13 research outputs found
Highly Functional Bioinspired Fe/N/C Oxygen Reduction Reaction Catalysts: Structure-Regulating Oxygen Sorption
Tuna
is one of the most rapid and distant swimmers. Its unique
gill structure with the porous lamellae promotes fast oxygen exchange
that guarantees tunaās 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>ā2</sup>, at zero back pressure is achieved
Ultrathin Carbon-Coated Pt/Carbon Nanotubes: A Highly Durable Electrocatalyst for Oxygen Reduction
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 encapsulationāgraphitization 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 ā¼0.8 nm (corresponding to ā¼2ā3
graphene layers) showed high activity, and excellent durability, with
no noticeable activity loss, even after 20āÆ000 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 metalāair
batteries
Pt/TiSi<sub><i>x</i></sub>āNCNT Novel Janus Nanostructure: A New Type of High-Performance Electrocatalyst
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 ā¼3 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
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>ā1</sup> at 50 mA g<sup>ā1</sup>), good cycling stability,
and remarkably outstanding high-rate performance (ca. 600, 450, and
290 mA h g<sup>ā1</sup> obtained at a current density of 1,
10, and 30 A g<sup>ā1</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 NāDoped Carbon Nanotubes as Pt Catalyst Support for the Oxygen Reduction Reaction in PEMFCs
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
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 ā¼6 times better activity (e.g., 1.91
mA cm<sup>ā2</sup> for Fe/N/C vs 0.32 mA cm<sup>ā2</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 metalāair
batteries and fuel cells
Chemical Structure of Nitrogen-Doped Graphene with Single Platinum Atoms and Atomic Clusters as a Platform for the PEMFC Electrode
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
<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-(1ā6)-branched Ī²-(1ā3) glucohexaose, that contains an Ī±-(1ā3)-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.
<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 manufacturerās 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.
<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 manufacturerās 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