In this paper, the mechanical degradation of a commercial gas diffusion layer subjected to repeated freeze⁻thaw thermal cycles is studied. In a fuel cell, the mechanical assembly state directly affects the performance of polymer electrolyte membrane fuel cells. Particularly, the gas diffusion layer repeatedly withstands the complex heat and humidity environmental conditions in which the temperature and humidity are always greatly changed. Studying the three-dimensional mechanical degradation of gas diffusion layers due to orthotropic properties is very useful in extending the lifetime and durability of fuel cells. To investigate this, we first established the standard freeze⁻thaw thermal cycle and studied the gas diffusion layer's mechanical degradation performance with up to 400 repeated freeze⁻thaw thermal cycles. Furthermore, different types of failure in the gas diffusion layer caused by the repeated thermal aging treatment were observed using a scanning electron microscope, to explain the change in the mechanical deterioration. As a result, the different thermal failure plays different roles in the explanation of the gas diffusion layer's mechanical degradation under different thermal cycles. In particular, the thermal failure that resulted from the first 100 thermal cycles has the greatest effect on the compressive and tensile performance, compared to the shear behavior.
Keywords: gas diffusion layers; polymer electrolyte membrane fuel cell; repeated freeze–thaw thermal cycles; scanning electron microscope images; thermal failure; three-dimensional mechanical degradation.