Research on porous carbon fibers is a step closer to use in the automotive industry

The synthesis of porous carbon fibers and the loading of MnO2. (a) A block polyacrylonitrile poly (methyl methacrylate) diblock copolymer (PAN-b-PMMA) is spun to form a polymer fiber mat. In the enlarged view, the microphase block copolymer splits into a bicontinuous lattice structure. (b) After pyrolysis, the fibers of the block copolymer are converted to porous (black) carbon fibers with continuous and uniform mesopores (white channels), which allow high loading of transition metal oxides. (c) Porous carbon fibers are loaded with manganese oxide (magenta). In the enlarged view, the continuous carbon fiber matrix and partially filled mesopores provide efficient fast pathways for electron conduction and ion diffusion, respectively. Credit: Virginia Tech

An update of recently reported research on porous carbon fibers shows how this material can be used in an industrial context, marking an important step from theory to application.

Guoliang "Greg" Liu, an assistant professor of chemistry at the College of Science and a member of the Institute of Macromolecules, is working on the development of carbon fibers with a uniform porous structure. In a journal article recently published in Progress of scienceLiu explained how his lab used block copolymers to create carbon fibers with uniformly dispersed mesopores, similar to sponges.

Just a week later, Liu published another article, this time in Nature Communications. The new article shows how Liu's porous carbon fibers can enable high energy density and high electron / ion charge rates, which generally exclude each other in energy storage devices. electrochemical.

"This is the next step that will be relevant to the industry," Liu said. "We want to create a process favorable to the industry.Now, the industry should seriously consider carbon fiber not only as a structural material, but also as a platform for energy storage for cars, planes and others. "

Introduction to pseudocapacitive materials

Carbon fibers are already widely used in the aerospace and automotive industries because of their high performance in various fields including mechanical strength and weight. Liu's long-term vision is to build outdoor car hulls from porous carbon fibers that can store energy in the pores.

But carbon itself is not enough. Although carbon is a material of choice in the structure, it does not have a sufficiently high energy density to create supercapacitors for very demanding applications.

The current industry standard associates carbon with so-called pseudocapacitive materials, which stores a large amount of energy but poses another problem of slow charge-discharge rate.

A commonly used pseudocapacitive material is manganese oxide (MnO2) because of its low cost and reasonable performance. To charge MnO2 on a carbon fiber or other material, Liu soaks the fibers in a KMnO4 precursor solution. The precursor then reacts with the carbon, removes a thin layer of carbon and settles on the rest of the carbon, creating a thin layer about 2 nm thick.

But the industry is facing a challenge with MnO2. Too little MnO2 means that the storage capacity is too low. Too much MnO2 creates a layer that is too thick and electrically insulating. And even worse, it slows the transport of ions. Both contribute to slowing charge-discharge rates.

"We want to couple carbon with pseudocapacitive materials, because they together have a much higher energy density than pure carbon.Now the question is how to solve the problem of the conductivity of electrons and ions" said Liu.

However, Liu discovered that his porous carbon fibers could overcome this impasse. The tests carried out in his laboratory showed the best of both worlds: high load of MnO2 and high and sustained charge and discharge rates.

Liu's lab proved that he could charge up to 7mg / cm2 of MnO2 before his performance dropped. This represents double or nearly triple the amount of MnO2 currently used by the industry.

"We reached 84% of the theoretical limit of this material with a mass load of 7 mg / cm2," said Liu. "If you load 7 mg / cm2 of other materials, you will not do it."

Short term applications

At the rate where Liu's lab publishes the results, cars equipped with outer shells could arrive here sooner than expected, but Liu is holding back this idea.

"In a long-term vision, we could replace gasoline with simple cars with supercapacitors," Liu said. "Right now, the minimum of what we could do is use it as an energy storage element in cars."

Mr Liu said that a short-term application could use carbon fiber parts to provide a lot of energy over a short period of time to accelerate cars.

But Liu also looks beyond the automotive industry in other transportation applications.

"If you want a drone to provide products for Amazon, you want the drone to have the most weight possible, and that it be as light as possible," Liu said. "Carbon-fiber drones can do both jobs.Carbon fibers are solid structural materials for transporting goods, and these are energy storage materials to provide energy to transport."

Research on this material accelerates in Liu 's lab, and he said that he still had plenty of ideas to test.

"What I believe is that porous carbon fibers are a platform material," Liu said. "In the first two articles, we focused on energy storage for vehicles, but we think this material can do more than that – hopefully we'll be able to tell more stories soon."

Explore further:
Researchers create the first carbon fiber with a uniform porous structure

More information:
Tianyu Liu et al. Uniform mesopores derived from the block copolymer allow ultra-fast transport of electrons and ions at high mass loads. Nature Communications (2019). DOI: 10.1038 / s41467-019-08644-w

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