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 aerogel.
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The tendrils have a negative curvature because of heptagons, which are nano-sized clusters of carbon with a regular hexagonal pattern, like in a graphite sheet.
Introduction to Carbon Nanofoam
At a density of 2 mg/cm3, carbon nanofoam is among the lightest solid materials known to date. It is an excellent electrical insulator with a large surface area, is translucent, fragile, and can resist temperatures of up to 1,200 degrees Fahrenheit.
Even more intriguingly, freshly synthesized carbon nanofoam at ambient temperature contains unpaired electrons that give rise to ferromagnetism that gradually fades away. However, the ferromagnetic feature of carbon nanofoam is retained at lower temperatures, for example, below 90 K.
Such an unusual intrinsic magnetic feature of an all-carbon material is believed to have great benefits in the realm of spintronics-based electronics. It could also be used in biomedicine for imaging purposes.
Preparation of Carbon Nanofoam
Different carbonaceous structures are generated through carbon vapor deposition and high energy laser ablation depending on the pressure of Argon gas inside the chamber. Carbon films that resemble diamonds form at a pressure of 0.1 Torr*.
Carbon nanofoam in the shape of diamond is formed at pressures greater than 0.1 Torr. Solubility and polymerization chemistry has an impact on carbon nanofoam's density.
A low-density foam's particle diameter can reach up to 100 nanometers, with a pore consisting of 500 nanometers diameter at least, making it the densest foam.
At 0.8 grams per cubic centimeter, high-density carbon foams feature pores smaller than 1000-angstrom units and ultrafine particles.
Carbon nanofoams, which have many of the same qualities as aerogels, are also being developed. These materials can be found in the form of powders, granules, monoliths, and sheets prepared using sol-gel processes.
Low-density, continuous-pore foams with high capacitance are frequently produced by these approaches.
Properties of Carbon Nanofoam
These Carbon nanofoams have many features similar to those found in standard aerogels.
The solid matrix and pore gaps have nanometer-scale dimensions, making these foams electrically conductive, synthetic, and lightweight. In carbon nanofoam, the most remarkable feature is that it is ferromagnetic. The nanofoam's intricate microstructure is to blame for this noteworthy feature despite being an allotrope of carbon, traditionally considered a non-magnetic element.
Carbon Nanofoams for Electrochemically Stable Lithium-Sulfur Cells
Carbon nanofoam substrates with a carbon nanofiber backbone and connected nano-porous carbon clusters serve as a porous current collector. Carbon nanofoam substrates are highly conductive and porous, allowing high sulfur usage and long-term stability.
High sulfur loading of 4.8 mg cm-2 in the cathode is possible because of the carbon nanofoam current collector. The cathode is stabilized with a high charge storage capacity of 490–452 mA. h g-1 over 100 continuous cycles, which indicates outstanding capacity retention of 90%.
Using a current collection made up of carbon nanofoam, it is highly possible to develop an improved electrochemical stable sulfur cathode with high performance along with better sulfur loading.
As a result of the cathode's conductive and porous carbon nanofoam structure, the conversion reaction between the liquid and solid-state active materials, which were sluggish before, is now hastened. Here, a large amount of sulfur is encapsulated and the polysulfides that migrate into the cathode as catholyte are trapped within the structure.
It is possible to improve the desirable material properties of carbon nanofoam by using modified graphene-coated and MoS2-coated nanofoams, which are coated with polysulfide trapping MoS2.
These cathodes have charge storage capacities of 672 mA.h g-1 for graphene- and MoS2-coated carbon nanofoam-coated cathodes after 100 cycles with outstanding cycle stability and high-capacity retention of 79% to 87%.
Other Applications of Carbon Nanofoam
Nanofoams of other metals can be replaced by carbon nanofoam as they contain high conductivity, are light in weight, have low density, and contain ferromagnetic properties.
It can be used in a variety of ways in the specialty optical industry, including as an ultrasonic transducer for the air, carbon nanofoam paper, and metal-air batteries that can give high performance.
Further Developments of Carbon Nanofoam and Applications
One of the lightest solid substances ever discovered is carbon nanofoam, which makes it ideal for a wide range of applications.
Carbon nanofoam's magnetic property is perhaps its most intriguing aspect. In light of the discovery that carbon nanofoam exhibits unique ferromagnetism, several eminent scientists and researchers have reexamined their theories on what makes a substance magnetic.
Carbon nanofoam can have many other applications in industry and can be used in developing current technologies due to its unique ferromagnetic property and other useful properties such as small pore sizes, low density, and high capacitances.
Hairy Nanoparticles: What and Why?
References and Further Reading
A.V. Rode, S. H. (1999). Structural analysis of a carbon foam formed by high pulse-rate laser ablation. Applied Physics A. Available at: https://doi.org/10.1007/s003390051522
Dr. Yongzhu Fu, Y.-S. S. (2013). Highly Reversible Lithium/Dissolved Polysulfide Batteries with Carbon Nanotube Electrodes. Angewandte Chemie, 6930-6935. Available at: https://doi.org/10.1002/anie.201301250
Gaoran Li, S. W. (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.-H. C. (2021). Advanced Current Collectors with Carbon Nanofoams for Electrochemically Stable Lithium—Sulfur Cells. Nanomaterials. Available at: https://doi.org/10.3390/nano11082083
Yun-ChungHoa, S.-H. (2021). A design of the cathode substrate for high-loading polysulfide cathodes in lean-electrolyte lithium-sulfur cells. Chemical Engineering. Available at: https://doi.org/10.1016/j.cej.2021.130363