Effects of Compression applied to Gas Diffusion Layers in PEM Fuel Cells

There is a global and urgent need to embrace alternative renewable power sources to mitigate the detrimental environmental effects of the greenhouse gases, in particular carbon dioxide. Proton electrolyte membrane (PEM) fuel cells have been an attractive clean technology to decarbonise a multitude of applications, particularly those in the automotive sector. Although PEM fuel cells have, compared to other types of fuel cells, high efficiency and low-operating temperature, there are still some very important challenges that need to be overcome so that the PEM has a wider application. One of the main issues that affect the lifetime of PEM fuel cells is the mechanical degradation of the gas diffusion layers (GDLs). Since GDLs are responsible for the transport of reacting gases, heat and electronic charge from/to the catalyst layers, any damage to their structure may have detrimental consequences on the above transport processes and, subsequently, the performance of the fuel cell. Typically, GDLs are subject to two types of compressive stresses: assembling and cyclic stresses. The assembling stress occurs due to the clamping pressure applied to assemble the various components of the fuel cell. The cyclic stress is due to the hydration/dehydration cycles of the membrane as it swells or shrinks. In this thesis, a novel and carefully designed compression test (mimicking the assembling and cyclic stresses that the GDL is subjected to within the fuel cell) has been performed on a set of commercially available GDLs. This was followed by a series of tests to examine the effects of compression on the mass transport (gas permeability test), morphology (SEM analysis), thermal stability (TGA analysis), and wettability (contact angle test) of the tested GDLs. Such tests and the related outcomes are of much importance to the researchers in the field, especially those who model PEM fuel cells as these tests provide much more accurate and realistic data for the physical properties being investigated. The same investigation was then performed in the presence of sealing gaskets in order to explore how the effects of compression are mitigated with the sealing gaskets. Finally, the experimental values for the GDL gas permeability and contact angle (before and after compression) were fed into a comprehensive three-dimensional PEM fuel cell model to investigate their effects on the overall performance of the cell. The key findings of the study are as follows: (i) the MPL-coated GDLs are more resistive to mechanical deformation than uncoated GDLs, (ii) the contact angle of the GDLs reduce by 3° - 15° after compression, (iii) GDLs are less deformed in presence of sealing gaskets, (iv) GDLs lose around 40% of its PTEF content after compression and (v) the performance of the modelled fuel cell is hardly affected by variation in GDL gas permeability.