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Membranes
Volume 2
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Membranes, Volume 2, Issue 2 (June 2012) – 9 articles , Pages 198-345

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953 KiB  
Article
NMR and Electrochemical Investigation of the Transport Properties of Methanol and Water in Nafion and Clay-Nanocomposites Membranes for DMFCs
by Isabella Nicotera, Kristina Angjeli, Luigi Coppola, Antonino S. Aricò and Vincenzo Baglio
Membranes 2012, 2(2), 325-345; https://doi.org/10.3390/membranes2020325 - 20 Jun 2012
Cited by 25 | Viewed by 9567
Abstract
Water and methanol transport behavior, solvents adsorption and electrochemical properties of filler-free Nafion and nanocomposites based on two smectite clays, were investigated using impedance spectroscopy, DMFC tests and NMR methods, including spin-lattice relaxation and pulsed-gradient spin-echo (PGSE) diffusion under variable temperature conditions. Synthetic [...] Read more.
Water and methanol transport behavior, solvents adsorption and electrochemical properties of filler-free Nafion and nanocomposites based on two smectite clays, were investigated using impedance spectroscopy, DMFC tests and NMR methods, including spin-lattice relaxation and pulsed-gradient spin-echo (PGSE) diffusion under variable temperature conditions. Synthetic (Laponite) and natural (Swy-2) smectite clays, with different structural and physical parameters, were incorporated into the Nafion for the creation of exfoliated nanocomposites. Transport mechanism of water and methanol appears to be influenced from the dimensions of the dispersed platelike silicate layers as well as from their cation exchange capacity (CEC). The details of the NMR results and the effect of the methanol solution concentration are discussed. Clays particles, and in particular Swy-2, demonstrate to be a potential physical barrier for methanol cross-over, reducing the methanol diffusion with an evident blocking effect yet nevertheless ensuring a high water mobility up to 130 °C and for several hours, proving the exceptional water retention property of these materials and their possible use in the DMFCs applications. Electrochemical behavior is investigated by cell resistance and polarization measurements. From these analyses it is derived that the addition of clay materials to recast Nafion decreases the ohmic losses at high temperatures extending in this way the operating range of a direct methanol fuel cell. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p><sup>1</sup>H-NMR spectra recorded on 4 M aqueous methanol solution (CH<sub>3</sub>OD/D<sub>2</sub>O) as prepared and confined in Nafion membrane, respectively. The chemical shift variation of the methanol's signal is caused by the different chemical environment and the strong interactions with the polymer backbone.</p> Full article ">Figure 2
<p>Self-diffusion coefficients of water and methanol (2 M and 4 M solution concentration) confined in filler-free Nafion membranes from 20 °C up to 130 °C; the data collected at 130 °C after 1 h is also plotted. In the legend, the water and solution uptakes are indicated.</p> Full article ">Figure 3
<p>(<b>a</b>) Self-diffusion coefficients and (<b>b</b>) longitudinal relaxation times (T<sub>1</sub>) of pure water and pure methanol confined in Swy/Nafion nanocomposite membrane from 20 °C up to 130 °C. Data collected at 130 °C after some hours are also plotted in the diffusion graph.</p> Full article ">Figure 4
<p>(<b>a</b>) Self-diffusion coefficients and (<b>b</b>) longitudinal relaxation times (T1) of water and methanol in 2 M and 4 M solutions confined in Swy/Nafion nanocomposite membrane from 20 °C up to 130 °C. Data collected at 130 °C after some hours are also plotted in the diffusion graph.</p> Full article ">Figure 5
<p>Evolution of proton spectra from methanol (on the left) and water (on the right) as a function of temperature on Swy/Nafion composite swollen in 2 M methanol solution. The spectra were referenced setting methyl protons and pure water at 0 ppm, respectively.</p> Full article ">Figure 6
