Why can flooding an electrode with electrolyte slow down a fuel cell?
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.
A fuel cell electrode typically functions through a three-phase reaction, where the gaseous or liquid fuel must simultaneously contact a catalyst and an electrolyte at specific solid sites.1
If an electrode becomes flooded with electrolyte, the operation rate of the fuel cell slows significantly because the liquid electrolyte blocks the fuel from reaching the catalyst sites. To prevent this, electrodes are often designed with a waterproof layer, typically incorporating polytetrafluoroethylene (Teflon), to maintain the necessary gas-liquid-solid interface and ensure stable performance.1