May 10, 2005

Engineers face major challenges to make fuel-cell cars reality

WEST LAFAYETTE, Ind. – Researchers conclude in an article to be published in June that it could take "several decades" to overcome daunting technical challenges standing in the way of the mass production and use of hydrogen fuel cell cars.

The article notes that "success is not certain" in efforts to develop inexpensive, hydrogen-powered fuel cells and to create the vast storage and transportation infrastructure needed for the vehicles, stressing that hydrogen's "wide-scale use is laden with potential technical, economic and societal impasses." In case fuel cells never do become practical for cars, the researchers conclude, it would be wise for the nation to "maintain a robust portfolio of energy research and development" in other areas.

"In my mind, developing practical hydrogen fuel cells for cars is definitely doable, but we must solve very daunting technical challenges," said Rakesh Agrawal, Purdue University's Winthrop E. Stone Distinguished Professor of Chemical Engineering.

The article will appear as the cover story in the June issue of the AIChE Journal, a publication of the American Institute of Chemical Engineers. The article was written by Agrawal, Martin Offutt, from the National Research Council, and Michael P. Ramage, a retired executive from ExxonMobile Corp.

"The main purpose of the published article is to point out challenges in hydrogen production, distribution and storage for which chemical engineers can potentially provide solutions through research," Agrawal said. "Finding such solutions sooner than later will accelerate the introduction of hydrogen fuel cell cars to the general public."

The three experts prepared a 240-page report on the prospects for developing a future "hydrogen economy," issued last year by the National Research Council. The U.S. Department of Energy adopted most of the recommendations in the report, "The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs."

"Today's fuel cells generate power at a cost of greater than $2,000 per kilowatt, compared with $35 per kilowatt for the internal combustion engine, so they are more than 10 times more expensive than conventional automotive technology," Agrawal said. "At the same time, fuel cells have an operating lifetime for cars of less than 1,000 hours of driving time, compared with at least 5,000 hours of driving time for an internal combustion engine.

"That means fuel cells wear out at least five times faster than internal combustion engines. If I buy a new car, I expect it to last, say, 10 years, which equates to about 3,000 hours of driving time. If my fuel cell only lasts 1,000 hours, you can see that's not very practical."

A fuel cell works by using a catalyst such as platinum to split hydrogen molecules, which contain two hydrogen atoms in a dumbbell shape. Breaking apart the dumbbell gives off electrons, which generate a current that can be used to run an electric motor. Because each hydrogen atom's single electron is removed, the hydrogen atoms become positively charged. The positively charged hydrogen atoms then pass through a special "proton-exchange membrane," entering another part of the fuel cell, where they are exposed to oxygen from the air. When the hydrogen and oxygen combine, they produce water, making fuel cells a clean power source.

To bring down the cost of fuel cells, less expensive catalysts and membrane materials are needed, Agrawal said.

Developing an infrastructure of hydrogen storage and transportation represents other significant challenges.

"A fuel-cell car built with today's technology would cost about $250,000, but you would have no place to fill up the tank," Agrawal said.

Hydrogen is a light gas, which makes it more expensive to transport and store. Because its molecular weight is only 2 – compared with heavier gases, such as methane, which has a molecular weight of 16 – less hydrogen is contained in the same space as heavier gases, making its transport more expensive.

Another concern is developing sustainable methods for producing hydrogen instead of deriving it from natural gas, oil and coal, all of which will eventually run out. Industry now extracts hydrogen from these sources in a process called "reforming," or "gasification," during which coal, oil or the methane in natural gas reacts with steam to form carbon dioxide and hydrogen.

Producing large amounts of hydrogen from natural gas, oil and coal, however, would potentially involve thorny environmental issues, said Agrawal.

"If we decided to produce hydrogen from coal, for example, the demand for coal would increase dramatically, perhaps doubling, and that would require much more mining activity, which would not be a pretty sight," said Agrawal, "In the long run, hydrogen must come from something that is sustainable, or what is the point of developing an economy based on hydrogen fuel cells?"

Possible sustainable sources for producing hydrogen are solar cells, wind power, nuclear power plants and agricultural products, such as grasses, which can either be burned or processed to produce the gas.

"I believe we can probably solve the technological problems related to making hydrogen fuel cells practical as a replacement for the internal combustion engine, but it won't be easy and it likely won't happen very soon," Agrawal said. "An optimistic prediction would be that a significant number hydrogen fuel cell cars will be entering the marketplace around 2020, and by 2050 everybody will be driving them."

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu

Source: Rakesh Agrawal, (765) 494-2257, agrawalr@purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu

Note to Journalists: An electronic or hard copy of this article is available from Emil Venere, (765) 494-4709, venere@purdue.edu.

Related Web sites:
Purdue University Home Page

The possibility of H₂ as an energy carrier has been proposed and widely debated. In such an energy system, H₂ would first have to be produced from an energy source since it is not available in the free form. Furthermore, H₂ needs to be transported, delivered and stored at the point of end use. This article discusses the thermodynamics, economics and engineering of the H₂ supply chain considered for fuel cell vehicles. The various primary resources from which H₂ can be derived are listed and their pros and cons examined with regard to energy security. Furthermore, while the use of H₂ as an energy carrier has been demonstrated, its wide-scale use is laden with potential technical, economic and societal impasses. The discussion in this article has outlined these key challenges to which chemical engineers can apply their expertise.

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