Graded Microporous Layers for Enhanced Capillary‐Driven Liquid Water Removal in Polymer Electrolyte Membrane Fuel Cells

A novel microporous layer (MPL) is designed and fabricated with spatially graded poly(tetrafluoroethylene) (PTFE) to alleviate liquid water flooding in the cathode gas diffusion layer (GDL) of the polymer electrolyte membrane (PEM) fuel cell. In operando GDL liquid water distributions are examined using synchrotron X-ray radiography and oxygen mass transport resistance via electrochemical characterizations, and it is found that the graded PTFE content in the MPL results in enhanced PEM fuel cell performance at high current densities (>= 1.0 A cm(-2)). Specifically, less liquid water accumulates within the cathode GDL substrate, and the oxygen mass transport resistance is substantially lowered. This lower substrate water content is attributed to enhanced capillary-driven removal of liquid water through the use of the graded MPL. This study demonstrates how strongly the spatial distributions of wettability and pore size of the MPL influence the performance of the PEM fuel cell.