Investigation of membrane degradation in polymer electrolyte fuel cells using local gas permeation analysis

Kreitmeier, Stefan; Schuler, Gabriel A.; Wokaun, Alexander; Büchi, Félix N.

doi:10.1016/j.jpowsour.2012.03.071

Cited by 71 publications

(51 citation statements)

References 21 publications

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“…1,2 Furthermore, during typical operation, cells experience both chemical and mechanical stresses simultaneously, which results in synergy between the degradation modes. Localized mechanical stresses increase PEM susceptibility to radical attack by reducing the activation energy necessary for such attacks to proceed 3,4 and chemical degradation of the ionomer diminishes the bulk mechanical properties of the PEM, such as ultimate tensile strength, strain-to-failure, and fracture toughness, which further increases its susceptibility to physical failure. [5][6][7][8][9][10][11] Owing to its rapid and regenerative redox with radical species and stability in acidic media, 7 cerium dramatically improves PEM durability by neutralizing radicals before they attack the ionomer.…”

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confidence: 99%

Cerium Migration during PEM Fuel Cell Accelerated Stress Testing

Baker¹,

Mukundan²,

Spernjak³

et al. 2016

J. Electrochem. Soc.

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Cerium is a radical scavenger which improves polymer electrolyte membrane (PEM) fuel cell durability. During operation, however, cerium rapidly migrates in the PEM and into the catalyst layers (CLs). In this work, membrane electrode assemblies (MEAs) were subjected to accelerated stress tests (ASTs) under different humidity conditions. Cerium migration was characterized in the MEAs after ASTs using X-ray fluorescence. During fully humidified operation, water flux from cell inlet to outlet generated in-plane cerium gradients. Conversely, cerium profiles were flat during low humidity operation, where in-plane water flux was negligible, however, migration from the PEM into the CLs was enhanced. Humidity cycling resulted in both in-plane cerium gradients due to water flux during the hydration component of the cycle, and significant migration into the CLs. Fluoride and cerium emissions into effluent cell waters were measured during ASTs and correlated, which signifies that ionomer degradation products serve as possible counter-ions for cerium emissions. Fluoride emission rates were also correlated to final PEM cerium contents, which indicates that PEM degradation and cerium migration are coupled. It is proposed that cerium migrates from the PEM due to humidification conditions and degradation, and is subsequently stabilized in the CLs by carbon catalyst supports. Widespread adoption of polymer electrolyte membrane (PEM) fuel cell technology is currently hindered by insufficient component durability and high cost.1 During operation, reactive radical species generated by electrochemical fuel cell processes attack vulnerable functional groups in the ion-conducting, or ionomer, molecules which constitute the PEM and are present in the catalyst layers (CLs).2 These attacks reduce PEM thickness and generate local pinholes, which release hydrofluoric acid (HF), sulfuric acid (H 2 SO 4 ), and fluorinated polymer fragments into effluent cell waters; increase crossover of reactant gases through the PEM; and lead to cell failure.1,2 Since the PEM is constrained by cell hardware, hygrothermal cycling generates mechanical stresses which cause physical damage to the PEM in the form of cracks, tears, and pinholes.1,2 Furthermore, during typical operation, cells experience both chemical and mechanical stresses simultaneously, which results in synergy between the degradation modes. Localized mechanical stresses increase PEM susceptibility to radical attack by reducing the activation energy necessary for such attacks to proceed 3,4 and chemical degradation of the ionomer diminishes the bulk mechanical properties of the PEM, such as ultimate tensile strength, strain-to-failure, and fracture toughness, which further increases its susceptibility to physical failure. 5-11Owing to its rapid and regenerative redox with radical species and stability in acidic media, 7 cerium dramatically improves PEM durability by neutralizing radicals before they attack the ionomer. Cerium ions may be directly exchanged with protons in the ionomer 12,13 or ...

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confidence: 99%

Cerium Migration during PEM Fuel Cell Accelerated Stress Testing

Baker¹,

Mukundan²,

Spernjak³

et al. 2016

J. Electrochem. Soc.

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“…Hydrogen permeation occurs in the bulk of the membrane and is driven by the hydrogen concentration gradient between the anode and cathode. Convection occurs when pinholes are formed in the membrane and reach a diameter typically greater than 0.5 mm [5].…”

Section: Diagnostic Tool Characterizationmentioning

confidence: 99%

“…[4,5] used a gas tracer concept to measure the amount of transfer leak. They supplied hydrogen with 10% helium to the anode and measured helium cross over using a mass spectrometer at the cathode.…”

Section: Introductionmentioning

confidence: 99%

“…This technique allowed them to monitor the development of transfer leaks under operating conditions. Furthermore, by adding tubes along the cell channel, they were able to measure the spatial distribution of the leaks, and by systematic change of anode pressure, they were able to separate cross over caused by convection vs. permeation [5]. While this technique is can accurately identify the rate and location of transfer leaks, it is not suitable for detecting leak rates in a typical fuel cell stack, as each individual cell requires a separate outlet for sampling the tracer gas.…”

Section: Introductionmentioning

confidence: 99%

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In-situ diagnostic tools for hydrogen transfer leak characterization in PEM fuel cell stacks part I: R&D applications

Niroumand

Pooyanfar

Macauley

et al. 2015

Journal of Power Sources

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h i g h l i g h t sIn-situ diagnostic tool to quantify hydrogen transfer leaks in PEM fuel cell stacks. Closed form relationship for the rate of hydrogen transfer leak. Requires hydrogen/nitrogen supply to anode/cathode with anode overpressure. Requires pressure, flow, temperature, humidity, and OCV measurements. Accurately estimates leak in each cell of a stack, suitable for R&D applications. a b s t r a c tThis paper describes a diagnostic tool for in-situ characterization of hydrogen transfer leak in individual cells of a Polymer Electrolyte Membrane (PEM) fuel cell stack, suitable for Research and Development (R&D) applications. The technique is based on supplying hydrogen and nitrogen to the anode and cathode of a PEM fuel cell stack while maintaining a prescribed anode overpressure. Under these conditions, hydrogen crosses over from the anode to the cathode, and the Open Circuit Voltage (OCV) represents the ratio of hydrogen partial pressure in the two electrodes. It is shown that by measuring temperature, pressure, flow, humidity, and individual OCVs, the proposed technique can accurately estimate the rate of hydrogen transfer leak in individual cells of a PEM fuel cell stack. This diagnostic tool is suitable for characterizing hydrogen transfer leaks during fuel cell R&D, as it only requires gasses and measurements that are readily available on fuel cell test stations, and does not need disassembling or modifying the fuel cell stack.

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“…The electrodes are connected to a Interface 1000 Gamry potentiostat, trials were carried out at constant potential difference (potentiostatic mode) of 1 V, 1.23 V, 1.5 V for a period of 10 minutes and continuous samples were taken to determine the concentration and the variation of the volume of water within the cell [7,8]. Figure 2 shows a photograph of the equipment configuration used.…”

Section: Degree Of Conversionmentioning

confidence: 99%