Search NASA⌕ Search

SEARCH · Search NASA

Results for “polymer membranes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Optimization of Extended-Surface PtNi Nanowire Oxygen Reduction Electrocatalysts Produced via Atomic Layer Deposition

Polymer electrolyte membrane fuel cells (PEMFCs) produce electricity with only heat and water as byproducts, but sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode and durability limitations restrict widespread commercialization, motivating the development of advanced catalysts. In this research, extended-surface platinum nickel (PtNi) nanowires (NWs) synthesized using the scalable atomic layer deposition (ALD) technique are investigated with the goal of exploring the durability benefits of high-aspect-ratio electrocatalysts and the tunability of beneficial kinetic properties. The surface and bulk composition and the structure of the PtNi NWs were investigated as a function of a series of postsynthesis modifications. The results from a combination of electron microscopy and X-ray spectroscopy characterization techniques were correlated to electrochemical performance to gain a comprehensive understanding of the structure-property-performance relationships. The robust structure of the ALD-derived NWs enabled additional postsynthesis optimization steps, which were not possible with previous-generation materials synthesized via spontaneous galvanic displacement, resulting in a catalyst with beneficial properties for catalyst kinetics as well as improved durability. Our study demonstrates potential pathways toward further improving the performance of this class of materials through optimization of bulk and surface properties of the catalyst.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Structure, Dynamics, and Hydrogen Transport in Amorphous Polymers: An Analysis of the Interplay between Free Volume Element Distribution and Local Segmental Dynamics from Molecular Dynamics Simulations

Polymers are attractive membrane materials owing to their mechanical robustness and relatively inexpensive fabrication. An important indicator of membrane performance are free volume elements (FVE): microporous void spaces created by the inefficient packing of bulky groups along the polymer chain. FVEs tend to degrade over time, as polymer chains reorganize irreversibly. While it is widely accepted that polymer flexibility has an impact on membrane transport properties, the molecular nature of this impact is still not well understood. By the establishment of a correlation between local chain dynamics and the distribution of free volume elements (FVEs), penetrant transport can be regulated more efficiently in amorphous polymer membranes. In this work, we implement all-atom molecular dynamics (MD) simulations to explore the relationship between chain dynamics and free volume in three polymers with different levels of backbone flexibility: polymethylpentene (PMP), polystyrene (PS), and HAB-6FDA thermally rearranged polymer (TRP). We construct these polymers at different temperatures and examine how temperature impacts the FVE distribution and segmental mobility. Our analysis shows that chain segments near FVEs have higher mobility compared with the atoms in the bulk; the extent of this difference increases with chain flexibility. Increasing the chain flexibility by increasing the temperature results in a broader FVE distribution. Rigid polymers such as TRP show the most robust FVE distribution and are not significantly affected by the temperature change. To capture penetrant diffusion through the polymer matrix, hydrogen is inserted and the diffusion is measured at different temperatures; hydrogen mobility is influenced by the FVE structure and overall mobility of polymer chains. Lastly, at low temperatures, hydrogen mobility is influenced by void distribution, while at high temperatures, polymer dynamics dictate hydrogen transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A comparative experimental study of the hygroscopic and mechanical behaviors of electrospun nanofiber membranes and solution–cast films of polybenzimidazole

This article reports a comparative experimental study of the hygroscopic and mechanical behaviors of electrospun polybenzimidazole (PBI) nanofiber membranes and solution-cast PBI films. As-electrospun nonwoven PBI nanofiber mats (with the nanofiber diameter of ~250 nm) were heat-pressed under controlled temperature, pressure and duration for the study; lab-made solution-cast PBI films and commercially available PBI films (the PBI Performance Product Inc., Charlotte, NC) were used as the control samples. Thermogravimetric and microtensile tests were utilized to characterize the hygroscopic (moisture absorption) and mechanical properties of the PBI nanofiber membranes at varying heat-pressing conditions, which were further compared to those of solution-cast PBI films. Experimental results indicated that the PBI nanofiber membranes carried slightly higher thermal stability and less hygroscopic properties than those of solution-cast PBI films. In addition, heat-pressing conditions significantly influenced the mechanical properties of the resulting PBI nanofiber membranes. The stiffness and tensile strength increase with increasing either the heat-pressing pressure or duration, and relevant mechanisms were explored. Here, the present study provides a rational understanding of the hygroscopic and mechanical behaviors of electrospun PBI nanofiber membranes and solution-cast PBI films that are beneficial to their reliable cutting-edge applications in high-temperature filtration, polymer electrolyte membranes (PEMs), etc.

