13 research outputs found

    Highly Functional Bioinspired Fe/N/C Oxygen Reduction Reaction Catalysts: Structure-Regulating Oxygen Sorption

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    Tuna is one of the most rapid and distant swimmers. Its unique gill structure with the porous lamellae promotes fast oxygen exchange that guarantees tunaā€™s high metabolic and athletic demands. Inspired by this specific structure, we designed and fabricated microporous graphene nanoplatelets (GNPs)-based Fe/N/C electrocatalysts for oxygen reduction reaction (ORR). Careful control of GNP structure leads to the increment of microporosity, which influences the O<sub>2</sub> adsorption positively and desorption oppositely, resulting in enhanced O<sub>2</sub> diffusion, while experiencing reduced ORR kinetics. Working in the cathode of proton-exchange membrane fuel cells, the GNP catalysts require a compromise between adsorption/desorption for effective O<sub>2</sub> exchange, and as a result, appropriate microporosity is needed. In this work, the highest power density, 521 mWĀ·cm<sup>ā€“2</sup>, at zero back pressure is achieved

    Ultrathin Carbon-Coated Pt/Carbon Nanotubes: A Highly Durable Electrocatalyst for Oxygen Reduction

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    Nanostructures constituted of Pt nanoparticles (NPs) supported on carbon materials are considered to be among the most active oxygen reduction reaction (ORR) catalysts for fuel cells. However, in practice, the usage of such ORR catalysts is limited by their insufficient durability caused by the low physical and chemical stability of Pt NPs during the reaction. We herein present a strategy to synthesize highly durable and active electrocatalysts composed of Pt NPs supported on carbon nanotubes (CNTs) and covered with an ultrathin layer of graphitic carbon. Such hybrid ORR catalysts were obtained by an interfacial in situ polymer encapsulationā€“graphitization method, where a glucose-containing polymer was grown directly on the surface of Pt/CNTs. The thickness of the carbon-coating layer can be precisely tuned between 0.5 nm and several nanometers by simply programming the polymer growth on Pt/CNTs. The resulting Pt/CNTs@C with a carbon layer thickness of āˆ¼0.8 nm (corresponding to āˆ¼2ā€“3 graphene layers) showed high activity, and excellent durability, with no noticeable activity loss, even after 20ā€Æ000 cycles of accelerated durability tests. These ultrathin carbon coatings not only act as a protective layer to prevent aggregation of Pt NPs but they also lead to better sample dispersion in solvent which are devoid of aggregates, resulting in a better utilization of Pt. We envision that this polymeric nanoencapsulation strategy is a promising technique for the production of highly active and stable ORR catalysts for fuel cells and metalā€“air batteries

    Pt/TiSi<sub><i>x</i></sub>ā€‘NCNT Novel Janus Nanostructure: A New Type of High-Performance Electrocatalyst

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    Novel Janus nanostructured electrocatalyst (Pt/TiSi<sub><i>x</i></sub>-NCNT) was prepared by first sputtering TiSi<sub><i>x</i></sub> on one side of N-doped carbon nanotubes (NCNTs), followed by wet chemical deposition of Pt nanoparticles (NPs) on the other side. Transmission electron microscopy (TEM) studies showed that the Pt NPs are mainly deposited on the NCNT surface where no TiSi<sub><i>x</i></sub> (i.e., between the gaps of TiSi<sub><i>x</i></sub> film). This feature could benefit the increase in the stability of the Pt NP catalyst. Indeed, compared to the state-of-the-art commercial Pt/C catalyst, this novel Pt/TiSi<sub><i>x</i></sub>-NCNT Janus structure showed āˆ¼3 times increase in stability as well as significantly improved CO tolerance. The obvious performance enhancement could be attributed to the better corrosion resistance of TiSi<sub><i>x</i></sub> and NCNTs than the carbon black that is used in the commercial Pt/C catalyst. Pt/TiSi<sub><i>x</i></sub>-NCNT Janus nanostructures open the door for designing new type of high-performance electrocatalyst for fuel cells and other oxygen reduction reaction-related energy devices

    Bioinspired Synthesis of Hierarchical Porous Graphitic Carbon Spheres with Outstanding High-Rate Performance in Lithium-Ion Batteries

