In-plane and through-plane electrical conductivities and contact resistances of a Mercedes-Benz catalyst-coated membrane, gas diffusion and micro-porous layers and a Ballard graphite bipolar plate: Impact of humidity, compressive load and polytetrafluoroethylene

Abstract

By precisely deconvoluting the bulk from the contact and residual resistances, the in-plane electrical conductivities of virgin (dry or as-is), wet and dried catalyst-coated membranes (CCMs), a micro-porous layer (MPL) and several dry and wet gas diffusion layers (GDLs) with different PTFE loading are accurately determined. The through-plane conductivities of the GDLs, MPL and a bipolar plate (BPP) are rigorously measured using the two-thickness method. The contact resistances of the BPP with the GDLs (3–25 mΩ cm2) and MPL (14–57 mΩ cm2) are precisely deconvoluted as well. Moreover, the impact of pressure, PTFE and humidity on the resistances are thoroughly investigated.This study reveals that the in-plane electrical conductivity of a wet CCM (70 S m−1) is three times lower than its dry version (210 S m−1). It is found that the in-plane conductivity of GDLs (∼6000 S m−1) does not change with PTFE, MPL and humidity and is significantly higher than those of wet and dry CCMs. The through-plane conductivities of BPP (1935 S m−1), untreated and PTFE-treated GDLs (300–1500 S m−1), and MPL (50–350 S m−1) are in descending order. The through-plane GDL conductivity increases with pressure and decreases with PTFE, MPL and cyclic loading but it is not affected by humidity. It is also found that MPL and high PTFE loading increase, but pressure decreases, the GDL-BPP contact resistance dramatically.