Interplay between temperature and biaxial loading on creep behavior of perfluorosulfonic-acid membranes

The durability and performance of polymer-electrolyte fuel cells largely depend on the mechanical durability of perfluorosulfonic-acid membranes. With the increasing demand for operating at higher temperature for fuel cells, creep is more detrimental to the mechanical durability of the membrane. Nevertheless, even though the membrane is in a biaxial stress state during fuel cell operation conditions, numerous studies on creep responses of the membrane are conducted under uniaxial loading, leaving the biaxial creep behavior unexplored. In this paper, the uniaxial and biaxial creep behavior at different temperatures are investigated. The biaxial stress states is found to suppress the delayed elastic strain at temperatures below 65 degrees C and retard the viscous flow strain at 80 degrees C. Master curves are constructed based on both uniaxial and biaxial creep tests, and it is found that even though the equilibrium time is much longer for biaxial creep tests, the activation energy is the same, indicating the same creep deformation mechanism from molecular level. In addition, increasing biaxial stress ratio from 0 to 0.1 causes substantial decrease in creep strain. The findings here are expected to provide new insights for understanding membrane failure and be helpful for fuel cell optimization.