Effect of Microstructure of Porous Transport Layer on Performance in Polymer Electrolyte Membrane Water Electrolyser

Abstract

The porous transport layer (PTL) is a vital component of the polymer electrolyte membrane water electrolyser (PEMWE) as it is both a conduit for current distribution and mass transport. This study aims to examine the influence of the microstructure of the PTL on the performance of a PEMWE by the combination of ex-situ and in-situ techniques. Two PTLs with distinctly different mean pore diameter were characterized to determine key properties such as surface morphology, porosity, pore size distribution and porosity distribution. The results of scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X-ray microtomography showed that the SP-PTL consist largely of small pores over a narrow pore range, and a relatively uniform porosity distribution compared to the LP-PTL which shows much larger pore sizes over a relatively wider pore range and significant variability in pore sizes and porosity distribution. Electrochemical characterization (steady-state polarization and electrochemical impedance spectroscopy) results show that the SP-PTL performed better over the current density range tested. Ohmic resistance was significantly lower in the SP-PTL at all current densities tested and the mass transport resistance in the SP-PTL, though slightly larger, was comparable to that obtained in the LP-PTL which makes the SP-PTL better overall. The result suggests that the contact resistance between anode PTL and the anode catalyst layer play a dominant role in electrolyser performance, and better performance can be obtained by reducing this component of the ohmic resistance.