Carbon Nanotubes Could Revolutionize Everything from Batteries and Water Purifiers to Auto Parts and Sporting Goods: Update from Lawrence Livermore National Laboratory

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-wall showerhead reactor. Credit: Image by Adam Samuel Connell/LLNL

Scientists at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL)  are scaling up the production of vertically aligned single-walled carbon nanotubes (SWCNT). This incredible material could revolutionize diverse 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 is unorganized CNT architectures that is used in bulk composite materials and thin films. However, for many uses, organized CNT architectures, like vertically aligned forests, provide critical advantages for exploiting the properties of individual CNTs in macroscopic systems.

“Robust synthesis of vertically-aligned carbon nanotubes at large scale is required to accelerate deployment of numerous cutting-edge devices to emerging commercial applications,” said LLNL scientist and lead author Francesco Fornasiero. “To address this need, we demonstrated that the structural characteristics of single-walled CNTs produced at wafer scale in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a broad range of process conditions.”

The team of researchers discovered that the vertically oriented SWCNTs retained very high quality when increasing precursor concentration (the initial carbon) up to 30-fold, the catalyst substrate area from 1 cm² to 180 cm², growth pressure from 20 to 790 Mbar and gas flowrates up to 8-fold.

LLNL scientists derived a kinetics model that shows the growth kinetics can be accelerated by using a lighter bath gas to aid precursor diffusion. In addition, byproduct formation, which becomes progressively more important at higher growth pressure, could be greatly mitigated by using a hydrogen-free growth environment. The model also indicates that production throughput could be increased by 6-fold with carbon conversion efficiency of higher than 90% with the appropriate choice of the CNT growth recipe and fluid dynamics conditions.

“These model projections, along with the remarkably conserved structure of the CNT forests over a wide range of synthesis conditions, suggest that a bulk-diffusion-limited growth regime may facilitate preservation 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 that is quantitatively described by a simple CNT growth kinetics model can facilitate process optimization and lead to a more rapid 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 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, 29 September 2022, Carbon.
DOI: 10.1016/j.carbon.2022.09.068

Other LLNL authors are Kathleen Moyer-Vanderburgh, Steven Buchsbaum, Eric Meshot, Melinda Jue and Kuang Jen Wu. The work is funded by the Chemical and Biological Technologies Department of the Defense Threat Reduction Agency.

Researchers at UC Santa Cruz – Use 3D printing to make ultrafast graphene supercapacitor

Yat Li (left) and Tianyu Liu worked with researchers at Lawrence Livermore National Laboratory to develop supercapacitors using 3D-printed graphene aerogel electrodes. Credit: T. Stephens

 
Scientists at UC Santa Cruz and Lawrence Livermore National Laboratory (LLNL) have reported the first example of ultrafast 3D-printed graphene supercapacitor electrodes that outperform comparable electrodes made via traditional methods. Their results open the door to novel, unconstrained designs of highly efficient energy storage systems for smartphones, wearables, implantable devices, electric cars and wireless sensors.

Using a 3D-printing process called direct-ink writing and a graphene-oxide composite ink, the team was able to print micro-architected electrodes and build supercapacitors with excellent performance characteristics. The results were published online January 20 in the journal Nano Letters and will be featured on the cover of the March issue of the journal.

“Supercapacitor devices using our 3D-printed graphene electrodes with thicknesses on the order of millimeters exhibit outstanding capacitance retention and power densities,” said corresponding author Yat Li, associate professor of chemistry at UC Santa Cruz. “This performance greatly exceeds the performance of conventional devices with thick electrodes, and it equals or exceeds the performance of reported devices made with electrodes 10 to 100 times thinner.”

LLNL engineer Cheng Zhu and UCSC graduate student Tianyu Liu are lead authors of the paper. “This breaks through the limitations of what 2D manufacturing can do,” Zhu said. “We can fabricate a large range of 3D architectures. In a phone, for instance, you would only need to leave a small area for energy storage. The geometry can be very complex.”

Fast charging

Supercapacitors also can charge incredibly fast, Zhu said, in theory requiring just a few minutes or seconds to reach full capacity. In the future, the researchers believe newly designed 3D-printed supercapacitors will be used to create unique electronics that are currently difficult or even impossible to make using other synthetic methods, including fully customized smartphones and paper-based or foldable devices, while at the same time achieving unprecedented levels of performance.

According to Li, several key breakthroughs made these novel devices possible, starting with the development of a printable graphene-based ink. Modification of the 3D printing scheme to be compatible with aerogel processing made it possible to maintain the important mechanical and electrical properties of single graphene sheets in the 3D-printed structures. Finally, the use of 3D printing to intelligently engineer periodic macropores into the graphene electrode significantly enhances mass transport, allowing the device to support much faster charge/discharge rates without degrading its capacity.

“This work provides an example of how 3D-printed materials such as graphene aerogels can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications,” Li said.

