Liquid metal membrane developed at WPI shows promise for cars

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A Toyota fuel-cell vehicle at a hydrogen “gas” station. Liquid-metal membranes could
make producing hydrogen for cars cheaper. WPI PHOTO

WORCESTER, Massachusetts: A new liquid metal membrane developed by a scientist at Worcester Polytechnic Institute (WPI) could make the hydrogen purification process cheaper, simpler, and replicable on a smaller scale. It could also change the car you drive.

“The development of liquid metal membranes allows us to overcome one of the key stumbling blocks in widespread usage of fuel cell automobiles,” said Ravindra Datta, professor of chemical engineering and director of the Fuel Cell Center at WPI. “The membrane allows hydrogen fuel to be more widely produced and available at hydrogen refilling stations to power the fuel-cell cars.”

Hydrogen fuel cells are like mini power plants that strip electrons off hydrogen – the most abundant element in the universe – to produce electricity. This electricity can in turn be used to drive an electric car. The technology is up to 30 percent more efficient than an internal combustion engine, Datta said.

But the fuel cells need pure hydrogen, and naturally-occurring hydrogen is almost always chemically bound to other elements – to oxygen in water, for example, or carbon in methane.


Virtually all of the hydrogen produced in the United States is obtained from hydrocarbon fuels, primarily natural gas, through a multi-step process in which the hydrocarbons react with steam in the presence of a catalyst to produce carbon monoxide, carbon dioxide and molecular hydrogen. The gases are then passed through a membrane filter that separates the hydrogen molecules from the CO, CO2 and other components.

Unfortunately, this filter is typically made of palladium – an expensive metal worth nearly as much as platinum. Because it is so expensive, the membrane is very thin and thus fragile.

Palladium vs gallium
But the membrane produced at WPI and described in a recent paper in the Journal of the American Institute of Chemical Engineers could change that.

The new membrane uses liquid gallium – another metal, which is liquid at room temperature – as the filter rather than palladium. Gallium is less expensive, and more permeable to hydrogen at higher temperatures. The membrane filter can thus be thicker and is more durable – impossible to crack because it is a liquid.

Datta said the discovery could make the hydrogen purification process cheaper because it uses more abundant materials.

This could in turn drive down the cost of hydrogen fuel cells and fuel cell-powered vehicles.

“Hydrogen itself will become cheaper and potentially remove a major impediment to wider adoption of fuel cells that are in hydrogen cars,” Datta said.

His colleague Nikolas Kazantzis, who was not involved in the research, agreed that the development could be important.

“Such a technology option could significantly increase fuel-cell overall efficiency, improve pertinent economic performance as well as enhance overall system reliability,” Kazantzis, a professor of chemical engineering at WPI, said.

The development could also solve the problem of a lack of hydrogen fuel stations. Hydrogen is so light that it is difficult to store and transport, Datta explained. Currently the only network of hydrogen fuel stations is on Highway 101 in California. But if the hydrogen purification process is simple and cheap enough, it can be done throughout the country.

“In each town you could have your own generation of hydrogen,” Datta said.

But before that happens there is much work to be done.

“This is very preliminary,” said Datta. “All we’ve shown is there is promise in the technology.”

The lab will continue to test the hydrogen purification process with other metals than gallium and with metal alloys. It will also work on scaling the technology up to see if it can work commercially.

Datta said he is optimistic. Gallium was the first material they tested – and it worked.

“We just picked gallium out of thin air and it worked,” Datta said. “The concept has merit; if it is practical needs to be explored.”

TELEGRAM & GAZETTE/TNS

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