Still Pursuing the Electric Car
A practical electric vehicle requires more than a hydrogen fuel cell.
The lead-acid-battery-powered, all-electric car of the late 20th century failed to attract consumers because of its high cost and limited range. In the future, the all-electric car may have a better chance of succeeding because of the Department of Energy's commitment to improving electrified vehicles. To enable more electric ground transportation, ORNL is developing improved materials for batteries and analyzing novel means such as hydrogen fuel cells to generate electricity on-board vehicles.
Tim Armstrong, manager of ORNL's Hydrogen, Fuel Cell and Infrastructure Program, says that the Laboratory is supporting DOE's hydrogen program primarily through research on hydrogen production, delivery, storage and fuel cells.
Hydrogen must be produced for storage on board the car and at service stations. ORNL characterizes and develops membranes for purifying hydrogen and separating it from hydrogen-containing gases.
Studies at ORNL's High Temperature Materials Laboratory are determining mechanical properties and durability of a palladium membrane being developed by Pall Corporation and partners. ORNL researchers are developing a next-generation, all-ceramic membrane based on molybdenum oxide for purifying hydrogen from coal gas and syngas, a mixture of hydrogen and carbon monoxide that can be made from biomass-derived gas.
In addressing the question of how to deliver hydrogen cost effectively to service stations, ORNL researchers are examining distributed hydrogen production hubs with 50-mile-long pipelines, like spokes of a wheel. Other approaches might be an all-hydrogen centralized pipeline network or the delivery of hydrogen through a centralized natural gas pipeline network.
ORNL is working with several universities on coating metallic pipelines to make the alloys withstand hydrogeninduced embrittlement. Various alloys are being studied to determine which are least likely to leak significant amounts of hydrogen and become brittle under pressures of approximately 1,500 pounds per square inch.
"Laying pipelines of different ironbased alloys costs $1 million a mile," says Armstrong. "One significant cost is welding. Every weld point changes the microstructure, making hydrogen leakage more likely." ORNL researchers led by Zhili Feng are examining friction stir welding as an economic alternative to in-field welding of metallic pipelines.
ORNL researchers also are developing a "smart," fiber-reinforced, polymer pipe composed of a high-density polymer core with a polymer liner and glassfiber wrap for improved strength to slow down diffusion of hydrogen from the gas stream. "To make the pipeline smart, fiber-optic sensors would be woven in the wrap to warn of potential leaks and failure points," Armstrong says. "Current polymer technology allows the manufacture of mile-long polymer pipelines for the oil industry, reducing the number of connections and potential leaks. Using mobile factories we estimate the cost of laying pipeline would be cut 50%, to half a million dollars a mile."
One ORNL-generated model suggests that the transition to hydrogen pipelines may be accommodated by tanker trucks that carry liquefied hydrogen to storage tanks at service stations where fuel-cell car tanks would be filled with high-pressure hydrogen gas. The technology for making hydrogen transportable by truck may come from a novel hydrogen liquefaction technique developed by Allen Crabtree at ORNL's Spallation Neutron Source. One ORNL team is examining metal hydrides, carbon nanohorns containing palladium, and activated carbon for adsorbing and storing hydrogen in tanks at the filling station and on board the fuel-cell car. Another team seeks to lower the cost of producing high-strength, aerospace-grade carbon fibers for building hydrogen tanks.
Armstrong says researchers are conducting groundbreaking transmission electron microscope studies of microstructure changes to determine failure mechanisms in fuel-cell materials. Working with major fuel-cell companies in the United States and Japan, Karren More has identified different degradation mechanisms in fuel cells and assisted companies in improving their use of platinum catalysts. With the SpaciMS mass spectrometer adapted by Bill Partridge to study real-time gas distributions in fuel cells, ORNL is well positioned to help partners improve or develop fuel-cell materials and models to get the electric car out of the laboratory and on the road.—Carolyn Krause
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