2 research outputs found
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<sub>0.7</sub>Pd<sub>0.3</sub> 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 H<sub>2</sub>O<sub>2</sub> 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 ABO<sub>3</sub> perovskite is an archetypal example of this class, formed
by the occupation of small octahedral B-sites within an AO<sub>3</sub> 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 AO<sub>3</sub> 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