CHEMISORPTION AND OXIDATION OF METHANOL AT POLYCRYSTALLINE PT IN ACID-SOLUTIONS

The oxidation of methanol has been studied over a wide range of concen tration using the electrochemical quartz crystal microbalance (EQCM) t echnique. Accumulation of strongly adsorbing species at the electrode surface is accompanied by a decrease in mass, relative to the backgrou nd electrolyte, and the rate of this increase is an indication of how rapidly the surface becomes covered by adsorbates. At lower methanol c oncentrations, removal of these adsorbates is accompanied by a stepped increase in the mass response and is followed by a small region of po tential where the mass is constant and where methanol is apparently ox idized by a reaction with OH at the electrode surface. There is some a dsorption in this region too, which increases with increasing methanol concentration. At 30 mM methanol and above, the step upon adsorbate r emoval and the subsequent region of constant mass can no longer be dis tinguished. Mass responses also reveal that increasing amounts of meth anol in the electrolyte cause a shifting of the oxidative removal of s trongly adsorbed intermediates to more positive potentials, a signific ant inhibition of the irreversible oxidation of the electrode surface and a more rapid removal of the oxide on the cathodic scan.