Gas diffusion layer durability under steady-state and freezing conditions

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. GDL strain was measured to occur under steady-state aging conditions (80 degrees C and 200 psi). A maximum strain of 0.98% was measured over 1500 h of aging time. Increasing temperature to 120 degrees 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 degrees C) had no effect on GDL strain. No change was observed for in-plane electrical resistivity, bending stiffness, surface contact angle, porosity and water vapor diffusion after 50 consecutive freeze-thaw cycles between -35 and 20 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.