Influence of the pH Value and the Carbonate Ion Concentration of the Electrolyte Solution on the Ethanol Oxidation at Polycrystalline Platinum

Recently, the use of alkaline anion exchange membranes has yielded some enhancement of direct ethanol fuel cells at least with respect to the achieved performances. However, so far reports have been made for cells operated with a large excess of KOH and mostly without cycling the anolyte. Under real fuel cell conditions with an anode loop, an accumulation of carbonate ions and a reduction of pH are to be expected. In order to evaluate the effect of these changes on the ethanol oxidation reaction, the ethanol oxidation was studied at polycrystalline platinum thin film electrodes in electrolyte solutions with different pH values and varying carbonate ion concentrations. No severe detrimental effects of high carbonate ion concentration were found. The pH of the electrolyte has an effect depending on the concentration of ethanol. At high ethanol concentrations relevant for fuel cells an optimum value would be around pH 12.