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Vijay Ramani - One of the best experts on this subject based on the ideXlab platform.

  • Model Studies of the Durability of a Titania-Modified Nafion Fuel Cell Membrane
    Journal of The Electrochemical Society, 2009
    Co-Authors: Yatin P. Patil, Vijay Ramani, Satheesh Sambandam, Kenneth A. Mauritz
    Abstract:

    Nafion Membranes degrade in polymer electrolyte Membrane fuel cells due to the interplay of physical and chemical degradation. In the interest of mitigating this problem, Nafion Membranes were modified via an in situ sol-gel polymerization of titanium isopropoxide to generate titania quasi-networks. These composite materials are viewed as model systems within the context of Durability without an immediate concern for cell performance. The modification did not influence Membrane equivalent weight but reduced its hydration capacity. Membrane modulus increased, dimensional stability improved, creep lessened, and the ability of constrained Membranes to withstand contractile stresses due to humidity change was greatly enhanced. The damage surface morphology of unmodified Nafion, viewed using scanning electron microscopy, and of constrained samples showed significant failure, whereas the modified Membranes showed considerably more structural integrity. Open-circuit voltage (OCV) testing showed that the inorganically modified Membrane held voltage better with fluoride emission at least an order of magnitude lower than that of the unmodified Membrane. However, the performance curve of the modified Membrane before the OCV test is inferior to that of Nafion; but after the test it is slightly better. This in situ sol-gel-derived inorganic modification offers a simple way to enhance Membrane Durability by reducing both physical and chemical degradation.

  • photocatalytically generated pt c tio2 electrocatalysts with enhanced catalyst dispersion for improved Membrane Durability in polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 2008
    Co-Authors: Norma R. De Tacconi, Krishnan Rajeshwar, Wen Yuan Lin, Thomas F. Carlson, Leszek Nikiel, Wesley Wampler, Satheesh Sambandam, Ramannair C Chenthamarakshan, Vijay Ramani
    Abstract:

    Platinum/carbon/titanium oxide (Pt/C-TiO 2 ) electrocatalysts were prepared by a heterogeneous photocatalysis method wherein the semiconductor optoelectronic properties of TiO 2 were exploited to facilitate photoreduction of a platinum precursor on the surface of the composite whole yielding excellent platinum dispersion. The TiO 2 loading in the electrocatalyst was varied in the ranges: 5-10 wt % and the Pt content was varied from 5 to 50 wt %. The physical and electrochemical characteristics of these new-generation electrocatalysts were benchmarked against commercial Pt/C samples. Membrane electrode assemblies were prepared using these composite electrocatalysts and tested with hydrogen as fuel and oxygen/air as oxidants. The fluoride emission rate (in units of μmol/h cm 2 ) was estimated by condensate water analyses and found to be reduced by approximately an order of magnitude upon addition of TiO 2 . Implications of these data for optimization of polymer electrolyte fuel cells in terms of Durability and performance are presented.

  • degradation mitigation in polymer electrolyte Membranes using cerium oxide as a regenerative free radical scavenger
    Electrochemical and Solid State Letters, 2008
    Co-Authors: Panagiotis Trogadas, Javier Parrondo, Vijay Ramani
    Abstract:

    The efficacy of CeO 2 nanoparticles in mitigating free-radical-induced polymer electrolyte Membrane (PEM) degradation is investigated. Commercially obtained CeO 2 and nanoparticles synthesized in-house were incorporated within a recast Nafion Membrane. Membrane electrode assemblies were prepared using Nafion and Nafion-CeO 2 composite Membranes (0.5, 1, and 3 wt % CeO 2 ). The composite Membranes exhibited very similar proton conductivities (∼35 mS/cm) and hydrogen crossover (∼ 1 mA/cm 2 ) as Nafion. However, the fluoride emission rate (from accelerated tests) was lowered by more than 1 order of magnitude upon addition of CeO 2 into the Nafion Membrane, suggesting that CeO 2 nanoparticles have tremendous potential to greatly enhance Membrane Durability.

