University Chemists Design Porous Carbon Fibers for Energy Storage

Graduate students Tianyu Liu (left) and Assad Khan (middle) worked with Virginia Tech professor Guoliang "Greg" Liu (right) on a project that uses block copolymers to create porous carbon fibers. Photo courtesy of Virginia Tech.

A Virginia Tech University (Blacksburg, Virginia, USA) professor has developed a method of synthesizing porous carbon fibers with uniform micro-holes for energy storage. Made from block copolymers, these carbon fibers could be used as an energy efficient power source for planes, cars, and other vehicles.

Guoliang "Greg" Liu, an assistant professor of chemistry in Virginia Tech’s College of Science, conceived of the project with one question in mind: “What if we can design [carbon fibers] to have functionality, such as energy storage?” Liu said. The answer he came up with informed the course of his project: “If you want them to store energy, you need to have sites to put ions in.”

With that in mind, Liu created carbon fibers from block copolymers, which are formed when two monomers cluster together to form blocks of repeating units. He designed the carbon fibers with micro-holes, or pores, scattered throughout the carbon fibers for storing ions of energy. These pores were of uniform size and spacing in order to ensure the best distribution of energy.

As detailed in an article he co-authored for Science Advances, Liu used a multistep chemical process involving two polymers-long repeating units: polyacrylonitrile (PAN) and poly(acrylonitrile-block-methyl methacrylate) (PMMA). PAN is the chemical precursor to carbon fibers, while PMMA is the place-holding material that helps create the pores. As opposed to other chemists who mixed PAN and PMMA separately, Liu bonded the two to create a block polymer to create a carbon fiber with smaller, uniform pores. “This is the first time we utilize block copolymers to make carbon fibers and the first time to use block copolymer-based porous carbon fibers in energy storage,” Liu said. “Often, we’re only thinking from the process point-of-view, but here we’re thinking from the materials design point-of-view.”

Once the block copolymer solution had been synthesized, it underwent a three-step chemical process: electrospinning to harden the solution into a paper-like material; oxidation heating to separate the PAN and PMMA; and pyrolysis to solidify the PAN and remove PMMA, resulting in the final porous carbon fiber product.

Since publishing his initial results in Science Advances, Liu has examined the industrial applications of his porous carbon fiber material. In particular, he demonstrated how his fibers can enable both high energy density and high electron/ion charging rates, which makes it a viable energy storage platform for various vehicles. While carbon fibers are widely used in the aerospace and automotive industries, Liu’s project can help make them a popular energy storage option for cars. “It opens the way we think about designing materials for energy storage,” Liu said. “Now we can also start to think about functionality. We not only use (carbon fibers) as a structural material but also a functional material.”

The Science Advances paper was co-authored by Liu, Zhengping Zhou, Liu’s former postdoctoral associate and current assistant professor at North Dakota State University, Tianyu Liu, another postdoctoral associate in the Liu Lab, and Assad Khan, a fifth-year doctoral student in the Department of Chemistry.

Source: Virginia Tech Daily,