If a voltage is applied to water by placing two electrodes into the liquid and connecting a battery across them, the voltage induces a chemical reaction; hydro- gen is produced at one electrode and oxygen at the other. Electrical energy is being used to force the reaction that causes water to dissociate into hydrogen and oxygen.

In 1839, Sir William Grove observed that this process, known as electrolysis, will proceed in the other direction too, and of its own accord. If two specially selected electrodes are placed in water and gaseous hydrogen and oxygen provided (one gas at each electrode), hydrogen will react at one electrode and oxygen at the other, producing water and an electrical voltage between the electrodes. This is the basis of fuel cell operation.

Although the principle was known in 1839, it was not until a century later that the English scientist Francis Bacon was able to develop a practical fuel cell. He demonstrated a 5 kW fuel cell stack in 1959 that he patented as the Bacon Cell. In the same year, Harry Ihrig, an engineer working for the Allis Chalmers Manufacturing Company, demonstrated a 20 horsepower tractor powered by fuel cells. Both were based on the alkaline fuel cell.

By the early 1960s, the Pratt and Whitney Aircraft Corporation had licensed Bacon’s fuel cell and began to develop the technology. At around the same time, scientists at U.S. company General Electric began to develop fuel cells based on proton exchange membranes. When NASA was planning its manned space pro- gram it identified fuel cells as the ideal power source for its space vehicles. Initially the organization chose the General Electric design and this was used in the Gemini space program. Subsequently it switched to the alkaline fuel cell for the Apollo program and this continued to be used in the space shuttle until it was decommissioned.

Interest in these and other fuel cells continued in the 1960s, 1970s, and 1980s, and a variety of new types of fuel cell were pursued. This led, in 1992, to the launch of the first commercial fuel cell by a company called Inter- national Fuel Cells, the parent company of which, United Technologies, owned Pratt and Whitney. This new fuel cell was based on a new acidic electrolyte called phosphoric acid, and the phosphoric acid fuel cell has since developed into the most successful commercial type of cell.

Meanwhile, environmental concerns that began to arise in the 1980s together with fears about oil supply led at the beginning of the 1990s to a revival of an old quest to develop practical electric vehicles that could replace the petrol engine car. While several potential technologies have been pursued, one of the leading contenders is a fuel cell power unit based on proton exchange membrane fuel cells. Development of these continues to receive high levels of investment.

Other types of fuel cell have also been developed. Among these are two high-temperature fuel cells: the molten carbonate fuel cell and the solid oxide fuel cell. The latter is an all solid-state fuel cell, making it potentially extremely durable. Alkaline fuels remain under development too and a sixth type, the direct methanol fuel cell, is seen as a potential new portable source of power.

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