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Recently, polybenzimidazole membrane doped with phosphoric acid (FBI) was found to have promising properties for use as a polymer electrolyte in a high temperature (ca. 150th 200°C) proton exchange membrane direct methanol fuel cell. However, operation at 200°C in strongly reducing and oxidizing environments introduces concerns of the thermal stability of the polymer electrolyte. To simulate the conditions in a high temperature fuel cell, FBI samples were loaded with fuel cell grade platinum black, doped with ca, 480 mole percent phosphoric acid (i.e., 4.8 H3P()4 tolecules per PBI repeat unit) and heated under atmospheres of either nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases weight loss below 400°C was found to be due to loss of water. Judging from the results of these tests, the thermal stability of FBI is more than adequate for use as a polymer electrolyte in a high temperature fuel cell.

Ethanol, 1-propanol, and 2-propanol have been evaluated as alternative fuels for direct methanol/oxygen fuel cells. The relative product distributions for the electro-oxidation of these alcohols under fuel-cell conditions were determined using on-line mass spectrometry. For water/ethanol mole ratios between 5 and 2, ethanal is the main product, while CQ is a minor product. However, an increase of the water/ethanol mole ratio increased the relative product distribution of CO2 slightly. Propanal was the main product of the electro-oxidation of 1-propanol with a similar percentage of CO2 being formed as for ethanol. In contrast, the electro-oxidation of 2-propanol yielded practically only acetone. Between 150 and 190~ the product distributions for the electro-oxidation of ethanol, l-propanol, and 2-propano] do not depend significantly on the temperature. No differences in the product selectivities of Pt-Ru and Pt-black were found. Ethanol is a promising alternative fuel for direct methanol fuel cells (DMFCs) with an electrochemical activity comparable to that of methanol. Conversely, l-propanol and 2-propanol are not suitable as fuels for DMFCs due to their low electrochemical activity.

Naf ion® is an important polymer electrolyte for polymer electrolyte fuel cell applications due to its inertness and high proton conductivity. Operation of these fuel cells for extended periods of time at temperatures approaching 10 0°C introduces concerns of the thermal stability of the Nafion electrolyte. To simulate the conditions in a fuel cell, Nafion samples were loaded with fuel-cell grade platinum black and heated under atmospheres of nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identif ication. In all cases, Nafion was found to be thermally stable up to 280°C, at which temperature the sulfonic acid groups began to decompose. A mechanism for the decomposition is proposed which explains many of the evolved compounds observed during heating.

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