Fuel cells are cells in which there is a continual supply of reactants and thus creates a continual amount of energy. This energy is made via spontaneous redox reactions just like galvanic cells.
Oxygen is always a reactant at the cathode for all fuel cell reactions; oxygen is always being reduced. The type of reductant used determines what type of fuel cell it is. For example, the use of OH- or methanol as reactants are for alkaline fuel cells and methanol fuel cells respectively. A simple fuel cell which uses oxygen and hydrogen as its reactants is shown below.
Overall equation:
Products of fuel cell reactions always lead to the production of water and electrical energy
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