Increases in the rate of methanol oxidation through the coadsorption of different anions: Theory and experiment

A theory is presented that describes an enhancement in the rate of the electrochemical oxidation of methanol. Replacing a fraction of the original electrolyte with a more inhibiting one causes the enhanced rate. Results from experiments conducted on the electrochemical oxidation of methanol at Pt are also presented. In the experiments, a fraction of the original supporting electrolyte, perchloric acid, was replaced with tetrafluoroboric acid. Although the fluoroborate anion is more inhibiting than the perchlorate anion, the replacement caused an increase in the rate of the oxidation of methanol. Previous results and results presented here provide evidence that surface reorganization, basicity, participation of anions in reactions, or a more efficient removal of surface bonded CO are highly unlikely to be the fundamental cause of the increased rate of methanol oxidation. A mathematical description of methanol oxidation coupled to anion adsorption reveals that an enhanced rate of oxidation can be achieved if forces between unlike surface anions are stronger than the forces between like surface anions. A sufficient condition for enhancement is derived, which consists of a relation between the anion adsorption coefficients and the parameter representing the interactions between unlike surface anions.