Degradation of Gas Diffusion Layers in PEM fuel cells during drive cycle operation

Polymer electrolyte membrane (PEM) fuel cells show voltage degradation when subjected to long-term drive cycle operation. While the kinetic losses in the fuel cells can be assigned to catalyst layer degradation, there is a significant mass transport loss of up to 100mV at 2 A/cm(2) in 400 hours of operation. This mass transport loss can be attributed to the Gas Diffusion Layer (GDL) degradation especially when using low surface area carbon based catalyst materials. Ex situ ageing studies where the GDL is oxidized in a peroxide solution seem to simulate this degradation mechanism in terms of both the increase in graphitic carbon and surface-oxide species. The ex situ aged GDLs result in similar voltage losses when operated with fresh membrane-electrode assemblies (MEAs). AC impedance results confirm that these losses are due to mass transport limitations, probably arising from loss of hydrophobicity of the GDL material. To alleviate these mass transport losses, various combinations of materials have been examined; improved performance under drive cycle operation was obtained with a GDL material that had carbon nano-tubes in the MPL.