<p>(<b>a</b>) Self-diffusion coefficients and (<b>b</b>) longitudinal relaxation times (T1) of water and methanol in 2 M and 4 M solutions confined in lap/Nafion nanocomposite membrane from 20 °C up to 130 °C. Data collected at 130 °C after some hours are also plotted in the diffusion graph.</p> Full article ">Figure 7
<p>Plots of the spectral area <span class="html-italic">vs.</span> temperature of water and methanol in both 2 M and 4M solutions confined in Lap/Nafion nanocomposite.</p> Full article ">Figure 8
<p>Cell resistance values as a function of temperature for the cells equipped with the different membranes.</p> Full article ">Figure 9
<p>DMFC polarization and power density curves at 90 °C for various membrane-electrode assemblies equipped with composite and filler-free membranes.</p> Full article ">Figure 10
<p>DMFC polarization and power density curves at 110 °C for various membrane-electrode assemblies equipped with composite and filler-free membranes.</p> Full article ">
0 pages, 972 KiB  
Article
RETRACTED: UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices
by Jijeesh R. Nair, Annalisa Chiappone, Matteo Destro, Lara Jabbour, Juqin Zeng, Francesca Di Lupo, Nadia Garino, Giuseppina Meligrana, Carlotta Francia and Claudio Gerbaldi
Membranes 2012, 2(2), 307-324; https://doi.org/10.3390/membranes2020307 - 19 Jun 2012
Cited by 4 | Viewed by 7656 | Retraction
Abstract
In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or [...] Read more.
In the present work, the preparation and characterization of quasi-solid polymer electrolyte membranes based on methacrylic monomers and oligomers, with the addition of organic plasticizers and lithium salt, are described. Noticeable improvements in the mechanical properties by reinforcement with natural cellulose hand-sheets or nanoscale microfibrillated cellulose fibers are also demonstrated. The ionic conductivity of the various prepared membranes is very high, with average values approaching 10-3 S cm-1 at ambient temperature. The electrochemical stability window is wide (anodic breakdown voltages > 4.5 V vs. Li in all the cases) along with good cyclability in lithium cells at ambient temperature. The galvanostatic cycling tests are conducted by constructing laboratory-scale lithium cells using LiFePO4 as cathode and lithium metal as anode with the selected polymer electrolyte membrane as the electrolyte separator. The results obtained demonstrate that UV induced radical photo-polymerization is a well suited method for an easy and rapid preparation of easy tunable quasi-solid polymer electrolyte membranes for energy storage devices. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Figure 1
<p>Appearance of the different quasi-solid polymer electrolyte membranes prepared: (<b>a</b>) RC-1 obtained by copolymerizing the monomers BEMA and PEGMA-475 via UV irradiation with the <span class="html-italic">in-situ</span> addition of a 1.5 M LiTFSI electrolyte solution; (<b>b</b>) modified-cellulose handsheet reinforced MC-PE polymer electrolyte membrane; and (<b>c</b>) microfibrillated cellulose reinforced MFC-PE polymer electrolyte membrane.</p> Full article ">Figure 2
<p>TGA analysis under N<sub>2</sub> flux (temperature range 25–600 °C) for the RC-1 polymer electrolyte membrane.</p> Full article ">Figure 3
<p>Ionic conductivity <span class="html-italic">vs</span>. temperature plot of sample RC-1. Data obtained by impedance spectroscopy.</p> Full article ">Figure 4
<p>(<b>a</b>) Time evolution of the interfacial stability of a Li/RC-1/Li symmetrical cell, stored under open circuit potential conditions at ambient temperature; (<b>b</b>) Impedance spectra (Nyquist plots) of the same Li/RC-1/Li symmetrical cell. Electrode area: 0.785 cm<sup>2</sup>. Frequency range: 1 Hz–100 KHz.</p> Full article ">Figure 5
<p>(<b>a</b>) Ambient temperature cycling performance of a LiFePO<sub>4</sub>/RC-1/Li polymer cell at different C-rates from C/20 to 5C (1C = 0.7 mA with respect to a LiFePO<sub>4</sub> active mass of about 4 mg); (<b>b</b>) Typical charge and discharge cycle run at ambient temperature.</p> Full article ">Figure 6
<p>Mechanical measurements through traction test of the reinforced MC-PE at ambient temperature.</p> Full article ">Figure 7
