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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Leveraging Triphenylphosphine-Containing Polymers to Explore Design Principles for Protein-Mimetic Catalysts

Complex interactions between noncoordinating residues are significant yet commonly overlooked components of macromolecular catalyst function. While these interactions have been demonstrated to impact binding affinities and catalytic rates in metalloenzymes, the roles of similar structural elements in synthetic polymeric catalysts remain underexplored. Using a model Suzuki–Miyuara cross-coupling reaction, we performed a series of systematic studies to probe the interconnected effects of metal–ligand cross-links, electrostatic interactions, and local rigidity in polymer catalysts. To achieve this, a novel bifunctional triphenylphosphine acrylamide (BisTPPAm) monomer was synthesized and evaluated alongside an analogous monofunctional triphenylphosphine acrylamide (TPPAm). In model copolymer catalysts, increased initial reaction rates were observed for copolymers untethered by Pd complexation (BisTPPAm-containing) compared to Pd-cross-linked catalysts (TPPAm-containing). Further, incorporating local rigidity through secondary structure-like and electrostatic interactions revealed nonmonotonic relationships between composition and the reaction rate, demonstrating the potential for tunable behavior through secondary-sphere interactions. Lastly, through rigorous cheminformatics featurization strategies and statistical modeling, we quantitated relationships between chemical descriptors of the substrate and reaction conditions on catalytic performance. Collectively, these results provide insights into relationships among the composition, structure, and function of protein-mimetic catalytic copolymers.

Catalysts↗
DOE OSTI2022

Design of a multi-functional gel polymer electrolyte with a 3D compact stacked polymer micro-sphere matrix for high-performance lithium metal batteries

We report lithium metal batteries (LMBs) are considered as promising high energy density batteries. However, they still suffer from poor cyclability due to the instability of solid electrolyte interphases (SEIs) and Li dendrite issues. Herein, a novel 3D densely packed multifunctional crosslinked gel polymer electrolyte (PHGPE) has been synthesized by in situ copolymerization of pentaerythritol tetraacrylate and 2-hydroxyethyl acrylate in a liquid electrolyte via a thermal initiation method. Due to intermolecular hydrogen bonding in the frameworks, the PHGPE exhibits a 3D compact-stacked and crosslinked micro-sphere structure, which benefits the construction of homogeneous Li + flux, enabling uniform Li plating/stripping and formation of robust SEIs onto the lithium electrode. Benefiting from the above advantages, symmetric Li cells in the PHGPE deliver excellent cyclabilities of 6000 h at a current density of 1 mA cm -2 (1 mA h cm -2 ) and 7700 h at 0.5 mA cm -2 (2 mA h cm -2 ). Moreover, the PHGPE has such a wide electrochemical window that it is compatible with both high-voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 and sulfur cathodes to realize long cycle life. Additionally, a LiFePO 4 based pouch size LMB also presents promising performance. Therefore, this study of the PHGPE has opened a new avenue for high-performance LMBs with excellent versatility and practicality.

25 ENERGY STORAGE↗
DOE OSTI2020

Utilizing ink composition to tune bulk-electrode gas transport, performance, and operational robustness for a Fe-N-C catalyst in polymer electrolyte fuel cell

With lower site density and turnover frequency, platinum group metal (PGM)-free catalysts based electrodes are often greater than 50 mu m thick in order to increase performance across the fuel cell operating range. Consequently, PGM-free electrodes have an additional bulk electrode transport resistance beyond the local or aggregate level transport in thin platinum-based electrodes. In parallel to the development of more active and durable PGM-free catalysts, advancements in understanding the interplay between PGM-free electrode fabrication, bulk-electrode transport, proton conductivity and performance are needed. Here, the relationship between ionic and gas phase transport through the electrode thickness is modified by adjusting electrocatalyst and ionomer flocculation/interaction at the ink level. The influence of the ink composition (water/n-propanol content) is examined via various in-situ electrochemical and ex-situ characterization techniques and the resulting electrode structure/performance relationship contrasted with electrode performance robustness across a range of relative humidity (RH). For the electrocatalyst examined here, a water-rich (82 wt% H2O) ink formulation was favorable for operation at high RH due to improved molecular diffusion through larger electrode pores. In contrast, the improved interactions between ionomer and electrocatalyst enabled a more robust electrode and higher performance during low RH operation for the 50 wt% H2O content ink.

