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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.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Impact of Ion–Ion Correlated Motion on Salt Transport in Solvated Ion Exchange Membranes

The influence of dynamical ion-ion correlations and ion pairing on salt transport in ion exchange membranes remain poorly understood. In this study, we use the framework of Onsager transport coefficients within atomistic molecular dynamics sim- ulations to study the impact of ion-ion correlated motion on salt transport in hydrated polystyrene sulfonate membranes and compare with the results from aqueous salt so- lutions. At sufficiently high salt concentrations, cation-anion dynamical correlations exert a significant influence on both salt diffusivities and conductivities. Anion-anion distinct correlations, arising from the imbalance between the concentration of free (mo- bile) cations and anions, and the retarding effect of the fixed charge groups on cations, proves to be an additional important feature for polymer membranes. Furthermore, our results demonstrate that dynamical correlations should become an important consideration in experimental measurements of salt diffusivities and conductivities for non-dilute salt solutions in polymer membranes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Creating Novel Gas Separation Constructs by Manipulating Free-Volume Distributions in Polymer-Grafted Nanoparticles

Polymer membranes are critical to many sustainability applications that require gas separation primarily based on differences in the sizes of the constituent molecules (“sieving”). The important figures of merit in this context are the rate at which the gas permeates through the membrane (or flux) and the resulting gas purity (as characterized by its selectivity). The overall goal is to maximize both gas permeability and selectivity. Currently, the ability to a priori design polymeric materials (either pure polymers or mixed matrix membranes where polymers are mixed with inorganic nanoparticles) with required permeability and selectivity remains an open challenge.

03 NATURAL GAS↗
DOE OSTI2022

Designing polymeric membranes with coordination chemistry for high-precision ion separations

State-of-the-art polymeric membranes are unable to perform the high-precision ion separations needed for technologies essential to a circular economy and clean energy future. Coordinative interactions are a mechanism to increase sorption of a target species into a membrane, but the effects of these interactions on membrane permeability and selectivity are poorly understood. We use a multilayered polymer membrane to assess how ion-membrane binding energies affect membrane permeability of similarly sized cations: Cu 2+ , Ni 2+ , Zn 2+ , Co 2+ , and Mg 2+ . We report that metals with higher binding energy to iminodiacetate groups of the polymer more selectively permeate through the membrane in multisalt solutions than single-salt solutions. In contrast, weaker binding species are precluded from diffusing into the polymer membrane, which leads to passage proportional to binding energy and independent of membrane thickness. Our findings demonstrate that selectivity of polymeric membranes can markedly increase by tailoring ion-membrane binding energy and minimizing membrane thickness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Chapter 10 - Economic Considerations for Hydrogen Production with a Focus on Polymer Electrolyte Membrane Electrolysis

This Chapter provides an overview of key economic considerations for hydrogen produced from water electrolysis, with the analyses presented here ranging from high-level summaries to detailed considerations of key market and technological drivers. As the electric power sector evolves to account for increasing shares of renewable energy, opportunities are emerging for technologies capable of storing renewable energy in various forms, including as hydrogen. Opportunities for reducing the cost of hydrogen produced from electrolysis include ensuring access to low-cost wholesale electricity, reducing the capital cost of electrolyzers, and development of systems capable of being dispatchable loads without experiencing significant efficiency penalties throughout lifetime. Our analysis indicates that numerous pathways exist for making hydrogen from electrolysis cost-competitive with hydrogen produced from conventional technologies, and significant opportunities exist for research and development to address performance targets for the future electrolysis systems envisioned here.

cost reduction↗
DOE OSTI2021

High-performance SO 2 -depolarized electrolysis cell using advanced polymer electrolyte membranes

Three different proton conducting polymeric membrane materials (Nafion® 115, Nafion® 212, and sulfonated Diels-Alder polyphenylene [SDAPP]) were evaluated for use in SO 2 -depolarized electrolyzers for the production of hydrogen via the hybrid sulfur cycle. Their performance was measured using different water feed strategies to minimize overpotential losses while maintaining high product acid concentration. Both thin membranes (Nafion® 212 and SDAPP) showed performance superior to that of the thicker Nafion® 115. Here, the SDAPP membrane electrode assembly (MEA) performed well at higher acid concentrations, maintaining low ohmic and kinetic overpotentials. Finally, short-term (100-h) stability tests under constant current conditions showed minimal degradation for the SDAPP and Nafion® 212 MEAs. SDAPP MEA performance approached the targets needed to make the hybrid sulfur cycle a competitive process for hydrogen production (product acid concentration ≥65 wt% H 2 SO 4 at ≤ 0.6-V cell potential and ≥0.5 A-cm –2 current density).

