What is graphene and why is it so good?
Author: Sean Lightheart
What is the structure of graphene and why is it special?
Graphene is a ground-breaking two-dimensional (2D) super material that possesses extraordinary electrical and mechanical properties that offer the material to a plethora of innovations and enhanced applications. The term “graphene” can be legitimately used to describe widely different forms of material depending on the context. Without any adjectives, the term “graphene” is defined by Carbon (2013) as “a single-atom-thick sheet of hexagonally arranged, sp2-bonded carbon atoms that is not an integral part of a carbon material, but is freely suspended or adhered on a foreign substrate.
Because graphene is composed of pure carbon as a single sheet in a flat hexagon pattern, any changes to its molecular structure mean that the resulting chemical is no longer technically graphene. At this point, it becomes a graphene derivative and derivatives such as graphene oxide displays reduced properties and inferior performance within applications when compared to pure graphene.
What are the unique properties of graphene?
1.Thinnest - At one atom thick, it’s the thinnest material we can see (with scientific equipment).
2. Lightest - One square meter of graphene weighs about 0.77 milligrams. For scale, one square meter of regular paper is 1000 times heavier than graphene and a single sheet of graphene is big enough to cover a football field would weigh less than a gram.
3. Strongest - Graphene is stronger than steel and Kevlar, with a tensile strength of 150,000,000 psi (x300 times stronger than Kevlar).
4. Stretchiest - Graphene has an amazing ability to retain its initial size after strain. Graphene sheets suspended over silicone dioxide cavities had spring constants in the region of 1-5 N/m and a Young’s modulus of 0.5 TPa.
5. Best Conductor of Heat - At room temperature, graphene’s heat conductivity is (4.84±0.44) × 10^3 to (5.30±0.48) × 10^3 W·m−1·K−1. Theoretically, graphene could absorb an unlimited amount of heat.
6. Best Conductor of Electricity – Graphene is better at conducting electricity than, for example, copper at room temperature.
What are the potential applications of graphene?
There is seemingly an endless list of applications ready to utilise graphene-enhanced solutions including:
Medical Applications – tissue engineering, contrast agents, biomedical sensors, drugs delivery, filtering of biological samples and DNA sequencing
Electronics Applications – transistors, electrodes, quantum dots, spintronics, optoelectronics, light detectors, heat management and filled conductive polymers
Energy Applications – supercapacitors, battery anodes, molecular filtering, ethanol distillation and biofuel purification
Sensor Applications – pressure sensors, nanoelectronicmechanical systems, gas sensors, molecular binding sensors, motion sensors, infrared sensors and contact lenses and magnetic sensors
Other Applications – construction materials, lubrication, radio wave absorption, sound transducers and coolant additives
Graphene’s properties have the potential to improve nearly all applications imaginable. The issue, however, is not what can graphene improve, but rather finding the right type of graphene that not only provides the required performance but is also commercially viable in the desired application. The source of the graphene and how it was prepared, have tremendous implications for its performance and as a result, there is a real variance in the quality of ‘graphene’ available, so it’s important to check you are getting the right type for your application.
What are the Different Types of Graphene?
There is a multitude of methods for producing graphene which generates varying different forms of graphene or graphene derivatives and they can take different physical forms such as powder, flakes, ribbons, and sheets. Most graphene producers currently produce graphene nanoplatelets (GNP) or graphene oxide (GO) and the main market for these types of graphene is for composites, batteries and thermal management markets. Graphene derivatives are scalable, and the cost is becoming more accessible to industry, however, they often show substandard performance due to inherent issues such as stacking, and poor reproducibility. They have yet been able to fulfil the largest market demand for graphene-enhanced products, such as biosensing and energy storage.
Applications of small graphene sheets, graphene oxide and graphene nanoplatelets are in composites, functional coatings, conductive inks, batteries and supercapacitors. Large-area graphene films are being developed for use in transparent electrodes in touch panels, displays and photovoltaic devices. They are also prime candidates for utilisation in next-generation electronics and optoelectronics such as flexible and wearable devices. Most sales of graphene at present are graphene nanoplatelets (GNP) and graphene oxide powders (GOP) for conductive inks and polymers. CVD graphene films are primarily used in R&D at present.
In areas such as biosensing, where there is significant demand for increased sensitivity, reproducibility and selectivity we are seeing the requirement for pure 3D Graphene Foam due to its large, porous, active surface area. Similarly, we expect to see the use of the integration of 3D Graphene Foam to develop supercapacitors to build the next generation of battery management systems due to its ability to deliver high power and high energy densities enabled, again, by the large, porous, electrochemically active surface area.
How to make graphene?
Since graphene was discovered, industrialists have been attempting to find the best fabrication methods for producing high quality, defect-free, stable and high yield and cost-effective graphene.
