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A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i.e. it produces electricity from an external fuel supply as opposed to the limited internal energy storage capacity of a battery.
Typical reactants used in a fuel cell are hydrogen on the anode side and oxygen on the cathode side (a hydrogen cell). In contrast, conventional batteries consume solid reactants and, once these reactants are depleted, must be discarded, recharged with electricity by running the chemical reaction backwards, or, at least in theory, having their electrodes replaced. Typically in fuel cells, reactants flow in and reaction products flow out, and continuous long-term operation is feasible virtually as long as these flows are maintained.
Fuel cells are also attractive in some applications for their high efficiency and low pollution. (The only byproduct of a hydrogen fuel cell is water vapor). Some applications that have been suggested include
There are a number of types of fuel cells:
Fuel cells are electrochemical devices, so they are not constrained by the maximum thermal ( CarnotA heat engine is an engine that uses heat to produce mechanical work by carrying a working substance through a cyclic process. The Carnot heat engine uses a particular thermodynamic cycle studied by Nicolas Leonard Sadi Carnot in the 1820s. The Carnot cyc) efficiency as combustion engines are. Consequently, they can have very high efficiencies in converting chemical energy to electrical energy.
In the archetypal example of a hydrogen/ oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un proton-exchange membrane (or "polymer electrolyte") fuel cell (PEMFC), a protonFor alternative meanings see proton (disambiguation). Proton Classification Subatomic particle Fermion Hadron Baryon Nucleon Proton Properties Mass: 938 MeV/ c2 Electric Charge: 1. 6 × 10−19 C Spin: 1/2 In physics, the proton is a subatomic particle-conducting polymer membrane separates the anode and cathode sides. Each side has an electrodeAlternative meanings: There is also an Electric-type Pokemon named Electrode''. An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Mi, typically carbon paper coated with platinumPlatinum is also a certification by the RIAA and other world recording industries, see: RIAA certification Platinum is a chemical element in the periodic table that has the symbol Pt and atomic number 78. A heavy, malleable, ductile, precious, gray-white catalyst.
On the cathode side, hydrogen diffuses to the cathode catalyst where it dissociates into protons and electrons. The protons are conducted through the membrane to the anode, but the electrons are forced to travel in an external circuit (supplying power) because the membrane is electronically insulating.
On the anode catalyst, oxygen molecules react with the electrons (which have travelled through the external circuit) and protons to form water.
In this example, the only waste product is water vapor.
Fuel cells can not store energy like a normal battery, but in some extreme applications, like military solar cell powered spy aircraft they are combined with electrolyzers and high pressure gas storage systems to form an energy storage system.