5 research outputs found
Excluded Volume Effect on the Power Factor of Carbon Nanotube based Polymer Composites
Investigations into polymeric materials as flexible thermoelectric (TE)
materials have encountered issues, such as conflicting thermoelectric property
behaviors that result in a low power factor. To tackle these issues, we propose
the use of two unique sorts of fillers - carbon nanotubes (CNT) and silica
particles -- embedded in polymer matrix for enhanced TE properties. Embedding
micro-scale segregated structures as the secondary fillers creates an excluded
volume within CNT networks, which leads to the simultaneous increase in the
electrical conductivity and Seebeck coefficient of the composite.
Polydimethylsiloxane (PDMS) is used as a suitable matrix because of its merits
such as solution processability, light weight, low thermal conductivity and an
internet of things. As silica content increased up to 40 wt%, electrical
conductivity and Seebeck coefficient increases in the segregated composite
framework, resulting in maximum power factor of approximately 25.96 and 42.89
microW/mK2 for 1 and 3 micrometer size silica particles, respectively.
Moreover, using much lower CNT content, such as 10 wt% CNT stacking, results at
a desired level of electrical conductivity and Seebeck coefficient. This study
ultimately develops the hypothesis that the network topology of CNT-based
polymer composites depends on the size and characteristics of the secondary
fillers
Plasma-Enhanced Carbon Nanotube Fiber Cathode for Li-S Batteries
Fiber-shaped batteries have attracted much interest in the last few years. However, a major challenge for this type of battery is their relatively low energy density. Here, we present a freestanding, flexible CNT fiber with high electrical conductivity and applied oxygen plasma-functionalization, which was successfully employed to serve as an effective cathode for Li-S batteries. The electrochemical results obtained from the conducted battery tests showed a decent rate capability and cyclic stability. The cathode delivered a capacity of 1019 mAh g−1 at 0.1 C. It accommodated a high sulfur loading of 73% and maintained 47% of the initial capacity after 300 cycles. The demonstrated performance of the fiber cathode provides new insights for the designing and fabrication of high energy density fiber-shaped batteries
Synergy Between Excluded Volume Effect with Co-embedded Microparticles and Chemical Doping in Carbon Nanotube Network-based Composites to Enhance Thermoelectric Power Factor
There is a growing momentum in recent thermoelectric materials research for
flexible materials which enhance power output and efficiency at human wearable
temperatures. In our previous work, we established the method to improve
thermoelectric properties with co-embedding microparticles in carbon nanotube
(CNT) network-based composites. In this work, we investigate the synergy of
excluded volume effect by silica microparticles with CNT doping toward the
enhancement of thermoelectric power factor. We find that the power factor can
be enhanced to 28.46 {\mu}W/mK2 when the CNT is doped with 0.5 {\mu}g/ml of
1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) before co-embedding silica
microparticles within the carbon nanotube-based composite. We also fabricated
and demonstrated flexible wearable thermoelectric devices made of the developed
composites that exhibits a power output of 0.025 {\mu}W/cm2 at a temperature
differential of only 4 K
Lightweight Copper–Carbon Nanotube Core–Shell Composite Fiber for Power Cable Application
The substitution of traditional copper power transmission cables with lightweight copper–carbon nanotube (Cu–CNT) composite fibers is critical for reducing the weight, fuel consumption, and CO2 emissions of automobiles and aircrafts. Such a replacement will also allow for lowering the transmission power loss in copper cables resulting in a decrease in coal and gas consumption, and ultimately diminishing the carbon footprint. In this work, we created a lightweight Cu–CNT composite fiber through a multistep scalable process, including spinning, densification, functionalization, and double-layer copper deposition. The characterization and testing of the fabricated fiber included surface morphology, electrical conductivity, mechanical strength, crystallinity, and ampacity (current density). The electrical conductivity of the resultant composite fiber was measured to be 0.5 × 106 S/m with an ampacity of 0.18 × 105 A/cm2. The copper-coated CNT fibers were 16 times lighter and 2.7 times stronger than copper wire, as they revealed a gravimetric density of 0.4 g/cm3 and a mechanical strength of 0.68 GPa, suggesting a great potential in future applications as lightweight power transmission cables
Three-Dimensional Graphene Sheet-Carbon Veil Thermoelectric Composite with Microinterfaces for Energy Applications
Over
the years, various processing techniques have been explored
to synthesize three-dimensional graphene (3DG) composites with tunable
properties for advanced applications. In this work, we have demonstrated
a new procedure to join a 3D graphene sheet (3DGS) synthesized by
chemical vapor deposition (CVD) with a commercially available carbon
veil (CV) via cold rolling to create 3DGS-CV composites. Characterization
techniques such as scanning electron microscopy (SEM), Raman mapping,
X-ray diffraction (XRD), electrical resistance, tensile strength,
and Seebeck coefficient measurements were performed to understand
various properties of the 3DGS-CV composite. Extrusion of 3DGS into
the pores of CV with multiple microinterfaces between 3DGS and the
graphitic fibers of CV was observed, which was facilitated by cold
rolling. The extruded 3D graphene revealed pristine-like behavior
with no change in the shape of the Raman 2D peak and Seebeck coefficient.
Thermoelectric (TE) power generation and photothermoelectric responses
have been demonstrated with in-plane TE devices of various designs
made of p-type 3DGS and n-type CV couples yielding a Seebeck coefficient
of 32.5 μV K–1. Unlike various TE materials,
3DGS, CV, and the 3DGS-CV composite were very stable at high relative
humidity. The 3DGS-CV composite revealed a thin, flexible profile,
good moisture and thermal stability, and scalability for fabrication.
These qualities allowed it to be successfully tested for temperature
monitoring of a Li-ion battery during charging cycles and for large-area
temperature mapping