The proper operation of a PEM fuel cell or electrolyzer requires the use of a Proton Exchange Membrane, or Polymer Electrolyte Membrane, hence the term “PEM fuel cell” and “PEM electrolyzer.” The proton exchange membrane enables the transfer of hydrogen ions i.e., protons, from the anode of the fuel cell to the cathode. The membrane also prohibits the electrons that were removed from the hydrogen atoms to pass through the membrane itself. The electrons instead flow out through the external electrical circuit to complete work on the load before returning to the cathode.
These membranes serve as solid electrolytes that conduct protons through the membrane but are reasonably impermeable to gases and are essential elements for various electrochemical processes without the need of a liquid electrolyte.
For PEM fuel cells, the membrane is key for the Membrane Electrode Assembly. During the electrochemical reaction, oxidation at the anode produces protons and electrons; while the reaction at the cathode combines protons and electrons with oxidants to generate water.
Within the Ion Exchange Membrane category, there are several different types of membranes that perform different functions: