First principles and Monte Carlo studies of adsorption and desorption properties from Pd${}_{1-\mathrm{x}}$Ag${}_{\mathrm{x}}$ surface alloy

Abstract

The FCC structure of Pd${}_{1-\mathrm{x}}$Ag${}_{\mathrm{x}}$ ($\mathrm{x}=$ 0.25, 0.50, 0.75) alloys is considered as a fuel cell component in this study. We have looked into its qualities as a component of a fuel cell to see whether it could be potentially used as an alternative replacement of the Pt catalyst. We used Density Functional Theory (DFT) to study H and CO interaction with the surface, and Kinetic Monte Carlo~(KMC) to study H and CO desorption from the surface. The bulk modulus and equilibrium crystal structures of Pd${}_{1-\mathrm{x}}$Ag${}_{\mathrm{x}}$ alloys were computed using the GPAW code within plane wave basis set $\&$ a PBE exchange correlation functional treatment. The best values of a lattice constant for the system are obtained by total energy calculations versus lattice cell volumes as fitted to the stabilized jellium model. Surface energies, cohesive energies, and\ binding energy of Pd${}_{1-\mathrm{x}}$Ag${}_{\mathrm{x}}$ alloys were computed to analyze the stability properties of structures. Band structure calculations reveal the electronic and optical properties of these alloys. The density of states~(DOS) and projected density of states~(PDOS) show the availability of the eigenstates for occupation. The desorption process is studied within the Arrhenius type desorption rate $\&$ a temperature programming. The effects of lateral interactions between adsorbed molecules on first order desorption (molecular adsorption) $\&$ second order desorption were taken into account. Adsorption energies of H and CO on Pd${}_3$Ag~(111) as calculated using DFT is used in the process. The outcomes show good qualitative agreement with literature.