Polyaniline Electrodes with Atomic Au n Pd 1 Alloys: Oxidation of Methanol and Ethanol
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Polyaniline Electrodes with Atomic AunPd1 Alloys: Oxidation of Methanol and Ethanol Ilana T. Schwartz • Alex P. Jonke • Mira Josowicz Jirˇ´ı Janata
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Received: 15 May 2013 / Accepted: 21 May 2013 / Published online: 4 June 2013 Ó Springer Science+Business Media New York 2013
Abstract The effect of addition of one atom of palladium to n atoms of gold (n = 1–5) dispersed in polyaniline electrodes, for the electrooxidation of methanol and ethanol in alkaline solution has been investigated. For comparison, oxidation at pure atomic metal electrodes, Pt/ PANI–Aun=2–7 and Pt/PANI–Pdn=2–6, was performed. It is shown that the one added Pd atom affects the oxidation peak currents and makes a significant difference in selectivity. Similar to our previous studies, the electrocatalytic activity has been correlated with the theoretically predicted HOMO–LUMO gap energies for the atomic metal alloys. Keywords Alkaline alcohol oxidation Gold–palladium catalysis Atomic metal electrodes
1 Introduction It is generally accepted that at sufficiently high pH, the selective electrocatalytic oxidation of alcohols involves deprotonation of the alcoholic group and the formation of the alkoxy anion, the active species in the oxidation reaction [1]. A key strategy in developing an efficient electrocatalyst is to favor the generation of the reactive adsorbed species while decreasing the amount of poisoning species (CO-like species), either by preventing its formation by blocking neighboring metal sites or by oxidizing them at a lower potential [2]. This can be achieved by alloying the catalyst [3].
I. T. Schwartz A. P. Jonke M. Josowicz J. Janata (&) School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA e-mail: [email protected]
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For practical economical applications, the amount of catalytic metal used must be minimized, especially when using expensive metals such as gold. It has been shown that metal clusters can be highly dispersed throughout a polyaniline (PANI) matrix to effectively increase the surface area of the catalyst to increase activity. Gold has been one of these metals and is effective for the oxidation of alcohols at high pH. Gold nanoparticles form a charge transfer complex with PANI and act as an electron acceptor [4]. It is possible to further increase the catalytic activity of a metal cluster by introducing a second type of metal to the cluster. The synergetic effect of a Au–Pd catalyst is revealed in its activity and stability and can be assigned to both electronic and geometric factors that are determined by the size of the alloyed Au and Pd atoms [5, 6]. Furthermore, recently calculated geometric, electronic, and bonding properties of palladium-doped gold clusters, AunPd (n = 1–5), demonstrated that the Pd-dopant atom could markedly change the properties of the atomic gold cluster [7]. It was found that Pd contributes one electron with the promotion of one electron from 4d to 5s in AunPd1. Due to the relatively strong bonding interaction contribu
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