Electrochemistry of graphene: not such a beneficial electrode material?

Abstract

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.

Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions

“…A combination of CNT and graphene may be an effective way to solve this problem [137,138]. Dai's group has demonstrated that CNT-graphene complexes can exhibit excellent activity and stability towards ORR in both acidic and basic electrolytes [139].…”

Improved heterogeneous electron transfer kinetics of fluorinated graphene derivatives

“…[6][7][8] Various types of graphene based sensors have been developed in the recent past, and role of edge and basal planes of graphene in determining the effective sensitivity have also been studied. 9 However, in a recent report, it was established that apart from the effects of basal and edge planes of graphene in net electron transfer process, its atomic thickness and structure are insignicant in electron transfer process, and the electrochemical response will not vary much from single to few layers of graphene.…”

Mechanical stability of substrate-bound graphene in contact with aqueous solutions

“…This method of preparation requires considerable skill and experience, which could be the main reason why very few research groups reported on electrochemistry of ME graphene flakes [2][3][4][5]. As a consequence, chemical vapour deposition (CVD) graphene, as well as fewlayer graphene sheets prepared via liquid-phase exfoliation or reduction of graphene oxide, are often substituted for ME graphene for simplicity and scalability [6][7][8][9]. However, these alternatives often yield graphene prepared in an uncontrolled and illdefined manner, which is reflected by inconsistencies between the conclusions drawn about the electrochemistry of graphene [2,3,7,8,10,11].…”