..... 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. Fuel cells have been used to generate electricity in space flights.
fuel cell
Device that converts chemical energy of a fuel directly into electricity (see electrochemistry). Fuel cells are intrinsically more efficient than most other energy-conversion devices. Electrolytic chemical reactions cause electrons to be released on one electrode and flow through an external circuit to a second electrode. Whereas in batteries the electrodes are the source of the active ingredients, which are altered and depleted during the reaction, in fuel cells the gas or liquid fuel (often hydrogen, methyl alcohol, hydrazine, or a simple hydrocarbon) is supplied continuously to one electrode and oxygen or air to the other from an external source. So, as long as fuel and oxidant are supplied, the fuel cell will not run down or require recharging. Fuel cells can be used in place of virtually any other source of electricity. They are especially being developed for use in electric automobiles, in the hope of achieving enormous reductions in pollution.
Like a Battery
Functioning similar to 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 is water. The hydrogen can be derived from gasoline, natural gas, propane or methanol.
The hydrogen, which comes into the anode side of the fuel cell, is converted into electrons and hydrogen ions. The electrons are repelled by the anode and flow to the cathode. The cathode accepts the electrons as well as oxygen, which combine with the hydrogen ions from the anode, and converts them into water.
The Energy Alternative?
Some predict this will be the largest, new industry of the 21st century, although there are many obstacles to overcome. It depends on which sources for hydrogen ultimately make sense. By itself, 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.
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| A Ballard Fuel Cell |
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| The core of this fuel cell comprises two electrodes (anode and cathode) separated by a polymer exchange membrane. Each electrode is coated on one side with a platinum catalyst, which causes the hydrogen fuel to separate into free electrons and protons (positive hydrogen ions) at the anode. The free electrons are conducted in the form of usable electrical current through an external circuit. The protons migrate through the membrane electrolyte to the cathode, where the catalyst causes the protons to combine with oxygen from the air and electrons from the external circuit to form water and heat. (Image courtesy of Ballard Power Systems.) |
fuel cell
fuel cell [′fyül ‚sel]
Fuel Cell
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.)
REFERENCES
Fetter, 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
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