Spring 2004 – vol. 22, no. 1 logos home page Contact the logos editor Argonne home page Feature articles Superconductivity team wins top research prizes Creating stability in a world of unstable electricity distribution Argonne tests, creates fuel cells to power the future Fueling the hydrogen future with Argonne's ceramic membrane Nuclear plants may be clean hydrogen source Argonne Update Stars surrender secrets to supercomputers Electricity controls nanocrystal architecture

Nuclear plants may be
clean hydrogen source

by David Baurac

CLEAN HYDROGEN SOURCE – A new generation of nuclear power plants may provide an energy-efficient, greenhouse-gas-free source of hydrogen.

For more than 100 years, visionaries have periodically espoused the dream of an economy driven by hydrogen - an efficient fuel that emits only water when burned. Today, their vision may be on the verge of reality: Energy policymakers around the world are increasingly recognizing the potential of hydrogen as a fuel for transportation, which accounts for more than one third of the nation's annual energy consumption.

One key problem that must be solved first is to develop a source and distribution system for the massive amount of new hydrogen that will be needed. A number of new and existing technologies are under study, but one strong candidate for providing hydrogen in future decades is nuclear energy.

Heightened interest in hydrogen as a widespread fuel is driven by environmental, political and technological factors:

• international concerns about the air pollution and greenhouse gases emitted by burning fossil fuels;
• the political vulnerability of world oil supplies; and
• advances in fuel-cell technology that have made hydrogen-powered electric vehicles a real near-term possibility.

Fuel cells combine hydrogen and oxygen to produce electricity. Their only waste product is water vapor. In the last five years, their power density - the ratio of power output to size - has increased ten-fold while their costs have decreased ten-fold. Every major automobile manufacturer has a program to develop fuel-cell-powered vehicles, and many experts predict that hydrogen-powered electric cars will appear on American roads in a few years.

But in the longer term, full conversion to hydrogen-based transportation will take decades, if only because of the enormous quantities of hydrogen required to fuel the dream.

"Americans drive nearly three trillion miles a year," said David Lewis, director of Argonne's Chemical Technology Division. "Even if you assume that electric cars will be twice as efficient as today's internal combustion engines, you'd still need 34 million metric tons of hydrogen to cover that many miles. That's a 70 percent increase in worldwide production just to handle this nation's current transportation needs. Add in the rest of the world, and the numbers become truly daunting."

Hydrogen is the most abundant element in the universe, but hydrogen gas, the form needed to power fuel cells, is rare in nature and must be manufactured. Current world production is about 50 metric tons per year, mainly as a feedstock for the oil and fertilizer industries.

About 95 percent of hydrogen is manufactured with an efficient, economical steam-reforming process that releases hydrogen from methane or natural gas. But a key goal for hydrogen power is to reduce carbon dioxide emissions, and here steam reforming has a problem: to create steam, the plants burn natural gas, which emits carbon dioxide.

"Using steam reforming to produce hydrogen for transportation," said Argonne engineer Leon Walters, "would eliminate some carbon-dioxide. But wouldn't it be better to manufacture hydrogen without making any greenhouse gas?"

Splitting water

One possibility is electrolysis, the use of electricity to split water into hydrogen and oxygen. Electrolysis has been used for more than 100 years to manufacture pure hydrogen and oxygen.

"If electric cars will be twice as efficient as cars with internal combustion engines, then electrolytically produced hydrogen is already close to competitive with dollar-fifty-a-gallon gasoline," said Walters. "Centralized hydrogen electrolyzers could be installed at corner gas stations and a home refueling station could soon be as close as the electrical outlet in your garage."

Large electrolysis units are operating around the world in demonstrations of central fueling for public transportation and auxiliary energy for large buildings.

But to displace the nation's automobile transportation fuel with electrolytically generated hydrogen would require 241 gigawatts of new generating capacity. "That's the equivalent of 241 modern 1,000-megawatt power plants," Walters said. "Clearly, it won't happen in only five or 10 years."

Where would all this additional electricity come from?

"Renewable energy technologies - wind, solar and geothermal - can make an important contribution," he said. "These technologies tend to be too intermittent to provide reliable base-load electricity, but they can generate hydrogen and store it when the wind is blowing or the sun is out. On the other hand, they are too diffuse to generate 241 gigawatts of new capacity. You'd need 640,000 windmills, for example, which would occupy a total land area of 71,000 square miles - nearly the size of Ohio and Indiana combined.