Electrochemistry of Q-Graphene

Abstract

A newly synthesised type of graphene, Q-Graphene, has been physically and electrochemically characterised with Scanning and Transmission Electron Microscopy (SEM, TEM), X-ray Photoelectron Spectroscopy (XPS) and Cyclic Voltammetry (CV). Interpretation of SEM, TEM and XPS data reveal the material to consist of hollow carbon nanospheres of multi-layer graphene (viz. graphite), which exhibit a total oxygen content of ca. 36.0% (atomic weight via XPS). In addition to the carbon structures present, spherical magnesium oxide particles of ≤50 nm in diameter are abundantly present in the sample (ca. 16.2%). Interestingly, although the TEM/SEM images show macroporous carbon structures, Raman spectroscopy shows peaks typically characteristic of graphene, which suggests the material is highly heterogeneous and consists of many types of carbon allotropes. Q-Graphene is electrochemically characterised using both inner-sphere and outer-sphere electrochemical redox probes, namely potassium ferrocyanide(II), hexaammine-ruthenium(III) chloride and hexachloroiridate(III), in addition to the biologically relevant and electroactive analytes, norepinephrine, β-nicotinamide adenine dinucleotide (NADH) and L-ascorbic acid. The electrochemical response of Q-Graphene is benchmarked against edge plane- and basal plane-pyrolytic graphite (EPPG and BPPG respectively), pristine graphene and graphite alternatives. Q-Graphene is found to exhibit fast electron transfer kinetics, likely due to its high proportion of folded edges and surface defects, exhibiting a response similar to that of EPPG – which exhibits fast electron transfer rates due to the high proportion of edge plane sites it possesses. Furthermore, we demonstrate that the specific oxygen content plays a pivotal role in dictating the observed electrochemical response, which is analyte dependant. Consequently there is potential for this new member of the graphene family to be beneficially utilised in various electrochemical applications.