The Chapel Hill News

December 11, 2002

Fuel of the Future?

By Phillip Manning

Twenty billion tons of carbon dioxide spewed out of the world's smokestacks and automobile exhausts in the year 2000. The increase of carbon dioxide (and other greenhouse gases) in the atmosphere during the 20th century contributed to raising global temperatures about one degree. To reverse this trend, we need a cleaner fuel, and the most likely possibility is hydrogen. In a fuel cell, hydrogen generates electricity and produces not greenhouse gases and other noxious fumes but . . . water. Furthermore, hydrogen is plentiful; it makes up 88 percent of all the molecules in the universe. It is ubiquitous on Earth, too, bound together with other atoms in molecules such as water and hydrocarbons. So, it is possible to imagine a future of electric cars powered by hydrogen cruising around on quiet and clean highways expelling only water vapor. So entrancing is this picture, writes Jeremy Rifkin in "The Hydrogen Economy" (Penguin Putnam, $24.95) that all major automobile manufacturers have programs aimed at producing the cars of the future, and hydrogen-powered prototypes are available now. However, there is a stumbling block that may keep us from realizing the benefits of hydrogen as a source of power. Scientists have yet to develop a clean, economical process for producing hydrogen gas.

The cheapest way to generate hydrogen is by a steam reforming process that uses natural gas. But this process also produces carbon dioxide and carbon monoxide, two of the gases that the hydrogen economy aims to eliminate. Another method for making it is to split water into hydrogen and oxygen. But that requires electricity. And the cheapest way to get electricity is by burning fossil fuels, which puts us are back to square one. Of course, you could hook up a water splitting device to a photovoltaic cell that generates electricity from sunlight. In goes sunlight, out comes hydrogen to be used in fuel cells that provide the electricity to run your car or house and produce only water, the same substance you started with. This process converts sunlight and water into a storable form of energy, namely hydrogen, without emitting any greenhouse gases or pollution. The catch is that the hydrogen made this way costs much more than hydrogen made by the reforming process. Thus, the two most common methods of making hydrogen - reforming with natural gas and splitting water with solar energy - are not completely satisfactory. One releases greenhouse gases, the other is too expensive. Before the full potential of hydrogen can be realized, scientists must find a better process for making the gas.

Bruce Logan and his colleagues at Pennsylvania State University and the Kwang-Ju Institute of Science and Technology in Korea have developed a novel approach to this problem. The team reported on their success at convincing microbes to produce hydrogen from glucose in the June 1 issue of "Environmental Science & Technology." Scientists have long known that certain types of bacteria can ferment biological waste and produce hydrogen. These fermenting bacteria are everywhere; Logan got his from soil taken from a tomato garden. Unfortunately, these hydrogen-producing bacteria are invariably mixed with hydrogen-consuming microbes. The producers and the consumers cancel each other and the bottom line is little or no net hydrogen production.

Logan and his colleagues discovered a simple technique to rid the soil of hydrogen consumers. They heated their soil samples to a temperature just above the boiling point of water, which destroyed the hydrogen consumers but left the producers alive. When these heat-shocked samples were mixed with glucose and allowed to ferment, a mixture gases was generated that contained up to 62 percent hydrogen (the rest was mostly carbon dioxide). Theoretically, then, waste water from a soft drink factory or food processing plant, which contains sugars and starches, could be fermented using this technique to produce hydrogen inexpensively and with relatively small emissions of greenhouse gases.

However, problems remain. No one knows if this laboratory process can be scaled up into a commercial facility. And even if it can, it is likely to be more expensive than the fossil-fuel alternative. In fact, as long as we can drill holes in the ground and burn the hydrocarbons we pump out, any approach to alternative energy is likely to be more expensive. But if oil production peaks in the next decade or so, as at least one respected geologist predicts (see "Hubbert's Peak: The Impending World Oil Shortage" by Kenneth S. Deffeyes), then the ball game will change dramatically. As the price of oil goes up, as it inevitably will, alternative sources of energy will become more attractive. When that happens, fermentation processes may become an important step toward the nonpolluting hydrogen economy that Rifkin so enthusiastically espouses.
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