Chemical Durability Studies of Perfluorinated Sulfonic Acid Polymers and Model Compounds under Mimic Fuel Cell Conditions

Zhou, Cheng; Guerra, Miguel Ángel Santos; Qiu, Zaozao; Zawodzinski, and Thomas A.; Schiraldi, David A.

doi:10.1021/ma071603z

Cited by 141 publications

(183 citation statements)

References 31 publications

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“…The hydrogen atom, in a sense, provides a foothold for hydroxyl radical attack and the thermodynamic driving force for formation of the strong O-H bond of H 2 O. Substrates that possess only a sulfonic acid end group, as would Note that the sulfonic acid groups exist exclusively in the sulfonate anion form in , 16 (2) 235-255 (2008) aqueous solution. The model compound studies have noted general increased reactivity of branched model compounds suggesting that branched materials are more fragile than their straight chain counterparts (29). This conclusion is unlikely; with a given end group, the rate differences observed between branched and straight compounds should be very similar.…”

Section: Pfsa Chemical Degradationmentioning

confidence: 99%

The Chemistry of Fuel Cell Membrane Chemical Degradation

2008

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A detailed thermochemical and kinetic analysis of PFSA ionomers and the reactive oxygen species formed in an operating fuel cell is reported. The analysis reveals that hydroxyl radical is the only oxygen species capable of abstracting a hydrogen atom from carboxylic acid intermediates, thereby propagating the PFSA main chain unzipping process. Two chemically specific, main chain scission mechanisms are proposed. The first involves formation of sulfonyl radicals under dry conditions and the second invokes the action of hydrogen atoms formed from hydrogen gas and hydroxyl radical. The thermochemical analysis provides a strong basis from which to rationalize the results from a broad range of in-situ and ex-situ fuel cell degradation studies.

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Section: Pfsa Chemical Degradationmentioning

confidence: 99%

The Chemistry of Fuel Cell Membrane Chemical Degradation

2008

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“…[32][33][34] Two compounds in particular, perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) * Electrochemical Society Active Member.…”

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confidence: 99%

“…As mentioned previously, model compounds DA-Naf and DA-3M represent experimentally determined degradation compounds of Nafion and 3M membranes respectively. 32 Model compounds nonafluoro-1-butanesulfonic acid (SA1) and tridecafluoro-1-hexanesulfonic acid (SA2) were chosen to gain fundamental insight on the adsorption effects solely due to sulfonic acid functional group and also to investigate the effect of fluorocarbon chain length on sulfonate anion adsorption. …”

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confidence: 99%

Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

Christ

Neyerlin

Richards

et al. 2014

J. Electrochem. Soc.

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The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 -C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resulting in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Greater than a 44% loss in ORR activity at 0.9 V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities. While there has been a concerted effort to develop membranes and electrocatalysts that significantly improve the performance of polymer electrolyte membrane fuel cells (PEMFCs), systematic studies on the magnitude and mechanism of electrocatalyst performance degradation due to contaminants arising from system components have been less prevalent. With a Department of Energy 2017 target of less than 10% voltage degradation over 5000 hours of automotive fuel cell performance, and a 2013 status of 3600 hours, improvement in the area of durability is still required.1 Air, fuel, and system derived chemical contaminants can contribute to irreversible performance loss. However, due to the fact that many factors can affect durability in a fuel cell system, it is difficult to relate the performance loss to the degradation of specific component(s). And failure mechanisms are not well understood. 2Numerous studies focusing on the performance impact of impurities found in the anode fuel stream (e.g. CO, CO 2 , H 2 S, NH 3 , CH 4 and HCOOH), as well as common airborne contaminants present in the cathode stream (e.g. SO x and NO x ) have been conducted. [3][4][5][6][7][8][9][10][11] In addition, various research groups have examined the impact of aromatic contaminants and environmentally common anionic and cationic species. and Co 2+ ), originating from the bipolar plates and catalyst layer. 19-25Results of these studies show, in many cases, severe effects on fuel cell performance due in large to anion adsorption and irreversible chemisorption of poisoning compounds on the catalyst layer, as well as foreign cation uptake in the membrane. More recently, an investigation of species originating from balance of plant (BOP) components (e.g. structural materials and assembly aids) has shown fuel cell performance loss due to additives and other compoun...

