38 research outputs found
A Display Module Implemented by the Fast High-Temperatue Response of Carbon Nanotube Thin Yarns
Suspending superaligned multiwalled carbon nanotube (MWCNT)
films
were processed into CNT thin yarns, about 1 μm in diameter,
by laser cutting and an ethanol atomization bath treatment. The fast
high-temperature response under a vacuum was revealed by monitoring
the incandescent light with a photo diode. The thin yarns can be electrically
heated up to 2170 K in 0.79 mS, and the succeeding cool-down time
is 0.36 mS. The fast response is attributed to the ultrasmall mass
of the independent single yarn, large radiation coefficient, and improved
thermal conductance through the two cool ends. The millisecond response
time makes it possible to use the visible hot thin yarns as light-emitting
elements of an incandescent display. A fully sealed display with 16
× 16 matrix was successfully fabricated using screen-printed
thick electrodes and CNT thin yarns. It can display rolling characters
with a low power consumption. More applications can be further developed
based on the addressable CNT thermal arrays
A Direct Grain-Boundary-Activity Correlation for CO Electroreduction on Cu Nanoparticles
Copper
catalyzes the electrochemical reduction of CO to valuable
C<sub>2+</sub> products including ethanol, acetate, propanol, and
ethylene. These reactions could be very useful for converting renewable
energy into fuels and chemicals, but conventional Cu electrodes are
energetically inefficient and have poor selectivity for CO vs H<sub>2</sub>O reduction. Efforts to design improved catalysts have been
impeded by the lack of experimentally validated, quantitative structure–activity
relationships. Here we show that CO reduction activity is directly
correlated to the density of grain boundaries (GBs) in Cu nanoparticles
(NPs). We prepared electrodes of Cu NPs on carbon nanotubes (Cu/CNT)
with different average GB densities quantified by transmission electron
microscopy. At potentials ranging from −0.3 V to −0.5
V vs the reversible hydrogen electrode, the specific activity for
CO reduction to ethanol and acetate was linearly proportional to the
fraction of NP surfaces comprised of GB surface terminations. Our
results provide a design principle for CO reduction to ethanol and
acetate on Cu. GB-rich Cu/CNT electrodes are the first NP catalysts
with significant CO reduction activity at moderate overpotential,
reaching a mass activity of up to ∼1.5 A per gram of Cu and
a Faradaic efficiency >70% at −0.3 V
A Display Module Implemented by the Fast High-Temperatue Response of Carbon Nanotube Thin Yarns
Suspending superaligned multiwalled carbon nanotube (MWCNT)
films
were processed into CNT thin yarns, about 1 μm in diameter,
by laser cutting and an ethanol atomization bath treatment. The fast
high-temperature response under a vacuum was revealed by monitoring
the incandescent light with a photo diode. The thin yarns can be electrically
heated up to 2170 K in 0.79 mS, and the succeeding cool-down time
is 0.36 mS. The fast response is attributed to the ultrasmall mass
of the independent single yarn, large radiation coefficient, and improved
thermal conductance through the two cool ends. The millisecond response
time makes it possible to use the visible hot thin yarns as light-emitting
elements of an incandescent display. A fully sealed display with 16
× 16 matrix was successfully fabricated using screen-printed
thick electrodes and CNT thin yarns. It can display rolling characters
with a low power consumption. More applications can be further developed
based on the addressable CNT thermal arrays
Grain-Boundary-Dependent CO<sub>2</sub> Electroreduction Activity
Uncovering
new structure–activity relationships for metal
nanoparticle (NP) electrocatalysts is crucial for advancing many energy
conversion technologies. Grain boundaries (GBs) could be used to stabilize
unique active surfaces, but a quantitative correlation between GBs
and catalytic activity has not been established. Here we use vapor
deposition to prepare Au NPs on carbon nanotubes (Au/CNT). As deposited,
the Au NPs have a relatively high density of GBs that are readily
imaged by transmission electron microscopy (TEM); thermal annealing
lowers the density in a controlled manner. We show that the surface-area-normalized
activity for CO<sub>2</sub> reduction is linearly correlated with
GB surface density on Au/CNT, demonstrating that GB engineering is
a powerful approach to improving the catalytic activity of metal NPs
Conformal Fe<sub>3</sub>O<sub>4</sub> Sheath on Aligned Carbon Nanotube Scaffolds as High-Performance Anodes for Lithium Ion Batteries
A uniform Fe<sub>3</sub>O<sub>4</sub> sheath is magnetron
sputtered
onto aligned carbon nanotube (CNT) scaffolds that are directly drawn
from CNT arrays. The Fe<sub>3</sub>O<sub>4</sub>–CNT composite
electrode, with the size of Fe<sub>3</sub>O<sub>4</sub> confined to
5–7 nm, exhibits a high reversible capacity over 800 mAh g<sup>–1</sup> based on the total electrode mass, remarkable capacity
retention, as well as high rate capability. The excellent performance
is attributable to the superior electrical conductivity of CNTs, the
uniform loading of Fe<sub>3</sub>O<sub>4</sub> sheath, and the structural
retention of the composite anode on cycling. As Fe<sub>3</sub>O<sub>4</sub> is inexpensive and environmentally friendly, and the synthesis
of Fe<sub>3</sub>O<sub>4</sub>–CNT is free of chemical wastes,
this composite anode material holds considerable promise for high-performance
lithium ion batteries
Ice-Assisted Transfer of Carbon Nanotube Arrays
Decoupling the growth and the application
of nanomaterials by transfer
is an important issue in nanotechnology. Here, we developed an efficient
transfer technique for carbon nanotube (CNT) arrays by using ice as
a binder to temporarily bond the CNT array and the target substrate.
