A fuel cell generates electricity directly by actuating a hydrogen/oxygen electrochemical reaction (see illustration above). Hydrogen can be extracted from many different substances, from natural gas to biogas, and because fuel cells do not burn fuel, they generally emit no harmful gases. Fuel cells have a theoretical energy conversion efficiency of 60%, and this can be boosted to more than 80% if the heat emitted by the chemical reaction is also used. These rates are higher than for any other generating system, and this is another distinct advantage. Fuel cells were first used in the 1960s as a power source for spacecraft, and since the oil crises of the 1970s, developers in a number of countries have been exploring how they can be used in place of thermal generating stations.

Fuel cell development has moved forward in Japan under two 10-year plans in a national project launched in 1981. One result of the project was commercialization of the Phosphoric Acid Fuel Cell (PAFC). When PAFCs were in their prime a few years ago, about 200 of the devices were installed in different parts of Japan, generating from 50 to more than 200 kW each. Several dozen remain in operation today, producing a total of about 10,000 kW for factories and public buildings. But electricity from PAFCs costs anywhere from 400,000 to 500,000 yen per kW, far more than the cost of electricity from a gas turbine. This explains why PAFCs are not widely used today.

Different fuel cells were developed under the national project, and the one that has been improved most rapidly over the last decade is the Polymer Electrolyte Membrane Fuel Cell (PEMFC). It generates plenty of electricity at room temperature, raising hopes that it will be able to power homes and cars. At the end of 2002, Toyota and Honda completed manufacture of their PEMFC-powered "fuel cell cars." The two companies have delivered a total of seven of these vehicles to Japan's Cabinet Office and Ministry of Economy, Trade and Industry. Honda has also delivered three of them to the City of Los Angeles in the U.S.

The Honda FCX fuel cell vehicle has a PEMFC with a maximum output of 78 kW. The high-pressure (350 atmospheres) tanks hold 156 liters of pure hydrogen. The car has a driving range of 355 km and a top speed of 150 km/h. When the car starts moving and accelerates, highly efficient, high output capacitors (see this page) supply the electric power instead of batteries. Test drivers were surprised at the acceleration rate. But a number of problems remain—for example, each vehicle costs more than 100 million yen, and it is still not clear how hydrogen filling stations will be set up. But with its long driving range and excellent acceleration, two advantages electric cars do not have, the fuel cell vehicle will probably be the first choice for the next-generation car.

One spin-off from the PEMFC is the Direct Methanol Fuel Cell (DMFC). It uses methanol instead of pure hydrogen as a fuel, releasing hydrogen from the methanol internally. The DMFC is less risky than the hydrogen-fueled PEMFC, and the fuel cell can be made quite compact. This has led major electronic manufacturers to pursue the development of small DMFCs to power notebook computers and cell phones.

In 2003, Toshiba released information on a separate-unit, palm-size DMFC prototype device for recharging cell phone batteries. The prototype's canister holds 25 cc of methanol, enough to supply the power of six lithium batteries in today's cell phones. Toshiba expects to have the device on the market in 2004 for notebook computers, and in 2005 for cell phones.

When generating electricity, fuel cells emit only water, or water and tiny amounts of carbon dioxide. This is the type of clean power source we could once only dream of. It will take many years before fuel cells can fulfill all of the electricity needs of an ordinary home, but one day fairly soon, they could be powering portable devices and many more cars.