Unravelling the Potential of Pristine Graphene Flakes: Comparison with Graphene Oxide
By Akanksha Urade, Ph.D. Scholar at IIT Roorkee
and Graphene & 2D Materials Science Writer
Graphene has been called the “wonder material” of the 21st century due to its unique properties and wide range of applications. Although there are numerous sources for graphene oxide, one of the major impediments to the growth of the Graphene Revolution is access to industrial quantities of affordably priced large, thin and defect free graphene (pristine) flakes. This article aims to shed light on the benefits and properties of pristine graphene flakes and how it differs from graphene oxide.
Importance of Pristine Graphene Flakes
To this day, almost all applications have concentrated on graphene-like materials such as graphene oxide (GO) or its derivatives (e.g., reduced graphene oxide (r-GO)) rather than pristine graphene flakes. To synthesize graphene oxide, however, processes such as liquid phase exfoliation or chemical reduction necessitate a lengthy sonication treatment and/or the use of toxic, environmentally hazardous chemicals. As a result, graphene oxide flakes not only contain significant compositional and structural defects that have a negative impact on their electronic properties, but they also fail to preserve the most fundamentally important (or the fundamentally unique) properties of graphene, resulting in degraded performance. In terms of applications, pristine graphene flakes provide significant advantages. In contrast, graphene oxide has found widespread use in low value applications, such as road construction where graphene oxide can reinforce asphalt or concrete making the road more durable and extending the lifetime of the road, according to Dr. Arun Raju at the University of Manchester.
Pristine Graphene Flakes vs Graphene Oxide
In contrast to graphene oxide flakes, which are hydrophilic by nature, researchers have discovered that pristine graphene flakes of a certain size (below 1-micron lateral size) can exhibit amphiphilic behavior. This graphene flake attracts water at its edges but repels it on its surface, making it a next generation surfactant that can stabilize oil and water emulsions.
Another point to consider is that graphene oxide requires an additional stabilizing agent to stabilize the oil/water emulsion. However, pristine graphene flakes are a new type of stabilizer that can stabilize oil/water emulsions without the use of any other agents.
Numerous studies have found that pristine graphene flakes outperform GO or r-GO in terms of electrical conductivity, mechanical flexibility, and chemical and thermal stability. According to a study conducted by Rice University researchers, pristine graphene flakes (10 nm thick) obtained by exfoliation have high electrical conductivity of 110,000 S/m compared to only 7,000 S/m for r-GO.
A study in the peer reviewed journal, Carbon, reported that mixing pristine graphene flakes with polymers yields composites with better mechanical and conducting properties than CNTs or graphene oxide alone.
Novel Applications of Pristine Graphene Flakes
It has been widely reported that pristine graphene flakes are well suited for use in gas sensors, transparent electrodes, and other electronic and electrical devices due to their low oxygen content, low sheet resistivity, and high transparency compared to GO or r-GO.
According to a study by Avadain, using 0.5% graphene flakes as the cathode/anode material of a supercapacitor allowed for 100% stable capacitive efficiency over a high current range of 10 A/g, while using r-GO caused a 25% decrease in capacitive efficiency.
Graphene flakes have the ability (as noted above) to act as a surfactant, making them a flexible 2D stabilizer perfect for a wide range of industrial uses, including the extraction of minerals and crude oil.
Graphene flakes are promising candidates for dispersing agents in the synthesis of paints, ceramics or composites, filters, conductive catalyst, etc. due to their amphipathic nature and robust ability to function under adverse conditions such as high temperature.
rGO has been extensively investigated for next generation medical devices for neural applications. However, its conductivity is frequently lower than that of pristine graphene due to defects and partial removal of functional groups on the basal plane. As a result of their enhanced electrical conductivity, pristine graphene flakes have been discovered as a better option for the use of bioelectrical neural interfaces (e.g., metal ). A September 2022 study published in Applied Materials Today found that “next generation neural medical devices” demand pristine graphene electroconductive materials that seamlessly integrate with delicate neural tissues, while minimizing deleterious secondary effects such as scarring and reduced bioactivity.
Future Challenges and Opportunities for Adoption of Pristine Graphene Flakes
The currently available methods for producing high-quality pristine graphene have a number of drawbacks, including low graphene yields, expensive and toxic exfoliating media, surfactants that are frequently difficult to remove, and long-term sonication that can reduce the lateral size of the graphene flakes.
These challenges are overcome by Avadain’s novel, environmentally friendly electrochemical exfoliation and expansion technology, which produced pristine graphene flakes with more than 70% yields by separating the atomic layers of graphite. The technique employs polar solvent as an exfoliation medium, with no surfactant or sonication treatment, making the entire process cost effective and yielding high quality defect-free graphene flakes. The technology is now being scaled up for mass production.
References
Kuziel, Anna W., et al. “The true amphipathic nature of graphene flakes: a versatile 2D stabilizer.” Advanced Materials 32.34 (2020): 2000608.
Du, Wencheng, et al. “From graphite to graphene: direct liquid-phase exfoliation of graphite to produce single-and few-layered pristine graphene.” Journal of Materials Chemistry A 1.36 (2013): 10592-10606.
Behabtu, Natnael, et al. “Spontaneous high-concentration dispersions and liquid crystals of graphene.” Nature nanotechnology 5.6 (2010): 406-411.
Roscher, Sarah, et al. “High voltage electrochemical exfoliation of graphite for high-yield graphene production.” RSC advances 9.50 (2019): 29305-29311.