<p>(<b>a</b>) Ionic conductivity <span class="html-italic">versus</span> temperature plot of the MC-PE reinforced quasi-solid polymer electrolyte. Data obtained by impedance spectroscopy; (<b>b</b>) Current <span class="html-italic">vs</span>. voltage curves at room temperature for MC-PE.</p> Full article ">Figure 8
<p>Ambient temperature galvanostatic charge-discharge profiles of the lithium polymer cell assembled by sandwiching the MC-PE reinforced polymer electrolyte between a LiFePO<sub>4</sub>/C cathode and a Li metal anode, at 1C current rate.</p> Full article ">Figure 9
<p>Mechanical measurements through traction test of the reinforced MFC-PE at ambient temperature.</p> Full article ">Figure 10
<p>(<b>a</b>) Conductivity <span class="html-italic">versus</span> temperature plot of the MFC-PE reinforced quasi-solid polymer electrolyte. Data obtained by impedance spectroscopy; (<b>b</b>) Current <span class="html-italic">vs</span>. voltage curves at ambient temperature for MFC-PE.</p> Full article ">Figure 11
<p>Ambient temperature cycling performance of a LiFePO<sub>4</sub>/MFC-PE/Li polymer cell, at different C-rates, from 1C to 3C.</p> Full article ">
455 KiB  
Review
Membranes for Redox Flow Battery Applications
by Helen Prifti, Aishwarya Parasuraman, Suminto Winardi, Tuti Mariana Lim and Maria Skyllas-Kazacos
Membranes 2012, 2(2), 275-306; https://doi.org/10.3390/membranes2020275 - 19 Jun 2012
Cited by 361 | Viewed by 30063
Abstract
The need for large scale energy storage has become a priority to integrate renewable energy sources into the electricity grid. Redox flow batteries are considered the best option to store electricity from medium to large scale applications. However, the current high cost of [...] Read more.
The need for large scale energy storage has become a priority to integrate renewable energy sources into the electricity grid. Redox flow batteries are considered the best option to store electricity from medium to large scale applications. However, the current high cost of redox flow batteries impedes the wide spread adoption of this technology. The membrane is a critical component of redox flow batteries as it determines the performance as well as the economic viability of the batteries. The membrane acts as a separator to prevent cross-mixing of the positive and negative electrolytes, while still allowing the transport of ions to complete the circuit during the passage of current. An ideal membrane should have high ionic conductivity, low water intake and excellent chemical and thermal stability as well as good ionic exchange capacity. Developing a low cost, chemically stable membrane for redox flow cell batteries has been a major focus for many groups around the world in recent years. This paper reviews the research work on membranes for redox flow batteries, in particular for the all-vanadium redox flow battery which has received the most attention. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Figure 1
<p>Schematic of a Vanadium redox flow battery (Adapted from [<a href="#B2-membranes-02-00275" class="html-bibr">2</a>]).</p> Full article ">Figure 2
<p>Schematic representation of an ion exchange process.</p> Full article ">Figure 3
<p>Schematic showing water transfer test cell (Adapted from [<a href="#B15-membranes-02-00275" class="html-bibr">15</a>])</p> Full article ">Figure 4
<p>Expected movement of water and ions for Anion and Cation exchange membranes (Adapted from [<a href="#B15-membranes-02-00275" class="html-bibr">15</a>]).</p> Full article ">Figure 5
<p>Structure of the precursor of perfluorinated ion exchange membranes [<a href="#B31-membranes-02-00275" class="html-bibr">31</a>].</p> Full article ">
1124 KiB  
Article
Synthesis, Multinuclear NMR Characterization and Dynamic Property of Organic–Inorganic Hybrid Electrolyte Membrane Based on Alkoxysilane and Poly(oxyalkylene) Diamine
by Diganta Saikia, Yu-Chi Pan and Hsien-Ming Kao
Membranes 2012, 2(2), 253-274; https://doi.org/10.3390/membranes2020253 - 13 Jun 2012
Cited by 14 | Viewed by 8821
Abstract
Organic–inorganic hybrid electrolyte membranes based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) complexed with LiClO4 via the co-condensation of tetraethoxysilane (TEOS) and 3-(triethoxysilyl)propyl isocyanate have been prepared and characterized. A variety of techniques such as differential scanning calorimetry [...] Read more.
