[Image above] Illustration of graphene aerogel microlattices printed with direct ink writing. Credit: Ryan Chen; LLNL
Researchers at Lawrence Livermore National Lab have combined three of the most promising and popular technologies today—3-D printing, graphene, and aerogels. The team is the first to 3-D print graphene aerogels, according to a LLNL press release.
Aerogels are materials that are made of up to 99.98% air by volume—which makes them incredibly lightweight. Because of all that air, a wide range of available aerogel flavors exhibit low thermal conductivity, high surface area, and low density.
Others have already made incredibly light graphene aerogels, but those suffer from a random pore microstructure that limits the ability to tailor the material’s mechanical properties.
To circumvent those limitations, the LLNL team used direct ink writing to 3-D print the aerogels with engineered microarchitectures. The result is a lightweight graphene aerogel with excellent electrical conductivity, high mechanical stiffness, and up to 90% compressive strain.
“Making graphene aerogels with tailored macro-architectures for specific applications with a controllable and scalable assembly method remains a significant challenge that we were able to tackle,” LLNL engineer and corresponding author Marcus Worsley says in the release. “3-D printing allows one to intelligently design the pore structure of the aerogel, permitting control over mass transport (aerogels typically require high pressure gradients to drive mass transport through them due to small, tortuous pore structure) and optimization of physical properties, such as stiffness. This development should open up the design space for using aerogels in novel and creative applications.”
To fabricate the super lightweight aerogels, the LLNL scientists mixed an aqueous suspension of graphene oxide with a silica filler to make a highly viscous graphene oxide ink. Extruding the ink through a micronozzle allowed the team to build 3-D structures with patterned architectures. Watch the video below to see how it works.
Credit: Lawrence Livermore National Laboratory; Youtube
Worsley says the biggest challenge in developing the technique was perfecting the ink’s rheology and adapting the direct ink write technique to be compatible with typical aerogel processing. “Formulating an ink with the proper rheology for printing without resorting to a polymer blend was challenging, but essential for achieving the desirable final properties of the aerogel lattice. Also, without the aerogel processing, it would have been difficult to realize key graphene properties like high surface area and low density,” he writes in an email.
Worsley adds that further developing the ink or the technique so that the team can write with smaller diameter tips is one of the challenges remaining before the technique is scalable and commercially feasible. The team’s current lower limit is ~200 μm.
“Scaling the aerogel processing (supercritical drying and thermal annealing) to commercial scale could also be a challenge,” Worsley writes.
Some of the most promising applications of graphene aerogels are for catalysis, separation/filtration (e.g., desalination), and energy storage applications, including batteries, supercapacitors, and hydrogen storage, Worsley says. But, he also adds that the most exciting/interesting applications are for electric vehicle batteries, like those in the Tesla.
Co-author Cheng Zhu adds in the article, “Adapting the 3-D printing technique to aerogels makes it possible to fabricate countless complex aerogel architectures for applications such as mechanical properties and compressibility, which has never been achieved before.”
The LLNL team is next exploring the performance of 3-D printed graphene aerogels for potential applications in supercapacitors and batteries.
Worsley acknowledges the work of all his coauthors, especially Cheng Zhu, and the lab’s funding from Laboratory Directed Research and Development program.
The open-access paper, published in Nature Communications, is “Highly compressible 3-D periodic graphene aerogel microlattices” (DOI: 10.1038/ncomms7962).