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oxide sheets. The authors obtained a nanocomposite with a mass ratio of PANI/graphene, 100 : 1, of which exhibited a high specific capacitance of 531 F g1 (obtained by charge–discharge analysis), and when compared to individual PANI (216 F g1), it is clear that the doping (and the ratio of graphene oxide) has a profound effect on the electrochemical capacitance perfor- mance of nanocomposites; graphene shows good application potential for super-capacitors or other power source systems of the future. Further work was conducted by Yan et al.,62 reporting that a GNS/PANI composite (synthesised using in situ poly- merisation) obtained a high specific capacitance of 1046 F g1, which compared to 115 F g1 for pure PANI, and 463 F g1 for MWCNT/PANI. It is evident that GNS/PANI modifications offer a highly conductive support material and well-dispersed deposition of nanoscale PANI particles attributable to GNSs large surface area. Other work on this topic59 has investigated the effect of a GNS/CNT/PANI composite, claiming that it is similar to the composites mentioned above, and that after 1000 cycles the capacitance decreased by only 6% of the initial (compared to 52 and 67 for GNS/PANI and CNT/PANI respectively), thus showing that a hybrid material may exhibit ultimately desired properties. In addition to these studies, other work has been completed showing graphene as a better capacitor than its counterparts; for example it has been highlighted that a graphene–ZnO composite exhibited enhanced capacitance when compared to CNTs, as well as an enhanced reversible charge/discharging ability.64–66 One explanation for this, in addition to graphene’s enhanced surface area (and other qualities discussed above), has been ascribed to the increase of lattice defect density exhibited by graphene (such as the fracture of graphene layers and the ratio of edge to basal carbon surface), where it is believed that increased edge plane increased the capacitance of a material.60 Li-ion storage/batteries Lithium based rechargeable batteries are another class of energy storage devices where graphene has been employed with several advantages. As with supercapacitors there is an increasing worldwide demand for advanced Li-ion batteries with higher energy capacities and longer cycle lifetimes. These devices are regarded as the most promising with regard to their application within electric vehicles.10,67 The anode material employed within these batteries is usually graphite, because it can be reversibly charged and discharged under intercalation potentials with reasonable specific capacity.68 However, to meet the increasing demand for batteries with higher energy densities more research is needed, and the exploration and exploitation of new electrode materials must occur. Graphene has already shown itself as a trusty replacement, for example papers have been published showing graphene based electrodes to have higher specific capacities than many other electrode materials (including graphite).2,10,67,68 Previous work68 has demonstrated that a graphene/SnO2 based nano-porous electrode exhibited a higher reversible capacity when compared to bare SnO2, bare graphene, and bare graphite electrodes, and in addition to this (as shown in Fig. 6), the graphene/SnO2 electrode exhibited a much improved cyclic performance when compared to the same electrodes.68 Enhanced cyclic ability of graphene based electrode over graphite for Li-ion battery applications: cyclic performances for (a) bare SnO2 nanoparticle, (b) graphite, (c) GNS, and (d) SnO2/GNS. Reproduced with permission from ref. 68. In light of this, one thing is for certain, all of the current literature regarding graphene as a Li-ion storage device indicates that it is better suited than graphite based electrodes, producing better cyclic performance and capacitance for applications within lithium ion batteries. Again, the future developments within this area are expected. Conclusions We have summarised the current literature regarding the rela- tively new and novel material, graphene, and explored its application and use as an electrode based material in many fields, focusing mainly upon sensing, and ranging through to fuel cells and energy storage. In the areas of sensing and other electro- chemical areas when using graphene we suggest that: (i) The electrochemical response is compared and contrasted to that of its nearest counterpart, typically edge or basal plane pyrolytic graphite electrodes of highly ordered pyrolytic graphite. (ii) The electrochemical response is compared to that of carbon nanotubes and graphite, using identical analytical conditions employed for graphene. (iii) The role of oxygenated species upon the electrochemical processes is also considered. (iv) Thin-layer effects, as observed in the case of carbon nanotubes, do not contribute to the observed ‘electro-cataly- sis’.69,70 (v) The role of surfactants, which may be beneficial or detri- mental, need to be considered.41 Although graphene is still a relatively new material, it has already made a wide and diverse impact within electro-analysis, and with the contribution of current literature already flaunting graphene as far-superior than its rival materials, much more is expected from this revolutionising material within the near future. This journal is a The Royal Society of Chemistry 2010 Analyst, 2010, 135, 2768–2778 | 2777 Fig. 6 View Article Online Published on 04 October 2010. 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