The advantages of graphene-based inks include their ultrahigh surface area, lightweight properties, elasticity, and superior electrical conductivity. The graphene composite aerogel supercapacitors are also extremely stable, the researchers reported, capable of nearly fully retaining their energy capacity after 10,000 consecutive charging and discharging cycles.

“Graphene is a really incredible material because it is essentially a single atomic layer that can be created from graphite. Because of its structure and crystalline arrangement, it has really phenomenal capabilities,” said LLNL materials engineer Eric Duoss.

Over the next year, the researchers intend to expand the technology by developing new 3D designs, using different inks, and improving the performance of existing materials.

Explore further: Energy storage of the future

More information: Cheng Zhu et al. Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores, Nano Letters (2016). DOI: 10.1021/acs.nanolett.5b04965

Journal reference: Nano Letters

Provided by: University of California – Santa Cruz

 

Preventing greenhouse gas from entering the atmosphere

A novel class of materials that enable a safer, cheaper and more energy-efficient process for removing greenhouse gas from power plant emissions has been developed by a multi-institution team of researchers. The approach could be an important advance in carbon capture and sequestration (CCS).

The team, led by scientists from Harvard Univ. and Lawrence Livermore National Laboratory, employed a microfluidic assembly technique to produce microcapsules that contain liquid sorbents encased in highly permeable polymer shells. They have significant performance advantages over the carbon-absorbing materials used in current CCS technology.

The work is described in a paper published online in Nature Communications.

“Microcapsules have been used in a variety of applications–for example, in pharmaceuticals, food flavoring, cosmetics and agriculture–for controlled delivery and release, but this is one of the first demonstrations of this approach for controlled capture,” says Jennifer A. Lewis, the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences (SEAS) and a co-lead author. Lewis is also a core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard.

This is an optical image of the cured silicone microcapsules, each with a diameter of approximately 600 microns. Image: John Vericella, Chris Spadaccini, and Roger Aines, LLNL; James Hardin and Jennifer Lewis, Harvard Univ.; and Nature

Power generating plants are the single largest source of carbon dioxide (CO₂), a greenhouse gas that traps heat and makes the planet warmer. According to the U.S. Environmental Protection Agency, coal- and natural gas-fired plants were responsible for one-third of U.S. greenhouse gas emissions in 2012.

That’s why the agency has proposed rules mandating dramatically reduced carbon emissions at all new fossil fuel-fired power plants. Satisfying the new standards will require operators to equip plants with carbon-trapping technology.

Current carbon capture technology uses caustic amine-based solvents to separate CO₂ from the flue gas escaping a facility’s smokestacks. But state-of-the-art processes are expensive, result in a significant reduction in a power plant’s output, and yield toxic byproducts. The new technique employs an abundant and environmentally benign sorbent: sodium carbonate, a.k.a. kitchen-grade baking soda. The microencapsulated carbon sorbents (MECS) achieve an order-of-magnitude increase in CO₂ absorption rates compared to sorbents currently used in carbon capture. Another advantage: amines break down over time, while carbonates have a virtually limitless shelf life.

“MECS provide a new way to capture carbon with fewer environmental issues,” says Roger D. Aines, leader of the fuel cycle innovations program at Lawrence Livermore National Laboratory (LLNL) and a co-lead author. “Capturing the world’s carbon emissions is a huge job; we need technology that can be applied to many kinds of carbon dioxide sources with the public’s full confidence in the safety and sustainability.”

Researchers at LLNL and the U.S. Dept. of Energy (DOE)’s National Energy Technology Lab are now working on enhancements to the capture process to bring the technology to scale.

The emission-scrubbing potential of CCS is not limited to the electric generation sector; Aines says that the MECS-based approach can also be tailored to industrial processes like steel and cement production, significant greenhouse gas sources.

“These permeable silicone beads could be a ‘sliced-bread’ breakthrough for CO₂ capture–efficient, easy-to-handle, minimal waste, and cheap to make,” says Stuart Haszeldine, professor of carbon capture and storage at the University of Edinburgh, who was not involved in the research. “Durable, safe, and secure capsules containing solvents tailored to diverse applications can place CO₂ capture for CCS firmly onto the cost-reduction pathway.”

MECS are produced using a double capillary device in which the flow rates of three fluids–a carbonate solution combined with a catalyst for enhanced CO₂ absorption, a photocurable silicone that forms the capsule shell, and an aqueous solution–can be independently controlled.

“Encapsulation allows you to combine the advantages of solid capture media and liquid capture media in the same platform,” says Lewis. “It is also quite flexible, in that both the core and shell chemistries can be independently modified and optimized.”

“This innovative gas separation platform provides large surface areas while eliminating a number of operational issues including corrosion, evaporative losses, and fouling,” notes Ah-Hyung (Alissa) Park, chair in applied climate science and associate professor of Earth and environmental engineering at Columbia Univ., who was not involved in the research.

Lewis has previously conducted groundbreaking research in the 3D printing of functional materials, including tissue constructs with embedded vasculature, lithium-ion microbatteries, and ultra-lightweight carbon-fiber epoxy materials.

Source: Harvard Univ.