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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: The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O2 reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies. [Copyright &y& Elsevier]

Abstract: In this paper, the electrochemical reduction of oxygen has been studied on gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) modified glassy carbon (GC) electrodes in 0.5M H2SO4 using the rotating disk electrode (RDE) method. The AuNP/MWCNT catalysts were prepared by chemical deposition of AuNPs onto MWCNTs spontaneously grafted with 4-nitrophenyl groups. The composite electrode was characterised by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The oxygen reduction behaviour of these electrodes was compared with that of a bulk gold electrode. The AuNP/MWCNT catalyst showed a pronounced electrocatalytic activity towards O2 reduction in acid media. The half-wave potential of O2 reduction on the AuNP/MWCNT catalyst shifted ca 80mV to more positive potentials as compared to that of a polished Au electrode. The kinetic parameters of oxygen reduction were determined and the specific activity of the hybrid electrode was slightly higher than that of the bulk Au electrode. [Copyright &y& Elsevier]

Abstract: Aryl layers on glassy carbon and gold electrodes were degraded by hydroxyl radicals from UV photolysis of hydrogen peroxide. The electrode surfaces were modified via electrochemical reduction of two structurally different azobenzene diazonium derivatives. The degradation of the aryl films was studied by AFM, XPS and electrochemical measurements using [Fe(CN)6]4− as solution probe. While the prepared aryl layers inhibited the electrochemical response of hexacyanoferrate, their degradation with OH radicals resulted in different electrochemical behaviours for glassy carbon and Au electrodes. The aryl layer on glassy carbon was thinned, indicated by the increasing reversibility of the [Fe(CN)6]4− response, whereas the aryl film on Au showed pinhole formation, indicated by the microelectrode behaviour of the hexacyanoferrate response without retarded reversibility. [Copyright &y& Elsevier]

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]

Abstract: The electrochemical response of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) on aryl-modified glassy carbon (GC) electrodes has been investigated. The electrochemical modification of GC surface with 4-nitrophenyl (NP) and 4-carboxyphenyl (CP) groups was performed using the diazonium reduction method. The 4-aminophenyl-modified GC electrodes were obtained by electroreduction of NP films. The surface coverage of aryl groups was altered by varying the number of potential scans during electrografting experiments. The electrochemical behaviour of ABTS was studied on bare and aryl-modified GC electrodes using cyclic voltammetry and the rotating disk electrode (RDE) methods. Electrochemical measurements were performed in acetate and phosphate buffers (pH=4–8) to study the effect of pH on the electron transfer process. The response of ABTS was independent of pH for bare GC and GC/NP electrodes (modified by 20 electrografting scans), whereas a slight pH-dependence was observed for other electrodes. The strongest blocking action was observed for the NP-modified GC electrodes of higher surface coverage and the lowest for reduced NP films (modified by a single electrografting scan). [Copyright &y& Elsevier]

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]

Abstract: The oxygen reduction reaction has been investigated on acid-treated single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT) modified glassy carbon (GC) electrodes in acid media using the rotating disk electrode (RDE) method. Different acids were used for the carbon nanotube (CNT) purification. A systematic study was carried out to elucidate whether the metal catalyst impurities of CNTs play a role in the electroreduction of oxygen on the CNT modified GC electrodes. The surface morphology of the carbon nanotube samples was examined by transmission electron microscopy and the concentration of metal catalysts in the CNT materials was determined by energy dispersive X-ray spectroscopy. The acid-treated MWCNTs were also characterised by Raman and X-ray photoelectron spectroscopies. Aqueous suspensions of SWCNTs and MWCNTs used for GC surface modification were prepared in the presence of Nafion. The RDE results indicated that the acid-treated CNT modified GC electrodes are less active catalysts for oxygen reduction than as-received CNTs which could be explained by the absence of metal catalysts on the surface of purified CNTs. [Copyright &y& Elsevier]

Abstract: FIB-SEM, XPS and gas adsorption methods have been used for the characterisation of physical properties of microporous carbide derived carbon electrodes prepared from Mo2C at 600°C (noted as CDC-Mo2C). Cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectroscopy have been applied to establish the electrochemical characteristics for supercapacitors consisting of the 1M Na2SO4, KOH, tetraethyl ammonium iodide or 6M KOH aqueous electrolyte and CDC-Mo2C electrodes. The N2 sorption values obtained have been correlated with electrochemical characteristics for supercapacitors in various aqueous electrolytes. The maximum gravimetric energy, E max, and gravimetric power, P max, for supercapacitors (taking into consideration the active material weight) have been obtained at cell voltage 0.9V for 6M KOH aqueous supercapacitor (E max =5.7Whkg−1 and P max =43kWkg−1). For 1M TEAI based SC somewhat higher E max (6.2Whkg−1) and comparatively low P max (7.0kWkg−1) have been calculated. [Copyright &y& Elsevier]