Papers by Keyword: Polymer Electrolyte Membrane

Abstract: Polymer Electrolyte Membranes (PEM) is an important component in a Direct Methanol Fuel Cell (DMFC) system that has a primary function as a proton conductor and separator between a cathode and anode. Due to the awareness of the comprehensive methanol crossover issue in the commercially available Nafion membrane, however, the main parameter of PEM for DMFC is low methanol permeability. The chitosan-based inorganic hybrid membrane is a promising organic–inorganic hybrid for the development of high-performance PEM. The study of composite membranes as PEM was initiated with the synthesis of silica from POFA (palm oil fuel ash). Using the phase inversion technique, the chitosan was mixed with silica filler in an acetic solution to produce Ch/Silica composite membrane. Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) analysis shows that pure silica has been successfully synthesized from POFA and can interact with chitosan in the layer of the membrane structure which is supported by the Fourier Transform Infrared Spectroscopy (FTIR) spectra results. Water uptake shows a value of 75%, while methanol uptake with a low value of 52%. The addition of silica gives the membrane the ability to reduce methanol crossover as indicated by the low value of methanol permeability of 0.00027 mg cm²s^-1. However, this membrane has good proton exchange performance as indicated by the Ion Exchange Capacity value of 1.56 mmol g^-1. These results indicate that the composite membrane of chitosan with silica from POFA has the potential as PEM in direct methanol fuel cell applications.

Abstract: Polymer electrolyte membranes (PEM) with good properties are essential for the improvement of electrochemical operations. The increase in properties of polymer electrolyte membranes will develop the performance of polymer electrolyte membranes in the fuel cells. The importance of polymer electrolyte membranes is increasing recently due to its activity and simplicity in energy associated applications like automobiles and various portable applications. PEM has various properties like proton conductivity, chemical stability, mechanical properties, thermal stability and so on. These properties are enhanced and influenced by various factors like morphology, the molecular weight of the membranes, chemical structures, cross linkages etc. The present chapter attempts to summarize about the properties of polymer electrolyte membrane involved in the different types of electrochemical utilizations. Keywords: Polymer electrolyte membrane, fuel cells, morphology, proton conductivity, chemical structure.

Abstract: Polymer electrolyte membranes of cellulose acetate-LiClO₄ were prepared from the cellulose acetate with various ratios of lithium perchlorate in tetrahydrofuran (THF) as solvent. The properties of polymer electrolyte membranes with various ratios of lithium perchlorate were studied by Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). The obtained TGA curves showed that these membranes were degraded thermally in three steps, which were attributed to dehydration, the main thermal degradation of the cellulose acetate chains, and the carbonization of the product to form ash. The thermal stability of the membrane decreased with the increase in LiClO₄ content. The initial temperatures of the main degradation process decreased gradually from 330 °C in pure cellulose acetate membrane to 258 °C in cellulose acetate membrane containing 25% lithium perchlorate. The morphology of the membranes transformed from dense to the more porous membrane along with the increase in lithium perchlorate ratios on membranes.

Abstract: The electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/montmorillonite nanofibrous composite membranes (esCPMs) were prepared by electrospinning technique using a mixture of different amounts of montmorillonite (0, 3, 5, 7 and 10 wt%) into 16 wt% of PVDF-HFP polymer solution in 7:3 wt% of acetone and dimethylacetamide as the solvent. The effect of montmorillonite (MMT) on electrospun PVdF-HFP membrane has been studied by XRD, DSC, TGA and tensile strength analysis. It is found that electrospun PVDF-HFP/MMT nanofibrous composite membrane obtained using 5wt% MMT has a higher porosity, electrolyte uptake, ionic conductivity, electrochemical stability window and showed higher specific capacitance and good compatibility with electrode materials.

Abstract: Variations of ortho-positronium (o-Ps) lifetime and gas permeability of the Aquivion® E8705 membrane were studied as functions of temperature under vacuum and relative humidity at room temperature. When the temperature was varied between 0 and 100 °C in vacuum, the hole volume of Aquivion® E8705, deduced from the ortho-positronium lifetime, gradually increased. However, when the relative humidity was changed at room temperature, the hole volume was essentially unchanged. Good linear correlations between the logarithm of permeabilities of O₂ and H₂ and reciprocal hole volume at different temperatures indicates the importance role of free volume in gas permeation in dry Aquivion® E8705. However, for hydrated Aquivion® E8705 the permeability less depends on hole volume.

Abstract: Nafion® is one of the most popular proton conducting membranes for polymer electrolyte fuel cells (PEFCs). For the integration of Nafion® to the catalyst layers, very thin layers of the polymer are often formed on the catalysts of PEFC from dilute solutions. We applied energy variable positron annihilation to characterizing the structure of thin Nafion® films prepared by spin and dip coating from ethanol/water solutions of Nafion® on Si substrates. Experimental data suggest that the nano-structure of 23 nm thick spin coated Nafion® film is different from 220 nm thick film and also from 26 and 227 nm thick dip coated films, possibly due to the preservation of the unique rod-like structure of Nafion® in the dilute solution.

Abstract: Annihilation process of positron in Nafion-117 was investigated under several kinds of conditions to elucidate degradation process of polymer electrolyte membrane. It was found that ortho-positronium stayed beside cluster wall and side chains and its lifetime reflected cluster size. Annihilation process of positron was found to be greatly influenced by the electronic state of sulfonic group. These results showed that positron annihilation spectroscopy would be good tool to detect degradation of polymer electrolyte membrane.

Abstract: The relationship between water sorption behavior and proton conduction in polymer electrolyte membranes based on sulfonated polyimide electrolyte membranes is studied from view points of polymer structure, ion exchange capacity, and percolation theory. The results indicate that the polymer chemical structure and ion exchange capacity show significant effects on water sorption and thus proton conductivity for various membranes. The density values of wet membranes decreased gradually with an increase in water uptake. Polymer electrolytes with flexible side-chain terminated with sulfonic acid group displayed smaller percolation threshold compared with main-chain-type polymer, indicating a better microphase-separation structure.

Abstract: Positron chemistry refers to chemical processes of high-energy positrons injected into molecular substances, the most interesting of which is the formation of positronium (Ps), the hydrogen-like bound state between a positron and an electron. Ps is formed predominantly by fast intra-track radiation chemical processes. In polymers it tends to be localized in intra/inter-molecular open space in the sparsely packed amorphous structure. Whilst short-lived singlet para-positronium (p-Ps) undergoes self-annihilation, the positron in long-lived triplet ortho-positronium (o-Ps) annihilates with one of the spin opposite electrons bound in the surrounding polymer molecules. This process is called pick-off annihilation. The pick-off annihilation lifetime reflects the polymer chain packing through the size of the volume, where Ps is localized. Positrons are used to probe the amorphous structure of various polymeric systems. In this article, basic concepts and experimental techniques of positron chemistry in polymers as well as applications to the characterization of functional polymeric materials are overviewed.

Abstract: Positron annihilation techniques were applied for irradiated Nafion-117 to investigate deterioration process in PEM. There were no significant changes in lifetime of positron/positronium, whereas the S-parameter showed fairly good correlation with proton conductivity.