Transient and Persistent Effects of Air Exposure on Electrocatalytic Activity of Sub-Nano Pt Clusters on Different Electrode Supports

Electrodes are exposed to air prior to use in most electrochemistry
experiments, but the resulting adventitious contaminants are easily
removed by cycling the electrode potential to drive reactions or desorption.
In most cases, the resulting changes to the electrode surface are
probably inconsequential, however, for electrodes with catalytic centers
consisting of sub-nanometer clusters or single atoms, potential cycling
may drive dissolution, migration, or other processes that significantly
alter the catalyst properties. We have developed the capability to
prepare clean electrodes in ultrahigh vacuum, decorated with precisely
controlled clusters or atoms, and to study their electrochemistry
within the vacuum system after controlled exposures to pure gases
or to air. Here, we examine the effects of air exposure on the activity
for hydrogen evolution, O2 reduction, and oxidation of
ethanol and 1-propanol, catalyzed by Pt4 clusters deposited
on both ITO and nitrogen-implanted HOPG electrodes. Air exposure was
found to have no significant effects on HER but did have substantial
effects on the other reactions. Some effects were transient, i.e.,
they decreased over the course of a few dozen CV cycles, but there
were also effects such as increased overpotentials and changes in
peak currents or potentials that persisted after extensive potential
cycling.