Origin of the Drastic Current Decay during Potentiostatic Alkaline Methanol Oxidation

The
current production from the alkaline methanol electro-oxidation
reaction does not reach a steady state on a smooth platinum catalyst
under potentiostatic conditions. We investigated two possible explanations
for this phenomenon: changes on the catalyst surface and changes in
the solution near the electrode. In situ Fourier transform infrared
spectroscopy experiments were conducted to evaluate the adsorbed species
on the catalyst surface and a simulation model was set up to describe
the changes of concentrations inside the solution. Linear- and bridge-bonded
carbon monoxide are the only organic compounds which can be detected
by in situ spectroscopy at fixed potentials, but their amount does
not increase over time. The simulation shows that the consumption
of hydroxide ions and production of carbonaceous species during alkaline
oxidation causes a local pH shift near the catalyst surface. Assuming
a one-electron transfer as the limiting step, this pH shift was found
to contribute to the observed current loss at a potential of 0.77
V.