Why do fuel cell electrodes remain usable during the chemical reaction?
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 a fuel cell, the electrodes remain usable during the chemical reaction because they are specifically designed to remain unchanged by the process, unlike the electrodes in a standard battery.1
To maintain this stability, engineers construct electrodes using a complex, multi-layered design that facilitates the necessary chemical reactions without degrading the electrode itself:
- Waterproof layer: Often utilizing polytetrafluoroethylene (Teflon), this layer prevents the electrode from flooding with electrolyte, which would otherwise slow down the operation.2
- Active catalyst layer: This layer, typically composed of materials like platinum, gold, or organometallic compounds on a carbon base, promotes the reaction without being consumed.2
- Conducting layer: This layer serves as an electrical conductor to carry current into or out of the cell.2
By carefully managing pressure and construction, the system ensures that fuel and oxidizer contact the catalyst and electrolyte at stable solid sites, allowing the cell to produce electricity continuously as long as reactants are supplied.12