Theoretical Methodology for Studying Oxygen Reduction Reaction (ORR) on Disordered Binary Alloy Surfaces
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Theoretical Methodology for Studying Oxygen Reduction Reaction (ORR) on Disordered Binary Alloy Surfaces Ernesto Lopez-Chavez1, Alberto García-Quiroz1, Gerardo González-García1, Juana Laura Islas-Gómez2, José A. I. Díaz-Góngora3, L. Cesar de la Portilla-Maldonado4 and F.L Castillo-Alvarado4 1 Universidad Autónoma de la Ciudad de México. Av. Fray Servando Teresa de Mier 92-110. Col. Centro Histórico, Del. Cuauhtémoc, CP 06080 Ciudad de México, D.F., México. 2 Universidad Autónoma Metropolitana. Av. San Pablo 180, Reynosa Tamaulipas, Azcapotzalco, 02200 Ciudad de México D. F., México. 3 Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada del Instituto Politécnico Nacional. Legaria 694, Col. Irrigación, Miguel Hidalgo, CP 11500 Ciudad de México D. F., México. 4 Instituto Politécnico Nacional. Edificio 9 Unidad Profesional Adolfo López Mateos, Zacatenco, México, D.F., CP 07738 Ciudad de México D. F., México.
ABSTRACT The catalytic activity of disordered binary alloy metal surfaces is investigated for the oxygen reduction reaction (ORR) by generating free energy diagrams and performing calculations on d-band centers of alloys. The disorder was simulated using virtual crystal approximation; then, based on periodic, self-consistent density functional theory (DFT) methods, we calculated adsorption energies of reaction intermediates. Alternative pathway for ORR mechanism, involving proton/electron transfer to adsorbed oxygen and hydroxyl, is considered. The methodology was applied to (111) surface of PdxCu1-x disordered binary alloys, with different values of x concentration. This study found that at the ORR equilibrium potential of 1.23 V, the reactivity of all surfaces is shown to be limited by the rate of OH removal from the surface. Among the surfaces studied, the surface of Pd0.80Cu0.20 shows the highest reactivity and is more active than other non-Pt alloys. These results are in excellent agreement with earlier experimental and theoretical work. INTRODUCTION The ORR reaction is one of the key for improving the performance of low-temperature proton-exchange-membrane fuel cells (PEMFCs). Platinum is the most used material as cathode in PEMFCs, however, there are some problems in these materials that must be addressed and overcome in order to improve efficiency and production costs of fuel cells, among them: the poisoning by hydroxyl species (OH) in these material, the cost related to shortage of these metals and the low rate of the cathode reaction. So, it is desirable to develop theoretical methodologies in order to design stable non-Pt catalysts that improve ORR activity and increased resistance to OH poisoning. In recent years, Pd has been tested as a new alternative to replace Pt, for example, Nilekar and Mavrikakis have theoreticaly tested a new class of electrocatalysts for ORR that are based on monolayers of Pt deposited on Pd [1]; Yu and co-workers [3] used periodic quantum mechanics calculations to determine new alloy candidates for PEMFCs cathodes, they
considered binary alloys composition Pd3X
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