Potential-Dependent Structural Memory Effects in Au–Pd Nanoalloys

Alloying of metals offers great opportunities for directing reactivity of catalytic reactions. For nanoalloys, this is critically dependent on near-surface composition, which is determined by the segregation energies of alloy components. Here Au–Pd surface composition and distribution of Pd within a Au_0.7Pd_0.3 nanoalloy were investigated by monitoring the electrocatalytic behavior for the oxygen reduction reaction used as a sensitive surface ensemble probe. A time-dependent selectivity toward the formation of H₂O₂ as the main oxygen reduction product has been observed, demonstrating that the applied potential history determines surface composition. DFT modeling suggests that these changes can result both from Pd surface diffusion and from exchange of Pd between the shell and the core. Importantly, it is shown that these reorganizations are controlled by surface adsorbate population, which results in a potential-dependent Au–Pd surface composition and in remarkable structural memory effects

Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO₃ perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO₃ network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO₃ network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation