jp312859x_si_001.pdf (1.59 MB)
Electrocatalysis on Shape-Controlled Palladium Nanocrystals: Oxygen Reduction Reaction and Formic Acid Oxidation
journal contribution
posted on 2013-02-28, 00:00 authored by Minhua Shao, Jonathan Odell, Michael Humbert, Taekyung Yu, Younan XiaA systematic study was conducted
on small Pd nanocrystals (5–6
nm) to understand the effects of catalyst structure and electrolyte
on the oxygen reduction reaction (ORR) and formic acid oxidation (FAO).
The ORR activities of Pd catalysts strongly depended on their structure
and the electrolyte used. It was found that Pd cubes were 10 times
more active than Pd octahedra for ORR in an aqueous HClO4 solution due to higher onset potential of OHad formation
on the cubic surface. In the case of a H2SO4 solution, the ORR activity of Pd cubes was 17 times higher than
that of Pd octahedra due to the stronger adsorption of (bi)sulfate
on the surface of octahedral nanocrystals in addition to OHad. In alkaline solutions, however, no structure dependence was observed
for ORR due to the outer-sphere electron-transfer mechanism in the
potential region for Pd oxide formation. For FAO, no advantage was
observed on shape-controlled Pd nanocrystals in comparison to conventional
Pd catalysts. The FAO current densities, both at peak current and
at 0.4 V, followed the order of conventional Pd > octahedral Pd
>
cubic Pd. It was hypothesized that steps and defects were more active
for FAO than terraces, which could be used to explain why the shape-selective
materials were less active than conventional Pd because they contained
fewer defects and edge sites.