In this article, an overview of graphene aerogel is provided. We discuss its fabrication method, properties, commercial availability, industrial application, and recent developments.
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What is Graphene Aerogel?
Graphene is an essential material for various applications due to its chemical stability, high surface area, and high strain-to-failure ratio. However, to fully utilize the potential of graphene, specific methods are used for its conversion from two-dimensional to three-dimensional structures, such as graphene aerogel (GA). It is a synthetic three-dimensional material with low density, high porosity, adsorption capacity, thermal resistance, electrical conductivity and mechanical strength.
Graphene aerogel is a solid material. It has a high specific strength that can bear six thousand times more weight than its own with fifty percent strain and has robust compressive properties. Even at fifty percent strain, it maintains eighty-five percent of its original compressive strength after thousand compressive cycles. Moreover, graphene aerogel is very lightweight and sometimes its weight is even lighter than air hence used as a substitute for helium.
How is Graphene Aerogel Made?
Graphene aerogels can be prepared via different methods, including template-directed reduction, chemical reduction, hydrothermal reduction, and cross-linking.
Among these methods, the most commonly used is the hydrothermal reduction method, in which graphene oxide (GO) is used to produce graphene hydrogel, which eventually produces graphene aerogel after drying under high pressure and temperature. Graphene nanosheets (GNS) self-assemble due to the reduction of graphene oxide forming 3D graphene structures.
Similarly, chemical reduction methods use mild agents like hydrazine or Vitamin C to restore the sp2 network and are considered superior to hydrothermal methods. Cross-linking methods, such as hydrogen bonds or multi-valent metal ions, strengthen the bonding between GO sheets.
Template-directed reduction methods prevent random structures and enable the creation of porous graphene aerogels with controlled pore sizes. These methods offer environmentally friendly approaches for producing aerogels with different functionalities and applications.
Is Graphene Aerogel Expensive?
Compared to conventional materials, the commercial availability of graphene aerogel is relatively limited due to challenges associated with its manufacturing procedure and scaling up, so its cost is comparatively higher.
The cost of graphene can also vary depending on certain factors, including its fabrication method, purity, density, and application requirements. However, with continuous research for improved manufacturing processes, the cost will likely decrease eventually, increasing commercial availability and enabling wider adoption across industries.
How is Graphene Aerogel Used?
High surface area and electrical conductivity make graphene aerogel an excellent material for energy storage devices like batteries and capacitors since its porous structure allows efficient ion transportation and charge storage.
Excellent electrical conductivity also allows graphene aerogel to be used as a material for various electronic devices and sensors. Even though the electric conductivity of the aerogel is high, its thermal conductivity is such that it makes a reasonable thermal insulator and can be utilized for the thermal insulation of electronics.
Graphene aerogel can also adsorb pollutants through the environment due to its pores which trap these contaminants through air or water, acting as a filter. This graphene aerogel property is used to clean oil spills by separating oil from water.
Graphene Aerogel: Recent Developments
Nitrogen-Doped Graphene Aerogel-Supported Ruthenium Nanocrystals
In a 2022 study, nitrogen-doped graphene aerogel (N-GA) was used as a support for ultrafine ruthenium nanocrystals (Ru-NCs) to create Ru-NCs/N-GA nanocomposites. The Ru-NCs were synthesized through an adsorption-pyrolysis method, and the size and conductivity were controlled by adjusting the pyrolysis temperature. The resulting nanocomposites demonstrated excellent activity and durability for the hydrogen evolution reaction (HER) in both acidic and alkaline media.
The HER performance of the Ru-NCs/N-GA nanocomposites was comparable to that of commercial platinum-based electrocatalysts. The introduction of nitrogen atoms enhanced the catalytic properties and ensured strong interactions between the N atoms and the Ru nanocrystals. Overall, this study provides a promising approach for the development of low-cost and efficient HER electrocatalysts using graphene aerogel as a support material.
Hygroscopic Holey Graphene Aerogel Fibers
In another 2022 study, researchers developed hygroscopic holey graphene aerogel fibers (LiCl@HGAFs) that possess multiple functionalities, including efficient moisture capture, heat allocation, and microwave absorption. The LiCl@HGAFs exhibit a high water sorption capacity of over 4.15 g g-1 due to their high surface area and water uptake kinetics.
These fibers can be regenerated through photo-thermal and electro-thermal approaches. Additionally, they demonstrate efficient heat transfer and have a heat storage capacity of 6.93 kJ/g. The LiCl@HGAFs also show broad microwave absorption with good impedance matching and a high attenuation constant.
The multifunctional LiCl@HGAFs have potential applications in water harvest, heat allocation, and microwave absorption, suggesting the possibility of functionalizing aerogel fibers for broader uses.
Graphene Aerogel: Future Outlook
In conclusion, graphene aerogel (GA) is a synthetic three-dimensional material with remarkable properties. It can be produced through methods such as hydrothermal reduction, chemical reduction, cross-linking, and template-directed reduction.
Graphene aerogel exhibits exceptional strength, lightweight nature, and high electrical conductivity. However, its commercial availability is currently limited, resulting in higher costs. Nevertheless, it finds applications in energy storage devices, electronic devices, sensors, and environmental remediation.
Recent developments include the use of nitrogen-doped graphene aerogel-supported ruthenium nanocrystals for efficient hydrogen evolution reaction and the development of hygroscopic holey graphene aerogel fibers with multiple functionalities like moisture capture, heat allocation, and microwave absorption. These advancements showcase the potential for expanding the applications of this graphene-based material in various fields in the future.
References and Further Reading
Ding, Y., Cao, K. W., He, J. W., Li, F. M., Huang, H., Chen, P., & Chen, Y. (2022). Nitrogen-doped graphene aerogel-supported ruthenium nanocrystals for pH-universal hydrogen evolution reaction. Chinese Journal of Catalysis. doi.org/10.1016/S1872-2067(21)63977-3
Gorgolis, G., & Galiotis, C. (2017). Graphene aerogels: a review. [Online] 2D Materials. Available at: https://iopscience.iop.org/article/10.1088/2053-1583/aa7883/meta#tdmaa7883s3
Hou, Y., Sheng, Z., Fu, C., Kong, J., & Zhang, X. (2022). Hygroscopic holey graphene aerogel fibers enable highly efficient moisture capture, heat allocation and microwave absorption. Nature Communications. doi.org/10.1038/s41467-022-28906-4
Mariana, M., HPS, A. K., Yahya, E. B., Olaiya, N. G., Alfatah, T., Suriani, A. B., & Mohamed, A. (2022). Recent trends and future prospects of nanostructured aerogels in water treatment applications. Journal of Water Process Engineering. doi.org/10.1016/j.jwpe.2021.102481
Yang, M., Zhao, N., Cui, Y., Gao, W., Zhao, Q., Gao, C., ... & Xie, T. (2017). Biomimetic architectured graphene aerogel with exceptional strength and resilience. ACS nano. Available at: https://pubs.acs.org/doi/pdf/10.1021/acsnano.7b01815