Strategies for Mitigation of PFSA Polymer Degradation in PEM Fuel Cells

Escobedo, Gonzalo; Raiford, Kimberly A. Gheysen; Nagarajan, Gowri S.; Schwiebert, Kathryn E.

doi:10.1149/1.2214563

Cited by 30 publications

(19 citation statements)

References 1 publication

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“…Commercial Nafion 212 membrane and the modified Nafion 212 membrane with CeO 2 layers with different coating densities were immersed in a Fenton solution (20 wt.% H 2 O 2 , 30 ppm Fe 2+ ) at 80 C for 72 hours. Hydroxyl radicals (OH•) were generated via this process as follows [51][52][53] :…”

Section: Characterizations Of Nafion Composite Membrane With Ceo 2 La...mentioning

confidence: 99%

Sandwich‐like Nafion composite membrane with ultrathin ceria barriers for durable fuel cells

Kang

Jang

Choi

et al. 2021

Intl J of Energy Research

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Improving the durability of the membrane electrode assembly (MEA) while obtaining high performance is required to further commercialize polymer electrolyte membrane fuel cells (PEMFCs). The durability of PEMFCs is improved by incorporating radical scavengers, such as CeO 2 (ceria), into the MEA, especially the membrane. However, nanosized ceria particles are generally mixed with ionomers and are cast on substrates to fabricate composite membranes. Inchemical degradation, durability, membrane electrode assembly, polymer electrolyte membrane fuel cell, radical scavenger Yun Sik Kang and Segeun Jang contributed equally to this study.

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Section: Characterizations Of Nafion Composite Membrane With Ceo 2 La...mentioning

confidence: 99%

Sandwich‐like Nafion composite membrane with ultrathin ceria barriers for durable fuel cells

Kang

Jang

Choi

et al. 2021

Intl J of Energy Research

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“…50 kcal/mol), consistent with prior studies 30,[46][47] (Supporting Information Table S10). Nevertheless, to explain experimental observations of trace [35][36] HF formed in ex situ experiments on Nafion 9,35 , we must either expect spontaneous generation of radicals capable of directly abstracting fluorine (e.g., H radical) or some alternative pathway for degradation of terminal carbon radicals formed (e.g., y1c) from C-S bond cleavage (Figure 6). One possibility that is consistent with experiments 11,19 would involve the continued degradation by an OH radical of a terminal carbon radical with moderate barriers similar to the equivalent steps considered on defect-containing Nafion (e3 to e7 in Figure 5 and Supporting Information Figure S4).…”

Section: C Degradation Mechanisms At Sulfonic Acid Functional Groupsmentioning

confidence: 99%

“…Fluoride release measurements conducted after ex situ Fenton's degradation tests indicate the release of more HF from defect-containing membranes than from defect-free ones 32,35 , indeed suggesting that such defects are more prone to radical attack. Even though defects are the most vulnerable sites for attack by OH radicals during ex situ degradation, Nafion still degrades in the absence of defects 9,32,[35][36] , as evidenced through some release of HF 9,35 .…”

Section: Introductionmentioning

confidence: 99%

Uncovering Alternate Pathways to Nafion Membrane Degradation in Fuel Cells with First-Principles Modeling

Bajaj¹,

Liu²,

Kulik

2020

Preprint

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Polymer electrolyte membrane fuel cells (PEMFCs) represent promising energy storage solutions, but challenges remain to maximize their utility. Nafion is frequently employed as the PEMFC membrane material, but degradation of Nafion can limit the life of PEMFCs. Using hybrid density functional theory (DFT), we carry out reaction pathway analysis on a range of candidate degradation pathways on both pristine and defect-containing models of Nafion. Degradation of pristine Nafion initiated by hydrogen radicals involves moderate (ca. 20 kcal/mol) barriers lower than alternative pathways initiated by hydroxyl radicals. We propose a new pathway for continued Nafion degradation after initial H radical attack in the presence of H<sub>2</sub>O<sub>2</sub>. This pathway has a modest barrier and provides a mechanistic basis for the production of experimentally observed trifluoroacetic acid and hydrogen fluoride. Our work suggests inherent limits to mechanistic studies that use hydroxyl radical as the sole radical source to model Nafion degradation under operating conditions. We observe that hydroxyl radical-only degradation mechanisms have barriers competitive with hydrogen radical species only for initiation at carboxylic acid defects on the main chain or sulfonic acid functional groups on the Nafion side chain. We confirm our observations with DFT by comparison to correlated wavefunction theory. Our study highlights the importance of thorough first-principles modeling to identify the most probable, low energy pathways for materials degradation.

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“…;000 Â 60 Â 60 (9) This ensures that the covariance would propagate in such a way that after 40,000 h, two standard deviations of the EMSA would encompass a 10% decline from the initial value with no updates from the measurements.…”

Section: Extended Kalman Filtering Algorithm For Mea Statementioning

confidence: 99%

“…[6] and [7]. Studies have shown that the degradation rate is affected by the frequency and duration of open circuit voltage (OCV) instances [8][9][10][11][12], low humidity operation [13][14][15][16], high humidity operation [17,18], and by the operating temperature [7]. In general, degradation tends to become worse with temperatures above 75 C, the use of gases that are not fully humidified, and with load cycling, particularly if the OCV potential is included [7].…”

Section: Introductionmentioning

confidence: 99%

Membrane Electrolyte Assembly Health Estimation Method for Proton Exchange Membrane Fuel Cells

Headley

Gross

Chen

2017

Journal of Electrochemical Energy Conversion and Storage

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Membrane electrolyte assembly (MEA) aging is a major concern for deployed proton exchange membrane (PEM) fuel cell stacks. Studies have shown that working conditions, such as the operating temperature, humidity, and open circuit voltage (OCV), have a major effect on degradation rates and also vary significantly from cell to cell. Individual cell health estimations would be very beneficial to maintenance and control schemes. Ideally, estimations would occur in response to the applied load to avoid service interruptions. To this end, this paper presents the use of an extended Kalman filter (EKF) to estimate the effective membrane surface area (EMSA) of each cell using cell voltage measurements taken during operation. The EKF method has a low computational cost and can be applied in real time to estimate the EMSA of each cell in the stack. This yields quantifiable data regarding cell degradation. The EKF algorithm was applied to experimental data taken on a 23-cell stack. The load profiles for the experiments were based on the FTP-75 and highway fuel economy test (HWFET) standard drive cycle tests to test the ability of the algorithm to perform in realistic load scenarios. To confirm the results of the EKF method, low performing cells and an additional “healthy” cell were selected for scanning electron microscope (SEM) analysis. The images taken of the cells confirm that the EKF accurately identified problematic cells in the stack. The results of this study could be used to formulate online sate of health estimators for each cell in the stack that can operate during normal operation.

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Strategies for Mitigation of PFSA Polymer Degradation in PEM Fuel Cells

Cited by 30 publications

References 1 publication

Sandwich‐like Nafion composite membrane with ultrathin ceria barriers for durable fuel cells

Sandwich‐like Nafion composite membrane with ultrathin ceria barriers for durable fuel cells

Uncovering Alternate Pathways to Nafion Membrane Degradation in Fuel Cells with First-Principles Modeling

Membrane Electrolyte Assembly Health Estimation Method for Proton Exchange Membrane Fuel Cells

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