Organic–inorganic hybrid electrolyte membranes based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) complexed with LiClO4 via the co-condensation of tetraethoxysilane (TEOS) and 3-(triethoxysilyl)propyl isocyanate have been prepared and characterized. A variety of techniques such as differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, alternating current (AC) impedance and solid-state nuclear magnetic resonance (NMR) spectroscopy are performed to elucidate the relationship between the structural and dynamic properties of the hybrid electrolyte and the ion mobility. A VTF (Vogel-Tamman-Fulcher)-like temperature dependence of ionic conductivity is observed for all the compositions studied, implying that the diffusion of charge carriers is assisted by the segmental motions of the polymer chains. A maximum ionic conductivity value of 5.3 × 10−5 Scm−1 is obtained at 30 °C. Solid-state NMR results provide a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Figure 1

Figure 1
<p>Schematic representation of the synthesis and structure of the present hybrid electrolyte.</p> Full article ">Figure 2
<p>Differential scanning calorimetry (DSC) thermograms of (<b>a</b>) pure ED2000 and TIE(2000)-Z hybrid electrolytes with various [O]/[Li] ratios, where Z = (<b>b</b>) ∞; (<b>c</b>) 32; (<b>d</b>) 24; (<b>e</b>) 16 and (<b>f</b>) 8.</p> Full article ">Figure 3
<p>FTIR spectra of (<b>a</b>) pure ED2000 and TIE(2000)-Z hybrid electrolytes with Z = (<b>b</b>) ∞; (<b>c</b>) 32; (<b>d</b>) 24; (<b>e</b>) 16 and (<b>f</b>) 8.</p> Full article ">Figure 4
<p>IR deconvolution results (in the range of 600 to 650 cm<sup>−1</sup>) of TIE(2000)-Zhybrid electrolytes with various [O]/[Li] ratios, where Z = (<b>a</b>) 32; (<b>b</b>) 24; (<b>c</b>) 16 and (<b>d</b>) 8.</p> Full article ">Figure 5
<p><sup>13</sup>C CPMAS NMR spectra of (<b>a</b>) pure ED2000 and TIE(2000)-Z hybrid electrolytes with Z = (<b>b</b>) ∞, (<b>c</b>) 32, (<b>d</b>) 24, (<b>e</b>) 16 and (<b>f</b>) 8.</p> Full article ">Figure 6
<p><sup>29</sup>Si MAS NMR spectra of (<b>a</b>) TIE(600)-32 and (<b>b</b>) TIE(600)-8 hybrid electrolytes. Different color lines represent the components used for spectral deconvolution.</p> Full article ">Figure 7
<p><sup>13</sup>C CPMAS NMR spectra (70.7 ppm) of TIE(600)-Z hybrid electrolytes with Z = (<b>a</b>) 32; (<b>b</b>) 24; (<b>c</b>) 16 and (<b>d</b>) 8, as a function of contact time.</p> Full article ">Figure 8
<p>Representative 2D <sup>1</sup>H–<sup>13</sup>C wide-line separation (WISE) NMR spectrum (<b>a</b>) and the projections of the <sup>1</sup>H dimension of 2D <sup>1</sup>H–<sup>13</sup>C WISE spectra associated with the 70.7 ppm peak in the <sup>13</sup>C dimension for TIE(600)-Z hybrids, where Z = (<b>b</b>) 32 and (<b>c</b>) 8.</p> Full article ">Figure 9
<p>Temperature dependence of ionic conductivity of TIE(2000)-Z hybrid electrolytes with Z = (<b>a</b>) 32; (<b>b</b>) 24; (<b>c</b>) 16 and (<b>d</b>) 8.</p> Full article ">Figure 10
<p>Temperature dependence of <sup>7</sup>Li static line widths of TIE(2000)-Z hybrid electrolytes with various [O]/[Li] ratios, where Z = (<b>A</b>) 32 and (<b>B</b>) 8, measured (a) without and (b) with proton decoupling. The dashed lines represent the <span class="html-italic">T</span><sub>g</sub> values obtained from DSC.</p> Full article ">
648 KiB  
Article
Impedance Spectroscopic Investigation of Proton Conductivity in Nafion Using Transient Electrochemical Atomic Force Microscopy (AFM)
by Steffen Hink, Norbert Wagner, Wolfgang G. Bessler and Emil Roduner
Membranes 2012, 2(2), 237-252; https://doi.org/10.3390/membranes2020237 - 6 Jun 2012
Cited by 15 | Viewed by 10888
Abstract
Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring [...] Read more.
Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane. It is demonstrated that good quality impedance spectra are obtained in a frequency range of 0.2–1,000 Hz. The extracted polarization curves exhibit a maximum current which cannot be explained by typical diffusion effects. Simulation based on equivalent circuits requires a Nernst element for restricted diffusion in the membrane which suggests that this effect is based on the potential dependence of the electrolyte resistance in the high overpotential region. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Figure 1

Figure 1
<p>Experimental set-up: A membrane separates two environmental chambers with gas atmospheres which can be controlled independently but were identical for the present work. The upper side is sealed off by a perfluorosilicone cap in which the cantilever holder is embedded. The cantilever deflection is measured through a small glass window. An external PC runs the chronoamperometric experiments.</p> Full article ">Figure 2
<p>Current traces measured in a series by increasing the potential jump from 0 V to the corresponding value given in the diagram. The measurements were performed at the same position in a hydrogen atmosphere with 76% RH. The dashed lines represent the fitted exponential decay with a time constant of around 0.24 ms.</p> Full article ">Figure 3
<p>Relative errors, calculated from several measurement series, are plotted as a function of the applied force between the tip, the relative humidity of the gas atmosphere, the tip position on the sample and the recovery time between the different measurements. The open symbols represent the arithmetic mean of the five measurements.</p> Full article ">Figure 4
<p>Starting at 0 V, different voltage steps were applied to a Nafion 117 sample in a hydrogen atmosphere at RH = 71% and an applied force of 30 nN between the sample and the tip. The resulting current traces are shown. The break between the measurements was 30 s.</p> Full article ">Figure 5
<p>Current-voltage polarization curves derived at three different times after the beginning of the measurement as indicated in <a href="#membranes-02-00237-f004" class="html-fig">Figure 4</a>. A maximum is observed near 0.6 V–0.7 V. The typical diffusion limitation is indicated by the dashed line. The inset shows a Tafel plot of the overpotential region &lt;0.5 V with the corresponding exponential fits.</p> Full article ">Figure 6
<p>(<b>a</b>): Bode plot of the impedance spectra from the measurements of <a href="#membranes-02-00237-f004" class="html-fig">Figure 4</a> with a voltage step from zero to 0.3 V, 0.7 V and 1.0 V. The upper curves are the fits of the real part to the experimental data (black dots), the lower curves and red squares represent the imaginary part. Note the different Y-scales for the impedance; (<b>b</b>): Nyquist diagram of the experimental and the simulated impedance spectra for the voltage steps given in the graph.</p> Full article ">Figure 7
<p>Equivalent circuits used for the simulations of the impedance spectra obtained from the data of <a href="#membranes-02-00237-f004" class="html-fig">Figure 4</a>. (<b>a</b>) The RC circuit is used for the simulation of the impedance spectra with low overpotential; (<b>b</b>) The equivalent circuit is similar to the Randles circuit but the Warburg impedance is replaced by a finite-length diffusion element (Nernst diffusion element). This circuit is used for the moderate and high overpotential region.</p> Full article ">Figure 8
<p>Simulated charge transfer resistance as a function of the voltage at different relative humidities, showing a pronounced decline with increasing voltage. The charge transfer resistance is smaller at higher relative humidity. In the section to the left of the dotted line the RC-circuit and to the right the modified Randles-circuit is used.</p> Full article ">Figure 9
