Ionomer Films Impact on The Structure, Flow Regime, and The Wettability of The Catalyst Layer of PEMFC

Karrar Alofari,Jeffrey Allen,Ezequiel Me´Dici,Kazuya Tajiri,V Cigolotti

doi:10.1051/e3sconf/202233404019

Abstract

Percolation testing and contact angle measurements have been used to investigate the role of relative humidity on structure, mass transport, and wettability of a PEM fuel cell catalyst layer and membrane. Four samples were tested, two catalyst layers and two membranes. Structure and mass transport changes in the catalyst layers resulting from RH changes were studied in terms of percolation pressure. A clear change in the structure between low and high RH conditioning was observed. Relative humidity (RH) cycling also impacted percolation pressures with an indication of catalyst layer cracking. In addition, RH effect on wettability of both catalyst layers and membranes was studied by measuring contact angles of sessile drops.

Highlights

Ionomer in the catalyst layer form nano-scale thin films [1, 2] that often have the same chemistry as the much thicker electrolyte membranes, though a distinctive difference in properties such as water uptake and conductivity are observed [3, 4]
The ionic domains in the ionomer retains water, where the number of water molecules per sulfonic acid group can reach up to 8 as in ionomer thin films in the catalyst layer [4], and 15in electrolyte membrane [10, 14] when saturated with vapor
Cycling the relative humidity of the catalyst layer results in the absorption/release of water to/from ionomer films, which in turn leads to structural stresses and potential defect growth [20]

Summary

Introduction

Ionomer in the catalyst layer form nano-scale thin films [1, 2] that often have the same chemistry as the much thicker electrolyte membranes, though a distinctive difference in properties such as water uptake and conductivity are observed [3, 4]. Transport properties of the ionomer are affected by hydration [4, 7, 8] Both thin (7nm [1]) and thick (> 10m [9, 10]) ionomer films interact with vapor to alter the orientation of sulfonic acid side chains [5, 11]. This affects wettability and conductivity in the ionomer films [12, 13]. The sessile drop method is adapted to observe the macroscopic changes in the wettability over a range of RH conditioning

Experimental Section

Contact Angle Measurement

Percolation Test Results

RH Effects on Wettability

Conclusion