Catalysis Meets Spintronics; Spin Potentials Associated with Open-Shell Orbital Configurations Enhance the Activity of Pt3Co Nanostructures for Oxygen Reduction: A Density Functional Theory Study

Abstract

One of the main obstacles in the implementation of hydrogen fuel cells (HFC) lies in the efficiency loss due to the overpotential of the oxygen reduction reaction (ORR). Nowadays, the best catalysts for cathodes in HFC are Pt3Co nanostructures. The superior activity of these magnetic Pt-alloys, compared to metallic platinum, correlates with the milder chemisorption of the oxygenated intermediates on the surfaces of the alloy. Quantum spin exchange interactions (QSEI), including interlayer exchange coupling due to magnetic inner Co layers, are determinant to make the active sites prone to bind adsorbed oxygen atoms in an optimal fashion for catalytic activity. We present a study on antiferromagnetic (AFM) and ferromagnetic (FM) Pt3Co (111) nanostructures conducted via spin-polarized DFT+U calculations. The study begins with a thorough screening of AFM, FM, and fictitious closed-shell Pt3Co slab models with different atomic distributions ranked in order of stability. The chemisorption enthalpy values of O∗ and H∗ atoms on the most stable AFM (A-type) and FM nanolayers show weaker binding of the adsorbate compared to isostructural Pt (111) nanolayers. Cooperative spin potentials, associated with open-shell orbital configurations, unequivocally lead to decreased enthalpies of adsorption for H∗ and O∗ atoms. Hence, a complete and realistic treatment of the structure-activity relationships in heterogeneous catalysis relies upon the correct evaluation of orbital magnetism: spin-dependent potentials are key factors to design optimal ORR catalysts.