Scientists at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL) are ramping up production of vertically aligned single-walled carbon nanotubes (SWCNTs). This incredible material could revolutionize various commercial products ranging from rechargeable batteries, sporting goods and automotive parts to boat hulls and water filters. The research was published recently in the journal Carbon.
Most carbon nanotube (CNT) production today consists of unorganized CNT architectures that are used in bulk composite materials and thin films. However, for many uses, organized CNT architectures, such as vertically aligned forests, provide critical advantages for exploiting the properties of individual CNTs in macroscopic systems.
“Robust synthesis of large-scale vertically aligned carbon nanotubes is needed to accelerate the deployment of many state-of-the-art devices to emerging commercial applications,” said Francesco Fornasiero, LLNL scientist and lead author. “To address this need, we demonstrated that the structural characteristics of single-walled CNTs produced at the wafer scale in a growth regime dominated by mass diffusion of the gaseous carbon precursor are remarkably invariant over a wide range. of process conditions.”
The research team found that the vertically oriented SWCNTs retained very high quality when increasing the concentration of the precursor (the initial carbon) up to 30 times the area of the catalyst substrate by 1 cm2 at 180cm2growth pressure from 20 to 790 Mbar and gas flow rates up to 8 times.
LLNL scientists have derived a kinetic model that shows that growth kinetics can be accelerated by using a lighter bath gas to facilitate precursor diffusion. Additionally, the formation of by-products, which becomes progressively more prominent at higher growth pressure, could be greatly mitigated by using a hydrogen-free growth environment. The model also indicates that the production throughput could be increased up to 6 times with a carbon conversion efficiency greater than 90% with the appropriate choice of CNT growth recipe and fluid dynamics conditions.
“These model projections, together with the remarkably conserved structure of CNT forests across a wide range of synthetic conditions, suggest that a bulk diffusion-limited growth regime may facilitate preservation of the performance of CNT-based devices. vertically aligned during scaling,” said LLNL scientist and first author Sei Jin Park.
The team concluded that operating in a growth regime quantitatively described by a simple model of CNT growth kinetics can facilitate process optimization and lead to faster deployment of cutting-edge, 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 Mass 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.
Other LLNL authors are Kathleen Moyer-Vanderburgh, Steven Buchsbaum, Eric Meshot, Melinda Jue and Kuang Jen Wu. The work is funded by the Department of Chemical and Biological Technologies of the Defense Threat Reduction Agency.
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