Effects of the electrical resistances of the GDL in a PEM fuel cell

In most PEM fuel cell models, the electrical resistance of the gas diffusion layers (GDL) is neglected under the assumptions that the GDL electrical conductivity is orders of magnitude higher than the ionic conductivity of the membrane. Recently some modeling efforts have taken the effects of electrical resistance of the GDL into consideration [H. Meng, C.Y. Wang, Electron transport in PEFCs, J. Electrochem. Soc. 151 (2004) A358–A367; B.R. Sivertsen, N. Djilali, CFD-based modeling of proton exchange membrane fuel cells, J. Power Sources 141 (2005) 65–78] and some of the results showed that under certain conditions, this effect was significant enough to alter the characteristics of current density distributions under the gas channels and the land areas. If these results are applicable to real-life fuel cells, the present design criteria and optimization procedures must be significantly changed to incorporate the effect of GDL electrical resistance. To examine this issue closely, a three-dimensional fuel cell model incorporating electron transport in the GDL is developed and employed to investigate the effect of electrical resistance through the GDL. In this model, the anisotropic nature of the GDL is taken into consideration by using different electrical conductivities in the through-plane and in-plane directions. The modeling results show that when realistic electrical conductivities for the GDL are used, the effect of the electrical resistance of GDL is slight and can be neglected for all industrial applications. It is believed that the over-estimations of the GDL resistance were mainly caused by neglecting the anisotropic nature of the GDL and/or lumping the contact resistance indiscriminately into the GDL, thus overestimating the electrical resistance of the GDL in the in-plane direction. Besides taking into consideration of the electrical resistance of GDL, the present model also take into consideration of the electron transport in the catalyst layers. When realistic values of electrical conductivities are used for both the GDL and catalyst layers, there is no significant change in the characteristics of current density distribution across the land and channel.