Hydrophilicity and hydrophobicity study of catalyst layers in proton exchange membrane fuel cells

Yu, Hongmei; Ziegler, Christoph; Oszcipok, M.; Zobel, Marco; Hebling, Christopher

doi:10.1016/j.electacta.2005.06.036

Cited by 115 publications

(87 citation statements)

References 15 publications

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“…MEA50 is still highly hydrophobic even though Nafion is already occupying more space in the catalyst layer, while with a further increase in Nafion content (MEA70) the surface becomes less hydrophobic. The contact angles of MEA50 are in the same range as the contact angles 13 measured on commercial catalyst coated membranes for hydrogen polymer electrolyte fuel cells (144-150°) [46], while on the other hand, the contact angle on MEA70 (112°) is similar to that of a clean Nafion film hydrated at 90 °C (~110°) [47] indicating that Nafion is covering almost the whole surface of the catalyst layer. A hydrophobic nature of the catalyst layer is good for the removal of gaseous CO2 produced through the oxidation of methanol, though a highly hydrophobic surface may prevent the proper wetting of the catalyst layer and the membrane leading to a decrease in their ionic conductivities.…”

Section: Fuel Cell Experimentssupporting

confidence: 58%

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

Kanninen

Borghei

Ruiz

et al. 2012

International Journal of Hydrogen Energy

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The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion ® contents (30, 50 and 70 wt % or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities. During the 9-day measurement at a constant current, the performance of MEA30 decreased the most (-124 µV h -1 ), while the MEA50 was almost stable (-11 µV h -1 ) and performance of MEA70 improved (+115 µV h -1 ). After the measurement, the MEA50 remained the best MEA in terms of performance. The optimum anode Nafion content for commercial Vulcan carbon black supported PtRu catalysts is between 20 and 40 wt %, so the GNF-supported catalyst requires more Nafion to reach its peak power. This difference is explained by the tubular geometry of the catalyst support, which requires more Nafion to form a penetrating proton conductive network than the spherical Vulcan.Mass transfer limitations are mitigated by the porous 3D structure of the GNF catalyst layer and possible changes in the compact Nafion filled catalyst layers during constant current production.2

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Section: Fuel Cell Experimentssupporting

confidence: 58%

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

Kanninen

Borghei

Ruiz

et al. 2012

International Journal of Hydrogen Energy

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“…Yu et al investigated the contact angle of membranes and of catalyst layers composed of Pt/C and ionomer by the sessile drop method and by environmental scanning electron microscopy. 48 For a Nafion membrane they observed a decrease of the contact angle from initially 93.9…”

Section: Journal Of the Electrochemical Society 163 (11) F3179-f3189mentioning

confidence: 99%

Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance

Bernt

Gasteiger

2016

J. Electrochem. Soc.

278

267

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In this study, the influence of ionomer content in IrO 2 /TiO 2 anode electrodes for a proton exchange membrane (PEM) electrolyzer is investigated (Nafion 212 membrane; 2.0 mg Ir cm −2 / 0.35 mg Pt cm −2 (anode/cathode)) and the contributions of ohmic losses, kinetic losses, proton transport losses in the electrodes, and mass transport losses to the overall cell voltage are analyzed. Electrolysis tests are performed with an in-house designed high pressure electrolyzer cell at differential pressure up to 30 bar. The best performance is obtained for an ionomer content of 11.6 wt% and a cell voltage of 1.57 V at 1 A cm −2 and less than 2 V at 6 A cm −2 (ambient pressure, 80 • C). Performance losses at lower ionomer contents are the result of a higher proton conduction resistance. For higher ionomer contents, on the other hand, performance losses can be related to a filling of the electrode void volume by ionomer, leading to a higher O 2 mass transport resistance, an increased electronic contact resistance, and the electronic insulation of parts of the catalyst by ionomer. At high pressure operation, the performance corrected by the shift of the Nernst voltage increases with H 2 pressure and we propose a new explanation for this effect. In the course of the transition from fossil-based to renewable energy sources, hydrogen technology has gained considerable attention during the past decades. Proton exchange membrane (PEM) electrolyzers are well suited to be coupled with intermittent energy sources such as wind and solar and could provide electrolytic hydrogen for long-term energy storage or fuel cell mobility. At the moment, the large-scale application of PEM electrolyzers is still hindered by their high capital costs.1,2 One attempt to overcome this challenge is to increase the H 2 output by operating an electrolyzer at current densities much higher than the values typically reported in the literature (1-2 A cm −2 ). 2 Recent publications have shown that current densities of 5 A cm −2 and higher are possible. 3,4 Another factor that can be economically beneficial is the operation at high pressure because it allows direct storage of H 2 without subsequent mechanical compression. However, high-pressure operation leads to more demanding materials requirements, imposes additional safety precautions, and reduces the faradaic efficiency due to a higher gas permeation through the membrane. 5,6 It was reported that an operating pressure of 30-45 bar could be a good compromise, 7 with differential pressure operation ( p O 2 ≈ ambient pressure) being more efficient than balanced pressure operation ( p O 2 ≈ p H 2 ).8 However, increasing the current density and the operating pressure of an electrolyzer will increase the cell voltage, leading to a lower overall voltage efficiency and thus higher operating costs. Since the latter are, along with the capital costs, one of the main cost drivers for large-scale applications, 9 minimizing cell voltage at high current densities and pressures is essential for economic competitiveness...

