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Membranes, Volume 2, Issue 4 (December 2012), Pages 687-878

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Research

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Open AccessArticle UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices
Membranes 2012, 2(4), 687-704; doi:10.3390/membranes2040687
Received: 11 October 2012 / Accepted: 12 October 2012 / Published: 17 October 2012
Cited by 5 | PDF Full-text (352 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Validation and Analysis of Forward Osmosis CFD Model in Complex 3D Geometries
Membranes 2012, 2(4), 764-782; doi:10.3390/membranes2040764
Received: 31 August 2012 / Revised: 29 October 2012 / Accepted: 29 October 2012 / Published: 9 November 2012
Cited by 7 | PDF Full-text (4082 KB) | HTML Full-text | XML Full-text
Abstract
In forward osmosis (FO), an osmotic pressure gradient generated across a semi-permeable membrane is used to generate water transport from a dilute feed solution into a concentrated draw solution. This principle has shown great promise in the areas of water purification, wastewater treatment,
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In forward osmosis (FO), an osmotic pressure gradient generated across a semi-permeable membrane is used to generate water transport from a dilute feed solution into a concentrated draw solution. This principle has shown great promise in the areas of water purification, wastewater treatment, seawater desalination and power generation. To ease optimization and increase understanding of membrane systems, it is desirable to have a comprehensive model that allows for easy investigation of all the major parameters in the separation process. Here we present experimental validation of a computational fluid dynamics (CFD) model developed to simulate FO experiments with asymmetric membranes. Simulations are compared with experimental results obtained from using two distinctly different complex three-dimensional membrane chambers. It is found that the CFD model accurately describes the solute separation process and water permeation through membranes under various flow conditions. It is furthermore demonstrated how the CFD model can be used to optimize membrane geometry in such as way as to promote the mass transfer. Full article
Open AccessArticle Microscopic Analysis of Current and Mechanical Properties of Nafion® Studied by Atomic Force Microscopy
Membranes 2012, 2(4), 783-803; doi:10.3390/membranes2040783
Received: 9 July 2012 / Revised: 3 October 2012 / Accepted: 31 October 2012 / Published: 16 November 2012
Cited by 16 | PDF Full-text (6391 KB) | HTML Full-text | XML Full-text
Abstract
The conductivity of fuel cell membranes as well as their mechanical properties at the nanometer scale were characterized using advanced tapping mode atomic force microscopy (AFM) techniques. AFM produces high-resolution images under continuous current flow of the conductive structure at the membrane surface
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The conductivity of fuel cell membranes as well as their mechanical properties at the nanometer scale were characterized using advanced tapping mode atomic force microscopy (AFM) techniques. AFM produces high-resolution images under continuous current flow of the conductive structure at the membrane surface and provides some insight into the bulk conducting network in Nafion membranes. The correlation of conductivity with other mechanical properties, such as adhesion force, deformation and stiffness, were simultaneously measured with the current and provided an indication of subsurface phase separations and phase distribution at the surface of the membrane. The distribution of conductive pores at the surface was identified by the formation of water droplets. A comparison of nanostructure models with high-resolution current images is discussed in detail. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Open AccessArticle A Study of the Effect of Heat-Treatment on the Morphology of Nafion Ionomer Dispersion for Use in the Passive Direct Methanol Fuel Cell (DMFC)
Membranes 2012, 2(4), 841-854; doi:10.3390/membranes2040841
Received: 14 November 2012 / Accepted: 26 November 2012 / Published: 6 December 2012
Cited by 5 | PDF Full-text (1658 KB) | HTML Full-text | XML Full-text
Abstract
Aggregation in heat-treated Nafion ionomer dispersion and 117 membrane are investigated by 1H and 19F Nuclear Magnetic Resonance (NMR) spectra, spin-lattice relaxation time, and self-diffusion coefficient measurements. Results demonstrate that heat-treatment affects the average Nafion particle size in aqueous dispersions. Measurements
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Aggregation in heat-treated Nafion ionomer dispersion and 117 membrane are investigated by 1H and 19F Nuclear Magnetic Resonance (NMR) spectra, spin-lattice relaxation time, and self-diffusion coefficient measurements. Results demonstrate that heat-treatment affects the average Nafion particle size in aqueous dispersions. Measurements on heat-treated Nafion 117 membrane show changes in the 1H isotropic chemical shift and no significant changes in ionic conductivity. Scanning electron microscopy (SEM) analysis of prepared cathode catalyst layer containing the heat-treated dispersions reveals that the surface of the electrode with the catalyst ink that has been pretreated at ca. 80 °C exhibits a compact and uniform morphology. The decrease of Nafion ionomer’s size results in better contact between catalyst particles and electrolyte, higher electrochemically active surface area, as well as significant improvement in the DMFC’s performance, as verified by electrochemical analysis and single cell evaluation. Full article
(This article belongs to the Special Issue Membrane Processes and Energy)

