The US National Aeronautics and Space Administration (NASA) powers spacecraft with them. Computers at the First National Bank of Omaha get energy from them. Some of Chicago's public transit buses use them.

They are fuel cells. Fuel cells are electrochemical devices that produce electrical power without combustion. They generate electricity chemically, much in the manner that batteries do. But the chemicals that fuel cells use are elemental hydrogen and oxygen, and the product of the chemical reaction is water. Inputs such as natural gas can also be used, though, of course, hydrocarbon fuels would generate some level of carbon dioxide emissions.

Because fuel cells can be made highly efficient and clean, they hold great promise as an environmentally sound energy source that could help reduce greenhouse gas emissions and other pollution. The main obstacle to widespread use of fuel cells is their high cost relative to other devices for generating electricity or powering vehicles.

The first fuel cell was demonstrated by Sir William Groves in 1839. Groves showed that the process of electrolysis -- the splitting of water into hydrogen and oxygen by the addition of an electric current -- could be reversed. That is, hydrogen and oxygen could be recombined chemically to produce electricity.

A few scientists and engineers labored away at the fuel cell after it was first demonstrated, but the invention of the internal combustion engine and the development of oil resource extraction infrastructure in the latter part of the 19th century left fuel cell development far behind. The expense of fuel cells further inhibited development.

Fuel cell development received a boost in the 1950s when NASA turned to fuel cells to fill the need for a compact electricity generator to power space missions. As a result of the investment, the Apollo and Gemini missions were powered by fuel cells, and today, the Space Shuttle is powered by fuel cells.

Fuel cells are still mostly experimental, but a few companies sell them commercially.¹ Only in the last decade or so have significant advances been made in commercial fuel cell technology. Some are highlighted here.

Fuel cells are like batteries in that they produce electricity directly as a result of a chemical reaction. By contrast, internal combustion engines burn fuel and hence generate heat, which is then converted to mechanical energy. Unless the heat in the exhaust gases is used in some way (for example, for heating or air conditioning), internal combustion engines are quite inefficient. For instance, the efficiency of fuel cells for use in vehicles, now under development, is expected to be more than double that of current typical gasoline engines in cars.

Although both batteries and fuel cells produce electricity by electrochemical means, they serve two very different functions. A battery is an energy storage device: the electricity that it generates is the result of a chemical reaction of material that is already stored inside. A fuel cell does not store energy, but converts a part of the energy in an externally supplied fuel into electricity. In this respect, the fuel cell is more like a conventional power plant.

There are several different types of fuel cells. The simplest fuel cell consists of a special membrane, known as an electrolyte. Powdery electrodes are deposited on the two opposite surfaces of the membrane. This arrangement -- an electrolyte surrounded by two electrodes -- comprises an individual cell. Hydrogen is added to one side (the anode), and oxygen (air) is added to the other (the cathode). At each electrode, different chemical reactions take place (see diagram).

At the anode, hydrogen dissociates into a mixture of protons and electrons. In some fuel cells, the electrodes are surrounded by a catalyst, usually made of platinum or some other precious metal, which facilitates this dissociation:

H₂ = diatomic hydrogen molecule, the form of hydrogen in hydrogen gas
H⁺ = ionized hydrogen, i.e., a proton
e^- = an electron

The key to the fuel cell is that the electrolyte allows protons to flow through it (toward the cathode), but not electrons. The electrons flow through an external pathway to the cathode. This movement of electrons constitutes an electric current, which can be used to drive a device external to the fuel cell, such as an electric motor or light bulb. Such a device goes by the generic term "load."

At the cathode side of the fuel cell, the protons (which have traveled through the electrolyte) and electrons (which have traveled through the external load) are "reunited" and react with supplied oxygen, forming water, H₂O:

4 H⁺ + 4 e^- + O₂ ==> 2 H₂O.

The overall reaction in the fuel cell is 2 H₂ + O₂ ====> 2 H₂O.

Fuel cells operate using hydrogen fuel and oxygen from the air. The hydrogen can be supplied directly or by extracting it from an external supply of fuel like natural gas, gasoline, or methanol. When the source is not hydrogen itself, it needs to be chemically converted in order to extract the hydrogen -- a process called "reforming."² Hydrogen can also be produced from ammonia, alternative resources such as gas from landfills and wastewater treatment plants, and by water electrolysis, which uses electricity to split hydrogen and oxygen elements³. Most technology currently uses methane (natural gas) or methanol.

Various means have been developed to reform fuel into hydrogen for fuel cells. The US Department of Energy developed a fuel processor that works within a vehicle to reform gasoline to provide hydrogen to an on-board fuel cell⁴. A compact fuel reformer, one-tenth the size of current units, was demonstrated by researchers at Pacific Northwest National Laboratory in the US. Northwest Power Systems and Sandia National Laboratory have demonstrated a fuel reformer that converts diesel into hydrogen for fuel cells.⁵

Individual fuel cells generate about 0.7 to 1.0 volts each. To create higher voltages, cells are "stacked," that is, connected in series. To create larger currents, sets of stacked cells are connected in parallel. Combining the fuel cell stacks with a fuel processor, air supply, cooling system, and controls creates a fuel cell engine. The engine can power a vehicle, stationary power plant, or portable power generator.⁶ Fuel cell engine sizes vary depending on the application, type of fuel cell, and fuel used. As an example, each of the four individual 200 kilowatt stationary power plants at the bank in Omaha is about the size of a truck trailer.⁷