  • Photocatalytically Generated Pt ∕ C – TiO2 Electrocatalysts with Enhanced Catalyst Dispersion for Improved Membrane Durability in Polymer Electrolyte Fuel Cells
    Journal of The Electrochemical Society, 2008
    Co-Authors: Norma R. De Tacconi, C. Ramannair Chenthamarakshan, Krishnan Rajeshwar, Wen Yuan Lin, Thomas F. Carlson, Leszek Nikiel, Wesley Wampler, Satheesh Sambandam, Vijay Ramani
    Abstract:

    Platinum/carbon/titanium oxide (Pt/C-TiO 2 ) electrocatalysts were prepared by a heterogeneous photocatalysis method wherein the semiconductor optoelectronic properties of TiO 2 were exploited to facilitate photoreduction of a platinum precursor on the surface of the composite whole yielding excellent platinum dispersion. The TiO 2 loading in the electrocatalyst was varied in the ranges: 5-10 wt % and the Pt content was varied from 5 to 50 wt %. The physical and electrochemical characteristics of these new-generation electrocatalysts were benchmarked against commercial Pt/C samples. Membrane electrode assemblies were prepared using these composite electrocatalysts and tested with hydrogen as fuel and oxygen/air as oxidants. The fluoride emission rate (in units of μmol/h cm 2 ) was estimated by condensate water analyses and found to be reduced by approximately an order of magnitude upon addition of TiO 2 . Implications of these data for optimization of polymer electrolyte fuel cells in terms of Durability and performance are presented.

Young Moo Lee - One of the best experts on this subject based on the ideXlab platform.

  • Sulfonated polyimide Membranes grafted with sulfoalkylated side chains for proton exchange Membrane fuel cell (PEMFC) applications
    Journal of Membrane Science, 2008
    Co-Authors: Chang Hyun Lee, Chi Hoon Park, Young Moo Lee
    Abstract:

    Abstract Grafted sulfonated polyimide (SPI) Membranes for use as proton-conducting polymer electrolytes for fuel cells were obtained using a fabrication method comprised of thermal-solution imidization and subsequent incorporation of sulfoalkylated grafting agents with different alkyl chain lengths. The additional sulfonic acid (–SO3H) groups in the sulfoalkylated side chains of the grafted SPI Membranes significantly contributed to enhancing ion exchange capacity (IEC) and proton conductivity, leading to excellent electrochemical single-cell performance. Simultaneously, the alkyl groups in the side chain functioned as an internal plasticizer, resulting in an approximate sevenfold improvement in ductility of the grafted SPI as compared to pristine SPI. Interestingly, grafted SPI with long side chains exhibited lower IEC than that with short side chains. However, a relatively high number of water molecules per –SO3H group and a large amount of bound water caused the SPI Membrane grafted with long side chains to have high proton conductivity. Also, the low acidity of the SPI grafted with long side chains leads to improved Membrane Durability to chemical attacks, such as hydrolysis and radical-induced decomposition. Initially, the electrochemical performance of the grafted SPI Membranes was superior to that of Nafion 117, whereas after a long duration for 1100 h in hot water, the single-cell performance of the grafted SPI Membranes diminished below that of Nafion 117, indicating a strong dependency of electrochemical performance with Membrane stability.

  • Sulfonated poly(arylene ether sulfone)-silica nanocomposite Membrane for direct methanol fuel cell (DMFC)
    Journal of Membrane Science, 2007
    Co-Authors: Chang Hyun Lee, Kyung A. Min, Ho Bum Park, Young Taik Hong, Byung Ok Jung, Young Moo Lee
    Abstract:

    Inorganic nanoparticles in nanocomposite Membranes significantly affect the characteristics of those Membranes, such as proton and methanol transport behavior, Membrane Durability, and electrochemical single cell result. Therefore, the inorganic nanoparticles should be deliberately chosen to fabricate composite Membranes with desirable properties for DMFC. In this study, sulfonated poly(arylene ether sulfone) (SPAES) and hydrophilic fumed silica (SiO2) were used as a polymer matrix and an inorganic nanoparticle, respectively. The SiO2 nanoparticles have various surface areas (150, 200, 300, and 380 m 2 g −1 ) and average particle sizes (7, 12, and 14 nm). The SiO2 nanoparticles are evenly dispersed in the SPAES matrix by aid of a non-ionic surfactant (Pluronics ® L64). Interestingly, SiO2 particles with a high surface area and small particle size showed the best results: high proton conductivity, long Membrane life time under oxidative conditions, good dimensional stability, outstanding single cell performance, and reduced methanol crossover. Moreover, SiO2 content plays an important role in Membrane microstructures and Membrane properties such as proton conductivity and methanol barrier behavior. An excessive SiO2 content caused a large aggregation of SiO2 particles, leading to the deterioration of mechanical properties in nanocomposite Membranes. In the present study, optimal SiO2 content for maximizing the fuel cell performance of current nanocomposite Membranes was ca. 2 wt.%. © 2007 Elsevier B.V. All rights reserved.

Erik Kjeang - One of the best experts on this subject based on the ideXlab platform.

