Power/Performance Bits: April 28

Printing graphene aerogels

Lawrence Livermore National Laboratory researchers have made graphene aerogel microlattices with an engineered architecture via a 3D printing technique known as direct ink writing, potentially leading to better energy storage, sensors, and nanoelectronics.

Aerogel is a synthetic porous, ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas.

The 3D printed graphene aerogels have high surface area, excellent electrical conductivity, are lightweight, have mechanical stiffness and exhibit supercompressibility. In addition, the 3D printed graphene aerogel microlattices show an order of magnitude improvement over bulk graphene materials and much better mass transport.

Lawrence Livermore researchers have made graphene aerogel microlattices with an engineered architecture via a 3D printing technique known as direct ink writing. (Source: Ryan Chen/LLNL)

Previous attempts at creating bulk graphene aerogels produced a largely random pore structure, excluding the ability to tailor transport and other mechanical properties of the material for specific applications such as separations, flow batteries and pressure sensors.

“Adapting the 3D 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,” said Livermore engineer Cheng Zhu.

Benefits of graphene defects

Engineers at the University of California, San Diego have discovered a method to increase the amount of electric charge that can be stored in graphene.

Making a perfect carbon nanotube structure ― one without defects, which are holes corresponding to missing carbon atoms ― is next to impossible. Rather than avoiding defects, the researchers figured out a practical way to use them instead.

The team used a method called argon-ion based plasma processing, in which graphene samples are bombarded with positively-charged argon ions. During this process, carbon atoms are knocked out of the graphene layers and leave behind holes containing positive charges ― these are the charged defects. Exposing the graphene samples to argon plasma increased the capacitance of the materials three-fold.

Zigzag and armchair defects in graphene. (Source: UC San Diego)

“It was exciting to show that we can introduce extra capacitance by introducing charged defects, and that we could control what kind of charged defect we could introduce into a material,” said Rajaram Narayanan, a graduate student at UC San Diego.

Additionally, electrochemical studies helped the team discover a new length scale that measures the distance between charges. According to mechanical engineering professor Prabhakar Bandaru, “this new length scale will be important for electrical applications, since it can provide a basis for how small we can make electrical devices.”