Properties Of Polymer Electrolyte Membranes Research Articles

Characterisation of mechanical behaviour and coupled electrical properties of polymer electrolyte membrane fuel cell gas diffusion layers

Local compression distribution in the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEMFC) and the associated effect on electrical material resistance are examined. For this purpose a macroscopic structural material model is developed based on the assumption of orthotropic mechanical material behaviour for the fibrous paper and non-woven GDLs. The required structural material parameters are measured using depicted measurement methods. The influence of GDL compression on electrical properties and contact effects is also determined using specially developed testing tools. All material properties are used for a coupled 2D finite element simulation approach, capturing structural as well as electrical simulation in combination. The ohmic voltage losses are evaluated assuming constant current density at the catalyst layer and results are compared to cell polarisation measurements for different materials. The results show that the largest part of the polarisation difference found between roll-good and batch type materials with wide channel flowfields is well captured by the simulation and is due to additional electrical losses in the locally low compressed GDL. Thus, for the first time a broader understanding of the significant performance impact of diffusion layer mechanical properties is generated. However, at higher loads an interaction of compression with electrical and additional heat and mass transport effects occurs, which will be included in the next part of the study. This part is limited to structural mechanics and coupled electrical transport effects.

An Analysis of The Water Transport Properties of Polymer Electrolyte Membrane

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Influence of grafting solvents on the properties of polymer electrolyte membranes prepared by γ-ray preirradiation method

The effect of grafting solvents, such as isopropanol (iPrOH), tetrachloroethane (TCE), tetrahydrofuran (THF), and toluene, on the preparation of poly(ethylene- co-tetrafluoroethylene)-graft-poly(styrene sulfonic acid) (ETFE-g-PSSA) electrolyte membranes by the γ-ray preirradiation grafting method was investigated. It was found that the iPrOH can drastically accelerate the grafting, resulting in a higher degree of grafting. However, for an appropriate degree of grafting of about 50%, the sulfonic acid groups in the ETFE-g-PSSA membrane prepared with the iPrOH were mainly distributed near the membrane surface, as shown by low proton conductivity in the membrane thickness direction. In contrast to this result, the ETFE-g-PSSA membranes prepared with the THF, toluene and TCE exhibited uniform distribution of the sulfonic acid groups in the membrane. Especially, in the case of the TCE grafting solvent, the chemical stability of the resultant electrolyte membrane was clearly higher than those prepared with the other grafting solvents.

Enhanced performance and improved interfacial properties of polymer electrolyte membrane fuel cells fabricated using sputter-deposited Pt thin layers

For this study, catalyst layers for polymer electrolyte membrane fuel cells (PEMFC) were prepared by spraying and sputtering to deposit Pt amount of 0.1 and 0.01 mg cm −2, respectively. These Pt layers were then assembled to fabricate membrane electrode assemblies (MEA) having either single- or double-layered catalysts. The PEM fuel cell with double layers showed a current density of 777 mA cm −2 at a cell voltage of 0.6 V, which is a higher current density than state-of-the-art fuel cells at 643 mA cm −2. These results indicate that Pt loading in state-of-the-art PEMFCs could be reduced by approximately 50% with no performance loss by using both spraying and sputtering method in the MEA fabrication process.

The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes

Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H+-, Fe3+- and mixed H+/Fe3+-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these in the Fe3+/Fe2+–H2/H+ fuel cell in the range of current densities 0–90 mA/cm2. It was found that the conductivities of these membranes in 1.09 M H2SO4 solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe3+-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe3+-form into H+-form of these membranes. Unlike the Nafion membranes, the Fe3+-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (more than 70 mA/cm2) that is most probably a result of concentration polarization.