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“…Also, detailed electrochemical experiments need to be carried out to separate the total peroxide generated into the fraction at the electrode and that in the membrane. A detailed understanding into the exact chemical mechanism of the degradation, including the degradation of the side chains is being carried out 30 The findings need to be correlated with long term durability studies where the membrane is tested for thousands of hours in a fuel cell, with constant monitoring of Fluoride from the anode and cathode and measurement of dimensional changes. To verify the degradation mechanism, end capped Nafion™ membranes can also be tested for fuel cell performance and the generation of fluoride measured and compared with data for regular Nafion™ membranes without end capping.…”

Section: Discussionmentioning

confidence: 99%

“…Calculations -Average gas pressure and temperature through GDL sample: Introducing (25) and (26) For each flow rate Q and corresponding pressure difference ∆P = P 1 -P 0 calculate x and y from (30). Plot the values x and y on a linear graph paper and obtain the straight line that best fits the points.…”

Section: Summary Of Test Methodsmentioning

confidence: 99%

Final Report - MEA and Stack Durability for PEM Fuel Cells

Yandrasits¹

2008

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The principal objectives of this program were to develop membrane electrode assemblies (MEAs) and systems that are durable up to 40,000 hours under stationary power conditions and at the same time can be manufacture in high volume, commercial processes.All MEA materials, process development work was carried out by 3M Co., at its St. Paul, MN, 3M Center campus and its Menomonie, WI, production plant. The 3M team included primarily members from the Fuel Cell Components Program, but significant assistance was received over Executive SummaryProton exchange membrane fuel cells are expected to change the landscape of power generation over the next ten years. For this to be realized one of the most significant challenges for stationary systems is lifetime, where 40,000 hours of operation with less than 10% decay is desired. This project conducted fundamental studies on the durability of membrane electrode assemblies (MEAs) and fuel cell stack systems with the expectation that knowledge gained from this project will be applied toward the design and manufacture of MEAs and stack systems to meet DOE's 2010 stationary fuel cell stack systems targets.The focus of this project was proton exchange membrane (PEM) fuel cell durabilityunderstanding the issues that limit MEA and fuel cell system lifetime, developing mitigation strategies to address the lifetime issues and demonstration of the effectiveness of the mitigation strategies by system testing. To that end, several discoveries were made that contributed to the fundamental understanding of MEA degradation mechanisms. (1) The classically held belief that membrane degradation is solely due to polymer end-group "unzipping" is incorrect; there are other functional groups present in the ionomer that are susceptible to chemical attack. (2) The rate of membrane degradation can be greatly slowed or possibly eliminated through the use of additives that scavenge peroxide or peroxyl radicals. (3) Characterization of gas diffusion layer (GDL) using dry gases is incorrect due to the fact that fuel cells operate utilizing humidified gases. The proper characterization method involves using wet gas streams and measuring capillary pressure as demonstrated in this project. (4) Not all Platinum on carbon catalysts are created equally -the major factor impacting catalyst durability is the type of carbon used as the support. (5) System operating conditions have a significant impact of lifetime -the lifetime was increased by an order of magnitude by changing the load profile while all other variables remain the same. (6) Through the use of statistical lifetime analysis methods, it is possible to develop new MEAs with predicted durability approaching the DOE 2010 targets. (7) A segmented cell was developed that extend the resolution from ~ 40 to 121 segments for a 50cm2 active area single cell which allowed for more precise investigation of the local phenomena in a operating fuel cell. (8) The single segmented cell concept was extended to a fuel size stack to allow the first of its kind moni...

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Chemical Durability Studies of Perfluorinated Sulfonic Acid Polymers and Model Compounds under Mimic Fuel Cell Conditions

Cited by 141 publications

References 31 publications

The Chemistry of Fuel Cell Membrane Chemical Degradation

The Chemistry of Fuel Cell Membrane Chemical Degradation

Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

Final Report - MEA and Stack Durability for PEM Fuel Cells

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