Aspects of fatigue failure mechanisms in polymer fuel cell membranes

Abstract

The swelling‐driven fatigue behavior of polymer fuel cell membranes during relative humidity (RH) cycling is investigated. In particular, swelling‐induced membrane stresses are obtained from a numerical model simulating fuel cell RH cycle tests, and compared to the lifetimes obtained experimentally from tests conducted in the absence of electrochemical effects. A strong correlation between the lifetimes of the membranes in the actual tests and model results is obtained. In general, higher RH (or swelling) amplitude results in larger stress amplitudes and shorter lifetime, that is, fewer cycles to failure. Tensile stresses are needed for forming local cavities in the membrane, which may eventually lead to craze formation. Cavitation is less likely to occur in compressed membrane at high humidities. The stress–lifetime plots for polymer fuel cell membranes exhibit similar features to those observed for other polymers. The crazing criterion for polymers suggests that craze initiation during RH cycling is more likely to occur in the low compression regions, such as under the channels, which is in agreement with experimental observations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1506–1517, 2011

Effect of Mechanical Compression on Chemical Degradation of Nafion Membranes

“…Even though in fuel cells the assembly pressures are on the order of a few MPa, the membrane, or part of it, could experience higher stresses due to the additional geometric constraints arising from the cell design. 4,5,[19][20][21][22] Moreover, hydration of the membrane generates additional compressive stresses of up to 10 MPa in the constrained regions of the membrane. 4,5,20,21 (More information on compression testing of membranes can be found in our previous studies).…”

“…4,5,[19][20][21][22] Moreover, hydration of the membrane generates additional compressive stresses of up to 10 MPa in the constrained regions of the membrane. 4,5,20,21 (More information on compression testing of membranes can be found in our previous studies). [23][24][25] Small-angle X-Ray scattering (SAXS).-SAXS experiments of the membranes were performed in beamline 7.3.3 at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL).…”

“…These latter stressors originate from the deformation of the membrane due to cell assembly (constraint) and subsequent operational stresses driven by the hydration/dehydration of the constrained membrane. [1][2][3][4][5][6][7] To understand the impact of various stressors, accelerated stress tests (ASTs) are typically conducted with the aim of enhancing a single failure mode, 1,2,8 with Fenton's tests accelerating chemical degradation 7,9-14 and relative-humidity (RH) cycling used for mechanical degradation. [1][2][3]6,8,15 However, failure mechanisms in operando are controlled by combination of chemical and mechanical stressors, which makes understanding any synergistic chemical/mechanical interactions of great importance.…”

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

“…Prolonged membrane exposure to these stresses causes mechanical rupture via fatigue (cyclic stress) and/or creep (constant stress) phenomena. 12,13,20,23,33 Moreover, mechanical properties of the membrane deteriorate during chemical degradation;…”

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

“…either facing the flow channel or in direct contact with the channel land). Calculations made by Kusoglu et al [237] revealed that residual stresses can be up to 10MPa which may lead to delamination of the membrane and the gas diffusion layer and similarly the high in-plane stresses were associated to crazing and its growth. The simulations of [296] suggest that in-plane stresses are much higher under the land regions than under the flow channels at any level of relative humidity of the reactant gases.…”