In response to your request on the web page, I am submitting this short description of fuel cells.
Marijan Papic, Ph.D., P.Eng.
A fuel cell is a device in which the chemical energy of reactants (hydrogen and air) is converted directly into usable energy in the form of electricity and heat without combustion as an intermediate step.
Fuel cell power plants are distinguished by high efficiency, low emissions, fuel flexibility, quick installation and quiet operation.
A single fuel cell is composed of an anode (an electrode where oxidation occurs) and a cathode (an electrode where reduction occurs) separated by an electrolyte. The electrodes are porous plates sandwiched around porous material holding the electrolyte.
The process concept is similar to that used in a common primary electrochemical cell and is the reverse of the water electrolysis process. Hydrogen rich gas is fed over the surface of anode where it is oxidized into positive hydrogen ions by releasing electrons. Electrons flow from the anode through an external circuit (wire) to the cathode and hydrogen ions travel through an electrolyte to the cathode. Oxygen rich gas (air) is fed over the surface of cathode where it is reduced to negative oxygen ions by accepting electrons released by hydrogen. Oxygen ions combine with hydrogen ions to form water. Electricity and heat are generated in the process.
A single fuel cell generates direct current at low density and low voltage (2 kA/m2, and 1V). Practical voltages are obtained by connecting many individual cells in series, i.e. stacks or batteries. Fuel cell stacks can further be configured in series, parallel, both series and parallel or as single units, depending on particular application.
There are different types of fuel cells identified by the kind of electrolyte used: solid polymer electrolyte, phosphoric acid electrolyte, molten carbonate electrolyte and solid oxide electrolyte fuel cells. Different fuel cells are being developed for different applications.
For a fuel cell power plant to be a practical energy generator it should be able to use commonly available fuels and be able to produce alternating current power, Thus a fuel cell power plant consists of three major subsystems - a fuel processor (where hydrogen is produced), a fuel cell power section (where dc power is produced) and a power conditioner (where power is conditioned for practical use).
Fuel cells have been developed for a number of diverse applications including space power, naval propulsion, electric vehicles, isolated power sources and utility applications.
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