The fuel cell works by processing a hydrogen-rich
fuel—usually natural gas or methanol—into hydrogen, which, when combined with
oxygen, produces electricity and water. This is the reverse electrolysis
process.
Rather than burning the fuel, however, the fuel cell
converts the fuel to electricity using a highly efficient electrochemical
process. A fuel cell has few moving parts, and produces very little waste heat or
gas.
A fuel cell power plant is basically made up of three
subsystems or sections. In the fuel-processing section, the natural gas or
other hydrocarbon fuel is converted to a hydrogen-rich fuel. This is normally
accomplished through what is called a steam catalytic reforming process.
The fuel is then fed to the power section, where it reacts
with oxygen from the air in a large number of individual fuel cells to produce
direct current (DC) electricity, and by-product heat in the form of usable
steam or hot water.
For a power plant, the number of fuel cells can vary from
several hundred (for a 40-kW plant) to several thousand (for a multi-megawatt
plant). In the final, or third stage, the DC electricity is converted in the
power conditioning subsystem to electric utility-grade alternating current
(AC).
In the power section of the fuel cell, which contains the
electrodes and the electrolyte, two separate electrochemical reactions take
place: an oxidation half-reaction occurring at the anode and a reduction
half-reaction occurring at the cathode.
The anode and the cathode are separated from each other by
the electrolyte. In the oxidation half-reaction at the anode, gaseous hydrogen
produces hydrogen ions, which travel through the ionically conducting membrane
to the cathode. At the same time, electrons travel through an external circuit
to the cathode.
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