25 ENERGY STORAGE↗
DOE OSTI2024

Interconnected Nanoporous Polysulfone by the Self-Assembly of Randomly Linked Copolymer Networks and Linear Multiblocks

Porous materials have attracted considerable attention due to their versatile applications, especially in water purification. Interconnected nanoporous structures are distinguished by their high degree of porosity and resistance to clogging, as well as their insensitivity to nanostructural orientation. Previous works on randomly linked copolymer systems have shown that they can effectively produce disordered cocontinuous nanostructures, which upon removal of one component yield interconnected nanoporous materials. However, the cocontinuous nanomaterials previously developed using polystyrene (PS) and poly(d,l-lactic acid) (PLA) strands, and the resulting interconnected nanoporous PS monoliths, were far too brittle to enable practical use as membranes. Here, we study the self-assembly of randomly linked copolymer networks prepared using blocks of the engineering polymer polysulfone (PSU). A wide cocontinuous regime (spanning 40 wt %) was found for randomly end-linked copolymer networks (RECNs) constructed from PSU and PLA strands, via a combination of mechanical testing, gravimetry, small-angle X-ray scattering, and scanning electron microscopy. The PSU/PLA cocontinuous nanomaterial with symmetric composition showed 2.4 times higher Young’s modulus and ~100 times greater toughness than the corresponding PS/PLA sample. The interconnected nanoporous PSU fabricated after etching of PLA even exhibited 1.6 times greater toughness than PS/PLA prior to PLA removal. To facilitate the production of thin films of cocontinuous nanomaterials, we applied solution-processable randomly linked linear PSU/PLA multiblock polymers onto ultrafiltration membranes. Here, the interconnected nanoporous PSU thin film generated by etching PLA was found to effectively reject 50 nm diameter particles without significantly compromising permeability. This discovery presents a valuable addition to the existing techniques used to fabricate PSU membranes. In contrast to traditional methods, which are sensitive to processing conditions, produce a wide range of pore sizes, and offer limited adjustability of pore size, the current technique is anticipated to enable interconnected PSU membranes with more uniform and tailorable porosity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Probing Membrane Degradation with Varying Catalyst Layer Thickness and Carbon Support

Understanding membrane degradation continues to be of significant importance when studying fuel cell durability. Fuel cell performance and durability depends heavily on the membrane's chemical and mechanical integrity. In Nafion® membranes, hydroxyl radicals are the primary cause of chemical membrane degradation as they attack the membrane's polymer structure. Radical formation can ensue via peroxide decomposition at the cathode or gases reacting on Pt particles within the membrane. Here, a previous research effort on membrane degradation as a function of ultra-low Pt loadings (≤ 0.1 mgPt cm -2 ) showed the degradation rate increases with Pt loading. This is most likely due to more heterogenous sites for radical formation. Manufacturing MEAs with ultra-low Pt loadings can yield thin, non-uniform catalyst layers. In this research effort we studied membrane degradation with ultra-low Pt loadings while varying catalyst layer thickness, I/C ratio, and types of carbon support.

25 ENERGY STORAGE↗
DOE OSTI2022

Membrane Strategies for Water Electrolysis

Hydrogen holds great promise as a clean energy resource to help the global carbon-free energy goal. Here, green hydrogen production from renewable energy-powered water electrolysis can decarbonize hard-to-abate industries and transport applications. Ion-exchange membranes are an essential component of membrane-based water electrolysis, enabling high hydrogen production efficiency through a zero-gap configuration. While perfluorosulfonic acids are the standard polymer electrolyte membrane material, research efforts for membrane alternatives have increased over the years to drive down the cost of electrolyzers and improve devices’ durability without sacrificing performance and efficiency. Here we present our perspectives on acidic, alkaline, and bipolar membranes for water electrolyzers and discuss future research directions to develop advanced membranes for green hydrogen production technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Co-Assembly of Carbon Nanotube Porins into Biomimetic Peptoid Membranes