Fuel cells can be used to power both stationary and mobile devices. In response to tightening emissions standards in the US, auto manufacturers including DaimlerChrysler, Toyota, Ford, General Motors, Volkswagen, Honda, and Nissan are experimenting with or demonstrating vehicles powered by fuel cells. The first commercially-available fuel cell powered cars are expected to hit the road in 2004 or 2005.⁸

A significant milestone in fuel cell technology was rolled out in June 1993: Ballard Power System's 32-foot demonstration transit bus powered by a 90 kilowatt hydrogen fuel cell engine. Many types and generations of fuel cell passenger vehicles have been developed and operated since then using a variety of fuels. Three hydrogen fuel cell golf carts have been in use in Palm Desert, California, since late-1996. The cities of Chicago, Illinois, Vancouver, British Columbia, and Oslo, Norway are conducting field trials of public transport buses run on fuel cells. Alkaline fuel cell powered taxis are being tested on the streets of London.⁹

Stationary applications of fuel cell technology are being demonstrated but are not widely commercially available. The First National Bank of Omaha in Nebraska uses a fuel cell system to power its computers because the system is more reliable than the Bank's old one of grid-based power backed up by batteries.¹⁰ The world's largest commercial fuel cell system, 1.2 megawatts, will soon be installed in a mail-processing center in Alaska.¹¹ Laptop computers, a sewage treatment plant, and vending machines powered by fuel cells are also being tested and demonstrated.¹²

Pros and Cons

Fuel cells have several benefits. While current internal combustion engines have an efficiency of only 12%-15%, that of fuel cells is approximately 50%.¹³ Fuel cells can also maintain their high efficiencies when run at a fraction of their rated capacity, a significant advantage over gasoline engines.

The modular nature of fuel cells means that the capacity of a fuel cell power plant can be increased simply by adding more stacks; this minimizes underutilized capacity, allowing supply to be better matched to demand. Because the efficiency of a set of fuel cells is determined by the performance of the individual cells, small fuel cell power plants are as efficient as large ones. Also, waste heat from stationary fuel cell systems can be used for space and water heating, further increasing efficiency of energy use.

Fuel cells are virtually emissions-free. When fueled by pure hydrogen, heat and pure water vapor are the only by-products. In fact, Space Shuttle astronauts drink the water generated by on-board fuel cells.¹⁴ Other emissions depend on the source of the hydrogen supply. Using methanol results in zero emission of nitrogen oxides and carbon monoxide and very small hydrocarbon emissions. Emissions increase going from hydrogen to methanol to gasoline, yet very low emissions would still be achieved using gasoline.¹⁵ In any case, displacing today's conventional internal combustion engines for fuel cells would result in a net decrease of CO₂ and nitrogen oxide emissions. (See table on emissions)

Fuel cells offer added flexibility to energy infrastructures, creating opportunities for distributed generation (multiple decentralized sources of energy, which can reduce transmission losses) and off-grid markets (particularly beneficial for remote or rural areas without access to electricity lines). Fuel cells could allow individual residences or neighborhoods to generate most of their own power, and in the process greatly increase energy efficiency.

Fuel cells offer increased reliability and high-quality power. They are durable, have no movable parts, and generate a steady output of energy.

However, further development is needed on fuel cell technology to improve performance, reduce costs, and thus make fuel cells competitive with other energy technologies. It should be noted that, when considering costs of energy technologies, comparisons should be based on all aspects of technology performance, including capital operating costs, emissions of pollutants, power quality, durability, decommissioning, and flexibility.

While hydrogen gas is the best fuel, the infrastructure or vehicle base for this does not yet exist. Existing fossil fuel delivery systems (gas stations, etc.) could be used in the near term to deliver a source of hydrogen in the form of gasoline, methanol, or natural gas. This would eliminate the need for special hydrogen fueling stations, but would require vehicles to have an on-board reformer to convert fossil fuels to hydrogen. The disadvantage of this approach is that it requires the use of fossil fuels and thus results in carbon dioxide emissions. Methanol, currently the leading contender, creates fewer emissions than gasoline but would require bigger on-board tanks since it takes up twice as much room for the same energy content. ¹⁶

Unlike fossil fuel delivery systems, solar and wind electricity systems (which use electricity to create hydrogen and oxygen from water) and direct photo-conversion systems (which use semiconductor materials or enzymes to produce hydrogen) could provide a source of hydrogen without requiring a reforming step, thus without the emissions of methanol or gasoline fuel cells. The hydrogen could be stored and reconverted to electricity in a fuel cell when needed. In the long term, coupling fuel cells with such renewable energy sources is likely to be an effective strategy for providing an efficient, environmentally sound and versatile source of energy.

IEER recommends that local, state, and federal governments devote some of their vehicle procurement budgets to fuel cell powered vehicles and to stationary fuel cell systems to provide electricity and heat to some of their new or existing buildings. This will encourage development of a vital technology and reduce greenhouse gas emissions.

Types of Fuel Cells
Recent Advances in Fuel Cells
Comparison of Electric Vehicles, Hybrids, and Fuel Cells
Emissions from Hydrogen Fuel Cell Vehicles and Battery-Powered Electric Vehicles Versus Conventional Vehicles
Internet Resources on Fuel Cells

16 Service, 1999, p. 684.