Traditionally there have been two principal methods that are being utilised at commercial scales: Micromechanical exfoliation, which is used in the manufacture of graphene powder and, Chemical vapour deposition (CVD). Both methods have not been able to fully capitalise on the excellent performance characteristics of 2D graphene due to the impurities encountered during the manufacturing process. Therefore, Integrated Graphene has developed a novel process for producing pure 3D Graphene Foam, which thanks to its single step production process, is able to retain the superlative performance capabilities of graphene.
So, what are these manufacturing methods and how do they compare?
What is the micromechanical exfoliation process to produce graphene?ene sheets are pulled away from graphite by either mechanical, chemical, or electrochemical means before Chemical methods employ plasma-enhanced chemical vapour deposition (PECVD), a process that has been used successfully across many other industries to deposit thin films onto substrate surfaces. This approach is well-established and allows for high volume production but resulting in a low-quality product that comprises multi-layer graphene flakes. For this reason, the use of graphene powder is restricted mainly to the production of composite materials such as coatings and inks.
Benefits: Reduced cost to manufacture, can be scaled, commercially available
Cons: poor reproducibility, prone to stacking (graphene reverting to graphite), limited performance increase
What is the CVD process for making graphene? graphene is most commonly produced
2D graphene is most commonly produced by chemical vapour deposition (CVD), a process that results in a classical single layer sheet where the carbon atoms are arranged as a flat lattice of hexagons linked together in a honeycomb pattern. This is achieved by growing the graphene on a catalyst surface (usually nickel or copper) before transferring it on to the substrate of choice. CVD has, for several years, been considered a leading approach for 2D graphene manufacturing since it yields a high-quality product with good uniformity. However, due to its requirement for a catalyst substrate, transfer to the end product and etching of the catalyst and vacuum, it means the process is slow, costly and adds imperfections.
Benefits: Yields a high-quality product (comparative with micromechanical exfoliation) with good uniformity, suited for small volume production of 2D graphene
Cons: Slow to manufacture, expensive and the number of treatments required adds imperfections, lessening the quality of the graphene
How is 3D graphene made?
3D graphene is deemed to be the most desirable and application diverse form of graphene, due to its large surface area, enabling a step-change in performance in nearly all applications.
Unlike CVD graphene production, Integrated Graphene’s 3D Graphene Foam can be grown on any substrate at room temperature and atmospheric pressure, with no need for a vacuum system. Not only does this considerably improve the safety of production methods, but it also allows for greater capacity manufacturing runs while eliminating the need for time-consuming transfer steps that can compromise product quality. This novel process removes all existing hurdles to commercialising graphene augmented products: it cost-effectively produces the highest quality graphene at speed. Produced with Design for Manufacture in mind, 3D Graphene Foam is a disruptive technology set to reshape multiple markets.
What are the benefits of 3D Graphene Foam?
Designed to overcome the major limitations of conventional 2D graphene, 3D graphene foam has sparked significant global interest in recent years. This has been driven mainly by the exceptionally high specific surface area of 3D graphene foam created by the porous structure of single and double-layer graphene, which promises miniaturisation of a broad range of technologies – from sensing to energy systems and many more besides. A further important advantage of Integrated Graphene’s 3D Graphene Foam compared to 2D graphene is that manufacturing is far more straightforward.
It is because of this larger active surface area, that is larger than the geometric surface area, which provides optimised pathways for ionic transport, making for better contact for electrode materials and electrolyte in an electrochemical system, such as a battery system. Compared with regular 2D graphene paper, 3D Graphene Foam electrode exhibits more excellent electrochemical performance. Due to the revolutionary and novel Integrated Graphene manufacturing process, we can produce graphene that is scalable, reproducible and exhibits good selectivity and high quality.
Is the future graphene-based?
The diversity of graphene formulations and associated range of properties support a wide range of applications and current and future market opportunities, e.g. energy storage and conversion, composites, biomedical, environment and sensors but to name a few. Based on the desired applications and benefits, it is hard to fathom a world that does not fully utilise the vast improvements forecast for graphene. The truth is though, for many applications, is that we are still at a stage of development, where the most exciting work on graphene is still years or even decade away from being deployed practically or en masse.
Companies are starting to focus on the development and commercialisation of graphene applications such as the launch of Integrated Graphene’s Gii-Sens. Gii- Sens uses the properties of a very large active surface area, high conductivity and a pure surface of 3D graphene to enable cost-effective disposable POC devices to be developed with laboratory LoDs using amplification free electrochemical biosensors / L-O-C methods. As more commercialised products come to market, we are bound to see a transformative role for graphene in several markets beyond the largely R&D landscape that presently it dominates.