Interfacial Kinetics of HOR/MOR at the AEM/Pt Microelectrode Interface: Investigation of the Influence of CO32− on the Reaction Kinetics and the Mass Transport through Membrane

Abstract

The kinetics of hydrogen oxidation reaction (HOR) and methanol oxidation reaction (MOR) at the Tokuyama anion exchange membrane/ Pt microelectrode interface were investigated using a solid state electrochemical cell. Carbonate ions in the membrane which are strongly adsorbing anions; suppress both HOR and MOR kinetics. Carbonate ions not only have a site blocking effect, but at low pHs sufficient amount of hydroxyl ions are not available for adsorption. Adsorption effects by the quaternary ammonium species in the membrane, on the Pt electrode is found to be minimal. However, an ionomer film (AS4) coated on the membrane, significantly decreased the rate of HOR. Diffusion of hydrogen molecules through the membrane was not influenced by the carbonate ions due to the smaller size of the gaseous molecule. However, hydrogen concentration in the anion exchange membrane is low in the presence of carbonate ions. Methanol diffusion is facilitated in the anion exchange polymer electrolyte due to its high water content. However, change of the diffusion path length in carbonate polymer electrolytes caused methanol permeability to drop significantly.