Fundamental Aspects of Direct Liquid-Alcohol Fuel Cells
Final Report Abstract
A direct ethanol fuel cells using a commercial Pt/Ru catalyst showed similar performance to a cell using a home made Pt/Rh catalyst found to show high catalytic activity for ethanol oxidation in a previous project. The use of a bilayer design for the direct alcohol fuel cell anodes results in reduced high frequency cell impedances with increasing amount of catalyst in the compacted layer within the electrode. However, compacting the catalyst layer resulted in noticeable mass transport effects above a current density of 20 mA/cm2. Compacted catalyst layers also showed improved mechanical stability and adhesion to the electrolyte membrane. A Nafion content of 15 wt% in the dry electrode mass has been found to minimize mass transport losses while still showing good mechanical stability of an non compacted electrode. Taking only the short term electrochemical cell performance into account, non compacted electrodes are showing the best performance. However, their stability to erosion from liquid flow and gas evolution during long term operation has to be investigated further. Under the experimental conditions investigated in this project, no evidence for significant total oxidation of ethanol at the anode has been observed. However, the overall liquid fuel utilization has been low that the products of incomplete ethanol oxidation (acetaldehyde, acetic acid) could not be detected in the current setup using mass spectroscopy after diffusion through a silicone membrane. Measurement of CO2 emission from the cathode successfully used to detect alcohol crossover in direct methanol fuel cells did not give conclusive results in direct ethanol fuel cells.
