Characteristics of water transport in relation to microscopic structure in Nafion membranes

Xie, Gang; Okada, Tatsuhiro

doi:10.1039/ft9969200663

Cited by 35 publications

(35 citation statements)

References 24 publications

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“…The duration over which the degradation is prolonged depends upon the concentration of the impurity ions [146] and the length of time that the impurity ions reside within the polymer electrolyte membrane. Impurities with large diameters can penetrate the membrane and induce a plugging effect, compromising hydration and thus proton conductivity [157]. In some instances, proton-induced water transfer due to electro-osmotic drag is necessary for counterflow configurations, as discussed previously.…”

Section: Impurity Ionsmentioning

confidence: 99%

“…For other ions, the magnitude of each contributory transport mode depends upon the existence of hydrophilic and hydrophobic parts of the ion. Through the investigation of ammonium derivatives, Xie and Okada [157] reported that such ions with hydrophobic skeletons tended not to have peripherally-bound water molecules and instead tended to contribute to the transfer coefficient simply through hydrodynamic pumping [157]. Other cations, including fully hydrophilic cations, with a high charge density and a high enthalpy of hydration tended to carry more water molecules during transport and that the electroosmotic drag increases with increased water content [150,157,159].…”

Section: Impurity Ionsmentioning

confidence: 99%

“…Young's modulus is shown to increase by one order of magnitude with increasing ionic radius, in the order Ni 2+ > Cu 2+ > Na + > K + . Water transfer coefficients reflect the combined contributions of: (a) electro-osmotic drag, where an ion transports peripherally bound water molecules, and (b) hydrodynamic pumping where water molecules are pumped by an ion during the ion transport process [157]. The transport of protons through the polymer electrolyte from the anode to the cathode is known to induce the aforementioned electro-osmotic drag flux [158].…”

Section: Impurity Ionsmentioning

confidence: 99%

“…Through the investigation of ammonium derivatives, Xie and Okada [157] reported that such ions with hydrophobic skeletons tended not to have peripherally-bound water molecules and instead tended to contribute to the transfer coefficient simply through hydrodynamic pumping [157]. Other cations, including fully hydrophilic cations, with a high charge density and a high enthalpy of hydration tended to carry more water molecules during transport and that the electroosmotic drag increases with increased water content [150,157,159]. Overall this illustrates that while the transfer of protons across the polymer electrolyte material induces an electro-osmotic drag, overall water transfer can indeed be unfavourably magnified as water interacts with impurity ions.…”

Section: Impurity Ionsmentioning

confidence: 99%

“…Cations in the form of foreign impurity ions can displace protons and enter the electrolyte membrane, decreasing the proton conductivity in proportion to the ionic charge of the cation [20]. [152][153][154][155]; rare earths La 3+ [152] and Al 3+ [155]; and ammonium derivatives R n NH + 4−n (where R = H, CH 3 , C 2 H 5 , C 3 H 7 , C 4 H 9 and n = 1 to 4) [156,157]. Sources of impurity ions include impure gas feeds, corroded materials in the fuel cell stack or reactant supply system, i.e.…”

Section: Impurity Ionsmentioning

confidence: 99%

See 4 more Smart Citations

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

Rama

Chen

Andrews

2008

Proceedings of the Institution of Mechanical Engineers, Part A:

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DOI: 10.1243/09576509JPE603Abstract: A qualitative account of the causes and effects of performance degradation and failure in hydrogen-fuelled polymer electrolyte fuel cells (PEFCs) is given in the present review. The purpose of the review is to establish a backbone understanding of the phenomenological processes that occur within the PEFC, how they interact, how they are influenced through elements of design, manufacturing and operation, and ultimately how they result in performance degradation and cell failure. In the current work, 22 common faults are identified which are induced by 48 frequent causes. The major PEFC components considered here that are susceptible to faults are the polymer electrolyte-based membrane, the anode and cathode catalyst layers, gas diffusion and microporous layers, seals and the bipolar plate. Faults pertaining to these components can cause irreversible increases in activation, mass transportation, ohmic and fuel efficiency losses, or indeed cause catastrophic cell failure.