08 HYDROGEN↗
DOE OSTI2024

The impact of hot-press conditions on the durability of polymer electrolyte membrane fuel cells

The proton exchange membrane integrity can be compromised during hot-press fabrication of membrane electrode assemblies (MEAs) causing premature cell failures during operation. In this work, infrared (IR) thermography was used as a diagnostic tool to spatially visualize hydrogen (H 2 ) crossover and identify process-induced-membrane irregularities (PIMs). These irregularities were identified as seed locations for MEA failures. Fine tuning of hot-press conditions was used to mitigate premature cell failures informed by accelerated stress testing (AST). The impact of PIMs on the initial performance, high-frequency resistances, open-circuit voltage, and H 2 crossover are reported. Nafion XL and 212 membranes, hot-pressed with a force of 16 kg/cm 2 and temperature of 120°C, were found to be consistently irregularity-free. Irregularity-free MEAs using Nafion 211, 212, and XL membranes demonstrated AST lifetime improvements of 58, 64 and 400%, respectively, compared to those fabricated with non-optimized conditions. In conclusion, this work highlights the importance of fabrication parameters on premature cell failures.

08 HYDROGEN↗
DOE OSTI2023

Enhancing durability of polymer electrolyte membrane using cation size selective agents

Radical species generated during proton exchange membrane fuel cell operation considerably limit the achievable durability, particularly for heavy-duty vehicle applications. A promising solution to the problem is the incorporation of radical scavenger additives such as cerium which mitigates chemical attacks on the membrane. However, these additives migrate during fuel cell operation causing a loss in durability and performance due to detrimental interaction with various components of the fuel cell. Here, we study cation size selective agents as a means to immobilize cerium within perfluorosulfonic acid (PFSA) membranes. We synthesized an organometallic complex of cerium with 15-Crown-5 and investigated the effectiveness of this complex to immobilize cerium. Over 300% increase in cerium retention and an 80% increase in chemical durability were observed owing to the stabilization effect of crown ethers on cerium. Migration under a potential gradient can be eliminated while the complex also contributes to the enhancement in cerium radical scavenging activity. In conclusion, current challenges with the proposed solution are highlighted and future work is discussed.

25 ENERGY STORAGE↗
DOE OSTI2020

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe–N–C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

In this paper, we present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe–N–C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1-propanol ( n PA). The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (H 2 O %) in the DM on the ink microstructure were studied. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks. In the absence of the ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure for catalyst concentrations as low as 2 wt %. The effect of H 2 O % in the DM on particle agglomeration was found to vary with particle concentration. In concentrated inks (≥2 wt % catalyst), increasing H 2 O % was found to increase agglomeration because of the hydrophobic nature of the catalysts. In dilute inks (<1 wt % catalyst), the trend was reversed with increasing H 2 O %, suggesting that electrostatic interactions are dominating the behavior. In inks with 5 wt % catalyst, the addition of an ionomer was found to significantly stabilize the catalyst against agglomeration. Maximum stability was observed at 0.35 I/C for all DM H 2 O % studied. At high ionomer concentrations (I/C > 0.35), interesting differences were observed between n PA-rich inks (H 2 O % ≤ 50%) and H 2 O-rich (82% H 2 O) inks. The n PA-rich inks remained predominantly stable—ink viscosity only weakly increased with I/C and the Newtonian behavior was maintained for I/C up to 0.9. In contrast, the H 2 O-rich inks exhibited a significant increase in viscoelasticity with increasing I/C, suggesting flocculation of the catalyst by the ionomer. These differences suggest that the nature of the interactions between the ionomer and catalyst is highly dependent on the H 2 O % in the DM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Compressive Creep of Polymer Electrolyte Membranes: A Case Study for Electrolyzers

For proton-exchange membrane (PEM) water electrolyzers to be commercially feasible, PEMs must perform over long lifetimes in liquid environments under compression while maintaining mechanical stability. A hydrated environment, while inherent for operation and conductivity, undermines PEM stability. Mechanical stability of PEMs is commonly characterized in tension, which is not applicable to electrolyzers, wherein PEMs could undergo high pressures. In this study, a compression creep procedure is developed using a custom-designed setup to monitor creep response of hydrated PEMs. Furthermore, our results show that PEMs exhibit continuous creep response under compression over 24 h, with a dependence on the applied pressure and hydration state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Nitrogen-Doped PtNi Catalysts on Polybenzimidazole-Functionalized Carbon Support for the Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

