What is the Gas Diffusion Layer (GDL)?

      The GDL is a porous structure made by weaving carbon fibers into a carbon cloth (e.g. GDL-CT and ELAT) or by pressing carbon fibers together into a carbon paper.  Many of the standard GDLs that are produced today come with a Micro Porous layer (MPL) and hydrophobic treatment (PTFE).  The MPL and PTFE help with the contact to the membrane and with water management.  The MPL typically provides a smooth layer with plenty of surface area for catalyst and good contact with the membrane.  The MPL often uses PTFE as a binder that increases hydrophobicity, which helps keep the water within the membrane from escaping – drying out the membrane and causing higher resistance (lower performance).  There is often an additional PTFE coating on the MPL surface to further augment this.

What Exactly Does a Gas Diffusion Layer (GDL) Do?

GDL essentially acts as an electrode that facilitates diffusion of reactants across the catalyst layered membrane. The surface area and porosity of the GDL is what allows for the reactants in the channels of the bipolar plate to diffuse along the active area (catalyst area) of the membrane.  With the increased surface area that the GDL provides, transportation of electricity from each individual catalyst site in the Membrane Electrode Assembly (MEA) to the current collectors increases.

The GDL is also the component that handles the fuel cell moisture control.  It does this by consistently helping to remove the by-produced water outside of the catalyst layer and prevent flooding chambers. The GDL also helps keep some water on the catalyst layer surface to improve conductivity throughout the membrane.  It is also important to note that the GDL allows for heat transfer during cell operation as well.