Palladium as a relatively abundant resource has been intensively
studied as the Pt-alternative electrocatalyst due to its
desirable activity toward the oxygen reduction reaction (ORR).1-3
It has been found that alloying Pd with other transition metals
can improve its catalytic activity.4 The alloying component
would play a synergistic role on the surface of Pd to affect the
thermodynamics and/or the kinetics of the elementary steps of
the ORR.5,6 Some researchers have also emphasized the
modulation effects on the electronic structure of Pd so as to
influence significantly the surface reactivity.4,7 Recent studies
have demonstrated that Pd exhibits even a higher activity than
Pt for alcohol electroxidation in alkaline media8-11 where the
electrocatalyst stability is also higher.12 The adoption of Pdbased
electrocatalysts might further reduce the cost of manufacturing
electrochemical devices like fuel cells. It is well-known
that Pd is inactive for alcohol electroxidation in acidic media.
However, no clear-cut explanation for the origin of this pH effect
has been provided so far. Herein, we report a first-principles
study, based on the density functional theory (DFT), along with
some experimental results, of the pH effect on the first stage of
ethanol oxidation leading to acetaldehyde formation