Design of PGM-Free Cathode Catalyst Layers for PEMFC Applications: The Impact of Electronic Conductivity

The impact of the electronic resistance of platinum-group-metal-free cathode catalyst layers (PGM-free CCLs) for proton-exchange-membrane fuel cells (PEMFCs) was systematically investigated. Here we selected two different PGM-free catalysts (having high and low electronic conductivity) and integrated them into CCLs without and with conductive carbon fiber additives. To investigate the impact of the electronic resistivity ( ρ e − ) of PGM-free catalysts and CCLs, their through-plane ρ e − values were quantified by an in situ electrochemical impedance spectroscopy (EIS) approach based on a one-dimensional transmission line model. The results indicate that the electronic conductivity of PGM-free CCLs can be increased by adding carbon additive, resulting in a significant improvement of the fuel cell performance (by ∼60 mV at 1 A cm −2 in H 2 /O 2 configuration). Ex situ four-point probe measurements of the in-plane ρ e − values of some of the CCLs were found to differ vastly from the through-plane ρ e − values. This difference is attributed to the anisotropic morphology of the CCLs, caused by preferential fiber orientation and/or cracks in the CCLs. In the end, we suggest guidelines for the design and evaluation of PGM-free CCLs and for assessing and improving their electronic resistance.