Ferromagnetic L1₂‐Pt₃Co Nanowires with Spin‐Polarized Orbitals for Fast and Selective Oxygen Reduction Electrocatalysis

Abstract

Magnetic alloys are key to develop efficient catalysts for oxygen reduction reaction (ORR) in fuel cells. During the last decade, it has been shown that spin manipulation of magnetic materials can improve the kinetics of triplet state 3O2 electrocatalysis, promoting the unification between the physics of strongly correlated materials and heterogeneous catalysis. In this study, structurally ordered Pt3Co nanowires (NWs) are synthesized, and their ORR catalytic performances are studied in detail. These intermetallic ordered L12‐Pt3Co NWs exhibit stronger ferromagnetism, superior ORR catalytic activity, and higher tolerance to carbon monoxide than related disordered A1‐Pt3Co NWs, and commercial Pt/C catalyst. These characteristics make them one of (if not) the best catalyst reported nowadays. Density functional theory calculations prove that the L12‐Pt3Co(111) surface displays a lower activation barrier at the ORR rate‐limiting step and better selectivity H2O2/H2O (i.e., lower production of H2O2) compared with disordered A1‐Pt3Co(111). ORR reactivity increases with the level of Co order in the slab. Moreover, L12‐Pt3Co(111) displays more favorable thermodynamics, decreasing the adsorption enthalpies of 3O2, and lower ORR rate‐limiting step, due to ferromagnetic quantum spin exchange interactions (QSEI), compared with Pt(111).

Experimental Evidences on Magnetism-Covalent Bonding Interplay in Structural Properties of Solids and during Chemisorption

“…These ordered intermetallic alloys experimentally show a more stable structure and a minor leaching of 3d-atoms in comparison with the corresponding disordered phase for the same chemical composition and nanoparticle size under the same catalytic operating conditions [9,46]. The chemical order is the most commonly used argument to explain the higher stability of these materials, even though one should also take into account their magnetic properties [9,46]. Indeed, these ordered intermetallic alloys are also characterized by the presence of a higher magnetic anisotropy than that of their corresponding disordered counterparts, which is responsible for their higher coercivity, higher Curie points, and their ability to retain magnetic properties at very small nanoparticle sizes [9].…”

“…In this regard, the use of platinum ordered intermetallic compounds (Pt 1-x M x where M is Fe or Co) as ORR solid catalysts (see Table 2) is outstanding. These ordered intermetallic alloys experimentally show a more stable structure and a minor leaching of 3d-atoms in comparison with the corresponding disordered phase for the same chemical composition and nanoparticle size under the same catalytic operating conditions [9,46]. The chemical order is the most commonly used argument to explain the higher stability of these materials, even though one should also take into account their magnetic properties [9,46].…”