Structure, Electronic, and Magnetic Properties of Binary PtnTM55-n (TM = Fe, Co, Ni, Cu, Zn) Nanoclusters: A Density Functional Theory Investigation

Bimetallic platinum-based transition-metal (PtTM, TM = Fe, Co, Ni, Cu, and Zn) nanodusters are potential candidates to improve and reduce the cost of Pt-based catalysts; however, our current understanding of the binary PtTM nanoclusters is far from satisfactory compared with binary surfaces. In this work, we report a density functional theory investigation of the structural, energetic, and electronic properties of binary PtTM nanodusters employing 55-atom model systems (PtnTM55-n). We found that the formation of the binary PtTM nanodusters is energetically favorable for all systems and compositions. Except small deviations at the icosahedron (ICO) core-shell configuration, Pt42TM13, we found that the excess energy, which measures the relative stability, and the chemical order parameter follow nearly a parabolic behavior as a function of the Pt concentration with a minimum at nearly 50% for both properties and all systems. From our structural analysis, the difference in the atomic size of the Pt and TM chemical species contributes to increase the segregation, which reaches its maximum for the ICO core-shell configuration, and hence, an ideal homogeneous distribution cannot be reached. Except for PtZn, we found that the average bond lengths increase almost linearly by replacing TM by Pt atoms in the PtnTM55-n systems, and hence, it follows approximately the Vegard's law. We found that the center of gravity of the occupied d-states of the surface atoms changes almost linearly for PtCo, PtNi, and PtZn; hence, the d-band center can be tuned by controlling the composition of the chemical species, while there are deviations from the linear behavior for PtFe and PtCu.