Carbon nanotubes could revolutionize everything from batteries and water purifiers to auto parts and sporting goods

Vertically aligned carbon nanotubes growing from catalyzed nanoparticles (golden color) on a silicon wafer above the heating stage (red glow). The diffusion of acetylene (black particles) through the gas phase to the catalyst sites determines the growth rate in the cold walled shower head reactor. Credit: Photo by Adam Samuel Connell/LLNL

Scientists at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL) are working to scale up production of vertically aligned single-walled carbon nanotubes (SWCNT). This amazing material can revolutionize various 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 of today’s production of carbon nanotubes (CNTs) is unstructured CNT architectures used in bulk composites and thin films. However, for many uses, structured CNT structures, such as vertically aligned forests, provide critical advantages for exploiting the properties of individual carbon nanotubes in macroscopic systems.

“Strong synthesis of vertically aligned carbon nanotubes at a large scale is required to accelerate the deployment of many advanced devices for emerging commercial applications,” said LLNL scientist and lead author Francesco Fornassiero. “To meet this need, we have shown that the structural properties of single-walled carbon nanotubes produced at a wafer scale in a growth system dominated by bulk diffusion of gaseous carbon precursors are remarkably constant over a wide range of process conditions.”

The team of researchers discovered that the vertically oriented SWCNTs retained very high quality when the precursor (elementary carbon) concentration was increased up to 30-fold, and the catalyzed substrate area of ​​1 cm2 up to 180 cm2growth pressure from 20 to 790 mbar and gas flow up to 8 times.

The LLNL scientists derived a kinetic model that shows that growth kinetics can be accelerated by using a lighter bath gas to aid the diffusion of the precursors. In addition, the formation of byproducts, which becomes progressively more important at higher growth pressures, can be significantly mitigated by using a hydrogen-free growth environment. The model also indicates that the production yield can be increased by 6-fold with carbon conversion efficiency above 90% with appropriate selection of carbon nanotube growth recipe and fluid dynamics conditions.

“These model predictions, together with the remarkably conserved structure of CNT forests over a wide range of synthesis conditions, suggest that a growth regime limited by bulk diffusion may facilitate the maintenance of device performance based on vertically aligned CNTs during scaling,” LLNL scientist and first author Sei Jin Park.

The team concluded that working in a growth regime quantitatively described by a simple kinetic model of CNT growth could facilitate process optimization and lead to faster deployment of vertically aligned cutting-edge CNT applications.

Applications include lithium-ion batteries, supercapacitors, water purification, thermal interfaces, breathable fabrics, and sensors.

Reference: “Chip-scale SWCNT forest synthesis with remarkably stable structural properties in a bulk-controlled kinetic regime” by Sei Jin Park, Kathleen Moyer-Vanderburgh, Steven F. Buchsbaum, Eric R. Meshot, Melinda L. Kwang Jin-Woo and Francesco Fornaciero, September 29, 2022, Available here. carbon.
DOI: 10.1016 / j.carbon.2022.09.068

Other LLNL authors are Kathleen Muir Vanderberg, Stephen Buchsbaum, Eric Michot, Melinda Jo, and Kwang Jin-Woo. The work is funded by the Department of Chemical and Biological Technologies of the Defense Threat Reduction Agency.

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