2 research outputs found
Reduction of Oxygen on Dispersed Nanocrystalline CoS<sub>2</sub>
The electrocatalytic properties of nanocrystalline CoS<sub>2</sub> have been investigated for the oxygen reduction reaction
(ORR) in
0.1 M HClO<sub>4</sub>. CoS<sub>2</sub> with pyrite structure was
prepared by hydrothermal synthesis and attached to a glassy carbon
electrode from solution with a mixture of carbon and Nafion. The prepared
CoS<sub>2</sub> electrode layers showed high activity toward the ORR
and very good stability under oxygen reducing conditions. Selectivity
of the ORR toward H<sub>2</sub>O<sub>2</sub> was determined by rotating
(ring) disk electrode measurements, and relatively high selectivity
was obtained with up to 80% H<sub>2</sub>O<sub>2</sub> formation around
0.4 V (vs Ag/AgCl), but this dropped to zero for potentials below
0.0 V. The amount of H<sub>2</sub>O<sub>2</sub> produced between 0.6
and 0.0 V was dependent on the quality of the CoS<sub>2</sub> dispersion
within the electrode layer, and decreasing CoS<sub>2</sub> particle
size resulted in significant improvement in the ORR electrocatalytic
activity, both by increasing the turnover frequency and through decreasing
the selectivity toward H<sub>2</sub>O<sub>2</sub> production
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