Humidity Flashcards
What part of the cell does humidity affect?
The PEM.
What does low humidity cause to the PEM?
No H+ skipping - low ionic conductivity.
What does a high humidity cause to the PEM?
More H+ movement - high ionic conductivity.
What is the effect of too high humidity?
Can’t remove product water so the cell floods.
What other properties need to be considered together with humidity?
Pressure and temperature.
How are humidity and temperature controlled?
In the inlet gases.
What are the two main sources of water transport?
Electro-osmotic drag and back diffusion.
How should electro-osmotic drag and back diffusion be balanced?
50/50 so that they cancel out.
Describe electro-osmotic drag.
Anode to cathode. Protons drag water with them (current dependent).
Describe back diffusion.
Cathode to anode. Water diffuses from more humid cathode to less humid anode.
Where is product water created?
At the cathode.
How is humidity managed at a system level?
Humidifiers transfer product water from the cathode to the exhaust inlet.