Robust and cost-effective membrane-based separations are essential to solving many global crises, such as the lack of clean water. Even though the current polymer-based membranes are widely used for separations, their performance and precision can be enhanced by using a biomimetic membrane architecture that consists of highly permeable and selective channels embedded in a universal membrane matrix. Researchers have shown that artificial water and ion channels, such as carbon nanotube porins (CNTPs), embedded in lipid membranes can deliver strong separation performance. However, their applications are limited by the relative fragility and low stability of the lipid matrix. In this work, we demonstrate that CNTPs can co-assemble into two-dimension (2D) peptoid membrane nanosheets, opening up a way to produce highly programmable synthetic membranes with superior crystallinity and robustness. A combination of molecular dynamics (MD) simulations, Raman spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM) measurements to verify the co-assembly of CNTP and peptoids are used and show that it does not disrupt peptoid monomer packing within the membrane. In conclusion, these results provide a new option for designing affordable artificial membranes and highly robust nanoporous solids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A Review on Bioinspired Proton Exchange Membrane Fuel Cell: Design and Materials

With the climate crisis gathering recognition, there has been significant interest in clean energy. As a reliable and clean energy solution, markets transitioning toward sustainable energy have identified polymer electrolyte membrane fuel cells (PEMFCs) as a critical technology. The increasing interest in PEMFCs is primarily due to their high energy density, high efficiency and zero greenhouse gas emission. However, additional development is required to overcome the current barriers associated with fuel cell component design, high manufacturing cost, and insufficient stability. Bioinspired designs have the potential to provide new and valuable insights using novel techniques for extracting design inspirations from biological structures. Applying these design concepts to develop materials and structures for various fuel cell components can be transformative. The well–adapted structures and functional features of biological systems have been proven to greatly enhance the performance of current designs through novel and optimized pathways. Bioinspired designs have indeed lived up to performance expectations and even exceed them. Herein, the potential and value of using these bioinspired designs are discussed. Recent studies and advancements based on nature–inspired structures for components of PEMFCs and how these design considerations substantiate their claim as an attractive alternative to conventional designs are discussed.

25 ENERGY STORAGE↗
DOE OSTI2023

Quaternized Polynorbornene Random Copolymers for Fuel Cell Devices

Quaternized polymers are critical components for various energy devices. Vinyl-addition polynorbornenes provide high mechanical strength, high ion conductivity, and chemical stability in a wide range of pH environments due to the all-C–C bond backbone. In this paper, we present the synthesis of a series of quaternized polynorbornene random copolymers via vinyl addition polymerization and elucidate the impact of polymer composition on their properties. The quaternary ammonium alkyl tether length and the ratio of n-hexylnorbornene to unsubstituted norbornene are systemically tailored. A copolymer of 5-(3-bromopropyl)-2-norbornene and norbornene with pendant trimethylammonium groups achieved hydroxide conductivity of 109 mS/cm at 80 °C with a modest water uptake of 72%. The addition of n-hexylnorbornene to the copolymer, to make a terpolymer, allows for the polymer composition to be tailored for properties, including a decrease in water uptake and higher processability, despite a slightly decreased hydroxide conductivity. Moreover, the developed membranes are chemically robust and highly mechanically stable, enabling thin membranes to be easily fabricated. This study provides insight into important design parameters for quaternized polynorbornenes for a variety of energy storage and conversion devices, especially fuel cells.

25 ENERGY STORAGE↗
DOE OSTI2026

Garnet/PVDF-HFP Hybrid Membranes for Li-Metal Batteries: Cooperative Research and Development Final Report, CRADA Number CRD-19-00807

Hazen Research, Inc., in collaboration with University of Colorado, Boulder (CU-B) and National Renewable Energy Laboratory (NREL), will develop and demonstrate a ceramic-polymer hybrid membrane based on garnet (Li7La3Zr2O12) and PVDF (Poly Vinylidene Fluoride)-HFP (Hexafluoropropylene) adaptable to Li-metal anodes. Under this CRADA, NREL will test the developed membranes providing feedback and advice to demonstrate hybrid membranes with Li-ion conductivity >10-4 S/cm at room temperature that are stable with Li-metal, followed by demonstration of full cells with Li-metal anode.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Evaluating the impact of functional groups on membrane‐mediated CO 2 / N 2 gas separations using a common polymer backbone

Abstract Polymeric membranes have shown tremendous promise for the separation of CO 2 from flue gas streams. However, few systematic studies have been conducted to better understand the impact that chemical functionalities have on membrane‐based gas separation performance. To address this gap, we herein describe the synthesis and gas separation performance of a series of vinyl‐addition polynorbornenes bearing various CO 2 ‐philic functional groups. To facilitate direct comparison between functional groups, each material was designed to maintain a common polymer backbone. Though the incorporation of CO 2 ‐philic moieties within a dense polymeric membrane is frequently hypothesized to enhance CO 2 solubility, and thereby increase CO 2 /N 2 selectivity, our results demonstrate that the incorporation of CO 2 ‐philic groups onto a common polymer backbone do not necessarily result in increased gas separation performance. Experimental and computational results demonstrate that the incorporation of amidoxime groups onto a polynorbornene backbone increase CO 2 /N 2 selectivity, whereas commonly employed ethereal side chains only increased permeability.