08 HYDROGEN↗
DOE OSTI2022

Core–Shell Covalently Linked Graphitic Carbon Nitride–Melamine–Resorcinol–Formaldehyde Microsphere Polymers for Efficient Photocatalytic CO 2 Reduction to Methanol

Photocatalytic reduction of CO 2 with light and H 2 O to form CH 3 OH is a promising route to mitigate carbon emissions and climate changes. Although semiconducting metal oxides are potential photocatalysts for this reaction, low photon efficiency and leaching of environmental unfriendly, toxic metals limit their applicability. Here, we report a metal-free, core-shell photocatalysts consisting of graphitic carbon nitride (g-C 3 N 4 , CN) covalently linked to melamine-resorcinol-formaldehyde (MRF) microsphere polymers for this reaction. Cova-lent linkage enabled efficient separation of photo-generated carriers and photocatalysis. Using 100 mg of a photocatalyst containing 15 wt.% CN, a CH 3 OH yield of 0.99 μmol·h -1 was achieved at a reaction temperature of 80 °C and 0.5 MPa with external quantum efficiencies ranging from 5.5% at 380 nm to 1.7% at 550 nm. The yield was about 20 and 10 times higher than that of its components CN and MRF, respectively. Characterization with XPS, TEM, and bulk and surface elemental analyses supported a core-shell structure and charge transfer at C-N bond at the CN-MRF interface between the methoxy group in the 2,4-trishydroxylmethyl-1,3-diphenol part of MRF and the terminal amino groups in the CN. This enhanced ligand-to-ligand charge transfer resulted in 67% of photo-excited internal charge transferred from CN to hy-droxymethylamino group in MRF, whose amino group was the catalytic site for CO 2 photocatalytic reduction to CH 3 OH. Furthermore, this study provides a series of new metal-free photocatalyst designs and insights into the molecular-level structure-mediated photocatalytic response

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

Universal dynamics of coarsening during polymer-polymer thin-film spinodal dewetting kinetics

The dewetting dynamics of a supported bilayer polymer thin film on a solid substrate is investigated using grazing incidence x-ray photon correlation spectroscopy. We find that the top layer dewets via the spinodal mechanism. The kinetics of the dewetting is studied by monitoring the time evolution of the surface diffuse x-ray scattering intensity. We study the time evolution of fluctuations about the average surface structure by measuring the two-time x-ray intensity fluctuation correlation functions. Using these two-time correlation functions we quantify the crossover from early-time diffusive dynamics to hydrodynamics. The early diffusive regime satisfies dynamic universality. The two-time correlation functions also quantify the onset of hydrodynamic effects. The hydrodynamic regime is observed during the spinodal dewetting process as these interactions are not screened.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Study of improved resins for advanced supersonic technology composites. Part 1: Heteroaromatic polymers containing ether groups. Part 2: Curing chemistry of aromatic polymers and composite studies

Fourteen ether-containing, aromatic dianhydrides have been synthesized from N-phenyl-3 or 4-nitrophthalimide and various bisphenols. The process involves nucleophilic displacement of activated nitro groups with bisphenolate ions. Ether-containing dianhydrides were indefinitely stable in the presence of atmospheric moisture. One-step, high temperature solution polymerization of the ether-containing dianhydrides with m-phenylene diamine, 4,4'-oxydianiline and 1, 3-bis(4-aminophenoxy)benzene afforded 42 polyetherimides. The polyetherimides were all soluble in m-cresol except two which were found to be crystalline. The glass transition temperatures of the polyetherimides ranged from 178 to 277 C. Soluble polybenzimidazopyrrolones containing ether groups were also prepared from the same ether-containing dianhydrides and aromatic tetraamines by one-step solution polymerization. Using low molecular weight polyetherimides, various thermoset resin systems were developed and tested as matrices for fiber-reinforced composites. The curing chemistry involving reaction of the phthalonitrile group and the o-diaminophenyl group was found to be generally applicable to crosslinking various aromatic polymers other than polyimides.

Takekoshi, T.↗
NASA NTRS1992

Semi-interpenetrating polymer network for tougher and more microcracking resistant high temperature polymers

This invention is a semi-interpenetrating polymer network which includes a high performance thermosetting polyimide having a nadic end group acting as a crosslinking site and a high performance linear thermoplastic polyimide. An improved high temperature matrix resin is provided which is capable of performing at 316 C in air for several hundreds of hours. This resin has significantly improved toughness and microcracking resistance, excellent processability and mechanical performance, and cost effectiveness.

Pater, Ruth H.↗