Bismuth decoration of electrodeposited platinum thin films with a preferential (100) orientation
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Bismuth decoration of electrodeposited platinum thin films with a preferential (100) orientation E. Bertin, S. Garbarino, M.H. Martin and D. Guay Institut National de la Recherche Scientifique, Énergie, Matériaux, Télécommunications, 1650 Boul. Lionel Boulet, J3X 1S2, Varennes, Québec, CANADA ABSTRACT Preferentially {100} oriented and polycrystalline platinum electrodes were prepared by potentiostatic electrodeposition. The surface of the electrodes was characterized by deconvolution of the hydrogen desorption region. The catalytic activity for formic acid oxidation was determined by cyclic voltammetry and chronoamperometry. The results indicate that although the maximum current observed in cyclic voltammogram does not increase, the long term performances as measured by chronoamperometry dramatically increase up to 33 times with increased Bi coverage despite the loss of electroactive Pt surface area. INTRODUCTION The development of fuel cells has regained considerable interest in the last years. The oxidation of potential fuels such as formic acid, methanol, ethanol, etc. has been studied on a wide spectrum of catalysts. In acidic media, platinum remains the most active catalyst available, despite its cost, scarcity, and its vulnerability to CO poisoning. To overcome this last issue, alloys such as PtCo, PtRu, etc. and core-shell nanostructures were prepared to increase the CO tolerance (1), allowing also a reduction of the electrode cost (2, 3) and in some cases an improvement of the catalytic activity (4, 5). More recently, a different approach has emerged as a new way to prepare electrocatalysts, based on the formation of well defined crystalline surfaces (6). In acidic solution, platinum (100) single crystals, nanoparticles and electrodeposited thin films were shown to display enhanced activity for formic acid oxidation. However, due to rapid poisoning, the activity decreases steadily with time and low current density is obtained for experiments lasting more than 30 min(7, 8). In this study, to increase the poisoning tolerance of platinum, polycrystalline and preferentially {100} oriented Pt thin films were decorated by bismuth atoms. The bismuth coverage (0-80%) was evaluated from the decrease of the charge in the hydrogen desorption region. The electrocatalytic performances for formic acid oxidation were determined by means of cyclic voltammetry and chronoamperometry. EXPERIMENT Platinum thin films were electrodeposited on titanium substrate (Alfa Aesar, 99%, 0.2 mm thickness), pretreated according to the procedure described elsewhere (9). The electroplating solution consisted of HCl 10 mM (Fisher Scientific, ACS) and Na2PtCl6·6H2O (Alfa Aesar) x mM (where x = 0.5 mM for preferentially {100} oriented film and 5.0 mM for polycrystalline). All depositions were achieved under potentiostatic conditions using a Solartron Si 1287
potentiostat-galvanostat, the deposition potential referred to the standard calomel electrode (SCE). Electrochemical characterisation was performed in a standard three-compartment cell us
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