  • Isolated chemical degradation induced decay of mechanical Membrane properties in fuel cells
    Electrochimica Acta, 2020
    Co-Authors: Sandeep Bhattacharya, J. Leung, Mike Lauritzen, Erik Kjeang
    Abstract:

    Abstract Membrane Durability is a major consideration for the operational lifetime of polymer electrolyte Membrane fuel cells. During fuel cell operation, the Membrane is exposed to combined chemical and mechanical degradation that could ultimately lead to hydrogen leaks and cell failure. In this work, a direct link between chemical degradation and Membrane mechanics is established by using a steady-state open-circuit voltage accelerated stress test (AST) to induce isolated chemical Membrane degradation. Cross-sectional microscopy reveals gradual Membrane thinning with AST time without crack and hole formation. Partially degraded catalyst coated Membranes are subjected to tensile tests at room and fuel cell conditions in order to quantify changes in mechanical properties during the chemical degradation process. Reductions in ultimate tensile stress, fracture strain, and elastic modulus are progressively observed during the AST and correlated to Membrane thinning and fluoride release. Additionally, hygrothermal expansion experiments reveal 33% decay in hygral expansion at 70 °C and 40% decay in thermal expansion at 90% relative humidity due to chemical degradation. Given the absence of mechanical degradation and associated physical damage such as cracks, the gradual decay in ductility is likely induced by polymer chain disentanglement as a precursor for mechanical failure.

  • Characterization of Membrane Degradation Growth in Fuel Cells Using X-ray Computed Tomography
    Journal of The Electrochemical Society, 2018
    Co-Authors: Dilip Ramani, Yadvinder Singh, Francesco P. Orfino, Monica Dutta, Erik Kjeang
    Abstract:

    Perfluorosulfonic acid ionomer Membranes are subjected to simultaneous chemical and mechanical degradation under fuel cell operation. Despite the importance of Membrane Durability, the understanding of its structural degradation and failure modes has been considerably restricted by conventional 2D imaging. In this work, non-invasive micro X-ray computed tomography (XCT) is adopted to visualize the 3D Membrane decay at different life stages during combined chemical and mechanical degradation. A detailed survey exhibits damage density of 6 and 10 cracks per mm2 observed at the near-final and final end of life stages respectively. Through-thickness Membrane cracks with unbranched I-shaped cracks and Y- and X- shaped cracks with one and two branches respectively are observed. The observed damage development at each life stage is correlated to supplementary diagnostic data including hydrogen leak rate, open circuit voltage, and tensile strength. In particular, large X-shaped cracks formed due to embrittlement from underlying chemical degradation are deemed to have a critical impact on the eventual failure development by facilitating large hydrogen leaks. Overall, the comprehensive 3D perspective enabled by XCT imparts new knowledge pertaining to the degradation process, and could also be extended to other fuel cell failure modes and degradation mechanisms.

  • Favorable effect of in-situ generated platinum in the Membrane on fuel cell Membrane Durability
    Journal of Power Sources, 2015
    Co-Authors: Natalia Macauley, Mark Watson, Ka Hung Wong, Erik Kjeang
    Abstract:

    Abstract The overall lifetime of polymer electrolyte fuel cells is often determined by the Membrane Durability. Platinum, which may dissolve from the catalyst layers during fuel cell operation and deposit in the Membrane, has been shown to have both positive and negative effects on Membrane stability. In the present work, we analyze what specific conditions are required in order to reach a favorable, Membrane stabilizing effect with the controlled use of platinum in the Membrane. Using accelerated Membrane Durability testing, field operated Membrane samples, and electron microscopy, we demonstrate that a high platinum concentration with specific particle shapes and sizes is essential for enhanced Membrane stability. Specifically, star shaped and dendritic particles with high particle density and high surface area are shown to be preferable. These particles contain high levels of Pt(111) and are expected to have high catalytic activity toward peroxide quenching and crossover gas consumption, thereby mitigating chemical Membrane degradation. On the other hand, small, dispersed cubic particles are found to have no effect or the opposite, negative effect on Membrane stability.

