Simultaneous Electrochemical Exfoliation and Functionalization of Graphene By Diazonium Compounds

Covalent functionalisation of graphene is considered as one method for enhancing the processability of graphene for various applications. The majority of the study to-date has focused on the functionalization of pre-made graphene. 1-3 In this contribution, we describe single stage simultaneous electrochemical exfoliation and functionalisation of graphene using diazonium compounds. Caesium salt (dissolved in dimethyl sulfoxide) as intercalating ions in combination with diazonium salt (either 4-nitrobenzenediazoniumtetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate or anthraquinone-1-diazonium chloride) as functionalisation moieties were used. Simultaneous exfoliation and functionalisation is beneficial for a number of reasons. First, the presence of diazonium salt in the exfoliation solution not only plays a role in functionalisation but also facilitate the exfoliation process through the generation of N 2 gas which assists the separation of the functionalised graphene layers. Second, this process is selective for edge functionalisation and finally as both functionalisation and exfoliation occurs at the same time, monolayer or few layer graphene can be functionalised in situ before they aggregate. Significantly, functionalisation enhanced the dispersibility of graphene in aqueous solution and its solubility was two orders of magnitude larger than the non-functionalised electrochemically exfoliated graphene. As also shown in Figure 1, the functionalisation introduced surface active redox reactions when used as a supercapacitor electrode. The redox reactions enhanced the charge storage capacity of graphene and the specific capacitance found to be highly dependent on the degree of graphene functionalization. 1. J. R. Lomeda, C. D. Doyle, D. V. Kosynkin, W.-F. Hwang and J. M. Tour, J. Am. Chem. Soc. , 2008, 130 , 16201-16206. 2. E. Bekyarova, M. E. Itkis, P. Ramesh, C. Berger, M. Sprinkle, W. A. de Heer and R. C. Haddon, J. Am. Chem. Soc. , 2009, 131 , 1336-+. 3. J. Greenwood, T. H. Phan, Y. Fujita, Z. Li, O. Lvasenko, W. Vanderlinden, H. Van Gorp, W. Frederickx, G. Lu, K. Tahara, Y. Tobe, H. Uji-i, S. F. L. Mertens and S. De Feyter, ACS Nano , 2015, 9 , 5520-5535. Figure 1. Cyclic voltammograms recorded at 100 mV s -1 in 6.0 M KOH (aq) using symmetrical coin cells constructed from electrochemical exfoliated restacked graphene and graphene functionalised insitu with 4-nitrobenzenediazoniumtetrafluoroborate (G-NBD). The voltage was swept between 0.0 V to 1.0 V Figure 1