The ion conducting electrolyte can be solid or liquid and its chemistry usually defines the type of fuel cell.
The most common types of fuel cells are Proton Exchange Membrane (PEM) fuel cells, Solid Oxide Fuel Cells (SOFC), Alkaline Fuel Cells (AFC), and Phosphoric Acid Fuel Cells (PAFC).
In a PEM fuel cell, the anode splits hydrogen into electrons and protons. The protons pass through the electrolyte membrane, while the electrons are forced through an external electric circuit. The cathode recombines the protons, electrons, and oxygen from air to produce water. Alkaline Fuel Cells use the same process as PEM fuel cells except that the ion is a hydroxyl (OH) and water is instead consumed at the cathode and produced at the anode.