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Multiple roads to the hydrogen car

Hydrogen powered vehicle.

In his 2003 State of the Union address, President George Bush communicated an ambitious vision that the United States will lead the world in developing clean, hydrogen-powered automobiles. "The hydrogen economy at a minimum is 20 years away," says Tim Armstrong, manager of the Hydrogen, Fuel Cells, and Infrastructure Program at ORNL. The big scientific challenges are hydrogen generation and distribution, hydrogen storage, and fuel cell durability."

The Laboratory is a leader in separation technologies for producing hydrogen. ORNL is the lead Department of Energy laboratory in studying hydrogen delivery and ranks third in DOE funding for research on vehicular fuel cells.

To produce hydrogen, ORNL is developing both microporous and proton separation membranes supported on porous metallic tubes. These membranes could separate hydrogen from carbon monoxide in syngas produced by coal gasification. The microporous membrane is derived from the declassified inorganic membrane developed to enrich uranium in its fissionable isotope at the old Oak Ridge Gaseous Diffusion Plant. A team led by Armstrong has developed a new proton conductor, a ceramic oxide, that enables hydrogen to diffuse rapidly through it at temperatures less than 700°C, where most conventional proton-conducting oxides operate. "Our material works at 500°C," Armstrong says. "This is the 'sweet spot' for separating hydrogen from coal gas."

Hydrogen also can be produced from natural gas and petroleum. To generate pure hydrogen, sulfur must be removed from these fossil fuels. ORNL and DOE's National Energy Technology Laboratory have developed a way to remove sulfur from hydrogen sulfide (H2S) gas streams using a carbon-based catalyst. The ORNL catalyst can remove both carbonyl sulfide (COS) and H2S, making it ideal for separating sulfur from coal gas; the sulfur-free gas can be a source of pure hydrogen for fuel cells. This sulfur-removal method has attracted the interest of General Electric, Chevron Texaco, and Conoco Phillips.

Schematic of molecular sieve membrane for separating hydrogen from mixed gas streams.

A team led by ORNL's James Lee seeks to produce hydrogen biologically. The project focuses on engineering wild algae's genetic structure and adding a proton channel to increase the algae's hydrogen production efficiency 10 to 100 times, possibly creating a renewable hydrogen resource.

For hydrogen delivery, ORNL researchers are developing and examining materials for pipes and welds that exhibit a very low hydrogen diffusion, or leak rate. The goal is to replace today's current natural gas pipeline materials with metallic systems and to improve welds, which are potential failure points in pipelines.

A new ORNL project would reduce the number of welds by adding distance between them while simplifying the assembly process. The goal is to develop a "smart" pipeline consisting of an extruded polymer pipe liner reinforced by a carbon fiber tow. The tow is integrated with leak sensors and failure sensors before being wrapped.

Jim Hardy's team at ORNL is developing a cost-effective, portable acoustic sensor to detect leaks from hydrogen gas pipelines. The researchers are also developing a fiber-optic–based hydrogen safety sensor that will monitor the pressure of compressed hydrogen in the fuel tanks of future fuel-cell–powered vehicles.

ORNL's Tim McIntyre leads a team devising a fiber-optic–based sensor to monitor the temperature and humidity in fuel cells. Measurements of inlet and outlet gas parameters will be used to validate computer models of fuel cell performance. These sensors will become an integral part of a fuel-cell control system.

Recently, a carbon-based bipolar plate developed by ORNL's Ted Besmann was licensed to Porvair for commercialization. Mike Brady has since developed a new metal bipolar plate for proton-exchange-membrane (PEM) fuel cells. "The plate has very high electrical conductivity and has shown no corrosion up to 5000 hours," says Armstrong. "We are partnering with fuel-cell manufacturers and automakers to develop further this and other ORNL technologies."



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