Electronic conductivity of catalyst layers of polymer electrolyte membrane fuel cells: Through-plane vs. in-plane

In this work, novel procedures are developed to measure in-plane and through-plane electronic conductivities of catalyst layers (CLs) for polymer electrolyte membrane fuel cells. The developed procedures are used in a parametric study on different CL designs to investigate effects of different composition and fabrication parameters, including ionomer to carbon weight ratio (I/C ratio), dry milling time of the catalyst powder, and drying temperature of the catalyst ink. Results show that CLs have anisotropic electronic conductivity with through-plane values being three orders of magnitude lower than the in-plane values. The reason for this anisotropy is speculated to be alignment of fibrillar nanostructures of ionomer by large shear forces during coating, which could result in better carbon-carbon contact in the in-plane direction. A simple order of magnitude analysis shows the significance of poor through-plane conduction for fuel cell performance. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.