Why impedance of the gas diffusion layer in a PEM fuel cell differs from the Warburg finite-length impedance?

- A physics-based model for GDL impedance in a PEM fuel cell is developed.
- An analytical expression for the GDL impedance differs from the Warburg finite-length impedance.
- The difference is due to finite double layer capacitance of the catalyst layer the GDL is attached to.
- In the limit of zero double layer capacitance, the GDL impedance reduces to the Warburg result.

We report a simple physics-based model leading to an analytical expression for impedance of the gas-diffusion layer (GDL) in a PEM fuel cell. We show that this expression differs from the classic Warburg finite-length impedance due to large double layer capacitance Cdl of a porous catalyst layer the GDL is attached to. It follows that the Warburg solution is obtained for the transport layer attached to a planar electrode with vanishingly small Cdl.