Membrane Degradation Mechanism Research Articles

Chemical Degradation Mechanism of Membranes for Alkaline Membrane Fuel Cells

not Available.

Effect of open circuit voltage on degradation of a short proton exchange membrane fuel cell stack with bilayer membrane configurations

In the present work, membrane electrode assembly degradation of a 4-cell stack with specially designed twin catalyst coated membranes (twin-CCMs) was carried out for 1600h under open circuit voltage (OCV) conditions. Four types of membrane with various thicknesses were employed in the experiment. Each twin-CCM was composed of two membranes of the same type with a catalyst layer coated only on one side. The purpose of this special configuration was to facilitate postmortem analysis of the membrane after degradation due to the detachable membrane structure. By means of several in situ electrochemical measurements, the performance of the individual cells was analysed every 200h during the degradation process. Postmortem analyses such as scanning electron microscopy, atomic force microscopy, and infrared imaging were also conducted to identify the membrane degradation mechanisms after exposure to OCV. The results indicate that membrane degradation, which correlates with electrode degradation, is the most direct reason for the failure of the whole cell/stack during OCV operation, especially for cells with thinner membranes.

C222 PEFC電解質膜内電位分布に及ぼす運転条件の影響(OS-5:燃料電池関連研究の新展開(II))

Potential distribution in the electrolyte membrane in the MEA of PEFC has been measured in order to help understand a recently suggested membrane degradation mechanism caused by Pt band. A thin metallic probe, Pt, is inserted in membrane to measure the potential distribution. The potential in the membrane at a certain position are measured under several experimental conditions, for example, cathode gas oxygen concentration, cell current density and so forth. As a result, it is found that the potential are influenced by several experimental conditions.

Membrane Degradation Mechanisms and Accelerated Durability Testing of Proton Exchange Membrane Fuel Cells

Molecular H2 and O2 reacting on the surface of Pt catalyst to form the membrane degrading species is the dominating membrane degradation mechanism in PEMFCs; not the formation of active oxygen species from H2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction. The source of H2 or O2 is from the reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H2 and O2 at the catalyst. The membrane degradation rate also depends on the residence time of the species in the membrane and the volume of the membrane. The sulfonic acid groups in the Nafion side chain are key to the mechanism by which the radical species attack the polymer.

Membrane Degradation Mechanisms and Accelerated Durability Testing of Proton Exchange Membrane Fuel Cells

not Available.

Hygrothermal aging of Nafion ®

The membrane durability is a critical issue for the development of Proton Exchange Membrane Fuel Cells (PEMFC). Since PEMFC in situ tests were not conclusive to determine Nafion ® membrane degradation mechanism, ex situ aging tests were performed on Nafion ® 112 in practical fuel cell usage conditions. The polymer chemical structure evolution was investigated by infrared spectroscopy (IR) and Nuclear Magnetic Resonance (NMR) while its hydrophilicity, directly linked to its protonic conductivity, is established through sorption isotherms by Dynamical Vapour Sorption (DVS). Durability studies over a period of 400 days revealed membrane degradation through a modification of sulfonic acid end-groups. Formation of sulfonic anhydride (from the condensation of sulfonic acids) was strongly demonstrated by IR spectroscopy and, indirectly, by NMR. The substitution of ionic end-groups by less hydrophilic anhydrides leads to a significant decrease of water uptake and thus of its hydrophilicity. Surprisingly, kinetic study reveals that the hygrometric level accelerates this condensation reaction.

R&D of Asahi Kasei Aciplex Membrane for PEM Fuel Cell Applications

Asahi Kasei Chemicals Co. (AKC) has been developing and producing perfluorinated ionomer membrane for PEFC (PEM) to become new business as the core of membrane and energy business in the future. Recently we focus on R&D of PEM for both stationary and automotive application. In this paper, our latest achievement is summarized and elucidation of membrane degradation mechanism is also conducted.

Membrane degradation mechanism during open-circuit voltage hold test

A detailed analysis is made of the relation between the degradation behavior of a membrane electrode assembly (MEA) and deposited Pt (Pt band) in the membrane during an open-circuit voltage (OCV) hold test. Molecular-structural changes in the membrane are investigated by micro-Raman spectroscopy. When the Pt band was not significantly observed in the membrane after the test, the membrane is relatively stable. In contrast, when the Pt band was clearly formed, the membrane around it was intensively degraded. The magnitude of the fluoride ion emission rate (FER) of the effluent water from the anode and the cathode was also consistent with the location of the Pt band. It was verified that the Pt band is one of the factors accelerating membrane degradation, and the catalyst materials strongly affects the degradation. Besides, not the cation transport which enhances the degradation but the kinetics of either the H 2O 2 and/or hydroxyl radical production might be the rate determining step.

