Fuel and oxidant gases are supplied to the backs of the porous electrodes by parallel grooves formed into carbon or carbon-composite plates.
These plates are electrically conductive and conduct electrons from an anode to the cathode of the adjacent cell.
In most designs, the plates are "bi-polar" in that they have grooves on both sides - one side supplies fuel to the anode of one cell, while the other side supplies air or oxygen to the cathode of the adjacent cell.
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.