The settling behavior of the carbon based gas diffusion layer in PEM fuel cells

Abstract

This thesis investigate how the Gas diffusion layer in Proton Exchange Membrane Fuel Cells settle when exposed to mechanical compression with cyclic load of 4.5 MPa and 7 MPa. A Zwick Roell material tester was used to carry out the mechanical testing. 3 different state of the art gas diffusion layers was examined, they are referred to as GDL "A", "B" and "C" in this report. Three different tests were carried out, the first with 10 cycle loading, with the load hold time of 60 s. The second test was a 10 cycle loading test as well, but with the load hold time of 60 min. The third test was a 50 cycle loading, with 60 s hold. Images in a Sweeping Electron Microscope was also taken, to evaluate the fiber structure in the GDLs. The initial reason was to evaluate the fiber structure before and after compression, this method was abandoned, but the images still presented us with some valuable information about the different structures of the GDLs and could be used to discuss the results. The results imply that the load hold time effects the settling, and also confirms previous research about the so called hysteresis effect where the first loading cycle is the most damaging to the GDL structure. Further on, the 50 cycle testing show that the settling of the GDLs continues after 10 cycles and more load testing, both cyclic and static, is of interest in future research.