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 energy. Devices that use a controlled combination of the two gases to generate energy in the form of electrical 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 petroleum-based fuels.

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 petroleum-based fuels.

Significant public and private research on fuel cells has been conducted to accelerate their development and successful introduction into the marketplace. In late 2014, the first commercial fuel-cell vehicles appeared in California. It is far too soon to determine what their impact will be on U.S. transportation. Even in California, where state policies favor “zero-emission” vehicles, there are very few hydrogen fueling stations compared to conventional gasoline stations. Fueling stations must be capable of filling automobile tanks with hydrogen compressed in the range of 10,000 pounds per square inch, more than three times the pressure in scuba air tanks. Whether a widely distributed network of fueling stations will emerge will depend on cost and on evolving consumer preferences.

Because fuel cells allow the regulated reaction of hydrogen (in a tank) and oxygen (from the air) to produce electricity, they are often perceived as non-polluting. However, that describes only the exhaust from the vehicle, not the processes involved in producing hydrogen gas.

Hydrogen (like electricity) is not a primary source of energy but rather an energy carrier. There are no natural reservoirs of pure hydrogen. To produce hydrogen, water can be electrolyzed in the reverse of the fuel-cell reaction. To force electrolysis to occur, considerable amounts of electricity are required, much of which is currently generated by burning fossil fuels. Alternatively, in commercial applications, the vast preponderance of hydrogen generated in the United States is extracted from a fossil fuel: natural gas. 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. This is called “reforming,” and the process produces carbon dioxide (CO2). Discussions about increasing hydrogen production by gas reforming are often accompanied by calls for carbon sequestration schemes.

Not all hydrogen fuel cells, however, are destined for vehicles. Stationary fuel cells for electric power generation have 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.

Still, the costs of hydrogen energy remain high compared to other energy sources; it is extremely difficult to store onboard, the use of natural gas as a feedstock emits CO2, and there are numerous technical challenges to overcome with these systems. It could take many years of research and development, as well as changes in the energy infrastructure, before hydrogen could have a significant impact on American energy use.

Nonetheless, the use of hydrogen for vehicle fuel has the potential to nearly eliminate gasoline use in light-duty vehicles by the middle of this century, while reducing fleet greenhouse gas emissions to less than 20 percent of current levels.