The root of all of this is that Nafion membranes must stay hydrated to function properly. If they are not fully humidified the conductivity decreases and therefore more of the electricity is converted directly to heat before it leaves the membrane (I2R heating). If it gets too dry it basically stops functioning as a proton transporter. All this sounds great since a Hydrogen Fuel Cell consumes Hydrogen and Oxygen to generate electricity and water, so you would think there should be plenty of it around right? Well there is, and that's the other problem.
The Hydrogen and Oxygen (Air) gasses need to get to the catalyst sites and the membrane in order to be converted into electricity. However, if there is any liquid water at the catalyst layer it covers up the catalyst and the gas cannot get to it, basically making the catalyst that's underwater useless – effectively reducing the active area that is available to convert H2 and O2 to electricity.
This is where the magic happens with the GDL. The GDL materials are all specially formulated with hydrophobic coatings and permeability properties. These are all designed to help get the water away from the catalyst layer while it's still in vapor form and not allow it to form to liquid until it is well clear of the catalyst sites. This is even further complicated when you consider that fuel cells are operating in widely varying environments. Some need to work in hot/dry desert environments while others need to work in very humid environments.
The various manufacturers each have various GDL types that they have optimized for different operating parameters and different physical properties (we'll get into those another time). Good thing we work with most major GDL manufacturers (and many of the smaller ones as well) so we can work with you to find which GDL will work best for you!
If you would like to take a look at some of our available GDL come by our web store.