The allotrope of carbon known as carbon nanofoam is a three-dimensional structure composed of several loosely connected tendrils that form a mist-like arrangement like an airgel.
Image Credit: pro500/Shutterstock.com
The tendrils have a negative curvature because of the heptagons, which are nanometer-sized clumps of carbon with a regular hexagonal pattern, like in a sheet of graphite.
Introduction to Carbon Nanofoam
Has a density of 2 mg/cm3, carbon nanofoam is one of the lightest solid materials known to date. It is an excellent electrical insulator with a large surface area, it is translucent, brittle and can withstand temperatures up to 1200 degrees Fahrenheit.
More intriguingly, freshly synthesized carbon nanofoam at room temperature contains unpaired electrons that give rise to gradually fading ferromagnetism. However, the ferromagnetic characteristic of carbon nanofoam is retained at lower temperatures, for example below 90 K.
Such an unusual intrinsic magnetic characteristic of an all-carbon material is believed to have great advantages in the field of spintronics-based electronics. It could also be used in biomedicine for imaging purposes.
Preparation of carbon nanofoam
Different carbon structures are generated by carbon vapor deposition and high energy laser ablation depending on the Argon gas pressure inside the chamber. Diamond-like films of carbon form at a pressure of 0.1 Torr*.
The diamond-shaped carbon nanofoam is formed at pressures greater than 0.1 Torr. The chemistry of solubility and polymerization impact the density of carbon nanofoam.
The particle diameter of a low density foam can be up to 100 nanometers, with a pore of at least 500 nanometers in diameter, making it the densest foam.
At 0.8 grams per cubic centimeter, high-density carbon foams feature pores smaller than 1000 Angstroms and ultra-fine particles.
Carbon nanofoams, which have many of the same qualities as aerogels, are also under development. These materials come in the form of powders, granules, monoliths and sheets prepared by sol-gel processes.
Low density, continuous pore foams with high capacity are frequently produced by these approaches.
Properties of carbon nanofoam
These carbon nanofoams have many characteristics similar to those found in standard aerogels.
The solid matrix and pore interstices have nanoscale dimensions, making these foams electrically conductive, synthetic and lightweight. In carbon nanofoam, the most remarkable characteristic is that it is ferromagnetic. The complex microstructure of nanofoam is to blame for this remarkable characteristic despite the fact that it is an allotrope of carbon, traditionally considered a non-magnetic element.
Carbon nanofoam for electrochemically stable lithium-sulfur cells
Carbon nanofoam substrates with a carbon nanofiber skeleton and connected nanoporous carbon clusters serve as a porous current collector. Carbon nanofoam substrates are highly conductive and porous, allowing for high sulfur utilization and long-term stability.
High sulfur load of 4.8 mg cm-2 in the cathode is possible thanks to the carbon nanofoam current collector. The cathode is stabilized with a high charge storage capacity of 490 to 452 mA. hg-1 over 100 continuous cycles, indicating an exceptional capacity retention of 90%.
By using a current collection made of carbon nanofoam, it is quite possible to develop an improved electrochemical stable sulfur cathode with high performance as well as better sulfur loading.
Due to the conductive and porous carbon nanofoam structure of the cathode, the conversion reaction between liquid and solid state active materials, which was previously slow, is now accelerated. Here a large amount of sulfur is encapsulated and the polysulfides which migrate into the cathode as a catholyte are trapped in the structure.
It is possible to improve the desirable material properties of carbon nanofoam by using modified graphene and MoS2polysulfide-coated nanofoams, which are coated with polysulfide-trapping MoS2.
These cathodes have charge storage capacities of 672 mA.hg-1 for graphene and MoS2Carbon nanofoam coated cathodes after 100 cycles with exceptional cycle stability and high capacity retention of 79%-87%.
Other applications of carbon nanofoam
Nanofoams of other metals can be replaced by carbon nanofoams because they contain high conductivity, are light, have low density and contain ferromagnetic properties.
It can be used in a variety of ways in the specialized optical industry, including as an ultrasonic transducer for air, carbon nanofoam paper, and metal-air batteries that can deliver high performance.
Further developments of carbon nanofoam and applications
One of the lightest solid substances ever discovered is carbon nanofoam, making it ideal for a wide range of applications.
The magnetic property of carbon nanofoam is perhaps its most intriguing aspect. In light of the discovery that carbon nanofoam exhibits unique ferromagnetism, several prominent scientists and researchers have re-examined their theories of what makes a substance magnetic.
Carbon nanofoam may have many other applications in industry and can be used in the development of current technologies due to its unique ferromagnetic property and other useful properties such as small pore size, low density and high capacities.
Hairy nanoparticles: what and why?
References and further reading
Dr. Yongzhu Fu, Y.-SS (2013). Highly reversible dissolved lithium/polysulfide batteries with carbon nanotube electrodes. Angewandte Chemie, 6930-6935. Available at: https://doi.org/10.1002/anie.201301250
Gaoran Li, SW (2018). Revisiting the role of polysulfides in lithium-sulfur batteries. ADVANCED MATERIALS. Available at: https://doi.org/10.1002/adma.201705590
Shu-Yu Chen, S.-HC (2021). Advanced current collectors with carbon nanofoam for electrochemically stable lithium-sulfur cells. Nanomaterials. Available at: https://doi.org/10.3390/nano11082083
Yun-ChungHoa, S.-H. (2021). A cathode substrate design for high-charge polysulfide cathodes in electrolyte-lean lithium-sulfur cells. Chemical Engineer. Available at: https://doi.org/10.1016/j.cej.2021.130363