Carbon fibers offer structural strength to a variety of products, including aircraft components, sporting goods, and wind turbines.

By introducing a porous structure into the carbon fibers, however, a lab team from Virginia Tech has added a new function to the popular material: energy storage.

Guoliang “Greg” Liu, an assistant professor of chemistry in the College of Science, has led the development of sponge-like carbon fibers  with uniform porous structures.

How could the sponge-like material someday change how vehicles are built? For starters, exterior car shells that store energy within their pores, says Liu.

Prof. Liu spoke with Tech Briefs about he envisions the porous carbon fiber supporting new kinds of automotive design.

Tech Briefs: What is it about the porous structure that enables energy-storage capabilities?

Prof. Greg Liu: It’s the surface area. Typically, if we have a single straight filament carbon fiber, the amount of surface area is limited. Once we introduce porous structures inside the carbon fiber, we significantly increase the surface area for ion adsorption and molecule interaction. In this way, ions can be adsorbed in the pores and stored as energy.

Tech Briefs: What inspired this work and this design?

Prof. Greg Liu: This ties to my personal interest. I am always interested in improving the quality of our life. Almost every one of us drives a vehicle. I always think about this question: “How can we make our vehicles better than what we have now?”

Tesla uses batteries to store energy underneath the car seats. What if we store energy everywhere — for example, in the car shell, hood, and door panels, so that we can have much less parasitic weight? In this way, we use the car shell not only to support the vehicle, but also to propel it.

Our expertise allows us to try this idea. Our group specializes in polymer materials. When we look at this problem, we realize that we can design new polymer materials from the molecular level to find potential solutions to this problem.

Tech Briefs: Can you take me through an example of how you envision a vehicle being able to store its energy “everywhere?”

One possible way to use this material is that we can replace our doorframes with carbon fibers. Today’s doorframes are mainly for protection of passengers in the vehicle. If we can use carbon fibers to provide protection and store energy, we will have energy right there to power many devices and sensors in the doorframe.

We can also use carbon fibers all over the entire body. Vehicles are mainly made of metals today, but the carbon fibers are lightweight, mechanically strong, and functional for energy storage. This will revolutionize the manufacturing of vehicles.

Tech Briefs: Are there other applications besides automotive where these can be used?

Prof. Greg Liu: I think the material that we have here is a platform material. Our target application are automotive vehicles, but we can go beyond that. We can use them in aircraft and drones. We can also use the carbon fibers in sensors, and filtration/separation membranes.

Tech Briefs: Was this a challenging material to make? How was this made?

Prof. Greg Liu: To come to this idea was not straightforward. It took some judicious design regarding the polymer precursor.Once we decide the polymer precursor, however, it becomes straightforward.

Our precursor materials can be inserted into today’s carbon fiber industry. Today in the industry carbon fibers are typically made from polyacrylonitrile. What we need to do is to replace polyacrylonitrile with a polyacrylonitrile-based copolymer. The new precursor goes through the same procedure of oxidation, stabilization, and pyrolysis to make carbon fibers. I believe that there is no huge technology barrier if we want to implement this material in the industry.

a diagram showing the synthesis of porous carbon fibers developed by Virginia Tech engineers, including Guoliang (Greg) Liu.
This figure shows the synthesis of porous carbon fibers and loading of MnO2. (a) A diblock copolymer of polyacrylonitrile-block-polymethyl methacrylate (PAN-b-PMMA) is spun into a polymer fiber mat. In the magnified view, the block copolymer microphase separates into a bicontinuous network structure. (b) After pyrolysis, the block copolymer fibers are converted to porous carbon fibers (black) with continuous and uniform mesopores (white channels), which afford high loadings of transition metal oxides. (c) The porous carbon fibers are loaded with manganese oxide (magenta). In the magnified view, the continuous carbon fiber matrix and partially filled mesopores provide effective expressways for electron conduction and ion diffusion, respectively. (Image Credit: Virginia Tech)

Tech Briefs: What will you be working on next?

Prof. Greg Liu: Porous carbon fibers give us an opportunity to use them not only as a structural material but also a functional material. There’s still a lot of room for further improvement. This is our first demonstration of the concept. To fully use the material in the industry, we want to scale it up so that we can make lots of polymer precursors and carbon fibers in an industrial scale.

Tech Briefs: What is most exciting to you about this material and what is possible?

Prof. Greg Liu: The most exciting part of this material is the structures. The uniform porous structures offer us opportunities to investigate and utilize the mass transport properties for molecules and ions. The conductive nature of carbon fibers enables us to use them as electrode materials. The combined electron/ion conductivities, as well as the good mass transport properties allow us to design them for applications beyond energy conversion and storage.

Prof. Liu's research was published recently in Science Advances and Nature Communications .

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