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Graphene

 

 

 

 

 

 

 
Graphene
 
Graphene is a two-dimensional single atomic planar sheet of sp2 bonded carbon atoms that are densely packaged into a honeycomb lattice structure, and is essentially a very large polyaromatic hydrocarbon.
 


Graphene is the essential building block for all fullerene allotropic dimensionalities, thus in addition to existing in its planar state, graphene can be ‘wrapped’ into zero-dimensional spherical buckyballs, ‘rolled’ into one-dimensional carbon nanotubes (CNTs) or stacked into three-dimensional graphite where stacks generally consist of more than ten graphene sheets.
 
 
Free-standing two-dimensional materials were presumed not to exist until the experimental discovery of graphene and other two-dimensional atomic crystals in 2004... Because of graphene’s spectacular physical, electrical, chemical and thermal properties it has since caused immense excitement amongst scientists within many fields, and with research into graphene rife it promises enhancements and vast applicability within many industrial aspects.
 
There are many routes for the synthesis of graphene, and because not one single method exists for producing graphene which is suitable for all of the potential applications it has to offer, fabrication routes are currently a heavily researched issue. The enormous selection of current methods of graphene synthesis include; dry mechanical exfoliation, the chemical exfoliation of graphite, the unzipping of CNTs through a variety of ways such as electrochemical, chemical, or physical methods, epitaxial growth of graphene (CVD), and the most recent and novel method of reducing sugar (such as glucose, fructose, or sucrose); this last method is leading the innovation for the cheap-large-scale production of graphene for applications in various fields.
 
Advancements of graphene, when used as an electrode material, are expected in sensing (including sensing of gaseous species, trace metal analysis, bio-sensing, and other interesting areas of sensing) and within areas of energy storage/generation (including its use as a supercapacitor, storage of ions, use within basic fuel cells, and enzymatic bio-fuel cells, as well as many other electrical applications).
 
All of the theoretical advantages spawn from graphene’s unique properties:
An essential characteristic of an electrode material is its surface area, which is important in applications such as energy storage, biocatalytic devices and sensors. Graphene has a theoretical surface area of 2630 m2 g-1, surpassing that of graphite (∼10 m2 g-1), and is two times larger than that of CNTs (1315 m2 g-1).  Additionally the electrical conductivity of graphene has been calculated to be ~64 mS cm-1, which is approximately 60 times more than that of   SWCNTs. Furthermore, graphene’s conductivity remains stable over a vast range of temperatures ranging as low as liquid-helium temperatures of which is essential for reliability within many applications. More interestingly, graphene is distinguished from its counterparts by its unusual band structure, rendering the quasiparticles in it formally identical to the massless Dirac Fermions. A further indication of graphene’s extreme electronic quality is that it displays the half-integer quantum Hall effect, with the effective speed of light as its Fermi velocity νF ~ 106 m/s which can be observed in graphene even at room temperature. The fast charge carrier properties of graphene (and other two-dimensional materials) were found not only to be continuous, but to exhibit high crystal quality, in which importantly for graphene charge carriers can travel thousands of inter-atomic distances without scattering. These isolated graphene crystallites demonstrate exceptional electronic qualities, and graphene has exhibited the fastest electron mobilities when compared to all other possible materials, ‘theoretically’ meaning that in many applications graphene based electrodes react much faster.
Carbon materials have been widely utilised in both analytical and industrial electrochemistry, where in many areas they have out-performed the traditional noble metals. This diversity and success stems largely from carbons structural polymorphism, chemical stability, low cost, wide potential windows, relatively inert electrochemistry, rich surface chemistry and electro-catalytic activities for a variety of redox reactions. Most recently though the classical carbon materials based on graphite, glassy carbon, diamond and carbon black have been out performed by the distinctive properties of micro-fabricated carbon structures, such as CNTs, enabling novel applications in sensing, electro-catalysis, and electronics. Until now CNTs have fore-fronted innovation and dominated the field, however, with the introduction of graphene, which is reported to offer more advanced properties and is likely to exhibit fewer of the weaknesses that plagued CNTs, enormous progress in this field is underway, led mainly because the relevant research concerning graphene can be built on the wealth of techniques and knowledge available from decades of research on graphite and CNTs, where it can possibly outperform them at each opportunity.
 
 
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