fuel cell

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 reduction). 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.

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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.

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A pollution-free electricity generation technology that is expected to compete with traditional methods of creating and distributing electricity. It is also expected to be used in electrically powered cars, trucks and buses. On-the-road testing began with prototype vehicles at the end of the 20th century. Self-contained fuel cell systems are also expected to power individual homes within 20 years.

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.

A Ballard Fuel Cell

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.)