The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells (original) (raw)
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The Development of New Membranes for Proton Exchange Membrane Fuel Cells
ECS Transactions, 2007
Recent work at 3M has focused on the development of solvent cast proton exchange membranes (PEM's) for use in PEM fuel cells. These new membranes are a perfluorinated sulfonic acids based on a low molecular weight perfluorinated monomer and they exhibit excellent mechanical properties and chemical stability and high ionic conductivity. The low molecular weight of the monomer allows membranes with equivalent weight as low as 800 g/mole to have good mechanical properties when hydrated. Stabilizing additives in these membranes have been shown to improve the oxidative stability in Fenton's tests. Physical property, conductivity and fuel cell tests have been performed. When incorporated into membrane electrode assemblies, these new membranes have provided excellent performance and a greater than 15-fold increase in durability under accelerated fuel cell test conditions, compared with similar commercial PEM's.
Electrochimica Acta, 2008
Perfluorinated sulfonic acid proton exchange membranes are in the forefront as solid electrolytes for fuel cell applications. Although expensive, its potential utilization in commercial fuel cells can be validated provided it can be established that it is highly durable. In this context, peroxide radical-initiated attack of the membrane electrode interface is one of the key issues requiring further systematic investigation under fuel cell operating conditions, to better determine the fundamental degradation mechanism. In this study, we attempt to analyze the durability of the membrane electrode assembly (MEA) made with different commercial electrodes from the perspective of peroxide radical-initiated chemical attack on the electrode/electrolyte interface and find the pathway of membrane degradation as well. A novel segmented fuel cell is employed for durability characterization, and use of this cell and pre and post analysis of the membrane are presented. Correlation of membrane degradation data with the peroxide yield determined by RRDE experiments is obtained. This method is able to separate the membrane evaluation process into cathode and anode aspects. Fenton type mechanism of peroxide radical generation from H 2 O 2 formed due to two-electron pathway of ORR is found to be the dominant membrane degrading factor.
Review of the proton exchange membranes for fuel cell applications
International Journal of Hydrogen Energy, 2010
Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising technology for clean and efficient power generation in the twenty-first century. Proton exchange membranes (PEMs) are the key components in fuel cell system. The researchers have focused to reach the proton exchange membrane with high proton conductivity, low electronic conductivity, low permeability to fuel, low electroosmotic drag coefficient, good chemical/thermal stability, good mechanical properties and low cost. These are classified into the "iron triangle" of performance, durability, and cost. Current PEMFC technology is based on expensive perflourinated proton-exchange membranes (PEMs) that operate effectively only under fully hydrated conditions. There is considerable application-driven interest in lowering the membrane cost and extending the operating window of PEMs. PEMFC system complexity could be reduced by the development of 'water-free' electrolytes that do not require hydration. It also enables the PEMFC to be operated under 'warm' conditions (i.e. above 100 C) thus further improving its efficiency. Capital cost could also be further reduced because at warmer conditions less Pt could be used. This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. A number of possible alternative candidates are reviewed and presented in this paper. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and durability needs of the PEM fuel cell industry. The alternative PEMs are classified into three categories: (1) modified Nafion Ò composite membranes; (2) functionalized non-fluorinated membranes and composite membranes therein; and (3) acidebase composite membranes. Several commonly used inorganic additives are reviewed in the context of composite membranes. Finally, the general methods of the measuring and evaluating of proton exchange membrane properties have been investigated such as proton conductivity, ion exchange capacity, water uptake, gas permeability, methanol permeability, durability, thermal stability and fuel cell performance test.
Journal of Applied Polymer Science, 2010
Changes in a perfluorosulfonated acid polymer membrane in membrane electrode assemblies were studied after different times under stationary conditions in fuel cells. A large series of characterizations demonstrated changes in the morphology, mechanical behavior, and thermal stability upon aging. Overall, the membrane evolution could be mainly attributed to both chemical degradation and cationic contamination. The reduction in the membrane thickness, detected by scanning electron microscopy, was ascribed to a radical unzipping mechanism and polymer chain erosion after 900 h in service. An additional monotonic decrease in the number of C tertiary F groups was observed even at 400 h. In parallel, membranes were cation-contaminated, and this led to drastic changes in the thermal and mechanical properties in the first stage of fuel-cell operation. The pollution cations were shown to have Lewis acid strengths close to 0.25 and thus strongly interacted with sulfonate anions of the membrane. The kinetic dependence of these membrane modifications and the influence of the platinum band were also examined.
Recent advances in proton exchange membranes for fuel cell applications
Chemical Engineering Journal, 2012
h i g h l i g h t s " We summarize recent developments of PEMs that maintain performance at high temperature and low relative humidity. " Three types of PEMs are evaluated: polymeric, ceramic, and inorganic-organic composite. " The advantages and limitations of three types of PEMs under different operation conditions are discussed.
Journal of The Electrochemical Society, 2009
A polymer electrolyte membrane ͑PEM͒ fuel cell model that incorporates chemical degradation in perfluorinated sulfonic acid membranes is developed. The model is based on conservation principles and includes a detailed description of the transport phenomena. A degradation submodel describes the formation of hydrogen peroxide via distinct mechanisms in the cathode and anode, together with the subsequent formation of radicals via Fenton reactions involving metal-ion impurities. The radicals participate in the decomposition of reactive end groups to form carboxylic acid, hydrogen fluoride, and CO 2 . Degradation proceeds through unzipping of the polymer backbone and cleavage of the side chains. Simulations are presented, and the numerical code is shown to be extremely time-efficient. Known trends with respect to operating conditions are qualitatively captured, and the exhibited behavior is shown to be robust to changes in the rate constants. The feasibility of a chemical degradation mechanism based on peroxide and radical formation is discussed.