<p>Simulated electrolyte resistance plotted for different relative humidities as a function of the voltage step. The dotted line marks the change from the RC-circuit (left side) to the modified Randles circuit (right side) used for the simulation. With increasing RH the electrolyte resistance decreases. a) indicates R<sub>el</sub> values which were fixed during the simulation of the impedance spectra.</p> Full article ">Figure 10
<p>Simulated Warburg coefficients W plotted against the voltage for different relative humidities. With increasing RH the diffusion limitation decreases. An exponential increase with overpotential is observed as indicated by the fits (dashed lines).</p> Full article ">
1315 KiB  
Article
Comparison of Polytetrafluoroethylene Flat-Sheet Membranes with Different Pore Sizes in Application to Submerged Membrane Bioreactor
by Tadashi Nittami, Tetsuo Hitomi, Kanji Matsumoto, Kazuho Nakamura, Takaharu Ikeda, Yoshihiro Setoguchi and Manabu Motoori
Membranes 2012, 2(2), 228-236; https://doi.org/10.3390/membranes2020228 - 1 Jun 2012
Cited by 12 | Viewed by 8043
Abstract
This study focused on phase separation of activated sludge mixed liquor by flat-sheet membranes of polytetrafluoroethylene (PTFE). A 20 liter working volume lab-scale MBR incorporating immersed PTFE flat-sheet membrane modules with different pore sizes (0.3, 0.5 and 1.0 μm) was operated for 19 [...] Read more.
This study focused on phase separation of activated sludge mixed liquor by flat-sheet membranes of polytetrafluoroethylene (PTFE). A 20 liter working volume lab-scale MBR incorporating immersed PTFE flat-sheet membrane modules with different pore sizes (0.3, 0.5 and 1.0 μm) was operated for 19 days treating a synthetic wastewater. The experiment was interrupted twice at days 5 and 13 when the modules were removed and cleaned physically and chemically in sequence. The pure water permeate flux of each membrane module was measured before and after each cleaning step to calculate membrane resistances. Results showed that fouling of membrane modules with 0.3 μm pore size was more rapid than other membrane modules with different pore sizes (0.5 and 1.0 μm). On the other hand, it was not clear whether fouling of the 0.5 μm membrane module was more severe than that of the 1.0 μm membrane module. This was partly because of the membrane condition after chemical cleaning, which seemed to determine the fouling of those modules over the next period. When irreversible resistance (Ri) i.e., differences in membrane resistance before use and after chemical cleaning was high, the transmembrane pressure increased quickly during the next period irrespective of membrane pore size. Full article
(This article belongs to the Special Issue Membranes in Water Purification)
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<p>SEM images of PTFE membrane (pore size 0.5 μm) laminated with polypropylene (PP) and its flat-sheet membrane module photo. (<b>a</b>) cross-section image with filtration direction from top to bottom (1000×); (<b>b</b>) surface image (5000×); (<b>c</b>) membrane module. Scale bars in <a href="#membranes-02-00228-f001" class="html-fig">Figure 1</a><b>a</b>, <b>b</b> shows 50 μm and 10 μm respectively.</p> Full article ">Figure 2
<p>Time course of transmembrane pressure (TMP) of each PTFE membrane module.</p> Full article ">Figure 3
<p>Hydraulic resistance: <span class="html-italic">R</span> (m<sup>−1</sup>) and its differences in each step at Run 1 and 2 in each PTFE membrane module. <span class="html-italic">R<sub>rp</sub></span>, <span class="html-italic">R<sub>rc</sub></span> and <span class="html-italic">R<sub>i</sub></span> mean the differences in membrane resistance after operation and after physical cleaning, after physical cleaning and after chemical cleaning, and before use and after chemical cleaning respectively.</p> Full article ">Figure 4
