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fuel cell,electric cell in which the chemical energy from the oxidation of a gas fuel is converted directly to electrical energy in a continuous process (see oxidation and reductionoxidation and reduction,
complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation
..... Click the link for more information. ). The efficiency of conversion from chemical to electrical energy in a fuel cell is between 65% and 80%, nearly twice that of the usual indirect method of conversion in which fuels are used to heat steam to turn a turbine connected to an electric generator. The earliest fuel cell, in which hydrogen and oxygen were combined to form water, was constructed in 1829 by the Englishman William Grove.
In the hydrogen and oxygen fuel cell, hydrogen and oxygen gas are bubbled into separate compartments connected by a porous disk through which an electrolyte such as aqueous potassium hydroxide (KOH) can move. Inert graphite electrodes, mixed with a catalyst such as platinum, are dipped into each compartment. When the two electrodes are connected by a wire, the combination of electrodes, wire, and electrolyte form a complete circuit, and an oxidation-reduction reaction takes place in the cell: hydrogen gas is oxidized to form water at the anode, or hydrogen electrode; electrons are liberated in this process and flow through the wire to the cathode, or oxygen electrode; and at the cathode the electrons combine with the oxygen gas and reduce it. The modern hydrogen-oxygen cell, operating at about 250°C; and a pressure of 50 atmospheres, gives a maximum voltage of about 1 volt.
A number of other fuel-cell technologies have been developed, but the fundamental design—anode catalyst, electrolyte, and cathode catalyst— remains the same; hydrogen is the most commonly used fuel, but other fuels, such as natural gas, are used. Fuel cells are combined in a fuel-cell stack to create greater voltages or currents. Characterized by high efficiency, cleanliness, and lack of noise, fuel cells have been used to generate electricity in space flights, to produce electricity in remote locations or from landfill or waste treatement gases, and, more recently, to power automobiles.
the most important component of an electrochemical generator, which directly converts the chemical energy of fuel and oxidant reactants into electricity.
At the heart of a fuel cell are two electrodes separated by a solid or liquid electrolyte (see Figure 1). The fuel and oxidant are introduced into chambers adjacent to the electrodes, and oxidation and reduction reactions occur on the electrolyte-electrode interface in the presence of a catalyst (seeOXIDATION-REDUCTION REACTION). As a result of these reactions, ions A~ and B+ are formed, which later recombine to yield the final reaction product AB, and heat Q is released or absorbed. The electrons liberated by the oxidation of the fuel create an excess negative charge on the corresponding electrode (anode), and an excess positive charge is produced on the cathode as a result of the reduction of the oxidant. When the external circuit is closed, an electric current appears, which performs useful work Euse. The overall reaction is A + B = AB + Q + Euse.
The electrolyte in a fuel cell not only contains substances that participate in the electrochemical reactions, but also substances that provide for the spatial separation of the oxidation and reduction processes. The efficient operation of a fuel cell requires an extensive electrode surface (up to hundreds of square meters per gram of substance), rational organization of the adsorption and
ionization processes and of the conduction of electrons and reaction products, and high purity of the reactants.
The idea of constructing a fuel cell was put forward in the early 19th century by the English physicist W. R. Grove, but it was only in the 1960’s that practical fuel cells were constructed— almost simultaneously in the USSR, USA, France, and Great Britain. By the mid-1970’s, many different types of fuel cells had been developed, differing in operating temperature (from room temperature to 1200°K), type of fuel (hydrogen, hydrogen-bearing substances, and metals), oxidant (oxygen, oxygen-bearing substances, and chlorine), catalyst (platinum, palladium, silver, nickel, and carbon), and electrolyte (alkalies or acids, solid metal oxides, salt melts, and ion-exchange polymers).
Fuel cells in which hydrogen, oxygen, and an alkali (or ion-exchange polymer) are used as fuel, oxidant, and electrolyte, respectively, have proved the most practical. Such fuel cells operate at moderate temperatures (up to 100°C), which ensures a long operating life—up to several thousand hours; their operating voltage is approximately 1 volt. In principle, however, any substance that reacts at the operating temperature with oxygen or halogens may serve as the fuel in a fuel cell. Fuel cells using the direct oxidation of hydrocarbons (propane or gasoline), alcohols, and ammonia also show promise for future development.
One of the major problems hindering the development of fuel cells is the need to develop a theory of catalysis and to devise practical methods for the production of catalysts with sufficient activity, corrosion resistance, and resistance to the poisoning effect of reaction products. (See alsoGROVE CELL.)
REFERENCESFetter, K. Elektrokhimicheskaia kinetika. Moscow, 1967. (Translated from German.)
Filstich, W. Toplivnye elementy. Moscow, 1968. (Translated from German.)
Muchnik, G. F. “Perspektivy i nauchnye problemy primeneniia metodov neposredstvennogo polucheniia elektroenergii iz khimicheskikh topliv.” Izv. AN SSSR: Energetika i transport, 1973, no. 2.
N. S. LIDORENKO and G. F. MUCHNIK
fuel cell[′fyül ‚sel]
fuel cellA pollution-free electricity generation technology that may power electric vehicles and even homes in the future. Road testing began at the end of the 20th century. Functioning like a battery, which uses electrochemical conversion, fuel cells take in hydrogen-rich fuel and oxygen and turn them into electricity and heat. The waste product of a fuel cell is water, and although not recommended for drinking, one test by Toyota showed fewer organic impurities than a glass of milk.
The Energy Alternative?
Although there are many obstacles, pundits predict fuel cells will be a huge industry in the 21st century. However, while hydrogen can be derived from gasoline, natural gas, propane or methanol, it depends on which sources ultimately make the most sense. In addition, hydrogen is difficult to distribute and stockpile, and installing hydrogen pumps in every gas station would be a gigantic undertaking. Currently, Ballard Power Systems, Inc., Burnaby, British Columbia (www.ballard.com) is the largest company making fuel cells.
|A Ballard Fuel Cell|
|Separated by a polymer exchange membrane (PEM), the anode and cathode are coated with a platinum catalyst that causes the hydrogen fuel to separate into free electrons and positive hydrogen ions (protons). The free electrons are the electricity, while the ions migrate through the PEM to the cathode and combine with oxygen and returning electrons to form water and heat. (Image courtesy of Ballard Power Systems.)|