Membrane electrode assembly with SiO2 nano particles was prepared. And direct ethanol fuel cells (DEFCs) were constructed. The DEFCs were operated under both oxygen gas flow and normal air atmosphere conditions on the cathode electrode. In addition to the current density, the concentrations of acetaldehyde and acetic acid (intermediate reaction products) were determined as a function of operation time. For normal air atmosphere condition, the concentration of acetaldehyde decreased at the condition of high current, and the fuel cell current also decreased as the operation time increased. On the other hand, under the oxygen gas flow condition, the amount of acetaldehyde, which was the result of proton production, increased as operation time increased. The concentration of acetic acid increased for the oxygen gas flow measurements. The balance between anode and cathode chemical reaction must have the essential importance in DEFCs.

The effect of various excess oxygen gas flows at the cathode of a direct ethanol fuel cell (DEFC) was investigated with respect to the reaction products/intermediates. The output current increased with the excess oxygen gas flow. For each oxygen flow, the acetic acid concentration at anode was 5 times higher than the acetaldehyde concentration; therefore, acetaldehyde is readily oxidized to acetic acid or acetic acid is formed directly. This suggests that the output current is mainly dependent on the amount of acetic acid produced. The maximum concentration of acetaldehyde with each output current was almost proportional to that of acetic acid for each oxygen flow condition. The effect of cerium oxide addition to the cathode as another oxygen source to enhance performance was also examined. After an excess oxygen gas flow of 0.6 L/min was stopped, the output current increased for approximately 2 minutes, after which the cerium oxide re-absorbed oxygen to attain equilibrium, which was accompanied by a decrease in the output current until it returned to the same level as that with the excess oxygen gas flow. Thus, the addition of cerium oxide to the cathode enhances oxygen supply for cathodic reactions with a corresponding increase in output current.