Ceramic membranes could help fuel hydrogen future

ARGONNE, Ill. (Dec. 19, 2003) — Ceramic membranes developed at Argonne could bring fuel-cell cars closer to reality by efficiently and inexpensively extracting hydrogen from fossil fuels.

"Ceramic membranes make possible the widespread use of hydrogen," said senior ceramist Balu Balachandran. "Hydrogen is a fuel of choice for the future. This technology provides the means to get there." Balachandran is section manager of the ceramics section in Argonne's Energy Technology Division.

Though the membranes currently used for research are only a few millimeters across, once scaled up for industrial use they could be installed at existing refineries or at individual refueling stations.

"Just as conventional cars need gas stations, fuel-cell cars will need an infrastructure to support them," Balachandran said. "Ceramic membranes could eliminate the need for costly, conventional hydrogen-manufacturing facilities; they could one day be small and efficient enough to have one at every gas station."

Membrane design

Industry uses membrane systems to filter wastewater or separate gases. Most work like a sieve, with small holes that allow only smaller molecules to pass through. But these membranes are not selective enough to isolate pure hydrogen, the simplest and smallest of all elements. For this task, Argonne ceramists developed a hydrogen-filtering ceramic membrane.

Ceramic membranes, such as Argonne's new hydrogen membrane, lack pores and are made of dense, conductive materials that only allow electrons and certain ions, or charged atoms, to pass through.

"There are no interconnected holes, or pores," Balachandran said. "A molecule cannot swim through from one side to the other side."

These ceramic membranes behave differently depending on the materials used to form them. After studying the conductivity and solubility of various substances, Balachandran's team developed a composite ceramic-oxide that transports only hydrogen and electrons. This allows the membrane to separate pure hydrogen suitable for use as a clean-burning fuel or to manufacture fertilizer.

At work, a hydrogen-rich gas mixture flows on one side of the membrane. Charged or atomic hydrogen flows through the membrane. The resulting pure hydrogen can be captured for immediate use, storage or transport.

Unlike most membrane systems, Argonne's hydrogen membrane tolerates temperatures as high as 900 degrees Celsius (1,650 degrees Fahrenheit). The elevated temperatures are an advantage to hydrogen production as they cause more hydrogen to be pushed through the membrane, accelerating the separation process.

Hydrogen from syngas

The most likely raw material for hydrogen separation with Argonne's ceramic membrane will be syngas, Balachandran explained. Syngas is often used to make liquid diesel and other transportation fuels, as well as chemicals for the petrochemical, rubber, plastics and fertilizer industries.

Short for synthesis gas, syngas is a mixture of hydrogen and carbon monoxide — carbon bound to oxygen. It is made by reacting natural gas with oxygen. The major component of natural gas, methane, contains hydrogen tightly bound to carbon. But the hydrogen is released when oxygen combines with the carbon in methane.

More membrane help

While Argonne's ceramic membrane can extract hydrogen from syngas, the challenge is to have an ample and affordable supply of hydrogen for power sources. Syngas can be expensive to produce using the energy-intensive process of steam reforming or by mixing methane with air.

The ceramics group wants to study the possibility of using a membrane they developed about 10 years ago to extract oxygen. They hope it will be a cost-effective alternative to perform the first half of the transition from natural gas to syngas to hydrogen fuel, according to Balachandran. The combination of membranes could be a two-step technique to provide pure hydrogen for transportation and power applications from fossil fuels such as methane or coal gas.

Electrons on one side of the oxygen-transport membrane combine with oxygen to create negatively charged oxygen ions that can migrate through the membrane. Once on the other side, electrons are stripped from the transported oxygen ions, converting them back into neutral oxygen atoms and freeing the electrons to migrate back across the membrane to form more ions.

Balachandran's team demonstrated that the oxygen membranes successfully separate oxygen and that this separated oxygen, when reacted with methane, forms syngas.

Because Argonne's oxygen and hydrogen membranes function at the same high temperatures, they could work in tandem: One membrane could add oxygen to methane to create syngas, and the other could extract hydrogen from the same syngas.

Membrane development

Ceramic membranes could be a key development in the Department of Energy's Vision 21 and SuperGen programs, which seeks to develop highly efficient power technologies that do not discharge pollutants.

Argonne's ceramic membranes were developed as part of a project funded by DOE's Office of Fossil Energy through the National Energy Technology Laboratory's Gasification Technologies Program. Balachandran's team also has cooperative research and development agreements with industry to address the problems of scaling up the hydrogen-separating membrane.

Though the technology is still in its infancy, Balachandran is pleased with the ceramic membranes' prospects.

"We have proven that this can work in principle," he said. "But to develop ceramic membranes for the marketplace, we need to meet several engineering challenges, such as scaling up the system and integrating it into existing systems in power plants.

"Industry-led consortia are currently working to develop engineering-scale prototypes of the Argonne process. If we can meet those challenges, we could see this technology on the market within five to six years," Balachandran said.

Argonne National Laboratory brings the world's brightest scientists and engineers together to find exciting and creative new solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

For more information, please contact Steve McGregor (630/252-5580 or media@anl.gov) at Argonne.