High temperature proton conducting polymer fuel cells

There are at least two technical challenges for developing a direct methanol polymer electrolyte fuel cell. One is lack of a sufficiently active anode catalyst. The other is a large methanol crossover rate of commercial available polymer electrolytes. To overcome these problems, a fuel cell employing an acid doped polybenzimidazole polymer electrolyte which can be operated at 200{dollar}spcirc{dollar}C was proposed. Operating a fuel cell at elevated temperature can enhance the reaction kinetics and depress the electrode poisoning, and cut down the methanol crossover rate due to lower gas permeability of the polymer electrolyte at elevated temperature.; This research demonstrates the feasibility of acid doped polybenzimidazole (PBI) membranes as a polymer electrolyte for both H{dollar}rmsb2/Osb2{dollar} and direct {dollar}rm CHsb3OH/Osb2{dollar} fuel cells operated at elevated temperature, although the performances of these fuel cells are far from being an optimized system.; A novel measurement combining a mass spectrometry with a direct methanol fuel cell was developed. The effects of temperature, current density, catalyst and water/methanol mole ratio on the product distribution during methanol oxidation in a direct methanol fuel cell were examined using this new system.; Two methods to evaluate the methanol crossover rate, that is the potentiostatic method and the mass spectrometric method were suggested. Both methods indicate a crossover rate of 10mA/cm{dollar}sp2{dollar} for a 3mil PBI film with 1atm methanol vapor on the cathode side. The mass spectrometry study revealed that the cathode polarization losses due to the methanol crossover are caused by a combination of a cathode poisoning and a mixed potential effect.; Ethanol, 1-propanol and 2-propanol have been evaluated as alternative fuels for direct methanol/oxygen fuel cells. It was found that ethanol is the most promising candidate for an alternative fuel for direct oxidation fuel cells. However, the energy density of ethanol is lower compared to methanol.; A macro-homogeneous porous electrode model that describes the reactions and transport within the catalyst zone of the methanol electrode was developed. The effects of the electrode structure such as catalyst loading, catalyst layer thickness and polymer electrolyte loading on the methanol crossover, electrode performance and CO{dollar}sb2{dollar} transport are examined.