<p>Correlation between the TMP, <span class="html-italic">R<sub>i</sub></span> and <span class="html-italic">R<sub>rp</sub></span>. (<b>a</b>) correlation between dates required for increasing TMP up to 25 kPa (<span class="html-italic">T</span><sub>25</sub>) and <span class="html-italic">R<sub>i</sub></span>; (<b>b</b>) correlation between <span class="html-italic">T</span><sub>25</sub> and <span class="html-italic">R<sub>rp</sub></span>; (<b>c</b>) correlation between <span class="html-italic">R<sub>i</sub></span> and <span class="html-italic">R<sub>rp</sub></span>; (<b>d</b>) correlation between <span class="html-italic">T</span><sub>25</sub> and <span class="html-italic">R<sub>rc</sub></span>; (<b>e</b>) correlation between <span class="html-italic">R<sub>i</sub></span> and <span class="html-italic">R<sub>rc</sub></span>.</p> Full article ">Figure 5
<p>PTFE membranes with pore size of 0.3, 0.5 and 1.0 μm (5000×) before use (new membrane) and after physical cleaning. Scale bars show 10.0 μm respectively.</p> Full article ">
417 KiB  
Review
Oxygen Selective Membranes for Li-Air (O2) Batteries
by Owen Crowther and Mark Salomon
Membranes 2012, 2(2), 216-227; https://doi.org/10.3390/membranes2020216 - 11 May 2012
Cited by 43 | Viewed by 10930
Abstract
Lithium-air (Li-air) batteries have a much higher theoretical energy density than conventional lithium batteries and other metal air batteries, so they are being developed for applications that require long life. Water vapor from air must be prevented from corroding the lithium (Li) metal [...] Read more.
Lithium-air (Li-air) batteries have a much higher theoretical energy density than conventional lithium batteries and other metal air batteries, so they are being developed for applications that require long life. Water vapor from air must be prevented from corroding the lithium (Li) metal negative electrode during discharge under ambient conditions, i.e., in humid air. One method of protecting the Li metal from corrosion is to use an oxygen selective membrane (OSM) that allows oxygen into the cell while stopping or slowing the ingress of water vapor. The desired properties and some potential materials for OSMs for Li-air batteries are discussed and the literature is reviewed. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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<p>Designs for Li-air batteries. In the protected anode approach shown at the left, the lithium anode is protected by a glass-ceramic disc (membrane) which is hermetically sealed to the anode. This solid-state glass-ceramic is a Li<sup>+</sup> conductor impervious to water. In the protected cathode design shown at the right, the glass-ceramic solid-state membrane is removed and instead a flexible OSM is attached to the surface of the air electrode facing the atmosphere.</p> Full article ">Figure 2
<p>Effect of O<sub>2</sub> permeability on maximum current density, <span class="html-italic">i<sub>max</sub></span>, for a 1 µm thick OSM. Black circle points correspond to n = 2, red triangle points correspond to n = 2.6, green square points correspond to n = 4 equivalent e<sup>−</sup> per mole of O<sub>2</sub>.</p> Full article ">Figure 3
<p>Pictures of Li metal negative electrode after cell discharge in humid air for cells using an OSM (left) and with no membrane (right).</p> Full article ">Figure 4
<p>Evaporation rates of a typical electrolyte from a pouch cell with and without an OSM [<a href="#B18-membranes-02-00216" class="html-bibr">18</a>].</p> Full article ">
134 KiB  