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    Inspired by the biomineralization of unicellular diatoms, a biomimetic approach based on template (pluronic F127 micelle cluster)-induced self-assembly of Ī±-cyclodextrin is developed to create hierarchical porous graphitic carbon spheres via hydrothermal treatment followed by pyrolysis. The as-obtained carbon spheres combine the features required for high-power electrode materials in lithium-ion batteries (LIBs), such as high degree of graphitization, large surface area with hierarchically distributed pore sizes as well as doping with heteroatoms, which synergistically contribute to their impressive electrochemical properties. When applied as an anode for LIBs, the carbon spheres exhibit high reversible capacity (ca. 700 mA h g<sup>ā€“1</sup> at 50 mA g<sup>ā€“1</sup>), good cycling stability, and remarkably outstanding high-rate performance (ca. 600, 450, and 290 mA h g<sup>ā€“1</sup> obtained at a current density of 1, 10, and 30 A g<sup>ā€“1</sup>, respectively), which is among the best of present pure carbon materials for LIBs applications. The fabrication process is straightforward and cost-effective, providing a new methodology for the tailored design of carbon materials with enhanced power densities for energy storage applications

    TiSi<sub>2</sub>O<sub>x</sub> Coated Nā€‘Doped Carbon Nanotubes as Pt Catalyst Support for the Oxygen Reduction Reaction in PEMFCs

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    Composite nanostrucutres of TiSi<sub>2</sub>O<sub>x</sub> coated nitrogen-doped carbon nanotubes (NCNTs) were synthesized by a combination of chemical vapor deposition (CVD) and magnetron sputtering processes. The synthesized nanostructures were used as supports for Pt catalyst for oxygen reduction reaction (ORR) in proton exchange memberane fuel cells (PEMFCs). An amorphous layer of TiSi<sub>2</sub>O<sub>x</sub> with controlled thicknesses was sputtered on NCNTs and followed by post-treatment at high temperature (1000 Ā°C, <i>An</i>-TiSi<sub>2</sub>O<sub>x</sub>-NCNTs), inducing TiO<sub>2</sub> nanoparticles of around 5 nm in diameter embedded in the amorphous layer. Further analyses via X-ray absorption spectroscopy of the Ti K edge and Si K edge revealed the Ti atoms were in a TiO<sub>2</sub> rutile environment and the Si atoms were in a SiO<sub>2</sub> environment. Pt nanoparticles with an average diameter of 3 nm were deposited on the composite support, and their electrochemical behaviors toward ORR were studied. It was revealed that, even with lower electrochemical surface area (ECSA), Pt/<i>An</i>-TiSi<sub>2</sub>O<sub>x</sub>-NCNTs showed better catalytic activity toward ORR than Pt/NCNT catalysts. The origin of enhanced activity of Pt/<i>An</i>-TiSi<sub>2</sub>O<sub>x</sub>-NCNTs was examined by high resolution transmission electron microscopy (HRTEM) and the X-ray absorption near edge structure spectra (XANES) of the deposited Pt nanoparticles

    3D Porous Fe/N/C Spherical Nanostructures As High-Performance Electrocatalysts for Oxygen Reduction in Both Alkaline and Acidic Media

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    Exploring inexpensive and high-performance nonprecious metal catalysts (NPMCs) to replace the rare and expensive Pt-based catalyst for the oxygen reduction reaction (ORR) is crucial for future low-temperature fuel cell devices. Herein, we developed a new type of highly efficient 3D porous Fe/N/C electrocatalyst through a simple pyrolysis approach. Our systematic study revealed that the pyrolysis temperature, the surface area, and the Fe content in the catalysts largely affect the ORR performance of the Fe/N/C catalysts, and the optimized parameters have been identified. The optimized Fe/N/C catalyst, with an interconnected hollow and open structure, exhibits one of the highest ORR activity, stability and selectivity in both alkaline and acidic conditions. In 0.1 M KOH, compared to the commercial Pt/C catalyst, the 3D porous Fe/N/C catalyst exhibits āˆ¼6 times better activity (e.g., 1.91 mA cm<sup>ā€“2</sup> for Fe/N/C vs 0.32 mA cm<sup>ā€“2</sup> for Pt/C, at 0.9 V) and excellent stability (e.g., no any decay for Fe/N/C vs 35 mV negative half-wave potential shift for Pt/C, after 10000 cycles test). In 0.5 M H<sub>2</sub>SO<sub>4</sub>, this catalyst also exhibits comparable activity and better stability comparing to Pt/C catalyst. More importantly, in both alkaline and acidic media (RRDE environment), the as-synthesized Fe/N/C catalyst shows much better stability and methanol tolerance than those of the state-of-the-art commercial Pt/C catalyst. All these make the 3D porous Fe/N/C nanostructure an excellent candidate for non-precious-metal ORR catalyst in metalā€“air batteries and fuel cells

