Deconvolution of electrical contact and bulk resistance of gas diffusion layers for fuel cell applications

Abstract

We report a novel characterization technique and experimental setup to separately evaluate the interfacial and bulk components of the through-plane electrical resistance of a gas diffusion layer (GDL). Using four sensing electrodes which are electrically insulated from the current-forcing electrodes and placing them at the relevant interfaces, between current collector (CC) and bipolar plate (BPP) and BPP and GDL, each bulk and interfacial resistance could be evaluated separately, which is not possible using conventional two-electrode measurements. Our design also allows for evaluation of the contact resistance for asymmetric GDL materials, with a microporous layer (MPL) on one side. We provide a step-by-step description and justification for each part of our experimental setup using finite element method (FEM) simulation and taking the pore size between the GDL fibres into account, specifically to find the optimum sensing electrode design. Experimental evaluation of the GDL-BPP interface and the GDL bulk electrical resistivity was performed as a function of clamping pressure and Teflon content for two BPP materials, graphite and stainless steel, and for a GDL with and without an MPL. The measured GDL bulk resistance was found to be at most 10% of the total ohmic resistance. The contact resistance between GDL and BPP was thus found to be the dominant resistance for all the tested GDL and BPP materials, which explicitly validates this implicit assumption that is made throughout existing literature for the first time.