Solvent transoport across cation-exchange membranes under a temperature difference and under an osmotic pressure difference

Tasaka, Masayasu; Hirai, Tsuneo; Kiyono, Ryotaro; Aki, Yasuo

doi:10.1016/0376-7388(92)85014-a

Cited by 42 publications

(37 citation statements)

References 5 publications

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“…When thermo-osmotic diffusivity found by Kim and Mench 8 is used, the calculation yields a comparable flux magnitude but again in the opposite direction. We note that the experimental conditions used by earlier investigators, 2,4,5,8 both sides of the membrane were completely in direct contact with liquid water. We further note that, as described by Eq.…”

Section: B308mentioning

confidence: 99%

Water Transport Across a Polymer Electrolyte Membrane under Thermal Gradients

Preston

Pasaogullari

et al. 2011

J. Electrochem. Soc.

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A fundamental experimental and numerical study of the water transport across a perfluorosulfonic acid membrane under a temperature gradient is presented. The water transport phenomenon was experimentally investigated through water flux measurement and neutron radiography. The experimental observations found that water is transported in the direction from the high temperature side to the low temperature side, when both sides of the membrane are sufficiently humidified, and suggest that the transport mechanism is concentration gradient driven. The neutron radiography measurements detected the presence of water content gradient across the membrane and higher water content is seen at a larger thermal gradient. A numerical model was developed to investigate the experimental results. Water transport predictions agreed qualitatively but more accurate material and transport property characterizations are needed for further improvement.High current density operation is desirable in automotive and portable applications of polymer electrolyte fuel cells ͑PEFCs͒ in particular to minimize the size and weight of the system balance of the plant. However, the resulting heat generation due to high overpotentials, predominantly in the cathode catalyst layer, and the Joule heating, especially in the electrolyte, cause a temperature gradient across the polymer electrolyte membrane ͑PEM͒ as well as in gas diffusion media ͑GDM͒. An experimental measurement of the temperature difference of nearly 2 K between the membrane electrode assembly ͑MEA͒ and the bipolar plates with 1.0 K differential across the MEA at current density of 0.6 A/cm 2 has been reported. 1 The nonisothermal nature of the PEFC contributes to a localized dry-out of the PEM, which leads to a deterioration of the performance even when the inlets are sufficiently humidified. On the other hand, during low temperature operation, such as during a start-up, the temperature gradient can also induce unwanted condensation of water in the GDM, a condition known as flooding, which impedes the transport of reacting species. Similar temperature differential across the GDM can also occur during the shutdown process. Thus, establishing a proper water and thermal management is essential for an optimized performance of PEFCs and has been an intensely studied subject over the years; therefore, the present paper aims to understand the description of water transport across a nonisothermal membrane.Water transport across the PEM is known to occur by several driving modes, which include electric potential, water concentration gradients, and hydraulic pressure gradients. In addition to the aforementioned transport modes, water transport in the through-plane direction induced by the presence of a thermal gradient across the PEM has been known to exist for some time but attention toward the phenomenon in PEFCs has been mostly nonexistent in the literature until recently. The few investigators who studied this phenomenon, however, arrived at various conclusions on the mechanism of the transport...

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Section: B308mentioning

confidence: 99%

Water Transport Across a Polymer Electrolyte Membrane under Thermal Gradients

Preston

Pasaogullari

et al. 2011

J. Electrochem. Soc.

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“…Non-isothermal transport phenomena in charged membranes have been reported occasionally in the literature since then [ 26 , 27 , 28 , 29 ]. In the 1970s and 1980s, Tasaka and co-workers were central [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], while new researchers joined in the 1990s [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ]. Different aspects were studied, such as the influence of the membrane type [ 40 , 41 , 42 , 51 , 52 ], the concentration and nature of the electrolyte solutions in contact with the membrane [ 39 , 42 ], and the membrane-transported entropy of ions [ 42 , 45 ].…”

