Electrocatalytic reduction of oxygen on bimetallic copper–gold nanoparticles–multiwalled carbon nanotube modified glassy carbon electrode in alkaline solution Çag ˘rı Ceylan Bakır a , Nihat S ßahin b , Ramazan Polat a , Zekerya Dursun a,⇑ a Department of Chemistry, Science Faculty, Ege University, 35100 Bornova, Izmir, Turkey b Department of Chemistry, Science Faculty, Istanbul Technical University, Istanbul, Turkey article info Article history: Received 7 March 2011 Received in revised form 8 June 2011 Accepted 14 June 2011 Available online 6 July 2011 Keywords: Oxygen reduction Cu–Au nanoparticle Carbon nanotube Glassy carbon Fuel cell abstract Multiwalled carbon nanotubes (MWCNTs) were functionalized with acid treatment and thereafter gold– copper nanoparticles were electrodeposited on the MWCNTs by applying several repetitive scans, thus forming a Cu–Au–MWCNT/GCE interface. The electrochemical reduction of oxygen was studied on this modified electrode in 0.1 M NaOH solution. The electrocatalytic activity on the Cu–Au–MWCNT/GCE showed a tendency towards the O 2 reduction. The peak potential of O 2 reduction on the Cu–Au– MWCNT/GCE shifted ca. 70 mV higher positive potentials as compared to that of a polished glassy carbon electrode. A significant current enhancement was obtained on the Cu–Au–MWCNT/GCE compared to that of bare GCE, MWCNT/GCE, Cu–MWCNT/GCE and Au–MWCNT/GCE. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed in order to investigate the surface morphol- ogy and elemental composition of the modified electrode, respectively. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Oxygen reduction is one of the most important reactions in chemistry due to its significant role in fuel cells, batteries, chlo- rine/alkali production, and electrosynthesis of hydrogen peroxide, metal corrosion, and gas sensors [1–4]. Investigations of renewable and clean power sources have been studied for several decades. In this way, fuel cells have been considered as candidates for mini- mizing the usage of fossil fuels [5]. Despite recent advances, sev- eral issues, such as limited oxygen reduction reaction due to its high overpotential, are expected to be sorted out. Therefore, recently, various new types of cathode catalysts, such as single crystals of noble metals [6,7], single crystals modified with different metal ad-layers [8,9], Pt-free catalysts [10,11] and Pt-based metal alloys [12,13] have been applied for electrocatalytic reduction of oxygen. Carbon nanotubes (CNTs) possess many special properties, such as high chemical stability, good electrical conductivity, enhanced mass transport capability, and high surface area [14–17]. Several studies have reported the use of carbon nanotubes as sensitive electrodes for some certain analyses involving coenzymes [18], neurotransmitters [19], nucleic acids [20], and also oxygen reduc- tion reaction [21–23]. Modified electrodes, particularly, metal nanoparticles modified electrodes have been extensively used in electrochemical studies due to their higher catalytic activity, electron transfer rate, and in- creased electrode surface area compared to the common regular electrodes [24,25]. The surface-catalyzed reactions on modified electrodes are extremely depends on catalytic surface composition and its preparation method. Therefore, various kind of methods have been used for preparation of modified electrode surfaces with metal nanoparticles such as electrodeposition [26], an in situ ion exchange method [27], and a supercritical liquid method [28]. Oxygen reduction has been intensively studied on various mod- ified electrodes such as platinum free catalyst synthesized on car- bon black [29], gold nanoparticles deposited boron-doped diamond film [30], gold nanoparticles modified GCE [31], gold nanoparticles/PDDA-MWCNT nanocomposite [22], and gold nano- particles/multiwalled carbon nanotube modified glassy carbon electrodes [32]. Previous reports also indicated that metal nano- particles have a rather significant effect on the oxygen reduction reaction with a lower cost [33–35]. The reaction mechanism of oxygen reduction is highly influ- enced by the electrode material leading a two-electron or direct four-electron process [35–37]. While hydrogen peroxide formation by two-electron reduction electrode process occurred on common electrodes [38,39], a direct four-electron reduction electrode 1572-6657/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2011.06.016 ⇑ Corresponding author. Tel.: +90 2323884000/2365; fax: +90 2323888264. E-mail addresses: dursunz@hotmail.com, zekerya.dursun@ege.edu.tr (Z. Dursun). Journal of Electroanalytical Chemistry 662 (2011) 275–280 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem