Magnetism and Heterogeneous Catalysis: In Depth on the Quantum Spin-Exchange Interactions in Pt3M (M = V, Cr, Mn, Fe, Co, Ni, and Y)(111) Alloys.

Abstract

Bimetallic Pt-based alloys have drawn considerable attention in the last decades as catalysts in proton-exchange membrane fuel cells (PEMFCs) because they closely fulfill the two major requirements of high performance and good stability under operating conditions. Pt3Fe, Pt3Co, and Pt3Ni stand out as major candidates, given their good activity toward the challenging oxygen reduction reaction (ORR). The common feature across catalysts based on 3d-transition metals and their alloys is magnetism. Ferromagnetic spin-electron interactions, quantum spin-exchange interactions (QSEIs), are one of the most important energetic contributions in allowing milder chemisorption of reactants onto magnetic catalysts, in addition to spin-selective electron transport. The understanding of the role played by QSEIs in the properties of magnetic 3d-metal-based alloys is important to design and develop novel and effective electrocatalysts based on abundant and cheap metals. We present a detailed theoretical study (via density functional theory) on the most experimentally explored bimetallic alloys Pt3M (M = V, Cr, Mn, Fe, Co, Ni, and Y)(111). The investigation starts with a thorough structural study on the composition of the layers, followed by a comprehensive physicochemical description of their resistance toward segregation and their chemisorption capabilities toward hydrogen and oxygen atoms. Our study demonstrates that Pt3Fe(111), Pt3Co(111), and Pt3Ni(111) possess the same preferential multilayered structural organization, known for exhibiting specific magnetic properties. The specific role of QSEIs in their catalytic behavior is justified via comparison between spin-polarized and non-spin-polarized calculations.