Review

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Open AccessReview Membranes for Environmentally Friendly Energy Processes
Membranes 2012, 2(4), 706-726; doi:10.3390/membranes2040706
Received: 2 August 2012 / Revised: 19 September 2012 / Accepted: 27 September 2012 / Published: 18 October 2012
Cited by 25 | PDF Full-text (903 KB) | HTML Full-text | XML Full-text
Abstract
Membrane separation systems require no or very little chemicals compared to standard unit operations. They are also easy to scale up, energy efficient, and already widely used in various gas and liquid separation processes. Different types of membranes such as common polymers, microporous
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Membrane separation systems require no or very little chemicals compared to standard unit operations. They are also easy to scale up, energy efficient, and already widely used in various gas and liquid separation processes. Different types of membranes such as common polymers, microporous organic polymers, fixed-site-carrier membranes, mixed matrix membranes, carbon membranes as well as inorganic membranes have been investigated for CO2 capture/removal and other energy processes in the last two decades. The aim of this work is to review the membrane systems applied in different energy processes, such as post-combustion, pre-combustion, oxyfuel combustion, natural gas sweetening, biogas upgrading, hydrogen production, volatile organic compounds (VOC) recovery and pressure retarded osmosis for power generation. Although different membranes could probably be used in a specific separation process, choosing a suitable membrane material will mainly depend on the membrane permeance and selectivity, process conditions (e.g., operating pressure, temperature) and the impurities in a gas stream (such as SO2, NOx, H2S, etc.). Moreover, process design and the challenges relevant to a membrane system are also being discussed to illustrate the membrane process feasibility for a specific application based on process simulation and economic cost estimation. Full article
(This article belongs to the Special Issue Membrane Processes and Energy)
Open AccessReview Investigation of Cross-Linked and Additive Containing Polymer Materials for Membranes with Improved Performance in Pervaporation and Gas Separation
Membranes 2012, 2(4), 727-763; doi:10.3390/membranes2040727
Received: 31 July 2012 / Revised: 24 September 2012 / Accepted: 25 September 2012 / Published: 22 October 2012
Cited by 26 | PDF Full-text (1701 KB) | HTML Full-text | XML Full-text
Abstract
Pervaporation and gas separation performances of polymer membranes can be improved by crosslinking or addition of metal-organic frameworks (MOFs). Crosslinked copolyimide membranes show higher plasticization resistance and no significant loss in selectivity compared to non-crosslinked membranes when exposed to mixtures of CO2
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Pervaporation and gas separation performances of polymer membranes can be improved by crosslinking or addition of metal-organic frameworks (MOFs). Crosslinked copolyimide membranes show higher plasticization resistance and no significant loss in selectivity compared to non-crosslinked membranes when exposed to mixtures of CO2/CH4 or toluene/cyclohexane. Covalently crosslinked membranes reveal better separation performances than ionically crosslinked systems. Covalent interlacing with 3-hydroxypropyldimethylmaleimide as photocrosslinker can be investigated in situ in solution as well as in films, using transient UV/Vis and FTIR spectroscopy. The photocrosslinking yield can be determined from the FTIR-spectra. It is restricted by the stiffness of the copolyimide backbone, which inhibits the photoreaction due to spatial separation of the crosslinker side chains. Mixed-matrix membranes (MMMs) with MOFs as additives (fillers) have increased permeabilities and often also selectivities compared to the pure polymer. Incorporation of MOFs into polysulfone and Matrimid® polymers for MMMs gives defect-free membranes with performances similar to the best polymer membranes for gas mixtures, such as O2/N2 H2/CH4, CO2/CH4, H2/CO2, CH4/N2 and CO2/N2 (preferentially permeating gas is named first). The MOF porosity, its particle size and content in the MMM are factors to influence the permeability and the separation performance of the membranes. Full article
