Princeton scientists have high hopes for hydrogen
By Steven Schultz
Princeton NJ -- In the lab of Professor of Chemistry Andy Bocarsly, the automobile of the future takes the form of a thin plastic film bolted between graphite and copper plates.
Bocarsly's lab, which collaborates on the project with Jay Benziger of chemical engineering, is one of several Princeton research groups investigating the science, technology and public policies needed to bring hydrogen fuel into widespread use. The subject has taken on a new focus with President Bush's announcement in January of an initiative to promote hydrogen as a next-generation fuel -- with a hydrogen-powered "Freedom-Car" as the centerpiece goal (see http://www.ott.doe.gov/freedom_car.shtml)
At the Princeton Environmental Institute, scientists are analyzing a range of technical issues related to the "hydrogen economy," including the best ways of producing and distributing the gas. In mechanical and aerospace engineering, Professor Chung Law is studying interim uses of hydrogen in combination with conventional fuels as well as issues of safety.
On March 5, Joan Ogden, a research scientist at the Princeton Environmental Institute and longtime analyst of alternative fuels, testified before the House Committee on Science as part of a hearing on "The Path to a Hydrogen Economy." The hearing was the first formal effort by Congress to respond to Bush's hydrogen initiative, and Ogden was the only academic scientist among five panelists from government and industry.
"Hydrogen fuel cells, although they are long term, potentially have a very high payoff," Ogden told the committee. "And I think they deserve signi- ficant government support now -- insurance, if nothing else, that they will be ready in 15 or 20 years if we want to deploy them on a very wide basis."
In interviews, Ogden and the other Princeton researchers emphasized that it would take at least 10 years for hydrogen to find widespread use in cars or industry. And it would likely take 40 years or more before use of hydrogen would eliminate U.S. dependence on fossil fuels. Currently, most hydrogen is extracted from fossil fuels, such as natural gas or coal. That process requires energy and leaves behind the greenhouse gas carbon dioxide, which would need to be disposed of safely. Eventually, hydrogen could be extracted from water, but that would also require energy from solar, nuclear or other sources.
Nonetheless, said Ogden, even when derived from fossil fuels, hydrogen could be used so efficiently and cleanly that it could reduce pollution and increase the nation's energy efficiency.
Toughest problem first
For Bocarsly, the pursuit of a practical and reasonably priced fuel cell is attractive, in part, because it's so hard.
"The good news is that our research area seems to be fitting the mood of the nation," said Bocarsly. "The bad news is that, from an engineering point of view, implementing a fuel cell in an automobile is one of the hardest things you could think about doing. We've chosen the toughest problem first."
Fuel cells are like batteries -- they produce electricity from chemical reactions. Even though hydrogen is referred to as a "fuel," fuel cells do not involve combustion or explosions. A simple chemical reaction converts hydrogen into water and electricity. A fuel-cell-powered car would be like today's hybrids; the fuel cell would produce electricity, which would run an electric motor or would be stored in conventional batteries. The idea behind fuel cells is simple, but there are major challenges in fine-tuning them and inventing the optimum materials for use inside the cell, Bocarsly said.
Bocarsly and Benziger already have made significant progress. They have invented a new class of fuel cells that run at a higher temperature than those normally considered for automobiles. Most research on automobile fuel cells has focused on devices that run at about the temperature of extremely hot tap water. Such fuel cells, however, stop functioning if they are contaminated by carbon monoxide, which is inevitably present in hydrogen derived from fossil fuels.
Bocarsly and Benziger have filed for patents on fuel cells that run at about 130 degrees Celsius, somewhat more than the boiling point of water, but not as hot as the large 200-degree-Celsius fuel cells that already are marketed for industrial applications. Fuel cells running at that middle temperature range are much less sensitive to carbon monoxide, yet could be made small enough and heated quickly enough to be practical in a car, said Bocarsly. Toyota and Volkswagen as well as some technology companies have expressed interest in the research, he said.
Princeton's rapid progress in the field, said Bocarsly, stems in part from the work of visiting research collaborator Supramaniam Srinivasan, an authority on fuel cells who came to Princeton in 1997 after a 30-year career at U.S. national laboratories, universities and private industry.
Despite the progress, said Bocarsly, it remains an open question how much more efficient fuel cells will be than finely tuned internal combustion engines. "Just because on paper you can get to a certain efficiency doesn't mean you're actually going to get there," he said.
Magic bullet needed
That is one reason why it's important to consider uses of hydrogen other than in fuel cells, said Law, who is an authority on the science of combustion. One possibility is to burn it like a conventional fuel, rather than converting it chemically to electricity. Conventional internal combustion engines might be modified to burn hydrogen, or a mix of hydrogen and gasoline, said Law.
"Certainly, compared to fuel cells, a hydrogen-burning engine is much more ready to implement," said Law.
Mixing hydrogen and fossil fuels could reduce some of the dangers associated with pure hydrogen, which is explosive and burns with an invisible flame, said Law. Public perception of hydrogen fuel suffers from a fear of catastrophic explosions -- "the Hindenburg syndrome," Law said -- but the dangers could be managed with the use of strong storage tanks and good sensors to detect leaks.
Even if all the technical hurdles were overcome, widespread use of hydrogen fuel would not fully solve the problem of greenhouse gas emissions and climate change, said Stephen Pacala, professor of ecology and evolutionary biology and co-director of the Princeton Environmental Institute's Carbon Mitigation Initiative. For the next 40 or 50 years, hydrogen will have to be extracted from fossil fuels, which means that scientists and engineers will need to invent ways to capture the leftover carbon components and prevent them from escaping into the atmosphere as greenhouse gasses. One solution would be to pump the carbon gasses deep into the earth. Unfortunately, carbon sequestration, as it is called, could be done safely for only about one-seventh of all the carbon that needs to be kept out of the atmosphere over the next 50 years to avoid major damage to the global environment, Pacala said.
"You basically have to grow every technology you can in order to do it," Pacala said, citing energy conservation as well as wind, solar and nuclear power as important elements of a successful plan to protect the planet. And just as all those technologies come together, said Pacala, further reductions in greenhouse emissions will be needed.
"After the next 50 years we still need a magic bullet," said Pacala. "There are a number of possible magic bullets -- nuclear fusion, being developed at the Princeton Plasma Physics Lab, is a big one -- but we can't wait another 50 years to do something or we are going to do irreparable damage to the environment. The science is very clear on that now."
With the Bush administration pledging $1.2 billion in funding for hydrogen fuel research over five years, Princeton scientists are hoping they may soon have a chance to accelerate their search for solutions. "It hasn't turned into real dollars yet," said Bocarsly. "But the national attention level has been raised, so that is good."
Andy Bocarsly is developing fuel cells that would be practical for use in next-generation cars. the cell shown here generates 10 to 13 amps of current at half a volt.
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