Michael A. Hofmann

High temperature transport properties of polyphosphazene membranes for direct methanol fuel cells

Experimental methods for studying the conductivity and methanol permeability of proton conductive polymers over a wide range of temperatures have been developed. The proton conductivity and methanol permeability of several polymer electrolyte membranes including sulfonated and phosphonated poly[(aryloxy)phosphazenes] was determined at temperatures up to 120 °C. Nafion 117 membranes were tested using the same methods in order to determine the reliability of the methods. Although the conductivities of the polyphosphazene membranes were either similar to or lower than that of the Nafion 117 membranes, they continue to hold promise for fuel cell applications. We observed similar activation energies of proton conduction for Nafion 117, and for sulfonated and phosphonated polyphosphazene membranes. However, the methanol permeability of a sulfonated membrane was about 8 times lower than that of the Nafion 117 membrane at room temperature although the values were comparable at 120 °C. The permeability of a phosphonated phosphazene derivative was about 40 times lower than that of the Nafion 117 membrane at room temperature and about 9 times lower at 120 °C. This is a significant improvement over the behavior of Nafion 117.

Evaluation of methanol crossover in proton-conducting polyphosphazene membranes

Abstract A diffusion cell was developed to evaluate the methanol crossover for a novel class of polyphosphazene electrolyte membranes. It was found that the methanol diffusion coefficients of phenyl phosphonic acid functionalized poly[aryloxyphosphazene] membranes in an aqueous methanol solution (50% v/v) were ∼40 times lower than for Nafion 117, and ∼10–20 times lower than for sulfonated polyphosphazene membranes.

A fire-resistant organophosphorus gel polymer electrolyte additive for use in rechargeable lithium batteries

Abstract The development of a small-molecule organophosphorus gel polymer electrolyte additive for use in rechargeable lithium batteries is described. This organophosphorus additive is less volatile and more resistant to ignition than propylene carbonate, a well known component of gel polymer electrolytes. Moreover, the ionic conductivities of gels containing the organophosphorus additive at low molar concentrations (11–21%) exceed the ionic conductivities of gels containing equimolar amounts of propylene carbonate (5.3×10 −5 versus 4.8×10 −5 S/cm). At higher molar concentrations (31–52%) there is evidence of phase separation, but conductivities remain comparable to propylene carbonate systems.

Sulfonimide polyphosphazene-based H2/O2 fuel cells

Sulfonimide-functionalized polyphosphazenes have been investigated as polymer electrolyte membranes for use in an H 2 /O 2 fuel cell. A sulfonimide polyphosphazene-based membrane electrode assembly (MEA) and a Nafion-basedMEA with similar catalyst loadings were fabricated and tested within a fuel cell system. The maximum power density for the sulfonimide polyphosphazene MEA was 0.36 W cm - 2 at 0.87 A cm - 2 and 22°C, and reached 0.47 W cm - 2 at 1.29 A cm - 2 at 80°C. The performance of the sulfonimide polyphosphazene-based H 2 /O 2 fuel cell was found to be comparable to that of the Nafion-based fuel cell.

Sulfonimide Polyphosphazene-Based H 2 / O 2 Fuel Cells

Sulfonimide-functionalized polyphosphazenes have been investigated as polymer electrolyte membranes for use in an H 2 /O 2 fuel cell. A sulfonimide polyphosphazene-based membrane electrode assembly (MEA) and a Nafion-basedMEA with similar catalyst loadings were fabricated and tested within a fuel cell system. The maximum power density for the sulfonimide polyphosphazene MEA was 0.36 W cm - 2 at 0.87 A cm - 2 and 22°C, and reached 0.47 W cm - 2 at 1.29 A cm - 2 at 80°C. The performance of the sulfonimide polyphosphazene-based H 2 /O 2 fuel cell was found to be comparable to that of the Nafion-based fuel cell.

Sulfonimide Polyphosphazene-Based H[sub 2]/O[sub 2] Fuel Cells

Sulfonimide-functionalized polyphosphazenes have been investigated as polymer electrolyte membranes for use in an H 2 /O 2 fuel cell. A sulfonimide polyphosphazene-based membrane electrode assembly (MEA) and a Nafion-basedMEA with similar catalyst loadings were fabricated and tested within a fuel cell system. The maximum power density for the sulfonimide polyphosphazene MEA was 0.36 W cm - 2 at 0.87 A cm - 2 and 22°C, and reached 0.47 W cm - 2 at 1.29 A cm - 2 at 80°C. The performance of the sulfonimide polyphosphazene-based H 2 /O 2 fuel cell was found to be comparable to that of the Nafion-based fuel cell.