The oxygen exchange kinetics of epitaxial Pr0.1Ce0.9O2−δelectrodes was modified
by
decoration with submonolayer amounts of different basic (SrO, CaO)
and acidic (SnO2, TiO2) binary oxides. The oxygen
exchange reaction (OER) rate and the total conductivity were measured
byin situPLD impedance spectroscopy (i-PLD), which allows to directly track changes of electrochemical
properties after each deposited pulse of surface decoration. The surface
chemistry of the electrodes was investigated by near-ambient pressure
XPS measurements (NAP-XPS) at elevated temperatures and by low-energy
ion scattering (LEIS). While a significant alteration of the OER rate
was observed after decoration with binary oxides, the pO2dependence of the surface exchange resistance and its activation
energy were not affected, suggesting that surface decorations do not
alter the fundamental OER mechanism. Furthermore, the total conductivity
of the thin films does not change upon decoration, indicating that
defect concentration changes are limited to the surface layer. This
is confirmed by NAP-XPS measurements which find only minor changes
of the Pr-oxidation state upon decoration. NAP-XPS was further employed
to investigate changes of the surface potential step on decorated
surfaces. From a mechanistic point of view, our results indicate a
correlation between the surface potential and the altered oxygen exchange
activity. Oxidic decorations induce a surface charge which depends
on their acidity (acidic oxides lead to a negative surface charge),
affecting surface defect concentrations, any existing surface potential
step, potentially adsorption dynamics, and consequently also the OER
kinetics.