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In an electrochemical fuel cell, a sufficient quantity of catalyst, effective for promoting the reaction of reactant supplied to an electrode, is disposed within the volume of the electrode so that a reactant introduced at a first major surface of the electrode is substantially completely reacted up

In an electrochemical fuel cell, a sufficient quantity of catalyst, effective for promoting the reaction of reactant supplied to an electrode, is disposed within the volume of the electrode so that a reactant introduced at a first major surface of the electrode is substantially completely reacted upon contacting the second major surface. Crossover of reactant from one electrode to the other electrode through the electrolyte in an electrochemical fuel cell is thereby reduced.

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1. A method of reducing reactant crossover from a first electrode to a second electrode in a liquid feed fuel cell, said first electrode having first and second oppositely facing major surfaces and a volume interposed therebetween, said fuel cell comprising a solid polymer ion-exchange membrane elec

1. A method of reducing reactant crossover from a first electrode to a second electrode in a liquid feed fuel cell, said first electrode having first and second oppositely facing major surfaces and a volume interposed therebetween, said fuel cell comprising a solid polymer ion-exchange membrane electrolyte interposed between said first and second electrodes and generating an electrical power output, said method comprising: (a) supplying a liquid stream comprising a reactant to said first electrode at a reactant supply rate; (b) reacting said reactant in the presence of a catalyst distributed throughout the volume of said first electrode between said first and second major surfaces; and (c) adjusting the rate of reactant supply to said first electrode in accordance with the electrical power output of said fuel cell. 2. The method of claim 1 wherein said rate of reactant supply is adjusted in proportion to the electrical power output of said fuel cell. 3. The method of claim 1 wherein said liquid stream is supplied to said first electrode at a flow rate and said rate of reactant supply is adjusted by adjusting said flow rate of said liquid stream supplied to said first electrode in accordance with the electrical power output of said fuel cell. 4. The method of claim 3 wherein said flow rate is adjusted in proportion to the electrical power output of said fuel cell. 5. The method of claim 1 wherein said liquid stream supplied to said first electrode has a concentration of reactant therein and said rate of reactant supply is adjusted by adjusting said concentration of said liquid stream supplied to said first electrode in accordance with the electrical power output of said fuel cell. 6. The method of claim 5 wherein said reactant supply rate is adjusted in proportion to the electrical power output of said fuel cell. 7. The method of claim 1 wherein step (c) comprises adjusting the rate of reactant supply to said first electrode such that substantially none of said reactant contacts said solid polymer ion-exchange membrane electrolyte. 8. The method of claim 1 wherein said reactant comprises an alcohol. 9. The method of claim 8 wherein said alcohol is methanol. 10. The method of claim 1 wherein said liquid stream comprises water. 11. The method of claim 1 wherein said liquid stream further comprises an acid. 12. A method of reducing reactant crossover from a first electrode to a second electrode in a liquid feed fuel cell, said first electrode having first and second oppositely facing major surfaces and a volume interposed therebetween, said fuel cell comprising a solid polymer ion-exchange membrane electrolyte interposed between said first and second electrodes and generating an electrical power output, said method comprising: (a) supplying a liquid stream comprising a reactant to said first electrode at a reactant supply rate; (b) reacting said reactant in the presence of a catalyst disposed within the volume of said first electrode such that substantially none of said reactant contacts said solid polymer ion-exchange membrane electrolyte; and (c) adjusting the rate of reactant supply to said first electrode in accordance with the electrical power output of said fuel cell.