Emerging Technologies

Hydrogen Fuel Cells

For more than 150 years, scientists have known that when hydrogen and oxygen combine to form water (H2O), the chemical reaction releases electrical energy. (It’s exactly the reverse of electrolysis, in which running a current through water separates H2O into its constituent elements.) Devices that use a controlled combination of the two gases to generate current are called fuel cells. This developing technology underlies the vision of a nationwide “hydrogen economy,” in which the only exhaust from fuel-cell-powered vehicles would be water vapor, and America would drastically reduce its dependence on foreign fuel supplies.

This developing technology underlies the vision of a nationwide “hydrogen economy,” in which the only exhaust from fuel-cell-powered vehicles would be water vapor, and America would drastically reduce its dependence on foreign fuel supplies.

There are several significant obstacles to achieving that vision. Present fuel cells are too expensive and unreliable for the mass market. And hydrogen is very difficult to store and transport in a vehicle unless it is compressed to thousands of pounds per square inch (psi). Automotive companies are using containers in their demo vehicles that can store hydrogen at 5,000 to 10,000 psi, but a cost-effective and safe distribution system would have to be put in place before these vehicles could become widely available.

Furthermore, hydrogen (like electricity) is not a primary source of energy but rather an energy carrier. There are no natural reservoirs of pure hydrogen; it must be extracted from compounds such asnatural gas or water. And the processes for separating it from these principal sources pose their own challenges. When natural gas (basically methane, a lightweight molecule made of carbon and hydrogen) is exposed to steam under high temperatures in the presence of a catalyst, it frees the hydrogen. However, the process itself also produces substantial amounts of CO2. Widespread use would require a carbon sequestration scheme.

Significant public and private research on fuel cells has been conducted to accelerate their development and successful introduction into the marketplace. And hydrogen-fuel-cell cars are receiving considerable attention in the press. Some car manufacturers, including General Motors and Honda, are putting a very limited number of these vehicles on the road. There are hydrogen fueling stations in about 16 states, the greatest number being in California. Most of these, though, are small, private facilities intended to support a few experimental vehicles.

Not all hydrogen fuel cells are destined for vehicles. Stationary fuel cells for electric power generation have also been under development for decades. Some applications of fuel cells to residential or commercial buildings could involve generating electricity from a fuel input like natural gas or hydrogen and using the waste heat from that process to heat the building. Such co-generation systems could be very efficient in meeting both the electrical and heating needs of buildings. Still, costs remain high and there are numerous technical challenges to overcome with these systems. It will take decades of research and development, as well as changes in the energy infrastructure, before a hydrogen economy on a broad scale can be achieved.

How We Use Energy

Transportation

In the United States we use 28% of our energy to move people and goods from one place to another. The transportation sector includes all modes of transportation—from personal vehicles (cars, light trucks) to public transportation (buses, trains) to airplanes, freight trains, barges, and pipelines. One might think that airplanes, trains, and buses would consume most of the energy used in this sector but, in fact, their percentages are relatively small—about 9% for aircraft and about 3% for trains and buses. Personal vehicles, on the other hand, consume more than 60% of the energy used for transportation.

Over the past century, dependence on vehicles burning petroleum-based fuels has become a defining component of American life, bringing countless benefits. In fact, the United States, with less than 5% of the world’s population, is home to one-third of the world’s automobiles. In 2007, automobiles, motorcycles, trucks, and buses drove nearly 3 trillion miles in our country—about the equivalent of driving to the sun and back 13,440 times. Over the next 20 years, the total number of miles driven by Americans is projected to grow by 40%, increasing the demand for fuel.

Over the next 20 years, the total number of miles driven by Americans is projected to grow by 40%, increasing the demand for fuel.

86% of all the energy used in this sector comes from gasoline and diesel fuels, a troubling fact. Combustion of gasoline and diesel fuel emits carbon dioxide, as well as particulate matter, oxides of nitrogen (a prime component of “smog”), carbon monoxide, and unburned hydrocarbons. Indeed, whenever any fossil fuels are burned, carbon dioxide is released into the atmosphere, where it functions as a heat-trapping greenhouse gas. Also of concern is that we are dependent on foreign sources for two-thirds of our oil supplies.

Efforts are already well under way to find suitable alternatives to oil.Biofuels are one possibility. Alternative types of vehicles—hybrids,electric vehicles, and vehicles powered by hydrogen fuel cells, for example—all have the goal of reducing our dependence on oil. Petroleum sources that could serve as alternatives to conventional oil, such as oil shale and tar sands, could reduce our dependence on foreign oil, but wouldn’t help solve the environmental issues surrounding burning fossil fuels. Mining these resources can have damaging environmental effects, as well. Converting coal to liquid fuel is another option but it, too, has significant implications on the environment. The AEF committee estimates that the coal-to-liquid plants could replace up to 3 million barrels of gasoline per day by 2035 but that would require a 50% increase in U.S. coal production.

Greater vehicle efficiency may be our greatest short term strategy for reducing demand for petroleum. The CAFE standards, initially adopted in 1975, made more stringent in 2007, and strengthened again in pending legislation, require automobile manufacturers to build cars with higher average fuel economy.

Explore Our Energy System to see how the transportation sector fits in with the rest of the energy flow in the United States.