R-3 Repository :: Browsing by Author "Yang, Yang"

Browsing by Author "Yang, Yang"

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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.
Computational study of structural and mechanical properties of two-dimensional nanomaterials and their derivatives
(2016-11-10) Yang, Yang; Yakobson, Boris I.
Two-dimensional Nanomaterials have been demonstrated to show superior properties and promising potential for applications. In this work, we investigate the structures and mechanical properties of several two-dimensional nanomaterials and their derivatives using various computational simulation methods, including boron, carbon nanotube, graphene, and boron nitride. The first part of the thesis focuses on the boron nanostructures. We report a comprehensive first-principles study of the structural and chemical properties of the recently discovered B40 cage. We also discover here a preferred structure of two-dimensional boron using the cluster expansion method and find it to be most table on reactive Cu and Ni. In the second part, an extensive analysis of the graphene grain boundaries is conducted and it is revealed that the sinuous grain boundaries based on dislocation theory and first-principles calculations can be energetically optimal once the global grain boundary line cannot bisect the tilt angle. In addition, we demonstrate here a contrasting behavior for grain boundaries in hybrid two-dimensional materials, which tend to be non-bisector and obey a universal law to optimally match the heterogeneous grains. In the last part, we propose an approach for determining the Gaussian bending modulus of graphene by utilizing carbon torus, whose topology enables its bending energy to be extracted from the coupled in-plane strain energy. Furthermore, we report a unique method to locally determine the mechanical response of individual covalent junctions between carbon nanotubes. Targeted synthesis of desired junction geometries can therefore provide a “structural alphabet” for construction of macroscopic carbon nanotube networks with tunable mechanical response.
Nanoporous metal-oxide memory
(2017-11-28) Tour, James M.; Wang, Gunuk; Yang, Yang; Rice University; United States Patent and Trademark Office
A nanoporous (NP) memory may include a non-porous layer and a nanoporous layer sandwiched between the bottom and top electrodes. The memory may be free of diodes, selectors, and/or transistors that may be necessary in other memories to mitigate crosstalk. The nanoporous material of the nanoporous layer may be a metal oxide, metal chalcogenide, or a combination thereof. Further, the memory may lack any additional components. Further, the memory may be free from requiring an electroformation process to allow switching between ON/OFF states.
Ni(OH)2 nanoporous films as electrodes
(2019-03-19) Tour, James M.; Yang, Yang; Rice University; United States Patent and Trademark Office
The present disclosure pertains to electrodes that include a nickel-based material and at least one porous region with a plurality of nickel hydroxide moieties on a surface of the nickel-based material. The nickel-based material may be a nickel foil in the form of a film. The porous region of the electrode may be directly associated with the surface of the nickel-based material. The nickel hydroxide moieties may be in crystalline form and embedded with the porous region. The electrodes of the present disclosure may be a component of an energy storage device, such as a capacitor. Additional embodiments of the present disclosure pertain to methods of fabricating the electrodes by anodizing a nickel-based material to form at least one porous region on a surface of the nickel-based material; and hydrothermally treating the porous region to form nickel hydroxide moieties associated with the porous region.
Porous SiOx materials for improvement in SiOx switching device performances
(2018-06-12) Tour, James M.; Wang, Gunuk; Yang, Yang; Ji, Yongsung; Rice University; United States Patent and Trademark Office
A porous memory device, such as a memory or a switch, may provide a top and bottom electrodes with a memory material layer (e.g. SiOx) positioned between the electrodes. The memory material layer may provide a nanoporous structure. In some embodiments, the nanoporous structure may be formed electrochemically, such as from anodic etching. Electroformation of a filament through the memory material layer may occur internally through the layer rather than at an edge at extremely low electro-forming voltages. The porous memory device may also provide multi-bit storage, high on-off ratios, long high-temperature lifetime, excellent cycling endurance, fast switching, and lower power consumption.
Production and use of flexible conductive films and inorganic layers in electronic devices
(2020-10-20) Tour, James M.; Yang, Yang; Ruan, Gedeng; Rice University; United States Patent and Trademark Office
Embodiments of the present disclosure pertain to methods of making conductive films by associating an inorganic composition with an insulating substrate, and forming a porous inorganic layer from the inorganic composition on the insulating substrate. The inorganic layer may include a nanoporous metal layer, such as nickel fluoride. The methods of the present disclosure may also include a step of incorporating the conductive films into an electronic device. The methods of the present disclosure may also include a step of associating the conductive films with a solid electrolyte prior to its incorporation into an electronic device. The methods of the present disclosure may also include a step of separating the inorganic layer from the conductive film to form a freestanding inorganic layer. Further embodiments of the present disclosure pertain to the conductive films and freestanding inorganic layers.
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.
Super-elasticity of three-dimensionally cross-linked graphene materials all the way to deep cryogenic temperatures
(AAAS, 2019) Zhao, Kai; Zhang, Tengfei; Chang, Huicong; Yang, Yang; Xiao, Peishuang; Zhang, Hongtao; Li, Chenxi; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.; Chen, Yongsheng
Until now, materials with high elasticity at deep cryogenic temperatures have not been observed. Previous reports indicated that graphene and carbon nanotube–based porous materials can exhibit reversible mechano-elastic behavior from liquid nitrogen temperature up to nearly a thousand degrees Celsius. Here, we report wide temperature–invariant large-strain super-elastic behavior in three-dimensionally cross-linked graphene materials that persists even to a liquid helium temperature of 4 K, a property not previously observed for any other material. To understand the mechanical properties of these graphene materials, we show by in situ experiments and modeling results that these remarkable properties are the synergetic results of the unique architecture and intrinsic elastic/flexibility properties of individual graphene sheets and the covalent junctions between the sheets that persist even at harsh temperatures. These results suggest possible applications for such materials at extremely low temperature environments such as those in outer space.
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.
Three-Dimensional Networked Nanoporous Ta2O5–x Memory System for Ultrahigh Density Storage
(American Chemical Society, 2015) Wang, Gunuk; Lee, Jae-Hwang; Yang, Yang; Ruan, Gedeng; Kim, Nam Dong; Ji, Yongsung; Tour, James M.; Richard E. Smalley Institute of Nanoscale Science and Technology
Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta2O5-x structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear I-V switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and vice versa, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field.

Browsing by Author "Yang, Yang"

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