Pt/Ru-functionalized magnetic spheres for a magnetic-field stimulated methanol and oxygen redox processes: Towards on-demand activation of fuel cells Joseph Wang * , Mustafa Musameh, Rawiwan Laocharoensuk, Olga Gonza ´lez-Garcı ´a, Joshua Oni, Don Gervasio Departments of Chemical & Materials Engineering and Chemistry and Biochemistry, Ira A. Fulton School of Engineering, The Biodesign Institute, Arizona State University, P.O. Box 876006, Tempe, AZ 85287-5801, USA Received 29 March 2006; received in revised form 24 April 2006; accepted 25 April 2006 Available online 12 June 2006 Abstract Pt/Ru-functionalized magnetic spheres were used for a magnetic-field stimulated methanol oxidation and oxygen reduction processes. The electrocatalytic alloy magnetic particles were prepared by a galvanostatic co-deposition of platinum and ruthenium onto nickel spheres. The electrocatalytic oxidation of methanol and reduction of oxygen could be triggered by switching the position of an external magnet below the surface of the carbon electrode to confine the Pt/Ru-coated particles. The magnetic stimulation of the redox processes of methanol and oxygen allowed the reversible activation and deactivation of the operation of direct-methanol fuel cells. Such switching of fuel cells would enable on-demand power generation, for meeting the specific needs of power consuming units. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Magnetic switching; Pt–Ru alloy; Methanol; Fuel cell; Oxygen; Nickel particles 1. Introduction Extensive research has been devoted recently to the magnetic control of bioelectrocatalytic [1,2] and electrocat- alytic [3] processes. Such magneto-switchable processes are commonly accomplished through cyclic attraction and retraction of functionalized magnetic beads by means of an external magnet. For example, magnetic particles func- tionalized with redox relay units (e.g., ferrocenyl, naphto- quinone) have been used for magnetic control of enzymatic reactions [1,2]. Similarly, reversibly magnetic stimulated oxidation of DNA was accomplished in the presence of nucleic-acid modified magnetic spheres [4]. Alkyl-chain functionalized magnetic particles were employed for regulating the interfacial properties of elec- trode surface and controlling biocatalytic transformations on such interfaces [5,6]. The magnetic and electrocatalytic properties of nickel microparticles have been exploited for magnetoswitchable control of the electrochemical reac- tivity without the need of functionalized ferromagnetic par- ticles [7]. Magnetic control of the electrochemical reactivity has also been accomplished by controlling the surface ori- entation of electrocatalytic/magnetic nanowires [8]. This communication reports on the use of Pt/Ru-func- tionalized magnetic spheres for switching ‘on/off’ the meth- anol and oxygen oxidation and reduction processes, respectively. We will also demonstrate on the use of such magnetically-stimulated redox processes for on-demand switching of fuel cells. Fuel cells represent attractive alter- natives to our present power sources. Direct-methanol fuel cells (DMFC) are attracting much attention because of their great promise for powering portable electronic devices. Pt–Ru alloys are considered as the most suitable anode electrocatalyst for the oxidation of methanol in DMFC owing to their extended lifetime and lower overpo- 1388-2481/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2006.04.019 * Corresponding author. Tel.: +1 480 727 0399. E-mail address: joseph.wang@asu.edu (J. Wang). www.elsevier.com/locate/elecom Electrochemistry Communications 8 (2006) 1106–1110