The Impact of Chemical-Mechanical Ex Situ Aging on PFSA Membranes for Fuel Cells

Abstract

A proton-exchange membrane fuel cell (PEMFC) constitutes today one of the preferred technologies to promote hydrogen-based alternative energies. However, the large-scale deployment of PEMFCs is still hampered by insufficient durability and reliability. In particular, the degradation of the polyelectrolyte membrane, caused by harsh mechanical and chemical stresses experienced during fuel cell operation, has been identified as one of the main factors restricting the PEMFC lifetime. An innovative chemical-mechanical ex situ aging device was developed to simultaneously expose the membrane to mechanical fatigue and an oxidizing environment (i.e., free radicals) in order to reproduce conditions close to those encountered in fuel cell systems. A cyclic compressive stress of 5 or 10 MPa was applied during several hours while a degrading solution (H2O2 or a Fenton solution) was circulated in contact with the membrane. The results demonstrated that both composite Nafion™ XL and non-reinforced Nafion™ NR211 membranes are significantly degraded by the conjoint mechanical and chemical stress exposure. The fluoride emission rate (FER) was generally slightly lower with XL than with NR211, which could be attributed to the degradation mitigation strategies developed for composite XL, except when the pressure level or the aging duration were increased, suggesting a limitation of the improved durability of XL.

Dynamic Mechanical Fatigue Behavior of Polymer Electrolyte Membranes for Fuel Cell Electric Vehicles Using a Gas Pressure-Loaded Blister

“…It is speculated that more water molecules act as a good plasticizer at relatively higher humidity because the membranes gradually reduce their toughness and extend stress relaxation time [ 28 ]. It is also observed that the composite membrane Nafion XL ( Figure 3 ) takes much longer than Nafion 211 ( Figure 2 ) to reach 15% mechanical loss under the same blistering conditions, presumably due to the improved mechanical properties of Nafion XL, as shown in Table 1 [ 29 ].…”

Anode defects’ propagation in polymer electrolyte membrane fuel cells

“…The AST (Figure 3) that was applied to the MEA was also designed to stress the membrane through humidity cycling and OCV hold sequences. As mentioned in the introduction, membrane aging mechanisms are governed by the mechanical and chemical stresses it undergoes during FC operation [ [41][42][43][44][45][46][47], and AST like this one ultimately lead to an increase of hydrogen crossover -evidenced for instance through the hydrogen permeation currents-and membrane failure [ 22,42 ]. In the present case, the AST was stopped before any noticeable increase of the hydrogen permeation current, but a significant thinning of membrane was however observed for the defective segments (Fig.…”

“…In addition to the CL, the membrane is also subjected to high mechanical and chemical stresses during FC operation [ [41][42][43][44][45][46][47]. The mechanical stresses are mainly due to humidity cycling, that causes the swelling and shrinking of the membrane following water-content variations.…”

“…Finally, it is also well-known that OCV, low RH and high temperature lead to accelerated membrane thinning [ 40,60,61 ]. Numerous studies have been conducted in the literature to better understand the membrane degradation mechanisms under chemical, mechanical, or combined chemical/mechanical stresses, through in situ [ 42,43,50,54,[62][63][64] ] or ex situ [ 44,46,[65][66][67] ] experiments.…”

Impact of sulfonated poly(ether ether ketone) membranes pretreatments on their physicochemical properties and fuel cell performances

“…The most common membranes used in PEMFC are thin films of perfluorosulfonic acid copolymers (PFSA) such as Nafion®, with a proton conductivity approaching 0.1 S cm −1 in ideal conditions, a good chemical stability, and fast hydration dynamics 4,5 . These remarkable properties stem from both the superacidity of the ionic functions and their unique microstructure 6,7 .…”