The Use of Limiting Current to Determine Transport Resistance in PEM Fuel Cells

Limiting current measurements are used to derive estimates of oxygen transport resistance through the cathode diffusion medium/micro-porous layer (DM/MPL) of a fuel cell. For the case of unteflonated Toray 060 (without an MPL), the estimates are compared to ex situ measurements of the effective diffusion coefficient for water vapor. For dry operating conditions at low currents, the comparison shows that the large majority of transport resistance detected by limiting current occurs in the Toray 060 and not through ionomer or water layers in the electrode. Effective diffusion coefficients at wetter conditions, derived from limiting currents, show a clear dependence on current density and thus on water production. An example of this behavior is given for SGL 25 BC (a DM with MPL).