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In this work, graphene and multi-walled carbon nanotubes were derivatised with anthraquinone (AQ) groups using spontaneous or electrochemical grafting of Fast Red AL salt. Glassy carbon (GC) electrodes were coated with AQ-modified carbon nanomaterials to study the oxygen reduction reaction (ORR). These nanomaterials were characterised by X-ray photoelectron spectroscopy and multilayer formation of AQ on the electrografted electrodes was observed. All the modified electrodes showed enhanced electrocatalytic activity towards the ORR in alkaline media. High AQ loading on the electrodes was found and the number of electrons transferred per O2 molecule was between 2 and 4. In addition, the stability testing of AQ-derivatised carbon nanomaterial-coated GC electrodes was performed. [ABSTRACT FROM AUTHOR]

Abstract: Three different azobenzene derivatives (azobenzene diazonium tetrafluoroborate, Fast Garnet GBC sulphate salt and Fast Black K salt) were covalently attached to glassy carbon (GC) electrodes by electrochemical grafting. The grafting of GC surfaces was controlled by varying the number of potential cycles during the modification procedures. The presence of azo groups on the modified electrode surfaces was confirmed by X-ray photoelectron spectroscopy. The electrochemical properties of the modified electrodes were characterised by cyclic voltammetry and the rotating disc electrode (RDE) technique using the redox system. The blocking behaviour of aryl films towards oxygen reduction was studied by linear sweep voltammetry and the RDE method. The blocking action of the aryl-modified electrodes for ferricyanide reduction was significantly greater than for O2 reduction. By estimating the parameter of relative blocking efficiency the best barrier properties were observed for azobenzene-modified GC electrodes. [Copyright &y& Elsevier]

In this paper, aryl films are grafted via electrochemical reduction of two different diazonium salts, 4-nitrobenzenediazonium tetrafluoroborate and Fast Red AL salt, in different conditions on polycrystalline copper electrodes. For the surface modification, “normal” electrografting, redox grafting (RG) and for the first time, RG and rotating disk electrode combined method are used. The obtained aryl films are characterized by X-ray photoelectron spectroscopy and atomic force microscopy. Surface concentrations of redox active moieties are determined in acetonitrile and highest values of ca. 25 and 12 nmol cm −2 are obtained in case of nitrophenyl and anthraquinone films, respectively. Different aryl films exhibit unequal blocking action toward ferricyanide probe and also variable degree of inhibition of the O 2 reduction rate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] O2 reduction was studied on GC electrodes modified with thick anthraquinone films. [•] AQ groups were electrografted onto GC surface using the diazonium reduction method. [•] The XPS analysis confirmed the presence of azo linkages within the AQ film. [•] The O2 reduction activity of the AQ films of various thickness was rather similar. [•] Two-electron reduction of oxygen to hydrogen peroxide was in evidence. [Copyright &y& Elsevier]