Section: Introductionmentioning

confidence: 99%

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Barragán

Kristiansen

Kjelstrup

2018

Entropy

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By thermoelectric power generation we mean the creation of electrical power directly from a temperature gradient. Semiconductors have been mainly used for this purpose, but these imply the use of rare and expensive materials. We show in this review that ion-exchange membranes may be interesting alternatives for thermoelectric energy conversion, giving Seebeck coefficients around 1 mV/K. Laboratory cells with Ag|AgCl electrodes can be used to find the transported entropies of the ions in the membrane without making assumptions. Non-equilibrium thermodynamics can be used to compute the Seebeck coefficient of this and other cells, in particular the popular cell with calomel electrodes. We review experimental results in the literature on cells with ion-exchange membranes, document the relatively large Seebeck coefficient, and explain with the help of theory its variation with electrode materials and electrolyte concentration and composition. The impact of the membrane heterogeneity and water content on the transported entropies is documented, and it is concluded that this and other properties should be further investigated, to better understand how all transport properties can serve the purpose of thermoelectric energy conversion.

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“…The direction of the electro-osmosis water transport depends on the membrane properties and is always in the direction of increased total entropy. 33,34 For Nafion membranes, it has been shown that the direction of electroosmosis is from cold to hot side but altogether, the magnitude of electro-osmosis flux is generally smaller than of the diffusion within the normal operational current density range of the PEFC. 19 The water transport in the gas diffusion medium is due to the pressure gradient (capillary pressure and vapor transport) and PCI flow.…”

Section: N M|t Hmentioning

confidence: 99%

Water Management in Polymer Electrolyte Fuel Cells through Asymmetric Thermal and Mass Transport Engineering of the Micro-Porous Layers

Gandomi

Edmundson

Busby

et al. 2016

J. Electrochem. Soc.

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For polymer electrolyte fuel cells (PEFCs) operating at very high current, prevention of anode dry-out through enhanced back flux of water and restriction of evaporation is required. In this work, back flux of water to the anode is engineered using an asymmetric anode and cathode micro-porous layer (MPL) configuration. Extensive experimental tests have been conducted to study the impact of thermal and mass transport resistances on the net water flux coefficient for extremes of wet and dry operating conditions. The net water drag coefficient was measured in the range of −0.17 to +0.18 depending on the operating conditions and material configurations. A simplified model has also been developed to investigate the effect of temperature gradient on the net water drag coefficient. It is shown that with an asymmetric configuration, the net flux of water can be reversed under certain conditions, greatly enhancing high current density performance. For wet operating conditions, the cell configuration with asymmetric mass transport resistance can be utilized to tailor the back flux of water. For dry operating conditions, the thermal resistance is the key controlling parameter to affect the net water drag. Water management remains an important topic in polymer electrolyte fuel cell (PEFC) systems. Water is required to keep the membrane hydrated to maintain ionic conductivity. However, excessive liquid-water accumulation in the gas flow channels and in the porous media (gas diffusion layer (GDL), and catalyst layers) limits reactants' transport to the electrocatalyst (a phenomenon called flooding). The membrane's transport properties are known to be a strong function of water content within the membrane. Extensive dry-out at the anode side and subsequent conductivity loss results in poor overall performance. Several passive and active approaches have been utilized for water management within the PEFCs (e.g. Refs. 1-6). A good review of these techniques has been provided in Ref. 7 and a recent review of water transport within PEFCs is discussed in Ref. 8. The micro-porous layer (MPL) at the electrodes have been used to improve the performance of PEFC via water management. Pasaogullari et al.9 modeled the two-phase transport in the porous layers of a PEFC cathode side. Their modeling results predicted that the existence of a MPL in the cathode side enhances liquid-water removal and reduces liquid saturation in the catalyst layer. Weber and Newman 10 explored the effects of MPL in terms of water management using a two-phase flow and membrane model. Their simulation predicted that the MPL acts as a valve that pushes water away from the GDL in the cathode side through the membrane and accordingly minimizes flooding. Yan et al.11 measured the net water flux transferred across the membrane under various operating conditions. They measured the net flux coefficients ranging from +0.93 to −0.2 depending on the current density and humidification of feed gases. R. Zaffou et al. 12 quantified the temperature-gradient-driven water tr...

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Solvent transoport across cation-exchange membranes under a temperature difference and under an osmotic pressure difference

Cited by 42 publications

References 5 publications

Water Transport Across a Polymer Electrolyte Membrane under Thermal Gradients

Water Transport Across a Polymer Electrolyte Membrane under Thermal Gradients

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Water Management in Polymer Electrolyte Fuel Cells through Asymmetric Thermal and Mass Transport Engineering of the Micro-Porous Layers

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