Strictly potentiostatic current oscillations during bulk CO electro-oxidation on platinum in the presence of inhibiting anions

We investigate bulk CO electrooxidation on a rotating Pt disk electrode in concentrated acidic electrolytes containing small amounts of BF4- anions with cyclic voltammetry and potentiostatic measurements. Under potentiodynamic conditions, the average reactivity decreases with increasing BF4--concentration. For fixed applied potential strictly potentiostatic current oscillations were observed. Both observations are reproduced with a mean field model for CO electrooxidation in which the anions are assumed to competitively adsorb on free electrode sites while the electrode potential is treated as a parameter. Bulk CO electrooxidation on Pt in the presence of inhibiting anions is thus an example of an electrochemical oscillator with purely chemical feedback loops.