PtM (M = 3d transition metals) alloys are known as the promising oxygen reduction reaction catalysts and have been considered as the replacement of pure Pt catalysts for the commercialization of proton exchange membrane fuel cells. Although great progress has been made in the past three decades, the performance and durability of PtM catalysts still face stringent challenges from practical applications. Functionalization of a catalyst carbon support with nitrogen-contained groups can add charges onto its surface, which can be utilized to build a more complete ionomer/catalyst interface, to reduce the catalyst particle size, and to improve particle size distribution. Nitriding of PtNi catalysts can effectively improve the catalyst activity and stability by the modification of lattice strain. Hereby, we propose a synergistic approach of combining polybenzimidazole-grafted Vulcan XC72 carbon as the catalyst carbon support and the nitriding of PtNi to develop PtNiN/XC72-polybenzimidazole catalysts. Such PtNiN/XC72-PBI catalysts exhibit the excellent performance of fuel cell membrane electrode assembly (i.e., mass activity, 440 mA mgPt –1 ; electrochemical surface area, 51 m 2 gPt –1 ; and rated power density, 836 mW cm –2 ) as well as promising catalyst stability. The developed PtNiN/XC72-PBI meets the US DOE 2020 targets of mass activity for the fuel cell catalysts. This work provides a novel approach and a promising pathway on the development of the catalyst using such a synergistic approach-modification of the catalyst structure by nitrogen doping and functionalization of carbon support by polybenzimidazole for both high performance and high durability.

25 ENERGY STORAGE↗
DOE OSTI2022

Fabrication of Polymer Membrane-Suspended Microstructures on Printed Circuit Boards

When microelectromechanical systems are manufactured in high densities, the necessary routing layer structures can become complex and thus expensive if executed in silicon technology. If, additionally, the microstructures are also to be fabricated suspended on membranes, complex thinning processes become necessary to form these often rather fragile membranes. Here, a novel fabrication concept is demonstrated that allows for the fabrication of membrane-suspended microstructures using standard microfabrication techniques directly integrated with printed circuit boards (PCB) by laminating polyimide (PI) films over cavities in the PCB. This results in cost-effective routing layer fabrication and direct compatibility with common electronic component standards such as SMT (surface-mount technology) and THT (through-hole technology). To illustrate the capabilities of the fabrication process, we fabricated an array of membrane suspended microheaters. Individual platinum microheater elements are suspended on PI membranes that are 25 μm thick and 500 μm in diameter. The fabricated PCB carries a 10x10 array of suspended microheaters on an area of 26,mm x 26,mm. Here, the characterization of the microheater array shows that a yield of 86% functional microheaters was achieved. An individual microheater shows an almost linear heating characteristic at least up to 200°C demonstrating the viability of the technique for creating functional membrane-suspended microstructures on a PCB. [2021-0226]

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Experimental Studies of Graphene-Coated Polymer Electrolyte Membranes for Direct Methanol Fuel Cells

The two main technical limitations of direct methanol fuel cells (DMFCs) are the slow kinetic reactions of the methanol oxidation reaction (MOR) in the anode and the crossing over of unreacted methanol through the proton exchange membrane (PEM). It is a common practice to use Nafion membranes as PEMs, which have high ion exchange capacity. However, Nafion-based membranes also have high fuel permeability, decreasing fuel utilization, and reducing the potential power density. This article focuses on using graphene-coated (Gr-coated) PEMs to reduce fuel crossover. Protons can permeate across graphene, and thus, it can be employed in various devices as a proton conductive membrane. Here, we report the efficiency of Gr-coated Nafions. We tested performance and crossover at three different temperatures with four different fuel concentrations and compared it to a Nafion PEM that underwent the same test conditions. We found that the adhesion of Gr on to PEMs is insufficient for prolonging fuel cell operation, resulting in Gr delamination at high temperatures and higher fuel crossover values compared to lower temperature testing. Furthermore, the results for 7.5M methanol fuel show a reduction of up to 25% in methanol crossover, translating to a peak power density that increases from 3.9 to 9.5 mW/cm 2 when using a Gr-coated PEM compared to a Nafion PEM at 30 °C.

25 ENERGY STORAGE↗