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“…The external CL contact angle has been measured in references. 42,43,44 However, a direct measurement of the CL internal contact angle has not been reported. In this study, the hydrophobic contact angle used in the CL is 93…”

Section: F532mentioning

confidence: 99%

A Mixed Wettability Pore Size Distribution Based Mathematical Model for Analyzing Two-Phase Flow in Porous Electrodes

Zhou

Pütz

Secanell

2017

J. Electrochem. Soc.

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A multi-dimensional, non-isothermal, two-phase membrane electrode assembly (MEA) numerical model is developed where the micro-structure of the porous layers is characterized by a mixed wettability pore size distribution (PSD). The PSD model is used to predict local water saturation based on gas and liquid pressures, and can be used to study the effect of varying pore size and wettability. The MEA model accounts for gas transport via molecular and Knudsen diffusion, liquid water transport, sorbed water transport by back-diffusion, electro-and thermo-osmosis, and heat generation and transport. Multi-step kinetic models are used to predict anode and cathode electrochemical reactions. Local transport losses are accounted for using a local transport resistance. The PSD model is used to predict capillary pressure vs. saturation and saturation vs. relative liquid permeability curves based on PSDs from several GDLs obtained using mercury intrusion porosimetry. The PSD-based MEA model electrochemical performance predictions are also compared to experimental data from the literature. Results show that the numerical model is able to capture the performance changes associated with varying temperate and the introduction of a micro-porous layer. Improving the performance of polymer electrolyte fuel cells (PEFCs) at high current density is critical for reducing stack size, cost and weight in automobile applications. Water accumulation in the electrode however, limits fuel cell performance at high current densities. [1][2][3] In order to mitigate the excessive water buildup in the cell, which hinders mass transport, gas diffusion layer (GDL) and catalyst layer (CL) microstructures and wettabilities must be advanced to achieve sufficient water retention in the electrolyte, reject excess water in vapor form and alleviate complete flooding of the electrode. For example, by modifying the weight percentage (wt%) of the hydrophobic content in the GDL, Wang et al. 4 reported a 10%-20% increase in performance. To understand fuel cell behavior in the two-phase region and optimize the design of GDL and CL, a two-phase model which includes microstructural information of the porous layers is needed.Two approaches have commonly been used to study liquid water transport in fuel cells. The first approach involves the solution of a saturation equation obtained by replacing liquid pressure by saturation in Darcy's law. [5][6][7] In this approach the Levertt J-function is commonly used to relate saturation with capillary pressure. The Leverett J-function is however, an empirically measured curve for a given material and it is obtained from porous media structure analysis. Thus, it is difficult to optimize the structure of the porous layers using Leverett J-functions. The second approach, known as the multi-phase approach, involves solving mass and momentum equations for gas and liquid phases independently and then relating the capillary pressure to saturation using a closure equation based on micro-structural information such as a pore size dist...

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Hydrophilicity and hydrophobicity study of catalyst layers in proton exchange membrane fuel cells

Cited by 115 publications

References 15 publications

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance

A Mixed Wettability Pore Size Distribution Based Mathematical Model for Analyzing Two-Phase Flow in Porous Electrodes

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Hydrophilicity and hydrophobicity study of catalyst layers in proton exchange membrane fuel cells

Cited by 115 publications

References 15 publications

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell

Influence of Ionomer Content in IrO2/TiO2Electrodes on PEM Water Electrolyzer Performance

A Mixed Wettability Pore Size Distribution Based Mathematical Model for Analyzing Two-Phase Flow in Porous Electrodes

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Product

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Influence of Ionomer Content in IrO₂/TiO₂Electrodes on PEM Water Electrolyzer Performance