Density functional theory study on the adsorption of H, OH, and CO and coadsorption of CO with H/OH on the Pt 2 Ru 3 sur
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This paper presents a periodic density functional theory study on the adsorption of H, CO, and OH on Pt2Ru3 alloy surfaces containing different conformations of Pt and Ru atoms. The results show that for separate adsorption, H is preferentially adsorbed at Pt sites, whereas CO and OH are preferentially adsorbed at Ru sites. The adsorption strengths of H, CO, and OH are affected by ratio of the alloying atoms in top surface, the nature of the neighboring atom nearest to the adsorption site, and the conformation of alloying atoms in subsurface. We also investigated the coadsorption of CO with OH and the coadsorption of CO with H and found that the Pt–CO bond strength weakens. We also uncovered some information about the competitive adsorption behavior of adsorbates (CO, OH) with the aim of designing CO-tolerant Pt–Ru alloy catalysts.
I. INTRODUCTION
The adsorption and oxidation of CO on metal electrodes fundamental problems in heterogeneous catalysis, electrochemistry, and fuel cell technology. Fuel cells function as electrochemical engines that convert the chemical energy released into the reaction of H2 and O2 and then into electrical energy. Polymer electrolyte fuel cells (PEFCs) have applications in a variety of areas such as electric vehicles and mobile devices because of their high electrical power densities and low working temperatures. However, several problems need to be solved before commercializing PEFCs. One of the most challenging tasks is related to electrodes. Pt is used for both the anode and cathode sides of PEFCs. At the anode side, H2 gas is adsorbed on the surface of the Pt electrode and is transformed into protons and electrons catalyzed by Pt. One problem is caused by CO impurities contained in the fuel gas. Even if contamination is of the order of parts per million, CO molecules almost fully cover the surface of the Pt electrode and prevent H2 fuel gas from reacting on the Pt surface.1 This loss of catalytic function caused by CO gas is known as CO poisoning. Bimetallic catalysts are useful due to their versatility; their catalytic activities and selectivity’s can be tuned by varying properties such as composition, particle size, and support. CO oxidation on transition metal and oxide catalysts has attracted much interest in recent years. Tremendous efforts have been devoted to the removal Contributing Editor: Susan B. Sinnott a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.286
of CO contamination from H2 fuel. Attempts to increase activity by alloying Pt with a second metal have also been reported recently. The presence of a second metal such as Ru, Sn, or Mo in the anode catalyst, either alloyed or co-deposited with Pt, has provided remarkable improvements in CO tolerance.2–7 Among the many reports, Pt–Ru alloys have been studied most intensively because they are known to be the most promising electrodes for overcoming the CO poisoning problem.8–10 Thus far, the alloying effects have been interpreted in terms of ligand and bifunctional e
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