Water sorption–desorption in Nafion® membranes at low temperature, probed by micro X-ray diffraction

Pinéri, M.; Gebel, Gérard; Davies, Richard J.; Diat, Olivier

doi:10.1016/j.jpowsour.2007.05.037

Cited by 66 publications

(60 citation statements)

References 35 publications

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“…Models of non-isothermal cold starts have shown that product water gets absorbed by the membrane, substantially reducing ice formation in the cathode CL. 44 Hence, a low initial membrane water content was suggested to increase the intrinsic capability of isothermal cold starts from −30…”

Section: F1318mentioning

confidence: 99%

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

Macauley

Lujan

Spernjak

et al. 2016

J. Electrochem. Soc.

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The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (−10 • C vs. −20 • C vs. −30 • C) and increasing current density (0.02 A cm −2 vs. 0.04 A cm −2 ). Ice formation monitored using in-situ highresolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈−20 • C) and high current densities (0.04 A cm −2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈−10 • C) and lower current densities (0.02 A cm −2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (−20 • C and −30 • C).

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Section: F1318mentioning

confidence: 99%

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

Macauley

Lujan

Spernjak

et al. 2016

J. Electrochem. Soc.

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“…Some studies based on differential scanning calorimetry (DSC) [21][22][23] conclude that part of the water in the membrane is freezable, while other studies using X-ray scattering contradict these findings. 24,25 Besides product water which is diffusing back into the membrane, water is present in the electrode. Concerning the aggregate state of water inside the electrode, contradictory findings have been published.…”

mentioning

confidence: 99%

When Size Matters: Active Area Dependence of PEFC Cold Start Capability

Biesdorf

Stahl

Siegwart

et al. 2015

J. Electrochem. Soc.

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Understanding the freezing mechanism of liquid water within polymer electrolyte fuel cells (PEFC) is crucial for its commercialization for mass market. Although various publications investigated the cold start capability of PEFCs, contradictory behaviors during cold starts at freezing temperatures have been published in literature. Interestingly, differences can be mainly identified between large and small size fuel cells: the latter have a significantly higher cold start capability than large size fuel cells. In order to understand the influence of different active areas, we present measurements of cold starts performed with cells sizes of 1 and 50 cm2 using the same materials, including a large count of experiments (>200) on the 1 cm2 cells to perform statistical analysis. The cold start capability is strongly reduced with an increasing size of the active area, and the operating times changes from stochastic values for small cells to reproducible values for large cells. Both effects can be explained by the higher probability of the aggregate state transition from super-cooled water to ice in large cells. Consequently this paper highlights the implications of downscaling PEFCs to draw conclusions for technical relevant cold-starts.

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“…It is assumed with reference to [3] that some water desorbs out of the membrane during cooling down, crystallises inside the Cathode Catalyst Layer (CCL) and finally leads to the reduction of the Pt active area. The CSP is then performed until the amount of water produced by one cell reaches 0.45 mg⋅cm -2 .…”

Section: Cyclic Voltammetry and Linear Voltammetry Resultsmentioning

confidence: 99%

“…The lower the temperature is, the higher the electronic resistance. This phenomenon is described in [3] and is linked with the water desorption in Nafion ® membranes at low temperature. The growth of the resistance is a consequence of the decrease of the liquid phase of water inside the membranes during the cooling down process.…”

Section: Spectroscopy Experiments During Cold Startsmentioning

confidence: 98%

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Electrochemical characterisation of fuel cell stack during cold start

Harel¹,

Bégot²,

Wasterlain³

et al. 2011

Eur. Phys. J. Appl. Phys.

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Fuel cell self start at negative temperature conditions is not an easy task due to the water produced by the reduction of oxygen at the cathode. This amount of water can turn into ice and block the reaction before the temperature inside the fuel cell reaches positive values. The mechanism of the physical process which leads to oxidant starvation phenomena when ice appears is not yet well identified. In order to obtain a deeper understanding of this problem, the article presents some experimental investigations conducted on a short fuel cell stack. These experiments simulate vehicle technology operated in cold start conditions not with the primary objective to reach a successful and rapid start-up but much rather to characterise and understand the cold start phenomena until starvation occurs. A number of polarisation curves, electrochemical spectroscopy and cyclic voltammetry measurements are done on the stack before, after and also during the cold starts experiments. It is observed that the process of drying and cooling down prior to cold start have a great impact on the electrochemical cathode area. The results obtained show the evolution of the stack behaviour during the low temperature operation with a slow production of frost. The consequence on the individual cells in terms of inhomogeneous degradation is highlighted.

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Water sorption–desorption in Nafion® membranes at low temperature, probed by micro X-ray diffraction

Cited by 66 publications

References 35 publications

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

When Size Matters: Active Area Dependence of PEFC Cold Start Capability

Electrochemical characterisation of fuel cell stack during cold start

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