Influence of Pore Size Distribution on Operando Gas Diffusion Layer Liquid Saturation

Abstract

Hydrogen fed polymer electrolyte fuel cells (PEFCs) have drawn attention as key technology for future decarbonized energy systems [1], in particular in the mobility sector, due to their high current density at low operating temperatures and rapid start-up [2]. The liquid water generated during high current density operation may saturate the pores of gas diffusion layers (GDLs), hence impede the gas transport to the catalyst layer, leading to performance losses. Higher performance requires, improved water management in GDLs. In this work, the liquid water distribution in GDLs has been studied with an operando X-ray tomographic microscopy (XTM) setup at the TOMCAT beamline of the Swiss Light Source (SLS) at Paul Scherrer Institut (PSI) [3,4]. XTM scans with a duration of 0.1 s and a voxel edge length of 2.75 um were employed to investigate PEFCs assembled with three types of GDL materials (Freudenberg I6, Toray TGPH-060 and SGL 24BA) with increasing pore size (see Figure 1). Properties of the operando liquid saturation were determined between OCV and 1.25 A/cm2 at current steps of 0.25 A/cm2 under H2/air operation with 100%/0% and 100%/100% humidified gases at start-up temperature of 25 oC. The influence of the GDL substrate pore size, current density and gas humidity on liquid water saturation and connectivity in the GDL will be presented.