  • creep properties of catalyst coated Membranes for polymer electrolyte fuel cells
    Journal of Power Sources, 2015
    Co-Authors: Alireza Sadeghi Alavijeh, Gary G Wang, Ramin M H Khorasany, Aronne Habisch, Erik Kjeang
    Abstract:

    Abstract Creep as a time-dependent mechanical damage acting either independently or in conjunction with other degradation mechanisms is known to reduce the Membrane Durability of polymer electrolyte fuel cells (PEFCs). Due to the important ionomer coupling of Membrane and catalyst layers in PEFCs, the present work evaluates Membrane creep when constrained within a catalyst coated Membrane (CCM). Three key factors dominating creep life in commonly used perfluorosulfonic acid (PFSA) ionomer Membranes, including creep stress, temperature, and relative humidity, were investigated by applying ex-situ creep loading and unloading experiments under controlled temperature and humidity conditions. The creep strain and recovery of the CCM were found to be highly dependent on the environmental conditions and applied stress levels, where the temperature effect on creep strain was the most significant. Repetitive creep – recovery cycles revealed that significant creep damage can accumulate in the material over time. This accumulated creep damage was found to be independent of the loading frequency while both peak strain and permanent deformation increased with the stress duration. Based on the present findings, it is recommended to reduce the operating temperature and ensure adequate Membrane hydration in order to mitigate harmful creep effects in PEFCs.

  • accelerated Membrane Durability testing of heavy duty fuel cells
    Journal of The Electrochemical Society, 2015
    Co-Authors: Natalia Macauley, Michael V. Lauritzen, Shanna Knights, Mark Watson, Joanna Kolodziej, Alireza Sadeghi Alavijeh, Gary G Wang, Erik Kjeang
    Abstract:

    Regular Durability testing of heavy duty fuel cell systems for transit bus application requires several thousand hours of operation, which is costly and time consuming. Alternatively, accelerated Durability tests are able to generate failure modes observed in field operation in a compressed time period, by applying enhanced levels of stress. The objective of the present work is to design and validate an accelerated Membrane Durability test (AMDT) for heavy duty fuel cells under bus related conditions. The proposed AMDT generates bus relevant Membrane failure modes in a few hundred hours, which is more than an order of magnitude faster than for regular duty cycle testing. Elevated voltage, temperature, and oxidant levels are used to accelerate Membrane chemical stress, while relative humidity (RH) cycling is used to induce mechanical stress. RH cycling is found to significantly reduce Membrane life-time compared to constant RH conditions. The role of a platinum band in the Membrane is investigated and Membranes with Pt bands demonstrate a considerable life-time extension under AMDT conditions, with minimal Membrane degradation. Overall, this research serves to establish a benchmark AMDT that can rapidly and reliably evaluate Membrane stability under simulated heavy duty fuel cell conditions. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0671501jes] All rights reserved.

Matthew M. Mench - One of the best experts on this subject based on the ideXlab platform.

  • Effect of material properties on evaporative water removal from polymer electrolyte fuel cell diffusion media
    Journal of Power Sources, 2010
    Co-Authors: Kyu Taek Cho, Matthew M. Mench
    Abstract:

    This work is devoted to delineating the fundamentals of evaporative water removal from diffusion media (DM) to achieve highly efficient and durable gas purge. Multiphase water transport from DM during gas purge is characterized by a balance of internal capillary liquid water flow and water vapor diffusion. In this study, DM with polytetrafluoroethylene (PTFE) content ranging from 0 to 20 wt%, and DM with three different geometric pore structures are utilized to understand this material property effect. It is found that overall evaporative water removal rate increases as PTFE content decreases and as the geometric pore structure changes from a two- to a more three-dimensional structure. This is due to the increase of wettability and porous space favorable for the water transport. The effect of phase-change-induced (PCI) flow and capillary flow on water removal is compared, and it is found that PCI flow is dominant at lower saturation of DM, whereas capillary flow is dominant at higher saturation. The results of this study build upon a previous study by the authors (Cho and Mench [17]), and are useful to understand the competing phenomena of water removal in PEFC DM. The ultimate goal of this work is to guide material design to achieve purge that preserves Membrane Durability with reduced shutdown power requirements.

  • Coupled effects of flow field geometry and diffusion media material structure on evaporative water removal from polymer electrolyte fuel cells
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Kyu Taek Cho, Matthew M. Mench
    Abstract:

    Abstract In this work, the coupled effects of flow field geometry and diffusion media (DM) material structure on evaporative water removal during gas purge are investigated with the ex-situ test methods developed in previous works [31] , [32] . Three different flow field structures with various land to channel width ratios (L/C) were utilized with paper and cloth-type DM to understand the impact of L/C and DM properties on evaporative water removal rate, water distribution in DM, purge efficiency, and irreducible saturation. In the capillary flow dominant regime, it was determined that evaporative water removal is not significantly affected by L/C or DM properties, and can be semi-empirically correlated with critical purge time. The cloth-type DM was found to be superior to paper-type to mitigate the in-plane impedance of the land on water removal. In addition to the ex-situ evaporative tests, neutron radiography was utilized to visualize the in-situ water removal behavior. Results validate a novel purge protocol suggested by the authors in a previous study to achieve a more efficient and durable gas purge that preserves Membrane Durability.

