What are gas-diffusion electrodes in fuel cells?
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.
Gas-diffusion electrodes are specialized components in fuel cells designed to facilitate a stable three-phase reaction between a gaseous or liquid fuel, a catalyst, and an electrolyte.1
Invented to improve the practicality of hydrogen-oxygen fuel cells, these electrodes effectively maintain controlled contact between the fuel gas on one side and the aqueous electrolyte on the other. To function reliably, they are typically constructed as thin sheets consisting of three distinct layers:2
- A waterproof layer: Usually incorporating polytetrafluoroethylene (Teflon) to prevent the electrode from flooding with electrolyte, which would significantly slow operation.1
- An active catalyst layer: Composed of materials such as platinum, gold, or complex organometallic compounds supported on a carbon base.1
- A conducting layer: Designed to carry the electrical current into or out of the electrode.1
Proper design and pressure control are essential to prevent the fuel from breaking through to the electrolyte side, which could lead to dangerous gas mixing and potential explosions.1