Review: Durability and Degradation Issues of PEM Fuel Cell Components

AbstractBesides cost reduction, durability is the most important issue to be solved before commercialisation of PEM Fuel Cells can be successful. For a fuel cell operating under constant load conditions, at a relative humidity close to 100% and at a temperature of maximum 75 °C, using optimal stack and flow design, the voltage degradation can be as low as 1–2 μV·h. However, the degradation rates can increase by orders of magnitude when conditions include some of the following, i.e. load cycling, start–stop cycles, low humidification or humidification cycling, temperatures of 90 °C or higher and fuel starvation. This review paper aims at assessing the degradation mechanisms of membranes, electrodes, bipolar plates and seals. By collecting long‐term experiments as well, the relative importance of these degradation mechanisms and the operating conditions become apparent.

Chlorine Resistant Membrane and The Mechanism of Membrane Degradation by Chlorine

Polyamide reverse osmosis membrane used successfully for water desalination is made from the interfacial reaction of meta-phenylenediamine (MPD) with trimesoyl chloride. One problem with the membrane is that its performance is deteriorated upon prolonged exposure to chlorine often used for disinfecting feed water. ATR-FTIR and XPS analysis show chlorine reacts with the amide hydrogen and is attached to the polyamide membrane. A chlorine resistant membrane has been made using a non-MPD amine and appears to be five times as chlorine-resistant as the MPD-based membrane. ATR-FTIR and XPS analysis also show the chlorine-resistant membrane picks up chlorine much less than the MPD-based membrane upon exposure to chlorine. Monochloramine does not appear to affect adversely polyamide membranes.

Effect of Relative Humidity on Membrane Degradation Rate and Mechanism in PEM Fuel Cells

The degradation rates and mechanisms of catalyst coated Nafion 212 membranes were investigated at a series of relative humidifies (RH). Degradation studies at open circuit voltage (OCV) showed that membrane degradation rates were faster at 60% RH than at 20% or 100% RH. Degradation studies performed under load (0.6V) showed that membrane degradation rates significantly increased after switching from high RH (100%) to low RH (25%) after 500 hours. This accelerated degradation was likely due to the dual effects of mechanical and chemical degradation. Gas chromatography performed on fuel cell exhaust gases has shown increased gas permeability at increased RH, but cannot fully explain the change of degradation rates with RH. A model is proposed to explain the effect of RH on membrane degradation rate. RH impacts the formation of oxygen radicals via both reactant concentration and reaction rate. Increased RH leads to higher gas permeability of hy drogen and oxygen thus higher reactant concentrations for oxygen radical formation. Conversely, the platinum surface tends to be more highly oxidized at high RH, lowering the reaction rates for oxygen radical formation. The tradeoffs between these phenomenon result in a higher membrane degradation rate at 60% RH than at either 20% or 100% RH for the conditions presented.

Development of a Method for Clarifying the Perfluorosulfonated Membrane Degradation Mechanism in a Fuel Cell Environment

A gas-phase exposure method in which a membrane was exposed to gaseous hydrogen peroxide to simulate the polymer electrolyte fuel cells (PEFC) environment was introduced to accelerate and assess membrane degradation. Gaseous hydrogen peroxide is able to degrade a membrane in the same manner as an actual fuel cell operation. This method is suitable for clarifying the membrane degradation mechanism because a membrane is degraded uniformly without contamination and mechanical degradation. The degradation mechanism of perfluorosulfonated membrane in a PEFC environment was investigated using the gas-phase exposure method. An increase in the number of carboxyl groups and a rapid drop of molecular weight in degraded membrane with time exposed to gaseous hydrogen peroxide was observed. We concluded that degradation of the perfluorosulfonated membrane was composed of the following two modes: (i) unzipping reaction at unstable polymer end groups and (ii) scission of main chains and forming new unstable polymer end groups at severed points. It is very likely that membranes can be degraded by hydrogen peroxide alone; ferrous ions are not necessary for membrane degradation.

