Electrografting and morphological studies of chemical vapour deposition grown graphene sheets modified by electroreduction of aryldiazonium salts Marek Mooste a , Elo Kibena a,1 , Jekaterina Kozlova b , Margus Marandi b , Leonard Matisen b , Ahti Niilisk b , Väino Sammelselg a, b , Kaido Tammeveski a,1, * a Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia b Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia A R T I C L E I N F O Article history: Received 5 December 2014 Received in revised form 2 February 2015 Accepted 4 February 2015 Available online 7 February 2015 Keywords: Graphene Chemical vapour deposition Diazonium salts Electrografting Surface modification A B S T R A C T This work focuses on investigating the electrografting of chemical vapour deposition (CVD) graphene electrodes grown onto Ni foil (Ni/Gra) with different diazonium salts (including azobenzene diazonium tetrafluoroborate, Fast Garnet GBC sulphate salt, Fast Black K salt, 4-bromobenzene diazonium tetrafluoroborate and 4-nitrobenzenediazonium tetrafluoroborate). Various grafting conditions (e.g. “normal” electrografting in the narrow potential range and redox grafting in the wider potential range) were used. The electrochemical grafting behaviour was similar for all diazonium compounds used, except for the 4-nitrobenzenediazonium tetrafluoroborate when redox grafting was applied. The X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy results confirmed the presence of the corresponding aryl layers on Ni/Gra surfaces. The formation of multilayers on Ni/Gra substrates was in evidence since the thickness of different aryl layers varied from few to 30 nm depending on the modification procedures as well as the diazonium compounds used and the XPS analysis revealed a peak at about 400 eV for all aryl-modified Ni/Gra samples suggesting the multilayer formation also through azo linkages. ã 2015 Elsevier Ltd. All rights reserved. 1. Introduction Since the successful isolation of graphene from highly oriented pyrolytic graphite (HOPG) by mechanical exfoliation with Scotch tape [1], this innovative two-dimensional one-atom thick nano- sheet with interesting properties has gained a lot of interest. On the one hand, a high quality monolayer graphene can be prepared by the Scotch tape method, but on the other hand this method is time- consuming and not suitable in mass production for commercial use [2]. According to the literature, the most promising route for synthesising a large-area graphene at present is by chemical vapour deposition (CVD) on different catalytic metal substrates (e.g. Ni, Cu, Pt) [3–6]. The choice of the metal substrate greatly depends on the cost and therefore the low-cost polycrystalline Ni has been widely employed in order to synthesise graphene by CVD [2]. It has been shown that mono- or bilayer graphene is usually formed on Ni single crystal surface, whereas multilayer graphene is grown on polycrystalline Ni by CVD [7]. Functionalisation of graphene with organic layers is of utmost importance. First, because of the specific properties of graphene itself [8,9] and secondly, since functionalised graphene has shown a number of promising applications, for example, graphene has been used as a platform for the development of biosensors [10,11]. Previous studies have shown that the diazonium reduction is an attractive way for modifying the electrode surfaces (e.g. glassy carbon, HOPG, graphene) because depending on the purpose different aryl groups can be strongly attached to the carbon-based materials [12–16]. This method was first introduced by Pinson and Savéant workgroup [17]. In short, it is based on the one-electron reduction of an aryldiazonium cation followed by elimination of dinitrogen giving an aryl radical, which reacts with the electrode surface forming a strong bond between aryl group and substrate (including CVD-grown graphene, see Scheme 1) [12–14,16]. Numerous studies reported the spontaneous reduction of various diazonium salts to modify graphene-based substrates (including CVD-grown graphene) [18–22]. To date, very few studies have addressed the electrochemical grafting of CVD-grown * Corresponding author. Tel.: +372 7375168; fax: +372 7375181. E-mail address: kaido.tammeveski@ut.ee (K. Tammeveski). 1 ISE member http://dx.doi.org/10.1016/j.electacta.2015.02.035 0013-4686/ ã 2015 Elsevier Ltd. All rights reserved. Electrochimica Acta 161 (2015) 195–204 Contents lists available at ScienceDirect Electrochimica Acta journa l home page : www.e lsevier.com/loca te/ele cta cta