Effect of Fuel Flow Rate, Fuel Concentration, and O₂ Concentration of the Cathode Gas on the CO₂ Evolution of a Direct Ethanol Fuel Cell

Abstract

This paper presents an experimental study on anode reactions in direct ethanol fuel cells with the effect of cell operating conditions on the generation ratio of anode reaction products (i.e. carbon dioxide, acetic acid, and methane). Decreasing the ethanol concentration in the fuel increased the generation ratio of carbon dioxide. Additionally, lowering the fuel flow rate produced more carbon dioxide. Thus, we conducted a detailed experiment using acetaldehyde which is an intermediate product of the anode reaction of ethanol. Similar to using ethanol as a fuel, more carbon dioxide was produced at a lower fuel concentration and at a slower flow rate. Additionally, increasing the oxygen concentration in the cathode gas significantly increased the carbon dioxide generation ratio, which was likely because the oxygen from the cathode side reaches at the anode via the electrolyte membrane to promote the carbon dioxide production reaction. The amount of carbon dioxide produced greatly exceeded the amount of oxygen permeated, and comparing the amount of generated current with the amounts of acetic acid and carbon dioxide suggests that another oxide is present at the anode. The methane generation ratio was not affected by the oxygen concentration. It is assumed that the decreasing fuel concentration at the electrode surface due to a lower fuel flow rate increases the carbon dioxide generation ratio. Isotope analysis on the generated carbon dioxide confirmed that the detected carbon dioxide was due solely to the oxidation of fuel and not due to the oxidation of electrode materials such as the catalyst support.