Correction
Correction: Self-Assembling Peptide Surfactants A6K and A6D Adopt a-Helical Structures Useful for Membrane Protein Stabilization. Membranes 2011, 1, 314-326
by Kamila Oglęcka, Furen Zhuang and Charlotte A. E. Hauser
Membranes 2012, 2(2), 214-215; https://doi.org/10.3390/membranes2020214 - 2 May 2012
Cited by 1 | Viewed by 5173
Abstract
We would like to request a correction to the author listing. The following changes should be made in respect to the original publication of this article [1]. [...] Full article
(This article belongs to the Special Issue Membranes for Health and Environmental Applications)
1276 KiB  
Article
Immobilization of Mucor miehei Lipase onto Macroporous Aminated Polyethersulfone Membrane for Enzymatic Reactions
by Nurrahmi Handayani, Katja Loos, Deana Wahyuningrum, Buchari and Muhammad Ali Zulfikar
Membranes 2012, 2(2), 198-213; https://doi.org/10.3390/membranes2020198 - 12 Apr 2012
Cited by 26 | Viewed by 15408
Abstract
Immobilization of enzymes is one of the most promising methods in enzyme performance enhancement, including stability, recovery, and reusability. However, investigation of suitable solid support in enzyme immobilization is still a scientific challenge. Polyethersulfone (PES) and aminated PES (PES–NH2) were successfully [...] Read more.
Immobilization of enzymes is one of the most promising methods in enzyme performance enhancement, including stability, recovery, and reusability. However, investigation of suitable solid support in enzyme immobilization is still a scientific challenge. Polyethersulfone (PES) and aminated PES (PES–NH2) were successfully synthesized as novel materials for immobilization. Membranes with various pore sizes (from 10–600 nm) based on synthesized PES and PES–NH2 polymers were successfully fabricated to be applied as bioreactors to increase the immobilized lipase performances. The influence of pore sizes, concentration of additives, and the functional groups that are attached on the PES backbone on enzyme loading and enzyme activity was studied. The largest enzyme loading was obtained by Mucor miehei lipase immobilized onto a PES–NH2 membrane composed of 10% of PES–NH2, 8% of dibutyl phthalate (DBP), and 5% of polyethylene glycol (PEG) (872.62 µg/cm2). Hydrolytic activity of the immobilized lipases indicated that the activities of biocatalysts are not significantly decreased by immobilization. From the reusability test, the lipase immobilized onto PES–NH2 showed a better constancy than the lipase immobilized onto PES (the percent recovery of the activity of the lipases immobilized onto PES–NH2 and PES are 97.16% and 95.37%, respectively), which indicates that this novel material has the potential to be developed as a bioreactor for enzymatic reactions. Full article
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Graphical abstract
Full article ">Figure 1
<p>MALDI-TOF spectrum of the synthesized PES.</p> Full article ">Figure 2
<p>Structure of synthesized PES (upper) and aminated PES (lower).</p> Full article ">Figure 3
<p>SEM image of membrane porosity with 40,000× magnification: (<b>a</b>) PES-10; (<b>b</b>) PES-10/D6; (<b>c</b>) PES-10/P4; (<b>d</b>) PESNH-10/D2/P5.</p> Full article ">Figure 4
<p>SEM photograph of the cross section of (<b>a</b>) PES10/D6 and (<b>b</b>) PESNH-10/D2/P5.</p> Full article ">Figure 5
<p>FT-IR spectra of PES–NH<sub>2</sub> and lipases immobilized onto PES–NH<sub>2</sub>, the black line is spectra of PES–NH<sub>2</sub> and the red line is spectra of lipase immobilized onto PES–NH<sub>2</sub>.</p> Full article ">Figure 6
<p>Profile of reusability test for immobilized enzyme on both PES and PES–NH<sub>2</sub> membranes (repeated four times).</p> Full article ">
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