We have been getting more questions and requests regarding Gas Diffusion Layers (GDL) that are water proof or which do not allow water to seep or leak through them. This is especially of interest when building Magnesium Air Batteries (also known as Magnesium Air Fuel Cells), Microbial Fuel Cells (MFC), and a host of other electrochemical reactions with a liquid electrolyte that needs access to gas or oxygen.
Most GDL materials have a high air permeability that also results in at least some water seepage. The GDLs with a microporous layer (MPL) typically have much higher resistance to seepage, but can only hold back water with heads (or pressures) of well less than 1″ H2O. Take a look at our GDL comparison table on our Tools page to see which GDLs have MPLs if you only need very moderate resistance to water or can deal with seepage.
GDL + Porous Hydrophobic Film
If you need something with better water resistance a water barrier can be applied. This is typically is a porous hydrophobic film that allows the gas to permeate but not the liquid. Typically we use a material that is fairly thin and has a high air permeability rate (>10 L/hr/cm²) while maintaining a resistance to water penetration at pressures >200 mbar.
This membrane can be applied to either side of a GDL/GDE to either allow wetting of the porous GDL structure and catalyst layer or not.
For example, the film can be applied to a GDL as:
GDL + MPL + Catalyst + Barrier
Barrier + GDL + MPL + Catalyst
Your application may dictate that one works better than another. The barrier can also be applied to many GDL materials that do not have MPL or catalyst layers, greatly expanding your options if you are simply looking for a carbon electrode material without any additional catalyst.
Conductivity of Film
The other consideration when using the film as a water barrier is that it is not conductive. There are a couple of options to improve the conductivity:
1) A connection can be made to the edge of the GDL. This is simple, but there will be a little higher resistance since the current will have to flow In Plane (IP) as apposed to Through Plan (TP). This essentially just makes the path length longer and therefore higher resistance. How critical or how much affect this will have on your system will be determined by your specific design.
2) Alternatively, a thin metallic mesh can be embedded under the barrier layer. We would probably recommend a thin Titanium Screen. This gives good conductivity across the surface, but would add to the cost due to the extra material and production costs.
Hopefully this helps those that are seeking electrodes with high gas permeability but that still act as a water or liquid barrier. As always, please let us know if you have any questions or application specific needs. We are always here to help in anyway we can.
You can also check out all of the Gas Diffusion Layers (GDL) we have available on our store website here: