Electrocatalytic Reduction of Oxygen on a Pd Ad-Layer Modified Au(111) Electrode in Alkaline Solution
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Electrocatalytic Reduction of Oxygen on a Pd Ad-Layer Modified Au(111) Electrode in Alkaline Solution Zekerya Dursun Æ S¸u¨kriye Ulubay Æ Buket Gelmez Æ F. Nil Ertas¸
Received: 27 March 2009 / Accepted: 4 June 2009 / Published online: 8 July 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Oxygen reduction was studied on palladium, cadmium and zinc ad-atom modified single crystal Au(111) electrodes. The electrodes were modified by underpotential deposition process and their activity towards oxygen reduction was studied in alkaline media by voltammetry. The reduction peaks obtained were compared with those of bare Au(111), Pd disc and bulk deposited Cd electrodes. Enhanced catalytic activity of the Au(111) electrode in the presence of Pd, Cd and Zn ad-layer can be attributed to a change in surface charge and energy by ad-layer formation. In oxygen saturated medium a well defined sharp reduction peak was observed at -0.12 V for 1/5 ML Pd ad atom modified Au(111) electrode while it was positioned at -0.18 V on a Pd disk electrode. The best shift in reduction peak potential was obtained with 2/5 ML Pd ad atom modified Au(111) electrode with similar current density of Pd disc electrode. Keywords Oxygen reduction UPD Pd ad-layer Au(111) single crystal electrode Fuel cell Catalyst
1 Introduction The electrochemical behavior of oxygen is particularly important for clean energy generation systems like fuel cells and other electrochemical technologies. The reaction mechanism includes multi-electron reduction in aqueous solution proceeding in two overall pathways depending on electrode material and solution pH [1–5]. Bare electrode Z. Dursun (&) S¸ . Ulubay B. Gelmez F. N. Ertas¸ Science Faculty, Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkey e-mail: [email protected]; [email protected]
surfaces generally induce oxygen reduction via a twoelectron reduction process at two different potentials. Numerous materials have been proposed to prepare a catalytic electrode surface on which a four-electron reduction takes place in one step [6, 7]. Among transition metals, gold has a distinguished performance due to its high electrocatalytic activity and therefore, single crystal gold electrodes were mostly used as active planes. In particular, OH- anions, specifically adsorbed on the single crystal electrode surface, were found to play a key role in increasing electrocatalytic activity in alkaline media. Fundamental studies on this area have revealed the orientation dependency on the kinetics and mechanism of oxygen reduction and the best activity was obtained with an Au(100) crystal electrode where a four-electron reduction of molecular oxygen to water occurred in pH [6.0 media [1, 8–14]. On the other hand, a surface modification is required to improve electrocatalytic activity of Au(111) crystal electrode where two-electron reduction takes place otherwise [15, 16]. Over the last decade, electrode surfaces have been frequently modified with ad-metals [17, 18] or metal nanoparti
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