Ice makes it an ultraclean transfer because the evaporation of ice
ensures that no contaminants are introduced. The transferred superaligned
carbon nanotube (SACNT) arrays not only keep their original appearance
and initial alignment but also inherit their spinnability, which is
the most desirable feature. The transfer-then-spin strategy can be
employed to fabricate patterned CNT arrays, which can act as 3-dimensional
electrodes in CNT thermoacoustic chips. Besides, the flip-chipped
CNTs are promising field electron emitters. Furthermore, the ice-assisted
transfer technique provides a cost-effective solution for mass production
of SACNTs, giving CNT technologies a competitive edge, and this method
may inspire new ways to transfer other nanomaterials
Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays
Aligned carbon nanotube (CNT) films
drawn from CNT arrays have
shown the potential as thermoacoustic loudspeakers. CNT thermoacoustic
chips with robust structures are proposed to promote the applications.
The silicon-based chips can play sound and fascinating rhythms by
feeding alternating currents and audio signal to the suspending CNT
thin yarn arrays across grooves in them. In additional to the thin
yarns, experiments further revealed more essential elements of the
chips, the groove depth and the interdigital electrodes. The sound
pressure depends on the depth of the grooves, and the thermal wavelength
can be introduced to define the influence-free depth. The interdigital
fingers can effectively reduce the driving voltage, making the chips
safe and easy to use. The chips were successfully assembled into earphones
and have been working stably for about one year. The thermoacoustic
chips can find many applications in consumer electronics and possibly
improve the audiovisual experience
New-Type Planar Field Emission Display with Superaligned Carbon Nanotube Yarn Emitter
With the superaligned carbon nanotube yarn as emitter,
we have
fabricated a 16 × 16 pixel field emission display prototype by
adopting screen printing and laser cutting technologies. A planar
diode field emission structure has been adopted. A very sharp carbon
nanotube yarn tip emitter can be formed by laser cutting. Low voltage
phosphor was coated on the anode electrodes also by screen printing.
With a specially designed circuit, we have demonstrated the dynamic
character display with the field emission display prototype. The emitter
material and fabrication technologies in this paper are both easy
to scale up to large areas
Sulfur Nanocrystals Confined in Carbon Nanotube Network As a Binder-Free Electrode for High-Performance Lithium Sulfur Batteries
A binder-free nano sulfur–carbon
nanotube composite material
featured by clusters of sulfur nanocrystals anchored across the superaligned
carbon nanotube (SACNT) matrix is fabricated via a facile solution-based
method. The conductive SACNT matrix not only avoids self-aggregation
and ensures dispersive distribution of the sulfur nanocrystals but
also offers three-dimensional continuous electron pathway, provides
sufficient porosity in the matrix to benefit electrolyte infiltration,
confines the sulfur/polysulfides, and accommodates the volume variations
of sulfur during cycling. The nanosized sulfur particles shorten lithium
ion diffusion path, and the confinement of sulfur particles in the
SACNT network guarantees the stability of structure and electrochemical
performance of the composite. The nano S-SACNT composite cathode delivers
an initial discharge capacity of 1071 mAh g<sup>–1</sup>, a
peak capacity of 1088 mAh g<sup>–1</sup>, and capacity retention
of 85% after 100 cycles with high Coulombic efficiency (∼100%)
at 1 C. Moreover, at high current rates the nano S-SACNT composite
displays impressive capacities of 1006 mAh g<sup>–1</sup> at
2 C, 960 mAh g<sup>–1</sup> at 5 C, and 879 mAh g<sup>–1</sup> at 10 C
Excitation of Surface Plasmon Resonance in Composite Structures Based on Single-Layer Superaligned Carbon Nanotube Films
Surface-enhanced Raman scattering
(SERS) provides valuable information
on the vibrational modes of molecules and the physical mechanism of
surface plasmon resonance (SPR). In this paper we study the localized
SPR process in Ag- or Ag/oxide-coated single-layer superaligned carbon
nanotube (SACNT) films. Because of the unidirectional alignment of
the carbon nanotubes in these films, the Raman signal is higher when
the laser is polarized parallel to the aligned direction than when
perpendicular to it. We investigated the polarization-dependent transmittance
and Raman spectra for various Ag particle sizes and different oxide
medium layers to study the localized SPR in these composite structures.
These results systematically characterize the properties of SACNT
film-based SERS substrates and clarify the origin of transmittance
peaks