Electro-Osmosis and Water Uptake in Polymer Electrolytes in Equilibrium with Water Vapor at Low Temperatures
Water uptake and electro-osmosis are investigated to improve the understanding and aid the modeling of water transport in proton-exchange membrane fuel cells (PEMFCs) below 0 C. Measurements of water sorption isotherms show a significant reduction in the water capacity of polymer electrolytes below 0 C. This reduced water content is attributed to the lower vapor pressure of ice compared to supercooled liquid water. At -25 C, 1100 equivalent weight Nafion in equilibrium with vapor over ice has 8 moles of water per sulfonic acid group. Measurements of the electro-osmotic drag coefficient for Nafion and both random and multiblock copolymer sulfonated poly(arylene ether sulfone) (BPSH) chemistries are reported for vapor equilibrated samples below 0 C. The electro-osmotic drag coefficient of BPSH chemistries is found to be {approx}0.4, and that of Nafion is {approx}1. No significant temperature effect on the drag coefficient is found. The implication of an electro-osmotic drag coefficient less than unity is discussed in terms of proton conduction mechanisms. Simulations of the ohmically limited current below 0 C show that a reduced water uptake below 0 C results in a significant decrease in PEMFC performance.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1023718
- Journal Information:
- Journal of The Electrochemical Society, Vol. 156, Issue 3, 2009; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
30 DIRECT ENERGY CONVERSION
25 ENERGY STORAGE
COPOLYMERS
DRAG
ELECTROLYTES
ELECTROPHORESIS
EQUILIBRIUM
ETHERS
FUEL CELLS
ICE
IONIC CONDUCTIVITY
ISOTHERMS
LIQUIDS
MEMBRANES
OSMOSIS
PERFORMANCE
POLYMERS
PROTON EXCHANGE MEMBRANE FUEL CELLS
REDUCTION
SIMULATION
SORPTION
SULFONIC ACIDS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TRANSPORT
UPTAKE
VAPOR PRESSURE
VAPORS
WATER
WATER VAPOR
WEIGHT
Hydrogen Technologies and Systems