Abstract
Pt-based catalysts are commonly used as cathode materials in various types of fuel cells. In this work we apply DFT calculations combined with cluster expansion method to elucidate the most stable structures of Pt-Co bulk alloy across the full range of Pt (or Co) concentrations. Our calculations reveal high stability of alloy configurations with alternating layers in (001) crystallographic planes of face centered cubic (fcc) structure exclusively occupied either by Pt or Co atoms. In particular, we find that Pt1Co1, Pt2Co1 and Pt3Co1 layered structures (periodically repeated 1–3 Pt layers, separated by single Co layers) have exceptionally high stability with Pt2Co1 possessing the lowest energy of formation among all analysed alloy configurations. Employing ab initio thermodynamics approach, we discuss stability of three types of surface terminations (Miller indices (100), (110) and (111)) for these three layered structures and also for highly symmetric fcc Pt3Co1 configuration, previously identified experimentally. Applying the Wulff construction, we obtain the nanoparticle shapes as functions of chemical potentials of constituent atoms (Pt or Co), allowing for design of computational models of Pt-Co nanoparticles and subsequent analysis of their chemical properties.
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