Carbon nanotubes could revolutionize everything from batteries and water purifiers to auto parts and sporting goods
Vertically aligned carbon nanotubes growing from catalytic nanoparticles (gold color) on a silicon wafer on top of a heating stage (red glow). Diffusion of acetylene (black molecules) through the gas phase to the catalytic sites determines the growth rate in a cold-walled showerhead reactor. Credit: Image by Adam Samuel Connell/LLNL
Scientists at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL) are increasing production of vertically aligned single-wall carbon nanotubes (SWCNT). This incredible material could revolutionize a variety of commercial products ranging from rechargeable batteries, sporting goods and auto parts to boat hulls and water filters. The research was recently published in the journal Carbon.
Most carbon nanotube (CNT) production today is disorganized CNT architectures used in bulk composites and thin films. However, for many applications, organized CNT architectures, such as vertically aligned forests, offer crucial advantages for exploiting the properties of individual CNTs in macroscopic systems.
“A robust synthesis of vertically aligned carbon nanotubes on a large scale is required to accelerate the deployment of many advanced devices for emerging commercial applications,” said LLNL scientist and lead author Francesco Fornasiero. “To meet this need, we demonstrated that the structural features of single-walled CNTs produced at the wafer scale in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably unchanging over a wide range of process conditions.”
The team of researchers found that the vertically oriented SWCNTs maintained a very high quality when increasing the precursor concentration (the initial carbon) to 30-fold, the catalyst substrate surface area of 1 cm2 up to 180 cm2growth pressure from 20 to 790 Mbar and gas flow rates up to 8-fold.
Scientists at LLNL have derived a kinetics model showing that growth kinetics can be accelerated by using a lighter bath gas to promote the diffusion of the precursor. In addition, by-product formation, which becomes increasingly important at higher growth pressures, could be greatly reduced by using a hydrogen-free growth environment. The model also indicates that production throughput could be increased by a factor of 6 with a carbon conversion efficiency greater than 90% with the right choice of CNT growth recipe and fluid dynamic conditions.
“These model projections, together with the remarkably conserved structure of the CNT forests over a wide range of synthesis conditions, suggest that a bulk diffusion-limited growth regimen may facilitate the maintenance of vertically aligned CNT-based device performance during scale-up,” said LLNL- scientist and first author Sei Jin Park.
The team concluded that operating in a growth regime quantitatively described by a simple CNT growth kinetics model can facilitate process optimization and lead to faster deployment of advanced vertically aligned CNT applications.
Applications include lithium-ion batteries, supercapacitors, water purification, thermal interfaces, breathable fabrics and sensors.
Reference: “Synthesis of wafer-scale SWCNT forests with remarkably invariant structural properties in a bulk diffusion-controlled kinetic regime” by Sei Jin Park, Kathleen Moyer-Vanderburgh, Steven F. Buchsbaum, Eric R. Meshot, Melinda L. Jue, Kuang Jen Wu and Francesco Fornasiero, September 29, 2022, Carbon.
DOI: 10.116/j.carbon.2022.09.068
Other LLNL authors include Kathleen Moyer-Vanderburgh, Steven Buchsbaum, Eric Meshot, Melinda Jue, and Kuang Jen Wu. The work is funded by the Defense Threat Reduction Agency’s Chemical and Biological Technologies Division.
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