PROTON EXCHANGE MEMBRANE FUEL CELLS
What is a PEM Fuel Cell?
The proper operation of a PEM fuel cell or electrolyzer requires the use of a Proton Exchange Membrane, or a high temperature 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:
How Cation and Anion Exchange Membranes Work
Cation exchange membranes (CEMs) are almost exclusively fluorinated polymer membranes (also known as perfluorosulfonic acid or PFSA) that support proton (H+) conductivity. Anion exchange membranes (AEMs) make use of different alkaline stable polymeric materials that can support hydroxide (OH-) conductivity through the membranes. Bipolar membranes are a directional combination membrane that allows for proton (or cation) conductivity and hydroxide conductivity on their respective sides. Chlor-alkali membranes are usually PTFE fabric reinforced membranes that are used to produce caustic solutions, bleach and other relevant electrochemical applications such as electroplating, gold salt generation, etc.