Water Permeation Through Catalyst-Coated Membranes

Adachi, Makoto; Romero, Tatiana; Navessin, Titichai; Xie, Zhong; Shi, Zhiqing; Mérida, Walter; Holdcroft, Steven

doi:10.1149/1.3357339

Cited by 13 publications

(8 citation statements)

References 31 publications

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“…It is unclear how the large area of the gas/ionomer interface in the electrodes of a fuel cell would affect the interfacial resistance. A recent study reported no change in interfacial resistance when electrodes were coated on the membrane, suggesting that the resistance might be a property that is specific to the membrane. One explanation would be that the interfacial transport resistance is a result of less-connected water channels at the gas/membrane interface.…”

Section: Resultsmentioning

confidence: 98%

Interfacial Water Transport Measurements in Nafion Thin Films Using a Quartz-Crystal Microbalance

2011

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Understanding the transport of water in a polymer electrolyte membrane, for example, Nafion, is important for optimizing and predicting fuel cell performance. It had been shown that the interfacial resistance could be responsible for a significant portion of the net water transport. In this study, water vapor sorption experiments were done on thin ionomer films (0.03À3 μm thick) by supporting them on a quartz-crystal microbalance (QCM). The high mass resolution of the QCM enables determination of the membrane water content (λ) of the thin films. A slight depression of the water content was observed in very thin films. Meanwhile, study on thin ionomer films minimizes the contribution of internal water diffusion in the film and allows for simplification of the analyses. Interfacial mass-transfer and mechanical relaxation coefficients were determined as a function of water content and temperature. Empirical equations for the mass-transfer coefficient governing absorption and desorption, each as a function of temperature and ionomer water content, were proposed.

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Section: Resultsmentioning

confidence: 98%

Interfacial Water Transport Measurements in Nafion Thin Films Using a Quartz-Crystal Microbalance

2011

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“…However, ex situ measurements of liquid and vapor water permeability through PFSA ionomer membranes and membranes coated with catalyst layers indicate that the catalyst layer exerts no influence on the interfacial water sorption/desorption kinetics of the membrane interfaces and that the bottleneck for water transport across catalyst-coated membranes appears to be related to the membrane. 117 Since it has previously been shown that significant interfacial water transport processes exist, these contradictory observations lead to the questions regarding the location, nature, and function of the membrane/ionomer interface in catalyst layer and how it influences interfacial water transport. While the TEM image and cartoon illustration 118 shown below (Figure 12) provide some insight into the catalyst layer/membrane interface, the molecular-level description is far from complete.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

Section: Properties Of the Ionomermentioning

confidence: 99%

Fuel Cell Catalyst Layers: A Polymer Science Perspective

2013

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The polymeric ionomer plays a vital role in PEM fuel cell device technology, not simply as the membrane that transports protons and water from one electrode to another but as the binder and transport medium responsible for electrochemical activity within the catalyst layer. This perspective examines critical features of the catalyst layer ionomer. It highlights the current understanding of interactions of ionomer in catalyst inks, where the microstructure of the catalyst layer is largely formed, and in the catalyst layer itself. Properties important to the design and function of next generation ionomers and the challenges faced in replacing PFSA ionomers with hydrocarbonbased analogues are closely examined.

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“…This phenomenon was ascribed to the slow rate of water transport at the membrane interfaces. In an experimental study by Adachi et al 35 it was also seen that a catalyst layer adjacent to the membrane had negligible influence on the absorption and desorption rates. Absorption and desorption of water on the membrane interface has also been included in modeling studies by for example Berg et al, 36 Gerteisten et al, 37 and Wu et al 38 In the present study, fuel cell performance at low humidities has been studied.…”

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confidence: 95%

Studying Low-Humidity Effects in PEFCs Using EIS II. Modeling

Wiezell¹,

Holmström²,

Lindbergh³

2012

J. Electrochem. Soc.

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Electrochemical impedance spectroscopy (EIS) and steady-state models have been developed to investigate the influence of water transport on the membrane and electrode performance, with focus on the low-frequency impedance. Models for the membrane, hydrogen anode and oxygen cathode were connected in order to take the influence of water concentration on proton conductivity and hydrogen kinetics into account. At low frequencies, below 1 Hz, a pseudo-inductive loop was predicted, resulting from the overlap of the responses from anode and membrane. The anode response could be coupled to changes in the kinetics and polymer conductivity in the active layer, and the membrane response to changes in conductivity with changing water profile. The low frequency capacitive part was attributed to drying of the anode side of the membrane, while the inductive part was attributed to the rehydration of the membrane with water produced at the cathode. The loop appeared at a frequency proportional to 1/L 2 , where L is the membrane thickness. The model was successfully fitted to experimental data at different membrane thicknesses, relative humidities and current densities. The modeled data follow the same trends as experimental data, giving an increase in impedance at dry conditions and with thicker membranes.Losses in polymer electrolyte fuel cells (PEFCs) have been widely investigated. Most studies have focused on membrane resistance, as well as the cathode performance, while losses from the anode are usually assumed to be small or negligible. Common electrochemical techniques utilized to study the performance losses are steady-state polarization curves, current interrupt and electrochemical impedance spectroscopy (EIS). EIS is a powerful tool for elucidation of ratelimiting processes in PEFCs, since it can separate processes with different rate constants. However, it is sometimes challenging to distinguish between different processes taking place. When the cathode is studied using EIS, the impedance of the whole cell is usually measured, assuming that the anode impedance can be neglected and that the membrane is acting as a pure resistance.In part I of this paper, 1 low humidity effects in polymer electrolyte fuel cells (PEFCs) are studied using electrochemical impedance spectroscopy (EIS). The effect of membrane thickness, relative humidity and current density was studied experimentally with focus on a low frequency loop. The size of the loop increased with increasing membrane thickness and decreasing humidity. The response also shifted to a lower frequency with a thicker membrane. A similar loop was studied in an earlier study 2,3 in a cell with hydrogen on both sides. A full cell model was developed, including water transport in the membrane, and fitted to experimental data. It was seen that the change in water content in the membrane and anode resulted in a low frequency loop due to changes in the membrane conductivity and anode kinetics. To describe a fuel cell under real conditions, the model must also include an oxygen redu...

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Water Permeation Through Catalyst-Coated Membranes

Cited by 13 publications

References 31 publications

Interfacial Water Transport Measurements in Nafion Thin Films Using a Quartz-Crystal Microbalance

Interfacial Water Transport Measurements in Nafion Thin Films Using a Quartz-Crystal Microbalance

Fuel Cell Catalyst Layers: A Polymer Science Perspective

Studying Low-Humidity Effects in PEFCs Using EIS II. Modeling

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