Membrane Degradation at Catalyst Layer Edges in PEMFC MEAs

Sompalli, Bhaskar; Litteer, B.; Gu, Wenbin; Gasteiger, Hubert A.

doi:10.1149/1.2789791

Cited by 84 publications

(40 citation statements)

References 28 publications

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“…This data indicates that gas crossover occurs not only through the catalyst edge but also through the center of the catalyst active area, even though the MEA edge is considered to be weaker compared to the center part of the MEA active area. The MEA edge failures reported in literature 27,28 are therefore likely due to the poorer mechanical properties of thinner PEMs, ca. 10 to 24 μm.…”

Section: Pem Degradation Mechanism-pem Thinning Vs Pinholementioning

confidence: 99%

The Effect of Cathode Structures on Nafion Membrane Durability

Choi

Langlois

Mack

et al. 2014

J. Electrochem. Soc.

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The effect of cathode structures on the chemical stability of Nafion membranes is investigated. Membrane electrode assemblies (MEAs) were prepared by using Nafion 212 membrane and commercially available carbon supported Pt electro-catalysts. The cathode structures were controlled by the use of long side chain (LSC) and short side chain (SSC) perfluorosulfonic acids (PFSAs) as well as three dispersing solvents for the electrode fabrication (a water-isopropanol mixture, N-methyl-2-pyrrolidone, or glycerol). The membrane durability was evaluated by the H 2 crossover current density after a 200-hour open circuit voltage accelerated stress test. The MEA with a glycerol-processed SSC PFSA-bonded cathode exhibited a 200-fold less H 2 crossover current density than the MEA with a water-isopropanol-processed LSC PFSA-bonded cathodes. The analyzes by electrochemical impedance spectroscopy and microscopy suggest that the structural uniformity of cathodes play the most significant role in the chemical stability of the Nafion membranes. This study emphasizes the importance of cathode structures on the durability of Nafion membranes. Polymer electrolyte membranes (PEMs) are a critical cell component for polymer electrolyte membrane fuel cells (PEMFCs). The durability of PEMs are important because the life of PEMFCs is often determined by PEM failure.1 The chemical stability of PEMs have been discussed since the 1960s, notably by engineers and scientists at GE.2 LaConti proposed a chemical degradation mechanism for perfluorosulfonic acids (PFSAs):3 oxygen molecules permeate through the membrane from the cathode and are reduced at the anode Pt catalyst to form hydrogen peroxide. Although PFSA membranes are stable in the presence of hydrogen peroxide, metal ions such as Fe 2+ and Cu 2+ in the catalyst layers greatly accelerate the membrane degradation rate by forming reactive oxygen species such as hydroxyl (HO·) and hydroperoxyl (HO 2 ·) radicals.Since the reactive oxygen species are generated in the catalyst layer, the membrane degradation is greater with a supply of H 2 and O 2 in the catalyst layers. Liu et al. reported about the substantially short lifetime for Nafion membranes when H 2 and O 2 gases were supplied to the catalyst-coated membrane, while no degradation is detected when H 2 /O 2 is decoupled to H 2 /N 2 or N 2 /O 2 .7 Later, Burlatsky et al. suggested that an extended catalyst layer between the cathode and the membrane could consume reactive oxygen species to produce water, thereby mitigating the membrane degradation. 8 The effect of gas permeability on membrane degradation has been also demonstrated. Sethuraman et al. compared the durability of wholly aromatic membranes, BPSH-35 and Nafion 112, under accelerated stress conditions. 9 Although the BPSH-35 membranes showed poor chemical stability in ex-situ Fenton tests, the membrane electrode assemblies (MEAs) Because the chemical degradation of membranes is related to the formation of reactive oxygen species in the catalyst layers and their access throug...

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Section: Pem Degradation Mechanism-pem Thinning Vs Pinholementioning

confidence: 99%

The Effect of Cathode Structures on Nafion Membrane Durability

Choi

Langlois

Mack

et al. 2014

J. Electrochem. Soc.

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“…The studies on the membrane degradation in PEM fuel cell operation have been carried out and some fundamental understandings on the failure mechanisms have been reported (8)(9)(10)(11)(12)(13)(14)(15)(16)(17) …”

Section: Membrane Failure and Analysismentioning

confidence: 99%

“…Membrane predominant thinning and microcrack fracture has usually been observed in local stress concentrated regions, such as the transition region, the edge of seals or the edge the flow channel where the polymer electrolyte may stretch by the pinching action of the flow field lands. Except mechanical stress, the failure near the boundary region may come from peroxide radical chemical degradation by reactant gas reached through imperfect sealing of gaskets (4,10). An edge protection film introduced during MEA lamination between the membrane and the catalyzed substrate could mitigate the MEA failure at the sealing edges and increase the MEA durability (4).…”

Section: R-cof + H 2 O → R-cooh + Hf (6)mentioning

confidence: 99%

Membrane Durability and Degradation under Dry Fuel Cell Operation Conditions

Wang

Yang

2009

ECS Trans.

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Membranes are a critical component of the fuel cell stack and must be durable in a wide range of operating conditions. In the present study, PFSA membranes were evaluated using accelerated stress testing (AST) methods of OCV and cyclic OCV under dry conditions at 95 °C. PFSA membrane degradation rates were determined by measuring fluorine release rate (FRR) and thickness change under different fuel cell operating conditions. The FRR was found to increase with a decrease in inlet relative humidity (RH) and an increase in stack temperature. The degradation active energy (derived from the Arrherius equation) was approximately 932.8 JK -1 mol -1 . A cyclic OCV test was designed to simulate membrane degradation caused by both mechanical and chemical stresses. Mechanically reinforced membranes showed much longer lifetime in the COCV test as compared to membranes without reinforcement. Under present operating conditions, membrane degradation is shown to initiate from cathode side.

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“…On the other hand, a loss of conductivity occurs at elevated temperatures (above 80 o C) due to dehydration. These issues may result in a reduction of mechanical properties [13] or poor membrane electrode assembly (MEA) performance and durability [1].…”

Section: Introductionmentioning

confidence: 99%