Degradation mechanism analysis of substrate and microporous layer of gas diffusion layer in proton exchange membrane fuel cell

Abstract

Robust electrochemical corrosion of gas diffusion layers (GDL) in proton exchange membrane fuel cell (PEMFC) could cause significant decline of cell performance. However, the detailed mechanism still remains elusive. Herein, the structural characteristics of GDL after electrochemical accelerated stress test (AST) and sequent impacts on the mass-transfer performance of membrane electrode assemblies were explored. With the electrochemical corrosion duration increasing, polytetrafluoroethylene (PTFE) peeling and carbon fibers exposure were observed on substrate layer surface, while corrosion pores were detected on microporous layer (MPL). Both substrate layer and MPL experienced significant increase in surface roughness, which was reflected in the surface and bulk resistance. Surface contact angle and water permeability threshold tests showed that surface and internal hydrophobicity of GDL degraded comprehensively. More significant carbon corrosion in MPL and PTFE loss in substrate layer were revealed by X-ray photoelectron spectroscopy and thermogravimetric analysis. Collectively, worse power density and severe ohmic and mass-transfer polarization after AST were confirmed and the oxygen mass-transfer performance was analyzed in single-cell tests. This work clearly explains the distinctive degradation mechanisms of the substrate layer and MPL and provides guidance for the design and application of GDL.