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Section: Impurity Ionsmentioning

confidence: 99%

Section: Impurity Ionsmentioning

confidence: 99%

Section: Impurity Ionsmentioning

confidence: 99%

Section: Impurity Ionsmentioning

confidence: 99%

Section: Impurity Ionsmentioning

confidence: 99%

See 3 more Smart Citations

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

Rama

Chen

Andrews

2008

Proceedings of the Institution of Mechanical Engineers, Part A:

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Proton Conductivity Study of a Fuel Cell Membrane with Nanoscale Resolution

et al. 2007

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Polymer electrolyte membrane fuel cells (PEMFCs) have attracted enormous attention as promising and environmentally friendly energy conversion devices for stationary and mobile applications due to their ability of attaining high power density and high energy conversion efficiency. One of the key components is the proton exchange (PEM) membrane which has to satisfy numerous demands such as high ionic conductivity, chemical, electrochemical and mechanical stability, and low permeability to reactants over a wide range of water content and temperature. [1][2][3][4] The fuel cell performance is directly related to ion conductivity in the membrane, which in turn depends strongly upon its degree of hydration and on the distribution of the ion transport channels which are a result of polymer microphase separation into hydrophilic and hydrophobic domains.[5] Nanoscale information is essential to understand the performance limiting features. Here we introduce an electrochemical atomic force microscopy (EC-AFM) method that provides, simultaneously, the surface topology of a Nafion 112 membrane and its proton conductivity with an unprecedented resolution of ca. 10 nm. They reveal discrete ion channels and suggest that an optimum pore size and structure governs proton conduction.Nafion, consisting of a hydrophobic polytetrafluoroethylene backbone and hydrophilic ÀSO 3 À H + acid groups connected to the backbone via ÀOÀCFÀCF 3 ÀCF 2 ÀOÀCF 2 ÀCF 2 À side chains, is the most widely used membrane material. It shows excellent chemical stability and proton conductivity when soaked with water which is the medium for proton transport. [6,7] One problem of present fuel cells is that not all catalyst particles are involved in the electrochemical reaction due to the fact that they are not in direct contact with the ionic network on the membrane surface. The inhomogeneity of the ion channel distribution causes an uneven current distribution and therefore gives rise to enhanced local dissipation of heat of reaction that leads to "hot spots" at places with very high reactant turnover.[8] This causes local membrane drying and higher resistance and can initiate free radical formation which accelerates membrane degradation. Especially in applications that involve numerous start-stop cycles, drying-swelling fatigue cycles lead to internal stress in the membrane and shear stress at the interface to the electrodes, which may promote aging and deterioration of the membrane-electrode interface. In order to increase the fuel cell lifetime, more information on the interface between ion-exchange membranes and catalyst particles is needed, preferably under conditions near practical fuel cell operation. In-situ studies are essential in order to reduce the gap between the "real world" and model systems.Several groups have extensively investigated the structure of the Nafion membranes using various electrochemical and instrumental techniques. Small angle X-ray and neutron scattering are well suited. However, their analysis is based on models which are na...

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Alkaline naphthoquinone‐based redox flow batteries with a crosslinked sulfonated polyphenylsulfone membrane

Lee

Konovalova

Tsoy

et al. 2022

Intl J of Energy Research

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Summary In this study, the performance of alkaline aqueous organic redox flow battery (AORFB) using an isomeric mixture of 1,2‐naphthoquinone‐4‐sulfonic acid sodium salt and 2‐hydroxy‐1,4‐naphthoquinone (NQSO) and potassium ferrocyanide (FeCN) as active materials dissolved in potassium hydroxide (KOH) is enhanced with replacing commercial Nafion membrane with new crosslinked sulfonated polyphenylsulfone (crosslinked‐SES) membrane. The optimal ratio of sulfonate and sulfone groups of the crosslinked‐SES membrane is determined to balance between mechanical strength and ionic conductivity by the handling of curing time. With that, ionic conductivity and mechanical strength depending on the amount of sulfonate and sulfone are well balanced. The thickness of membrane is also optimized. Such optimized crosslinked‐SES (crosslinked‐SES24) membrane induces better mechanical stability and ionic conductivity than Nafion 211 (Young's modulus and in‐plane conductivity of the potassium form of crosslinked‐SES24 and Nafion 211 are 1108 and 214 MPa, and 20‐23 and 7.8 mS·cm−1) with lower cost. In tests of AORFB using crosslinked‐SES24 that is operated at a high current density of 200 mA·cm−2 over 1000 cycles, the AORFB shows stable coulombic, voltage and energy efficiencies of 99.7, 65.3, and 65.0%, while its capacity loss rate is as low as 0.01% per cycle.

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Characteristics of water transport in relation to microscopic structure in Nafion membranes

Cited by 35 publications

References 24 publications

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

Proton Conductivity Study of a Fuel Cell Membrane with Nanoscale Resolution

Alkaline naphthoquinone‐based redox flow batteries with a crosslinked sulfonated polyphenylsulfone membrane

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