UBC Theses and Dissertations
An ex-situ study of polymer electrolyte membrane fuel cell gas diffusion layer durability under steady-state and freezing conditions Lee, Charles Sim Jem
Polymer electrolyte membrane fuel cells (PEMFCs) are being developed to meet the lifetime requirements expected in commercial applications. While the effect of the gas diffusion layer (GDL) on performance has been studied, little is known of the impact of GDL materials and designs on PEMFC durability. Successful development of durable components such as the GDL is essential to achieving PEMFC system requirements for commercial applications. In this study, GDL compressive strain under steady-state and freezing conditions, and the effects of freezing conditions on GDL properties of electrical resistivity, bending stiffness, air permeability, surface contact angle, porosity and water vapor diffusion were studied. A GDL was aged ex-situ and its characteristics were evaluated as a function of aging time. GDL strain was measured to occur under steady-state aging conditions (80 °C and 200 psi). A maximum strain of 0.98 % was measured over 1500 hours of aging time. Increasing temperature to 120 °C or applied load to 400 psi resulted in maximum strains of 2.0 % and 1.5 %, respectively. Water phase transition during freezing conditions (54 freeze-thaw cycles between -35 and 20 °C) had no effect on GDL strain. No change in in-plane electrical resistivity, bending stiffness, surface contact angle, porosity and water vapor diffusion, through 50 consecutive freeze-thaw cycles between -35 and 20 °C, was measured. An increase in in-plane and through-plane air permeability (18 and 80 % respectively) was attributed to material loss during permeability measurements. Ex-situ tests showed that convective air flow can cause material loss, resulting in increased permeability and further convection. The GDL was shown to be much more resilient to material loss in the absence of water phase transitions.
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