A Pollution-Free Hydrogen Economy? Not So Soon

Energy

A Pollution-Free Hydrogen Economy? Not So Soon

Electric cars powered by hydrogen fuel cells don't produce greenhouse-enhancing carbon dioxide. But producing hydrogen does-and if we want to reduce our petroleum dependence, we're going to have to reconcile ourselves to that fact.

July 11, 2003
By Richard A. Muller

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Think hydrogen-the clean fuel of the future. It burns with oxygen to make water vapor, and only water vapor-no soot, no nitrous oxides, no carbon dioxide with its potential greenhouse warming. In his State of the Union message in January, President Bush announced a major new initiative. He proposed $1.2 billion in research funding that he said would enable the United States to "lead the world in developing clean, hydrogen-powered automobiles." Spurred by this new federal support, Bush said, "our scientists and engineers will overcome obstacles to taking these cars from laboratory to showroom, so that the first car driven by a child born today could be powered by hydrogen, and pollution-free." His surprise announcement met with enthusiastic applause.

Now here is a more pessimistic view of the hydrogen economy: huge open pit mines scarring much of Pennsylvania, Illinois, Utah, and Colorado. Billions of tons of carbon dioxide are dumped into the atmosphere every year from facilities that produce hydrogen-by burning the fossil fuels coal, oil, and natural gas.

Where is the truth? Undoubtedly somewhere in between-but it probably involves heavy burning of fossil fuels.

The key fact is this: Hydrogen is not a source of energy. It is only a way of storing and transporting it. Although hydrogen is the most abundant element in the Universe (and in the more immediate neighborhood, it makes up 90 percent of the atoms in the Sun and Jupiter), there is virtually no hydrogen gas on Earth. Our gravity is so weak that essentially all our primordial hydrogen-except that which bound itself into heavier compounds-escaped into space billions of years ago. So hydrogen fuel must be "manufactured" by extracting it from water and methane. You get out from hydrogen fuel only the energy you put into extraction, or from burning carbon in the process.

Water can be split into hydrogen and oxygen by electric current, the process known as electrolysis. Plain heat will do the trick too. Above 2,700 C water spontaneously decomposes. On a sufficiently hot fire (e.g., the oil well fires of Kuwait), water decomposes and then recombines when it cools above the well.

But splitting water is expensive, and we don't need the oxygen. There's a much cheaper way to produce hydrogen: spray steam on white-hot coals and out comes mostly hydrogen gas (40 percent) and carbon monoxide (50 percent), a mixture known appropriately as "water gas." It's the least expensive way to make hydrogen. Unfortunately, the carbon monoxide produced along with it is highly poisonous. To extract the last bit of energy, the carbon monoxide can be burned, and that turns it into the greenhouse gas carbon dioxide.

The production of water gas began in earnest in the 1870s. The other common "manufactured" gas back then was coal gas, extracted from bituminous coal by heating it in an oxygen-free environment. Coal gas went to streetlamps and homes, and the more dangerous water gas was used by industry. Water gas is still extensively in steel manufacture and in the so-called Fisher-Tropsch process, which is used to make synthetic gasoline and alcohols.

In the 1920s, the discovery of large underground reserves of methane provided a cheaper alternative to coal gas. Since it wasn't manufactured, it was called "natural gas," the name still used today. Methane also replaced coal for water gas production. As with coal, producing hydrogen from methane yields abundant carbon monoxide that upon combustion becomes carbon dioxide.