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Recent advances in fuel-cell technology (or, more likely, sudden awareness
on the part of the press) have prompted The Economist (Oct. 25,
1997) to title an article optimistically, "The third age of fuel: Just
as coal gave way to oil, oil may now give way to hydrogen." Nothing of
the sort is happening.
Pundits have long spoken of "the hydrogen economy," a concept that means one thing to the technically literate and quite another to The Economist's editors. The main difference comes in understanding where the hydrogen comes from. There are no hydrogen wells, period. However, there are oceans full of hydrogen in the form of dihydrogen monoxide (water), vast reserves of hydrogen in petroleum and natural gas, and the hydrogen in plant and animal life. Petroleum contains a vast number of different chemicals, including the rich variety of chemicals known as gasoline, once considered a useless and dangerous by-product of kerosene production. For the most part, there are approximately two atoms of hydrogen for every atom of carbon in petroleum. When petroleum is burned, some energy is required to separate the molecules into individual atoms, but much more energy is given back as the carbon and hydrogen atoms combine with oxygen to give carbon dioxide and water vapor. Natural gas is primarily methane, composed of individual molecules that have one central carbon atom and four hydrogen atoms on the outside, positioned as if at the corners of a triangular pyramid (a tetrahedron). As with petroleum, some energy is required to separate the molecule into separate atoms, but the energy is more than returned when the carbon and hydrogen burn to form carbon dioxide and water vapor respectively. From an energy standpoint, we simply recognize that burning either petroleum or natural gas involves oxidation of both carbon and hydrogen, with the release of energy. As well, plants and animals contain carbon and hydrogen, but also a fair amount of minerals that make their presence known as ash residue after burning. Biomass is not a substantial source of energy, let alone just of energy from its hydrogen, for if it were, nobody would have ever started using coal. Water does not burn, of course. In order to release hydrogen from water we have to supply energy. We may regard water as an energy-negative source of hydrogen. If the earth's petroleum, coal, and natural gas would suddenly disappear, there would still be plenty of energy available from nuclear and --- if society would tolerate the huge environmental impact --- solar sources. But, what would provide motive power for transportation? Clearly, a liquid is easiest to use, but gaseous hydrogen could be made to suffice. Hydrogen burns in air, so one can easily imagine using hydrogen instead of fossil fuels to supply energy for our transportation needs that cannot be met by electric trolleys and trains. (We are ignoring numerous problems associated with how we actually handle the hydrogen.) The hydrogen economy, in its original sense, is based on central power stations (most likely nuclear ones) that would use energy to remove hydrogen from water. The energy put in by the power stations would be released when the hydrogen was used elsewhere. In other words, hydrogen would be somewhat like a portable battery _ not a source of energy, but a means of transporting it. Nobody, however, has rushed out to design systems for internal combustion engines to burn hydrogen. Why bother adding energy to a combustible liquid (gasoline) to remove hydrogen --- a gas --- that would be harder to use anyway? There is one device, however, for which hydrogen is uniquely suited. The fuel cell is rather like a battery that has continuously replaceable "electrodes," hydrogen at the anode and oxygen (from the air) at the cathode. It is not an engine that converts heat to work, with efficiency limited by temperatures of reservoirs (see The Energy Advocate, November, 1997), but rather one that converts the electrical potential energy of the atoms into an electric current directly. The hydrogen used in fuel cells normally comes from either natural gas or gasoline, but the commentators at The Economist imagine that the hydrogen would be extracted from biomass! But they also underestimate the resistance from self-styled "environmentalists." These people who regard humans as nothing more than a source of protein for mountain lions have a long history of opposing large-scale farming for food. How likely are they to approve large-scale farming for energy? Not a chance. The Green Gang doesn't like that much green, especially if it benefits humans. |