In this study, we have demonstrated the fine structure effect of PdCo electrocatalyst on oxygen
reduction reaction activity with different alloy composition and heat-treatment time. In order to
identify the intrinsic factors for the electrocatalytic activity, various X-ray analyses were used,
including inductively coupled plasma-atomic emission spectrometer, transmission electron microscopy,
X-ray diffractometer, and X-ray Absorption Spectroscopy technique. In particular, extended X-ray
absorption fine structure was employed to extract the structural parameters required for understanding
the atomic distribution and alloying extent, and to identify the corresponding simulated structures by
using FEFF8 code and IFEFFIT software. The electrocatalytic activity of PdCo alloy nanoparticles
for the oxygen reduction reaction was evaluated by using rotating disk electrode technique and correlated
to the change in structural parameters. We have found that Pd-rich surface was formed on
the Co core with increasing heating time over 5 hours. Such core shell structure of PdCo/C showed
that a superior oxygen reduction reaction activity than pure Pd/C or alloy phase of PdCo/C electrocatalysts,
because the adsorption energy of adsorbates was apparently reduced by lowering the dband
center of the Pd skin due to a combination of the compressive strain effect and ligand effect.