GDL(Gas Diffusion Layer) is between the catalyst layer and the bipolar plate. GDL does not directly participate in the electrochemical reaction, while it plays important roles as below in PEMFC.

1. It provides a path for the reactant gas from the plate flow field channel to the catalyst layer.

2. It provides a pathway for the produced water from the catalyst layer to the plate flow field channels.

3. The catalyst layer is electrically connected to the plate so that the electrons form a complete circuit.

4. Conducts the heat generated in the electrochemical reaction of the catalyst layer to the plate

5. It provides mechanical support for the MEA to prevent sagging into the plate flow field channels