Huamin Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of the differences between the in situ open circuit voltage test and ex situ Fenton test for PEM oxidation characterization
    International Journal of Hydrogen Energy, 2011
    Co-Authors: Shaohua Xiao, Huamin Zhang, Zhensheng Mai
    Abstract:

    In order to clarify the differences between the in situ open circuit voltage (OCV) accelerated test and ex situ Fenton test, black polypyrrole (PPy) was specially selected to modify NafionMembrane via in situ chemical oxidative polymerization. OCV decay rate, scan- ning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) techniques are employed to characterize the Membrane oxidation stability. It is found that the incorporation of PPy greatly enhances the Membrane Durability in the OCV test, while it makes no difference in Fenton test. And then, the differences between the OCV test and Fenton test are proposed in terms of the generation mechanism of free radicals, the amount of free radicals and the degradation mode.

  • Membrane degradation mitigation using zirconia as a hydrogen peroxide decomposition catalyst
    Journal of Power Sources, 2010
    Co-Authors: Shaohua Xiao, Huamin Zhang, Zhang Yining, Hexiang Zhong, Yu Zhang
    Abstract:

    Zirconia as a hydrogen peroxide decomposition catalyst is firstly investigated to mitigate the Membrane degradation in terms of the in situ open circuit voltage (ocv) test and the ex situ fenton test. ocv decay rate and fluorine emission rate (fer) are used to quantify the Membrane degradation rate. the rotating ring-disk electrode (rrde) is also employed to further confirm the effect. the zro(2)-nafion Membrane exhibits more stable ocv and lower fer than the recast nafion, suggesting that zro(2) nanoparticles have the potential to enhance Membrane Durability. (c) 2010 elsevier b.v. all rights reserved.

  • MnO2/SiO2–SO3H nanocomposite as hydrogen peroxide scavenger for Durability improvement in proton exchange Membranes
    Journal of Membrane Science, 2010
    Co-Authors: Dan Zhao, Huamin Zhang
    Abstract:

    Membrane Durability was a key problem to the development of proton exchange Membrane fuel cells (PEMFCs). A novel nanocomposite MnO2/SiO2–SO3H was prepared to mitigate the hydrogen peroxide attack to the Membranes at fuel cell condition. The nanocomposites were synthesized by the wet chemical method and three-step functionalization. The crystal structure was characterized by X-ray powder diffraction (XRD), the crystallite size and the distribution of the nanocomposites were investigated by TEM. SEM-EDX was used to analyze the elemental distribution on the surface of the nanocomposite. And the surface functional groups (–SO3H) were evaluated by FT-IR. The amount of sulfonic acid groups introduced onto the silica surface was determined by titration method. The radical scavenging ability was estimated by UV–VIS spectroscopy using dimethyl sulfoxide (DMSO) as the trapping agent. The Membrane Durability was investigated via ex situ Fenton test and in situ open circuit voltage (OCV) accelerated test. In these tests, the fluoride emission rate (FER) reduced by nearly one order of magnitude with the dispersion of MnO2/SiO2–SO3H nanocomposites into Nafion Membrane, suggesting that MnO2/SiO2–SO3H nanocomposites had a promising application to mitigate the degradation of the proton exchange Membrane.

  • Degradation location study of proton exchange Membrane at open circuit operation
    Journal of Power Sources, 2010
    Co-Authors: Shaohua Xiao, Huamin Zhang, Zhang Yining, Yu Zhang, Hua Dai, Zhensheng Mai
    Abstract:

    In order to investigate the location of the radical-initiated Membrane degradation at open circuit operation, ceria (CeO2) nanoparticles are firstly placed at different locations of the Membranes to scavenge free radicals generated there. Scanning electron microscopy (SEM) is used to characterize cross-sectional morphology of Membrane before and after the open circuit voltage (OCV) test. OCV decay rate is used as an indicator of Membrane degradation rate. Composite Membranes with CeO2 nanoparticles facing anode or cathode show improved Membrane Durability than that of plain Membrane in terms of OCV decay rate and cross-sectional morphology. CeO2–Nafion composite Membrane with the same thickness is subsequently proposed and it obtains the best Durability. It is concluded that the chemical degradation at open circuit operation occurs at both sides of anode and cathode.