Gas diffusion layers are mainly based on Carbon cloth, felt graphite or Carbon paper and they can be treated to acquire various properties. They ensure the uniform distribution of reactive gases on the surface of the electrodes, and they also aid the transport of electrons to or from the external electrical circuit. Gas diffusion layers structurally help the stack withstand the extension caused by the water absorbency. In addition to that, they aid with heat transfer, electrical surface conductivity, and the removal of excess water from the electrodes that is produced by redox reactions. Finally, and most importantly, they clear the path for the Fuel and the Oxidizing agent towards the catalyst layers.

Their two main roles are:

1. Substrates for Electrodes / Catalyst layers
2. Gas diffusion layers for 5 layer membrane assemblies

As an electrode we combine them with a catalyst ink to create the electrodes that go on either side of the ion exchange membranes.

Gas Diffusion Layers (GDLs) are key components in various types of fuel cells, including:

• Proton Exchange Membrane(PEM) stacks
• Direct Methanol (DMFC) stacks
• Phosphoric Acid (PAFC) stacks
• Electrolyzers
• Redox Flow Batteries
• Other electrochemical devices

In fuel cells, this thin, porous sheet must provide high electrical and thermal conductivity and chemical/corrosion resistance, in addition to controlling the proper flow of reactant gases (hydrogen and air) and managing the water transport out of the membrane electrode assembly (MEA).

This layer must also have controlled compressibility to support the external forces from the assembly, and not deform into the bi-component plate channels to restrict flow.

Other uses require different criteria, for example, electrolyzers require thicker, higher density porous plates, while humidifiers have most of the same requirements as fuel cell stacks, but the GDLs do not need to be electrically conductive.

Porosity, pore distribution and pore volume are important parameters to measure the pore structure of the diffusion layer. Commonly used pore structure measuring instruments are mercury porosimeter and capillary flow porosimeter. The former uses mercury as a wetting fluid, and applies a certain pressure to press the mercury into the hole of the sample to be tested. The latter uses a low surface energy silicone resin (silwick) as the medium, which wets the sample to be tested under the action of capillary force, and then pressurizes it to force it to flow out of the pores. 

However, neither of the two methods can reflect the real substance transport channel in the diffusion layer when the battery is running, because the non-connected pores in the gas diffusion layer material are meaningless for substance transport, and when measuring by mercury intrusion method or capillary flow porosimeter Broken holes and dead holes are included

Sheets, Papers, Plates or Panels?

Gas Diffusion Layers are “graphitized“ carbon fiber-based nonwovens known as either carbon sheets, papers, plates or panels. Though the difference in these terms is often trivial, thinner substrates are often called sheets or papers, whereas thicker ones are more often referred to as panels or plates. Both can be machined into "disks" which is often the preferred shape for circular stack-type applications. In all cases, these carbon fiber substrates are specifically designed for use in PEM, DMFC and PAFC fuel cells to transport reactant gases into and excess liquid product water out of the electrocatalyst layers.

Their porosity is typically above 70%, leaving enough room for the reactions to take place. If you were to use sintered titanium, the cost of drilling and the materials would far exceed that of the carbon papers.

LINQCELL Gas Diffusion Layer (GDL) sheets are optimized for:

• Electrical Conductivity
• Mechanical Strength and Durability
• Gas/Air Permeability
• Water Management

All values are indicative and subject to tolerance

Click to learn more about GDL Graphitized Carbon Paper & Panels

Activated Carbon Fabric

Activated Carbon Fabrics (ACF) are high surface area, drapeable cloths that are used in various electrochemical devices including ultracapacitors, electrical double layer capacitors, and battery electrodes. They also serve as the high surface area electrode in many electrochemical purification and electrosorption processes, as well as unique applications such as a carrier for thin film oxides in various devices. They are used in numerous research programs and articles related to energy storage, purification and electrochemical processes.

Our previous popular 2225A Spectracarb grade has been discontinued so we are looking into developing a direct alternative. Contact us for more information.