Preparation of a novel composite micro-porous polymer electrolyte membrane for high performance Li-ion battery

A novel composite micro-porous polymer electrolyte membrane based on optimized composition of PVdF- co-HFP-ZrO 2 was prepared by a preferential polymer dissolution process. The effect of porosity on the electrochemical properties of polymer electrolyte membranes, such as ionic conductivity and lithium transference number was studied by electrochemical AC-impedance spectroscopy and steady state current method, respectively. The results show that the formation of micro-porous by the removal of poly vinyl alcohol in the PVdF-HFP-ZrO 2 matrix can enhance the ionic conductivity and lithium transference number when polymer membrane is soaked in 1 M LiClO 4 electrolyte solution containing 1:1 (v/v) ratio of EC and DEC . It is also found that the ionic conductivity data follows the Arrhenius equation. Finally, the charge–discharge studies were carried out by fabricating a cell with carbon as the anode and LiMg 0.10Mn 1.90O 4 as the cathode and composite micro-porous polymer electrolyte membrane as the separator. The excellent performance, such as high ionic conductivity, high lithium transference number, good compatibility with electrode materials and higher discharge capacity of PVdF- co-HFP-ZrO 2 based polymer electrolyte membrane suggest that the polymer electrolyte can be used as the best candidate for high performance lithium-ion batteries.

Influence of pre-irradiation atmosphere on the properties of polymer electrolyte membranes prepared using radiation grafting method

The influence of pre-irradiation atmosphere, argon and air, on radiation grafting of styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and the properties of the ETFE-based radiation-grafted polymer electrolyte membranes were investigated. The preparation and properties of the membranes were found to be strongly influenced by the γ-ray pre-irradiation atmosphere. The proton conductivity was measured in its water-saturated state at 25 °C, and the membrane durability was tested in a 3% H2O2 aqueous solution at 60 °C. The proton conductivity of the membrane prepared by pre-irradiation under air was higher than that of the membrane prepared under argon with the same ion exchange capacity level. However, the durability of the former was considerably lower than that of the latter. For instance, the membrane with an ion exchange capacity of about 1.0 mmol g−1 prepared under argon was twice as durable as that prepared under air. It was considered that the lower durability of the membrane prepared by pre-irradiation under air was because of the unstable ether bond introduced between the graft chains and the backbone chains.

Nafion composite membranes containing rod-shaped polyrotaxanes for direct methanol fuel cells

Cast Nafion-based composite membranes containing different amounts of organic, nanorod-shaped polyrotaxane were prepared and characterized, with the aim of improving the properties of polymer electrolyte membranes for direct methanol fuel cell applications. Polyrotaxane was prepared using the inclusion-complex reaction between α-cyclodextrin and poly(ethylene glycol) (PEG) of different molecular weights. The addition of polyrotaxane to Nafion changed the morphology and reduced the crystallinity. The conductivity of the composite membranes increased with increasing polyrotaxane content up to 5 wt%, but then decreased at higher polyrotaxane contents. Well-dispersed, organic polyrotaxane inside the membrane can provide a tortuous path for the transport of methanol, as the methanol permeability depends on the aspect ratio of polyrotaxane, which is controlled by the molecular weight of PEG. All of the Nafion-based, polyrotaxane composite membranes showed a higher selectivity parameter than the commercial Nafion films did.

In situ EPR investigation of polymer electrolyte membrane degradation in fuel cell applications

The main long-term purpose of this investigation is a profound understanding of the degradation mechanisms and the identification of fuel cell operating conditions and polymer electrolyte membrane properties which warrant a long lifetime and more reliable behaviour in general. The work involves the development and application of electron paramagnetic resonance (EPR) electrochemistry techniques to study polymer proton exchange membrane degradation in fuel cell applications. As a first step, a miniature cell that can work in a cavity of an X-band EPR spectrometer was built. This is the first report of an in situ fuel cell in an EPR spectrometer. We plan to identify different organic radicals which form in the running cell as intermediates of the degradation reactions. The objects of our research are different types of ionically, covalently, and covalent–ionically cross-linked polyaryl-blend membranes. It is demonstrated that tuning of the microwave cavity with a running fuel cell inside is possible, and a pronounced single-line EPR signal is observed. The signal has a g-value of 2.0030, thus it probably originates from the electrode material that is 0.00–2.00 mg/cm 2 Pt on Vulcan XC-72 E-Tek. Its behaviour depends strongly on the fuel cell conditions. It is interesting to note that when the cell is fed with oxygen and hydrogen, the signal intensity diminishes considerably, both under open circuit and under closed circuit conditions. This phenomenon is observed for different membrane types. When the gases are switched off the signal intensity is restored with a characteristic time of 1–2 h. For different membranes, this time differs. In general, water plays a very important role in the observation of EPR-spectra from the in situ fuel cell. © 2003 Elsevier B.V. All rights reserved.