Membrane Degradation Mechanisms in PEMFCs

Nafion membrane degradation was studied in a polymer electrolyte membrane fuel cell (PEMFC) under accelerated decay conditions. Fuel cell effluent water was analyzed to determine the fluoride emission rate. Experimental findings show that formation of active oxygen species from decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs. Instead, membrane degradation occurs because molecular and react on the surface of the Pt catalyst to form the membrane-degrading species. The source of or is from reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of and at the catalyst. The membrane degradation rate also depends on the residence time of active oxygen species in the membrane and volume of the membrane. The sulfonic acid groups in the Nafion side chain are key to the mechanism by which radical species attack the polymer.

Effect of Relative Humidity on Membrane Degradation Rate and Mechanism in PEM Fuel Cells

not Available.

Soluble EMMPRIN (extra-cellular matrix metalloproteinase inducer) stimulates the migration of HEp-2 human laryngeal carcinoma cells, accompanied by increased MMP-2 production in fibroblasts

The basement membrane functions as a barrier against the invasion of cancer cells. It is therefore important to investigate the mechanism of basement membrane degradation by matrix metalloproteinases (MMPs). Previously, cancer cells were long considered to be the major source of MMPs; however, current evidence indicates that most MMPs in cancer tissue are produced by stromal rather than cancer cells. A glycoprotein highly expressed on the cancer-cell membrane, EMMPRIN (extra-cellular matrix metalloproteinase inducer), exhibits the potential role of the MMP inductor in stromal cells. Depending on the cell type, EMMPRIN can stimulate the production of MMP-1, MMP-2, and MMP-3. We here report that soluble full-length EMMPRIN is liberated from HEp-2 human laryngeal epidermoid carcinoma cells, probably via microvesicle shedding. Soluble EMMPRIN stimulates human fibroblasts to produce MMP-2, after which the augmented migration of HEp-2 cells occurs, as observed in an invasion chamber assay with separately cultured fibroblasts. An anti-EMMPRIN function-blocking antibody reduced MMP-2 activity in the conditioned medium and inhibited the migration of HEp-2; obviously, EMMPRIN activity contributes to cancer-cell migration. We postulate that soluble EMMPRIN probably triggers the promotion of cancer invasion in vivo.

Membrane Degradation Mechanisms in PEMFCs

Based on experimental findings it is suggested that formation of active oxygen species from H2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs, instead it is the molecular H2 and O2 that react on the surface of the Pt catalyst to form the membrane degrading species. The source of H2 or O2 is from reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H2 and O2 at the catalyst. The membrane degradation rate also depends on the residence time of the species in the membrane and the volume of the membrane. The sulfonic acid groups in the Nafion® side chain are key to the mechanism by which the radical species attack the polymer.

Effect of Catalyst Properties on Membrane Degradation Rate and the Underlying Degradation Mechanism in PEMFCs

Nafion membrane degradation was studied in a polymer electrolyte membrane fuel cell (PEMFC) under accelerated decay conditions. Fluoride emission rate (FER) determined by fuel cell effluent water analysis was used to quantify the membrane degradation. Membrane degradation is most likely caused either directly or indirectly by the species formed as a result of the and reaction on the catalyst. To further understand the mechanism, the effects of the catalyst location, type, its interaction with and , and cell current density on the FER were investigated and their implications on the underlying membrane degradation mechanism are discussed.

Membrane Degradation Mechanisms in PEMFCs

not Available.

Polymer Electrolyte Membrane Degradation Mechanisms in Fuel Cells - Findings Over the Past 30 Years and Comparison with Electrolyzers

This paper summarizes some of the progress that has been made over the past 30 years in identifying chemical and mechanical degradation mechanisms in proton-exchange membrane fuel cells (PEMFCs), as well as approaches in refining stack operating conditions, cell hardware configurations and membrane- electrode assembly (MEA) stabilization to mitigate degradation and extend life. New analytical methods have been brought to bear to understand the relationships between PEM degradation and fuel cell operating conditions, especially low relative humidity, elevated temperatures, and frequent open-circuit periods. PEM/MEA degradation similar to that observed in PEMFC may also occur under certain accelerating conditions for proton-exchange membrane water electrolyzers (PEMELCs) that typically operate for 30 to 100 thousand hours without incident when properly hydrated, thermally managed and mechanically supported. A comparison is made of common hardware and operational factors for PEMELCs and PEMFCs that can lead to PEM/MEA degradation.

Role of Anode and Cathode in Membrane Degradation Mechanism in PEM Fuel Cell

not Available.