Ruquan; Vicente, Paz Del Angel; Liu, Yuanyue; Arellano-Jimenez, Josefina; Peng, Zhiwei; Wang, Tuo; Li, Yilun; Yakobson, Boris I.; Wei, Su-Huai; Yacaman, Miguel Jose; Tour, James M.; Smalley Institute for Nanoscale Science and Technology
    A MoS2(1-x)Px solid solution (x = 0 to 1) is formed by thermally annealing mixtures of MoS2 and red phosphorus. The effective and stable electrocatalyst for hydrogen evolution in acidic solution holds promise for replacing scarce and expensive platinum that is used in present catalyst systems. The high performance originates from the increased surface area and roughness of the solid solution.
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    Laser-induced porous graphene films from commercial polymers
    (Nature Publishing Group, 2014) Lin, Jian; Peng, Zhiwei; Liu, Yuanyue; Ruiz-Zepeda, Francisco; Ye, Ruquan; Samuel, Errol L.G.; Yacaman, Miguel Jose; Yakobson, Boris I.; Tour, James M.; Smalley Institute for Nanoscale Science and Technology
    The cost effective synthesis and patterning of carbon nanomaterials is a challenge in electronic and energy storage devices. Here we report a one-step, scalable approach for producing and patterning porous graphene films with three-dimensional networks from commercial polymer films using a CO2 infrared laser. The sp3-carbon atoms are photothermally converted to sp2-carbon atoms by pulsed laser irradiation. The resulting laser-induced graphene (LIG) exhibits high electrical conductivity. The LIG can be readily patterned to interdigitated electrodes for in-plane microsupercapacitors with specific capacitances of >4 mF cm-2 and power densities of ~9 mW cm-2. Theoretical calculations partially suggest that enhanced capacitance may result from LIG's unusual ultra-polycrystalline lattice of pentagon-heptagon structures. Combined with the advantage of one-step processing of LIG in air from commercial polymer sheets, which would allow the employment of a roll-to-roll manufacturing process, this technique provides a rapid route to polymer-written electronic and energy storage devices.
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    Rebar Graphene
    (American Chemical Society, 2014) Yan, Zheng; Peng, Zhiwei; Casillas, Gilberto; Lin, Jian; Xiang, Changsheng; Zhou, Haiqing; Yang, Yang; Ruan, Gedeng; Raji, Abdul-Rahman O.; Samuel, Errol L.G.; Hauge, Robert H.; Yacaman, Miguel Jose; Tour, James M.; Richard E. Smalley Institute for Nanoscale Science and Technology
    As the cylindrical sp2-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π–π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry.
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    Three-Dimensional Nanoporous Fe2O3/Fe3C-Graphene Heterogeneous Thin Films for Lithium-Ion Batteries
    (American Chemical Society, 2014) Yang, Yang; Fan, Xiujun; Casillas, Gilberto; Peng, Zhiwei; Ruan, Gedeng; Wang, Gunuk; Yacaman, Miguel Jose; Tour, James M.; Smalley Institute for Nanoscale Science and Technology
    Three-dimensional self-organized nanoporous thin films integrated into a heterogeneous Fe2O3/Fe3C-graphene structure were fabricated using chemical vapor deposition. Few-layer graphene coated on the nanoporous thin film was used as a conductive passivation layer, and Fe3C was introduced to improve capacity retention and stability of the nanoporous layer. A possible interfacial lithium storage effect was anticipated to provide additional charge storage in the electrode. These nanoporous layers, when used as an anode in lithium-ion batteries, deliver greatly enhanced cyclability and rate capacity compared with pristine Fe2O3: a specific capacity of 356 μAh cm–2 μm–1 (3560 mAh cm–3 or ∼1118 mAh g–1) obtained at a discharge current density of 50 μA cm–2 (∼0.17 C) with 88% retention after 100 cycles and 165 μAh cm–2 μm–1(1650 mAh cm–3 or ∼518 mAh g–1) obtained at a discharge current density of 1000 μA cm–2(∼6.6 C) for 1000 cycles were achieved. Meanwhile an energy density of 294 μWh cm–2 μm–1(2.94 Wh cm–3 or ∼924 Wh kg–1) and power density of 584 μW cm–2 μm–1 (5.84 W cm–3 or ∼1834 W kg–1) were also obtained, which may make these thin film anodes promising as a power supply for micro- or even nanosized portable electronic devices.