The use of graphene, a one atom thick individual planar carbon layer, has exploded in a plethora of scientific disciplines since it was reported to possess a range of unique and exclusive properties. Despite graphene being explored theoretically since the 1940s and known to exist since the 1960s, the recent burst of interest from a large proportion of scientists globally can be correlated with work by Geim and Novoselov in 2004/5, who reported the so-called "scotch tape method" for the production of graphene in addition to identifying its unique electronic properties which has escalated into graphene being reported to be superior in a superfluity of areas. Consequently, many are involved in the pursuit of producing new methodologies to fabricate pristine graphene on an industrial scale in order to meet the current world-wide appetite for graphene. One area which receives considerable interest is the field of electrochemistry, where graphene has been reported to be beneficial in various applications ranging from sensing through to energy storage and generation and carbon based molecular electronics. Electrochemistry is an interfacial technique which is dominated by processes that occur at the solid-liquid interface and thus with the correct understanding can be beneficially utilised to characterise the surface under investigation. In this tutorial review we overview fundamental concepts of Graphene Electrochemistry, making electrochemical characterisation accessible to those who are working on new methodologies to fabricate graphene, bridging the gap between materials scientists and electrochemists and also assisting those exploring graphene in electrochemical areas, or that wish to start to. An overview of the recent understanding of graphene modified electrodes is also provided, highlighting prominent applications reported in the current literature.

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We critically evaluate the reported electro-catalysis of graphene using inner-sphere and outer-sphere electrochemical redox probes, namely potassium ferrocyanide (II) and hexaammine-ruthenium(III) chloride, in addition to L-ascorbic acid and b-nicotinamide adenine dinucleotide. Well characterised commercially available graphene is utilised which has not been chemically treated, is free from surfactants, and as a result of its fabrication has an extremely low oxygen content allowing the electronic properties to be properly de-convoluted. Surprisingly we observe that graphene exhibits slow electron transfer towards the electrochemical probes studied, effectively blocking underlying electron transfer of the supporting electrode substrate likely due to its large basal and low edge plane content. Such observations, never reported before, suggest that graphene may not be such a beneficial electrode material as widely reported in the literature. Density Functional Theory is conducted on symmetric graphene flakes of varying sizes indicating that the HOMO and LUMO energies are concentrated around the edge of the graphene sheet, at the edge plane sites, rather than the central basal plane region, consistent with experimental observations. We define differentiating coveragebased working regions for the electrochemical utilisation of graphene: 'Zone I', where graphene additions do not result in complete coverage of the underlying electrode and thus increasing basal contribution from graphene modification leads to increasingly reduced electron transfer and electrochemical activity; 'Zone II', once complete single-layer coverage is achieved, layered graphene viz graphite materialises with increased edge plane content and thus an increase in heterogeneous electron transfer is observed with increased layering. We offer insight into the electrochemical properties of these carbon materials, invaluable where electrode design for electrochemical sensing applications is sought.

Convincing evidence is presented demonstrating that the electro-catalytic nature of graphene resides in electron transfer from the edge of graphene which structurally resembles the behaviour of edge plane (rather than basal plane) of highly ordered pyrolytic graphite. The impact of surfactants intrinsic to graphene on the electrochemical response is highlighted.

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