(Nanowerk Spotlight) Carbon nanomaterials offer significant potential for transforming industries that depend on lightweight, high-strength, and conductive materials. Among them, buckypaper – a thin sheet made of entangled carbon nanotubes (CNTs) – stands out for its exceptional combination of properties: high tensile strength, excellent thermal and electrical conductivity, and lightweight structure. These characteristics make it an ideal candidate for a wide range of applications, from aerospace and energy storage to electronics and medicine.
However, despite decades of research, the widespread use of buckypaper has been held back by two persistent issues: the high cost of synthesizing CNTs and the significant environmental impact of traditional production methods, particularly chemical vapor deposition (CVD). The production costs of high-quality carbon nanotubes has historically been expensive, and CVD itself is an energy-intensive process that generates its own carbon emissions.
“The inability to scale carbon nanotube production efficiently has prevented buckypaper from becoming a material of choice for large-scale industrial applications, even though its potential is well-known,” Stuart Licht, a professor of Chemistry at George Washington University, tells Nanowerk. “However, recent developments in carbon capture technology and advances in electrochemical processes have opened new avenues for addressing these barriers.”
“Using CO2 as a raw material to produce valuable carbon-based products, while simultaneously reducing atmospheric CO2 levels, presents a powerful solution to two major global challenges: material sustainability and climate change,” Licht points out. “Our process can use CO2 from a variety of sources, including industrial emissions and direct air capture, making it flexible enough to adapt to different carbon capture scenarios.”
In a new paper in RSC Advances (“Buckypaper made with carbon nanotubes derived from CO2“), Licht and his team present a novel method of synthesizing buckypaper by directly capturing CO2 and converting it into carbon nanotubes through molten carbonate electrolysis.
This method not only addresses the cost and environmental issues associated with traditional CNT production but also consumes CO2, offering a scalable, eco-friendly approach to producing advanced materials. The process outlined in the paper demonstrates how four tonnes of CO2 can be consumed for every tonne of CNTs produced, providing a dual benefit: creating high-performance materials while simultaneously sequestering CO2.
A 35 cm diameter carbon nanotube buckypaper prepared via the electrolysis of CO2. (Image: Stuart Licht, George Washington University)
At the heart of this research is molten carbonate electrolysis, a process in which CO2 is split into carbon and oxygen by passing electricity through a molten lithium carbonate electrolyte. “We applied this method to capture CO2 directly from industrial emissions or from the atmosphere and convert it into carbon nanotubes,” Licht explains. “The electrolysis takes place at a high temperature – around 770 °C – causing the CO2 to break down and form solid carbon at the cathode in the form of carbon nanotubes, while oxygen gas is released as a byproduct. The nanotubes produced in this way form a network structure called a carbanogel, which is subsequently processed into buckypaper.”
Unlike traditional methods that require complex steps like sonication and filtration to form buckypaper sheets, this process allows for direct pressing of the carbanogel into thin, durable sheets, simplifying the overall production and improving scalability.
One of the major advantages of this method is its ability to produce high-quality carbon nanotubes with control over their structure. By adjusting parameters such as temperature, current density, and electrolyte composition, the researchers were able to fine-tune the properties of the carbon nanotubes.
For example, lower temperatures during electrolysis favored the production of carbon nano-onions, while higher temperatures produced multi-walled carbon nanotubes, which are ideal for applications requiring both strength and electrical conductivity. This level of control allows the production of buckypaper tailored for specific industrial needs, from flexible electronics to energy storage devices.
The researchers demonstrate in their paper that the buckypaper produced through this method offers exceptional mechanical properties, including high tensile strength and lightweight composition, which make it suitable for applications in the aerospace industry. Additionally, its electrical conductivity, which can be enhanced through chemical doping, opens up possibilities for use in batteries and supercapacitors, where energy storage and charge delivery efficiency are critical.
The team found that doping the carbon nanotubes with elements like boron and nitrogen improved their catalytic activity and conductivity, further expanding the potential applications of buckypaper in fields such as chemical reactors, water purification, and even medical devices.
Perhaps the most significant implication of this research is its potential to mitigate climate change. The electrolysis process consumes CO2, turning it into a stable, valuable material while releasing oxygen as a byproduct. Given the stability of carbon nanotubes, this method offers a means of long-term carbon sequestration, locking carbon away for millions of years in the form of CNTs. Moreover, the process is powered by electricity, meaning that as renewable energy sources like solar and wind become more prevalent, the overall carbon footprint of this production method will decrease even further.
From an economic perspective, this process offers substantial cost savings. “We estimate that producing buckypaper through molten carbonate electrolysis could reduce the cost of CNT production to around $1,000 per tonne—significantly less than the costs associated with traditional CVD methods,” says Licht. “This dramatic reduction in cost, combined with the scalability of the process, could make buckypaper a commercially viable material in the near future, replacing metals like steel or aluminum in certain applications.”
In addition to its standalone uses, buckypaper can also be combined with other materials to form composites. The team demonstrated that when infused with polymers such as epoxy resin, buckypaper creates a composite that combines the strength and conductivity of carbon nanotubes with the flexibility and durability of the polymer. These composites could be used in industries ranging from automotive manufacturing to construction, where materials need to be strong yet lightweight.
Furthermore, because buckypaper can be infused with active materials such as catalysts or magnetic particles, it holds promise for use in advanced sensors and chemical reactors.
“The scalability of this method is one of its most promising aspects,” Licht concludes. “We showed that large sheets of buckypaper could be produced by increasing the size of the electrolysis cells and adjusting the pressure applied during pressing. This scalability is key to making the material commercially viable, as industries such as aerospace and electronics would require large quantities of buckypaper.”
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