(This article belongs to the Special Issue Membrane Processes and Energy)
Open AccessReview Biofouling of Water Treatment Membranes: A Review of the Underlying Causes, Monitoring Techniques and Control Measures
Membranes 2012, 2(4), 804-840; doi:10.3390/membranes2040804
Received: 3 August 2012 / Revised: 2 November 2012 / Accepted: 5 November 2012 / Published: 21 November 2012
Cited by 84 | PDF Full-text (278 KB) | HTML Full-text | XML Full-text
Abstract
Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies.
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Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies. This paper highlights the underlying causes of membrane biofouling and provides a review on recent developments of potential monitoring and control methods in water and wastewater treatment with the aim of identifying the remaining issues and challenges in this area. Full article
(This article belongs to the Special Issue Membranes in Water Purification)
Open AccessReview U.S. DOE Progress Towards Developing Low-Cost, High Performance, Durable Polymer Electrolyte Membranes for Fuel Cell Applications
Membranes 2012, 2(4), 855-878; doi:10.3390/membranes2040855
Received: 26 October 2012 / Revised: 6 December 2012 / Accepted: 7 December 2012 / Published: 18 December 2012
Cited by 23 | PDF Full-text (2128 KB) | HTML Full-text | XML Full-text
Abstract
Low cost, durable, and selective membranes with high ionic conductivity are a priority need for wide-spread adoption of polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Electrolyte membranes are a major cost component of PEMFC stacks at low production
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Low cost, durable, and selective membranes with high ionic conductivity are a priority need for wide-spread adoption of polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Electrolyte membranes are a major cost component of PEMFC stacks at low production volumes. PEMFC membranes also impose limitations on fuel cell system operating conditions that add system complexity and cost. Reactant gas and fuel permeation through the membrane leads to decreased fuel cell performance, loss of efficiency, and reduced durability in both PEMFCs and DMFCs. To address these challenges, the U.S. Department of Energy (DOE) Fuel Cell Technologies Program, in the Office of Energy Efficiency and Renewable Energy, supports research and development aimed at improving ion exchange membranes for fuel cells. For PEMFCs, efforts are primarily focused on developing materials for higher temperature operation (up to 120 °C) in automotive applications. For DMFCs, efforts are focused on developing membranes with reduced methanol permeability. In this paper, the recently revised DOE membrane targets, strategies, and highlights of DOE-funded projects to develop new, inexpensive membranes that have good performance in hot and dry conditions (PEMFC) and that reduce methanol crossover (DMFC) will be discussed. Full article
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)

Other

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Open AccessRetraction Publisher’s Note: Withdraw and Republication of “UV-Induced Radical Photo-Polymerization: A Smart Tool for Preparing Polymer Electrolyte Membranes for Energy Storage Devices”
Membranes 2012, 2(4), 705; doi:10.3390/membranes2040705
Received: 10 October 2012 / Accepted: 10 October 2012 / Published: 17 October 2012
PDF Full-text (123 KB) | HTML Full-text | XML Full-text
Abstract
It has been brought to the corresponding author’s attention by the administration office that some of the authors present in this paper [1] are contradicting with the rules and regulation of some of the confidential industrial projects which have been signed with strict
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It has been brought to the corresponding author’s attention by the administration office that some of the authors present in this paper [1] are contradicting with the rules and regulation of some of the confidential industrial projects which have been signed with strict regulations. Now it has aroused as a big trouble and, consequently, to solve this problem all the authors have determined that it should be retracted. This decision has been taken purely for bureaucratic aspect. We apologize for any inconvenience this may cause. Full article

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