Physical Description of the Gas Diffusion Layer (GDL)

Porous and electrically conductive material is the kind of material that is used for gas diffusion backings. Usually, the gas diffusion layer is single or composite, and the last means that there is a junction with a micro-porous layer. Water management and electrical properties can be improved with a treatment composed of fluoropolymer and carbon black. Diffusion of the reactant gases to the membrane/electrode assembly are improved with these material types. The structure is made it so that it spreads out the gas to maximize the contact surface area of the catalyst layer membrane. Carbon cloth and carbon paper are the most usually used GDL materials.

The purpose of the GDL is to limit the amount of water that reaches the membrane/electrode assembly. Additionally, it helps with the removal of liquid water from the cathode side to prevent excess flooding. One required characteristic for this layer is that it has to be water-proofed so that the layer does not get clogged with water.

Different kinds of treatment exist for the GDL to make it hydrophobic so that flooding can be avoided in the fuel cell. The cathode and the anode layers can be Nafion/PTFE treated. The diffusion material is dipped into a 5% to 30% PTFE solution, followed by drying and sintering. The interface with the catalyst layer can be fi tted with a coating or microporous layer to ensure better electrical contact and effi cient water transport in and out of the diffusion layer. This layer consists of carbon or graphite particles mixed with PTFE binder. The resulting pores are between 0.1 and 0.5 microns (mm) and are, therefore, much smaller than the pore size of the carbon fiber papers.

Source: SPIEGEL, Colleen. PEM Fuel Cell Modeling and Simulation Using MATLAB^®. Burlington, MA, USA: Academic Press, 2008. 440 p.

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