Mass transfer through polymer membranes due to a temperature gradient

Tasaka, Masayasu; Mizuta, Takao; Sekiguchi, Osamu

doi:10.1016/s0376-7388(00)82079-7

Cited by 54 publications

(42 citation statements)

References 17 publications

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“…Figure 4 shows that there was no water movement for sufficient duration under the 10 °C temperature gradient at the average cell temperature, 65 °C. This result agrees with the literature that porous membrane with large pores shows negligible thermo-osmotic water flux, due to negligible entropy change between bulk water and water in the porous membrane (14). Figure 3 also shows that water accumulated in the hot side increased linearly with time for the assembly of reinforced A membrane and SGL 10AA diffusion media, indicating water flows from the cold side to the hot side.…”

Section: Resultssupporting

confidence: 90%

“…Thermo-Osmotic Water Flux of Different Membranes Figure 5 shows that thermo-osmotic water flux in the Nafion ® 112 membrane increases linearly with temperature difference between two flow-field plates, and increases with cell average temperature. Note that the water flux direction is from the cold to hot side, which agrees with the literature for Nafion ® membranes (14,16). The thermo-osmotic water flux in reinforced A and reinforced B membranes also linearly increased with temperature difference and increased with membrane average temperature.…”

Section: Resultssupporting

confidence: 88%

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Temperature Gradient Induced Water Transport in Polymer Electrolyte Fuel Cells

Kim

Mench

2008

ECS Trans.

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The objective of this work is to investigate water transport of polymer electrolyte fuel cell (PEFC) materials subjected to a temperature gradient. Direct thermo-osmotic experiments on different polymer membrane types (non-reinforced Nafion ® , reinforced A, and reinforced B membrane) were performed using an in-house fuel cell fixture with a parallel flow field. Thermoosmotic flow was observed in all membranes, and the water flow direction (in the membrane only) was determined to always flow from the cold side to the hot side. The water flux was found to be proportional to temperature gradient and increased with average temperature. The dependency of the thermo-osmotic diffusivity on average temperature showed predictable Arrhenius-type behavior. For the membrane electrode assembly (MEA), net flow was determined to be from the hot to cold side due to a phase-change effect, which will be discussed in detail in a later publication. Interface temperatures of membrane were estimated using 2-dimensional thermal model, leading to empirical relations of thermo-osmotic diffusivity across the membrane.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 88%

Temperature Gradient Induced Water Transport in Polymer Electrolyte Fuel Cells

Kim

Mench

2008

ECS Trans.

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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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“…Depending on the type of charged membrane, the thermo-osmotic coefficient may have positive or negative values. Tasaka et al 22 observed movement of water from the cold to hot side for a hydrophilic membrane and reversed flux for a hydrophobic membrane. They have also argued that the physical reason for this motion was based on the entropy change.…”

Section: Temperature-gradient-driven Water Transport Modes In Pefc Comentioning

confidence: 99%

Model to Predict Temperature and Capillary Pressure Driven Water Transport in PEFCs After Shutdown

Khandelwal

Lee

Mench

2009

J. Electrochem. Soc.

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To enhance durability and cold-start performance of polymer electrolyte fuel cells ͑PEFCs͒, residual water in the fuel cell components must be minimized during operation and after shutdown. A transient two-phase mathematical and computational model is developed to describe water redistribution in the PEFC components after shutdown, which for the first time includes thermo-osmotic flow in the membrane. The model accounts for capillary and phase-change induced flow in the porous media and thermo-osmotic and diffusive flow in the polymer membrane. In the porous media, liquid-water flow is dominated by capillary transport until irreducible saturation is achieved, after which water removal is dominated by phase-change induced flow. In the membrane, thermo-osmotic flow can significantly help or hinder water drainage from the catalyst layer, depending on the situation. During shutdown to the frozen state, residual water at the cathode can be controlled, and freeze damage can be avoided, through balancing the phase-change induced flux in the diffusion media with the net balance of thermo-osmosis and diffusion flux in the membrane.Fuel cell technology faces a number of technical challenges for automotive application that must be surmounted in order to compete against the internal combustion engine. Two key issues of fuel cell durability and cold-start performance have gained considerable attention. 1-4 Apart from various design choices and operating conditions, one of the key parameters affecting durability and cold-start performance is the residual water redistribution in the fuel cell components.Recent studies performed by Mench and co-workers have shown that residual water plays a key role in freeze-damage 4-7 and fuel cell cold-start ability. 8-10 Khandelwal et al. 8,9 have shown that if not purged, almost 15-20% of the total energy required to achieve successful cold start can be consumed in melting ice. Studies performed by Kim and Mench 4 have identified various physical degradation modes and have shown that liquid water in contact with the catalyst layer ͑CL͒ must be minimized to mitigate damage. Cho et al. 11 showed that gas purge or solution purge can be used to reduce the residual water, preventing fuel cell degradation. Garzon et al. 2 also investigated the impact of freeze-thaw cycling on fuel cell components and properties and recommended that a membrane water content of ϳ7-12 ͑corresponding to vapor-equilibrated membrane͒ represents an ideal situation for minimum freeze-damage.Neutron-imaging studies 12-14 have shown images of liquid-water redistribution during normal operation and after fuel cell shutdown. Most of the imaging studies have focused on the design or material changes or operating condition variations. Currently, various purging methods are being utilized to minimize the residual water in the fuel cell. In practice, purge is traditionally restricted to a short duration due to the high parasitic energy requirement. Recently, various nonparasitic methods using temperature gradients 15,16 have g...

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Mass transfer through polymer membranes due to a temperature gradient

Cited by 54 publications

References 17 publications

Temperature Gradient Induced Water Transport in Polymer Electrolyte Fuel Cells

Temperature Gradient Induced Water Transport in Polymer Electrolyte Fuel Cells

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

Model to Predict Temperature and Capillary Pressure Driven Water Transport in PEFCs After Shutdown

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