Mechanical degradation of fuel cell membranes under fatigue fracture tests

Khorasany, Ramin M.H.; Alavijeh, Alireza Sadeghi; Kjeang, Erik; Wang, G.G.; Rajapakse, R. K. N. D.

doi:10.1016/j.jpowsour.2014.10.135

Cited by 91 publications

(37 citation statements)

References 46 publications

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“…The s t in wet 5 vol.% H 2 eN 2 is higher compared to that measured in wet air in the research regions, but the difference diminishes at high temperature. In 5 vol.% H 2 eN 2 , partial of Sm 3þ might be reduced to Sm 2þ [40], increasing the Sm 2þ concentration, as well as the electron conductivity by promoting the electron transfer between Sm 3þ and Sm 2þ via the reversible reaction (6). The increased ion conductivity (s i ) might also contribute to the enlargement of s t .…”

Section: Resultsmentioning

confidence: 99%

Enhanced electrical conductivity of LaNbO4 by A-site substitution

Cao

Duan

Dong

et al. 2016

International Journal of Hydrogen Energy

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Section: Resultsmentioning

confidence: 99%

Enhanced electrical conductivity of LaNbO4 by A-site substitution

Cao

Duan

Dong

et al. 2016

International Journal of Hydrogen Energy

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“…1,2 Chemical degradation initiates the overall degradation processes 3,4 and further damages the membrane when combined with mechanical stress, strain, and fatigue induced by hygrothermal fluctuations in the MEA. [5][6][7][8][9][10][11][12] The resulting physical damage in the form of cracks and holes eventually causes hydrogen leaks across the membrane which is considered one of the main lifetime limiting failure modes in fuel cells. 4,[13][14][15][16] The primary chemical degradation in PEFCs is caused by reactions of reactive radicals with the PFSA ionomer membrane.…”

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confidence: 99%

In-Situ Modeling of Chemical Membrane Degradation and Mitigation in Ceria-Supported Fuel Cells

Wong

Kjeang

2017

J. Electrochem. Soc.

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Ceria-supported membrane electrode assemblies (MEAs) have recently been proposed to address chemical membrane degradation in polymer electrolyte fuel cells. Although ceria is known to effectively protect the membrane at open circuit voltage (OCV) conditions, its effectiveness has not been demonstrated for cell voltages below OCV and associated conditions relevant for field operation. In the present work, a comprehensive, transient in situ chemical degradation model for ceria stabilized MEAs is developed and applied to investigate the mitigation effectiveness of ceria additive. At high cell voltages, abundant Ce 3+ ions are available in the membrane to quench hydroxyl radicals which is the primary mitigation mechanism observed at OCV conditions. However, the mitigation is suppressed at low cell voltages, where electromigration drives Ce 3+ ions into the cathode catalyst layer (CL). Without an adequate amount of Ce 3+ in the membrane, the hydroxyl radical scavenging is significantly reduced, leading to a ten-fold reduction in mitigation effectiveness at cell voltages below 0.7 V. The simulated results also suggest that significant ceria precipitation may occur in the cathode CL due to the increased local Ce 3+ concentration at low to medium cell voltages. Ceria-supported MEAs may therefore experience higher rates of chemical membrane degradation at low cell voltages than at OCV. Hydrogen powered polymer electrolyte fuel cells (PEFCs) generally use perfluorosulfonic acid (PFSA) ionomer membranes to separate the two electrodes in the membrane electrode assembly (MEA). Their high proton conductivity at low temperatures, relatively low reactant permeation, and superior electrical insulation lead to high fuel cell performance. However, the ionomer membrane can be degraded in the fuel cell environment which reduces its stability and limits its lifetime.1,2 Chemical degradation initiates the overall degradation processes 3,4 and further damages the membrane when combined with mechanical stress, strain, and fatigue induced by hygrothermal fluctuations in the MEA. [5][6][7][8][9][10][11][12] The resulting physical damage in the form of cracks and holes eventually causes hydrogen leaks across the membrane which is considered one of the main lifetime limiting failure modes in fuel cells. 4,[13][14][15][16] The primary chemical degradation in PEFCs is caused by reactions of reactive radicals with the PFSA ionomer membrane.17-21 For instance, hydrogen peroxide (H 2 O 2 ) can be generated via the twoelectron oxygen reduction reaction (ORR) resulting in hydroxyl radical (·OH) formation due to decomposition of hydrogen peroxide in the presence of metal contaminants. 22,23 The hydroxyl radical formed is highly reactive and can attack the ionomer membrane in terms of side chain cleavage and unzipping 18,20,21,24,25 which is responsible for the deteriorated physicochemical properties observed in degraded membranes. Radical scavenging is therefore proposed to mitigate the chemical damage by quenching the radicals before they attack t...

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“…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;…”

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confidence: 99%

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

Singh

Orfino

Dutta

et al. 2017

J. Electrochem. Soc.

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Lifetime-limiting failure of fuel cell membranes is generally attributed to their chemical and/or mechanical degradation. Although both of these degradation modes occur concurrently during operational duty cycles, their uncoupled investigations can provide useful insights into their individual characteristics and consequential impacts on the overall membrane failure. X-ray computed tomography is emerging as an advantageous tool for fuel cell failure analysis due to its non-destructive and non-invasive 3D imaging capabilities at ambient conditions. In the present work, post-mortem failure analysis of pure mechanical and pure chemical membrane degradation modes is performed three-dimensionally using this technique. A uniquely comprehensive analysis afforded by this technique reveals that membrane failure is almost exclusively characterized by crack formations during mechanical degradation and by severe thinning accompanied by electrode shorting and pinhole formation during chemical degradation, respectively. Catalyst layer cracks, particularly on the cathode side, are found to interact strongly with mechanically induced membrane cracks. The conjoint effect of chemical and mechanical stressors is established as a necessary requirement for: (i) exclusive membrane crack development independent of catalyst layer cracks; and (ii) crack branching during membrane crack propagation. Overall, the membrane failure analysis improves its reliability and quantitative character with the adoption of 3D imaging. The transportation sector is a significant contributor to global greenhouse gas emissions and with ever-growing concerns around the global warming effect, research and development of novel clean energy based automotive solutions is being pursued worldwide. Hydrogen fuel cells have thus far emerged as a promising alternative to fossil fuel based internal combustion engines due to their clean, noisefree, and efficient operation.1 Polymer electrolyte membrane (PEM) fuel cells 2 are widely used in fuel cell electric vehicles (FCEVs) and supply electrical energy from the electrochemical conversion of hydrogen and oxygen (usually supplied as air) into water. In automotive applications, the fluctuating operating conditions due to vehicle dynamics, variations in loads and environmental conditions, startups and shutdowns, fuel starvation, contamination, and freeze-thaw cycles pose significant durability challenges for the PEM fuel cells. 3Understanding the specific durability problems and developing suitable solutions remains a key research focus in automotive PEM fuel cell technology research and is critical to the long-term and large-scale commercial adoption of this technology. Given the complex interplay of multiple physical phenomena that are simultaneously active in an operating PEM fuel cell, various deleterious factors affecting PEM fuel cell components can collectively lead to a gradual performance loss and eventual failure.In PEM fuel cells, the electrodes are separated by a polymeric membrane which allows selective tran...

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Mechanical degradation of fuel cell membranes under fatigue fracture tests

Cited by 91 publications

References 46 publications

Enhanced electrical conductivity of LaNbO4 by A-site substitution

Enhanced electrical conductivity of LaNbO4 by A-site substitution

In-Situ Modeling of Chemical Membrane Degradation and Mitigation in Ceria-Supported Fuel Cells

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

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