    Chemical Structure of Nitrogen-Doped Graphene with Single Platinum Atoms and Atomic Clusters as a Platform for the PEMFC Electrode

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    A platform for producing stabilized Pt atoms and clusters through the combination of an N-doped graphene support and atomic layer deposition (ALD) for the Pt catalysts was investigated using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). It was determined, using imaging and spectroscopy techniques, that a wide range of N-dopant types entered the graphene lattice through covalent bonds without largely damaging its structure. Additionally and most notably, Pt atoms and atomic clusters formed in the absence of nanoparticles. This work provides a new strategy for experimentally producing stable atomic and subnanometer cluster catalysts, which can greatly assist the proton exchange membrane fuel cell (PEMFC) development by producing the ultimate surface area to volume ratio catalyst

    Immunomodulatory Activity of a Novel, Synthetic Beta-glucan (Ī²-glu6) in Murine Macrophages and Human Peripheral Blood Mononuclear Cells

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    <div><p>Natural Ī²-glucans extracted from plants and fungi have been used in clinical therapies since the late 20th century. However, the heterogeneity of natural Ī²-glucans limits their clinical applicability. We have synthesized Ī²-glu6, which is an analog of the lentinan basic unit, Ī²-(1ā†’6)-branched Ī²-(1ā†’3) glucohexaose, that contains an Ī±-(1ā†’3)-linked bond. We have demonstrated the stimulatory effect of this molecule on the immune response, but the mechanisms by which Ī²-glu6 activates innate immunity have not been elucidated. In this study, murine macrophages and human PBMCs were used to evaluate the immunomodulatory effects of Ī²-glu6. We showed that Ī²-glu6 activated ERK and c-Raf phosphorylation but suppressed the AKT signaling pathway in murine macrophages. Additionally, Ī²-glu6 enhanced the secretion of large levels of cytokines and chemokines, including CD54, IL-1Ī±, IL-1Ī², IL-16, IL-17, IL-23, IFN-Ī³, CCL1, CCL3, CCL4, CCL12, CXCL10, tissue inhibitor of metalloproteinase-1 (TIMP-1) and G-CSF in murine macrophages as well as IL-6, CCL2, CCL3, CCL5, CXCL1 and macrophage migration inhibitory factor (MIF) in human PBMCs. In summary, it demonstrates the immunomodulatory activity of Ī²-glu6 in innate immunity. </p> </div

    Ī²-glu6 regulates the production of cytokines and chemokines in human PBMCs.

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    <p>Human PBMCs were incubated with Ī²-glu6 (100 Ī¼g/mL) (lower panels) or PBS (upper panels) in medium for 24 h, and the cell culture supernatants were collected. The status of the production of cytokines and chemokines was detected by Human Cytokine Array Panel A according to the manufacturerā€™s instructions. The images below the panels are enlarged dots from Human Cytokine Array Panel A. </p

    Ī²-glu6 modulates the production of cytokines and chemokines in murine macrophages.

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    <p>Macrophages were incubated with Ī²-glu6 (100 Ī¼g/mL) (lower panels in A and B) or PBS (upper panels in A and B) in medium for 24 h, and the cell culture supernatants were collected. The mouse cytokine array Panel A was used to detect the production of cytokines and chemokines according to the manufacturerā€™s instructions. The densitometric analysis of spot intensity at 5 min (A) and 1 min (B) after exposure was analyzed by Quantity One software (C, D). Data represent one of three representative experiments.</p
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