The National Academies: What You Need To Know About Energy

The National Academies

What You Need To Know About Energy

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 as natural 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.

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Energy Hands-on

What do you know about energy?

In 2008, what percentage of the United States' total energy consumption came from oil?

  • Sorry, that’s incorrect.

    In 2008, 37% of the United States' total energy consumption came from oil, more than any other energy source.

  • Sorry, that’s incorrect.

    In 2008, 37% of the United States' total energy consumption came from oil, more than any other energy source.

  • Correct!

    In 2008, 37% of the United States' total energy consumption came from oil, more than any other energy source.

Energy Defined

Algal Biodiesel

A type of diesel fuel made by chemically processing oils from algae.

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