Three-Dimensional Anisotropic Electrical Resistivity of PEM Fuel Cell Transport Layers as Functions of Compressive Strain

We report on a method and apparatus for the determination of the three-dimensional electronic resistance of proton-exchange membrane fuel cell porous transport layers (PTLs) as a function of compression. Attention is given to the anisotropic nature of the fiber-based materials; between through- and in-plane directions and the differences within in-plane. For the first time, in-plane resistivities are resolved as functions of strain with a square four-point probe (4PP) arrangement; these are acquired in multiple directions to determine principal components of resistivity. Through-plane information is acquired with a linear 4PP apparatus with parallel capture of sample stress and strain. Results are presented for a selection of PTLs of different PTFE contents and thicknesses. In-plane resistivities exhibit linear decreases in resistivity with increasing compressive strains. We estimate an order of magnitude lower resistivity in-versus through-plane. Further, we reinforce that anisotropy in-plane undermines reports based on two or less measurements. Three methods are presented and contrasted for analyzing data in the through-plane direction. We demonstrate the limitations of common assumptions regarding contact resistances and of using PTLs of different thicknesses. It is proposed a total area resistance approach is presently the most accessible and communicable for the fuel cell community. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. All rights reserved.