Renewable Energy - Hydrogen—a Fuel Of The Future?

Hydrogen is the lightest and most abundant chemical element. It contains only one proton and one electron. From an environmental point of view it is also the ideal fuel. Its combustion as a fuel or conversion to electricity produces only water vapor—it is entirely carbon-free. The National Aeronautics and Space Administration (NASA) has used liquid hydrogen for decades to power rockets into space.

Three-quarters of the mass of the universe consists of hydrogen; however, it is combined with other elements, as in water. The elemental, combustible, form of hydrogen is not found in the atmosphere. Hydrogen-containing compounds cannot be converted into pure gas hydrogen without the expenditure of energy. Most elemental hydrogen is currently obtained by separating it from hydrocarbons, such as natural gas, gasoline, or methanol. This process is called "reforming." However, reforming requires energy in the form of heat. Therefore, with today's technology little or nothing can be gained from an overall energy point of view.

Hydrogen has considerable potential as a clean fuel and, because it is a gas, can be distributed with essentially FIGURE 10.14
Total shipments of photovoltaic modules, 1982–2001 the same technology as natural gas. Scientists are researching ways to economically produce hydrogen gas. The possibility of a transition to hydrogen has been considered for more than a century, and many see hydrogen as the logical "third-wave" fuel—hydrogen gas following oil, just as oil replaced coal decades earlier.

The most promising application of hydrogen is in fuel cells. A fuel cell works like a battery, except it never runs down as long as hydrogen is supplied. It contains two electrodes—a negative electrode or anode and a positive electrode or cathode—surrounding an electrolyte. An electrolyte is a substance that can conduct electricity. Hydrogen is fed to the anode, and the atoms are separated into protons and electrons that travel along different paths to the cathode. The electrons travel along an external circuit creating an electricity flow. The protons travel through the electrolyte to the cathode, where oxygen is fed in. The protons mix with the oxygen atoms and electrons, forming water and generating heat.

Research in the United States is focused on the use of traditional hydrocarbon fuels (like gasoline) as the hydrogen source for vehicles containing a fuel "reformer" and a fuel cell. This takes advantage of the existing infrastructure of gasoline stations.

In March 2004 the DOE introduced its "Hydrogen Posture Plan," which outlines a plan to create a hydrogen-based transportation energy system in the United States. President Bush requested that $227 million be spent on research in 2005 to support this hydrogen fuel initiative.

FIGURE 10.15
World energy production by source, 1970–2001