Why must water be removed from an alkaline fuel cell?

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Diagram of a proton exchange membrane (PEM) fuel cell showing labeled layers, including flow field plates, electrodes, and the proton exchange membrane, with arrows indicating hydrogen and oxygen inputs, electricity generation, and water and heat as outputs. — fuel cell Proton exchange membrane (PEM) fuel cell
The proton exchange membrane is one of the most advanced fuel cell designs. Hydrogen gas under pressure is forced through a catalyst, typically made of platinum, on the anode (negative) side of the fuel cell. At this catalyst, electrons are stripped from the hydrogen atoms and carried by an external electric circuit to the cathode (positive) side. The positively charged hydrogen ions (protons) then pass through the proton exchange membrane to the catalyst on the cathode side, where they react with oxygen and the electrons from the electric circuit to form water vapour (H₂O) and heat. The electric circuit is used to do work, such as power a motor.

In an alkaline fuel cell, water is produced as a chemical reaction product when hydrogen and oxygen combine. This water must be removed from the system to maintain the proper concentration and performance of the alkaline electrolyte, which is typically an aqueous solution of potassium hydroxide or sodium hydroxide.

If the water is not removed—usually through evaporation from the electrolyte via the electrodes or a separate evaporator—it can dilute the electrolyte, potentially impacting the efficiency and operational stability of the cell.1