Multi-Analytical Study of Gas Diffusion Layer PTFE Content Local Variation

Abstract

PEMFC GDL materials with different PTFE content (8-35%) were analyzed using three methods: MIP, SEM/image analysis and XPS. PTFE particles from the impregnation suspension (up to 0.5 μm) are segregated within the GDL and only occupy medium size pores (0.4-50 μm). Other pores are unaffected because particles easily move through large pores (50-150 μm) and are geometrically excluded from small pores (0.05-0.4 μm). SEM images were deconvoluted into low and high frequency components. The high frequency component, ascribed to the GDL microstructure, increases with PTFE content and locally provides superhydrophobic properties. This observation was supported by current density distribution measurements at a 0.4 V cell voltage favoring product water formation which were correlated with the high frequency SEM image component. Zones of higher hydrophilicity were also identified and ascribed to partially fluorinated species detected by XPS.