Higgins, Morgan A.↗
DOE OSTI2023

Electrolyzer and method of use

Disclosed are membrane electrode assemblies having a cathode layer comprising a carbon oxide reduction catalyst that promotes reduction of a carbon oxide; an anode layer comprising a catalyst that promotes oxidation of a water; a polymer electrolyte membrane (PEM) layer disposed between, and in contact with, the cathode layer and the anode layer; and a salt having a concentration of at least about 10 uM in at least a portion of the MEA.

Cave, Etosha R.↗
DOE OSTI2020

Synthetic membranes and methods of use thereof

The present invention relates to synthetic membranes and use of these synthetic membranes for isolation of volatile organic compounds and purification of water. The synthetic membrane includes a hydrophobic polymer layer located on a polymeric membrane support layer. The invention includes a method of isolating volatile organic compounds with the synthetic membrane by contacting a volatile organic mixture with the hydrophobic polymer layer of the synthetic membrane and removing volatile organic compounds from the polymeric membrane support layer of the synthetic membrane by a process of pervaporation. The invention also includes a method of purifying water with the synthetic membrane by contacting an ionic solution with the hydrophobic polymer layer of the synthetic membrane and removing water from the polymeric membrane support layer of the synthetic membrane by a process of reverse osmosis. The invention also relates to methods of isolating non-polar gases by gas fractionation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthetic membranes and methods of use thereof

The present invention relates to synthetic membranes and use of these synthetic membranes for isolation of volatile organic compounds and purification of water. The synthetic membrane includes a hydrophobic polymer layer located on a polymeric membrane support layer. The invention includes a method of isolating volatile organic compounds with the synthetic membrane by contacting a volatile organic mixture with the hydrophobic polymer layer of the synthetic membrane and removing volatile organic compounds from the polymeric membrane support layer of the synthetic membrane by a process of pervaporation. The invention also includes a method of purifying water with the synthetic membrane by contacting an ionic solution with the hydrophobic polymer layer of the synthetic membrane and removing water from the polymeric membrane support layer of the synthetic membrane by a process of reverse osmosis. The invention also relates to methods of isolating non-polar gases by gas fractionation.

Belfort, Georges↗
DOE OSTI2021

Synthetic membranes and methods of use thereof

The present invention relates to synthetic membranes and use of these synthetic membranes for isolation of volatile organic compounds and purification of water. The synthetic membrane includes a hydrophobic polymer layer located on a polymeric membrane support layer. The invention includes a method of isolating volatile organic compounds with the synthetic membrane by contacting a volatile organic mixture with the hydrophobic polymer layer of the synthetic membrane and removing volatile organic compounds from the polymeric membrane support layer of the synthetic membrane by a process of pervaporation. The invention also includes a method of purifying water with the synthetic membrane by contacting an ionic solution with the hydrophobic polymer layer of the synthetic membrane and removing water from the polymeric membrane support layer of the synthetic membrane by a process of reverse osmosis. The invention also relates to methods of isolating non-polar gases by gas fractionation.

Belfort, Georges↗
DOE OSTI2021

Performance and durability of anion exchange membrane water electrolyzers using down-selected polymer electrolytes

Over the last decade, several stable anion exchange polymer electrolytes have been developed for electrochemical devices. Herein, we investigate how chemical structure and physical properties of polymer electrolytes affect performance and durability of anion exchange membrane water electrolyzers (AEMWEs). We select polymer electrolytes with high alkaline stability and consider their polymer properties including conductivity, mechanical/chemical stability, and material interactions to interpret the performance and durability of AEMWEs. Here, the AEMWE with a poly(phenylene) membrane and a poly(fluorene) ionomeric binder exhibited the best performance among those tested in this study; the AEMWE showed ~1 A cm –2 at 2 V under 1 wt% K 2 CO 3 -fed conditions. The voltage degradation rate was 270–550 μV h –1 for several hundred operating hours at a constant current density of 750 mA cm –2 and a differential pressure of 100 pounds per square inch gauge. Based on these results, we discuss research needs of polymer electrolytes for practical AEMWEs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