The byproduct water is removed as steam on the cathode (air or oxygen) side of each cell by flowing excess oxidant past the backs of the electrodes.
This water removal procedure requires that the system be operated at temperatures around 375°F (190°C).
At lower temperatures, the product water will dissolve in the electrolyte and not be removed as steam. At approximately 410°F (210°C), the phosphoric acid begins to decompose.
Excess heat is removed from the fuel cell stack by providing carbon plates containing cooling channels every few cells.
Either air or a liquid coolant, such as water, can be passed through these channels to remove excess heat.