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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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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.
Tuning the Coarse Space Construction in a Spectral AMG Solver
Abstract not provided
Postsynthetic Tuning of Metal–Organic Frameworks for Targeted Applications
Metal–organic frameworks (MOFs) are periodic, hybrid, atomically well-defined porous materials that typically form by self-assembly and consist of inorganic nodes (metal ions or clusters) and multitopic organic linkers. MOFs as a whole offer many intriguing properties, including ultrahigh porosity, tunable chemical functionality, and low density. These properties point to numerous potential applications, including gas storage, chemical separations, catalysis, light harvesting, and chemical sensing, to name a few. Reticular chemistry, or the linking of molecular building blocks into predetermined network structures, has been employed to synthesize thousands of MOFs. Given the vast library of candidate nodes and linkers, the number of potentially synthetically accessible MOFs is enormous. Nevertheless, a powerful complementary approach to obtain specific structures with desired chemical functionality is to modify known MOFs after synthesis. This approach is particularly useful when incorporation of particular chemical functionalities via direct synthesis is challenging or impossible. Here, the challenges may stem from limited stability or solubility of precursors, unwanted secondary reactivity of precursors, or incompatibility of functional groups with the conditions needed for direct synthesis. MOFs can be postsynthetically modified by replacing the metal nodes and/or organic linkers or via functionalization of the metal nodes and/or organic linkers.
Tuning Electrical, Optical, and Thermal Properties through Cation Disorder in Cu[subscript 2]ZnSnS[subscript 4]
Abstract not provided
Insights into Boron-Based Polyanion-Tuned High-Nickel Cathodes for High-Energy-Density Lithium-Ion Batteries
Ultrahigh-Ni layered oxide cathodes (Ni content > 90%) are at the forefront for potentially enabling higher-energy density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade, poor thermal stability, and increased air sensitivity. Introduction of boron-based polyanion into layered cathodes has been found to be effective in stabilizing high-Ni cathodes, but the mechanism behind it is not yet fully understood. To develop a better understanding, we present here an extensive characterization of the ultrahigh-Ni cathode LiNi 0.94 Co 0.06 O 2 (NC) and B 2 O 3 -LiNi 0.94 Co 0.06 O 2 (B-NC). The B-NC delivers a capacity of 223 mA h g -1 with 80% capacity retention after 400 cycles in full cells with graphite anodes, superior to 61% retention for NC. In-depth interphase investigations reveal that the improved cyclability is attributed to the development of a well-passivated boron/phosphorus-rich cathode-electrolyte interphase in B-NC. Moreover, B-NC demonstrates a considerably enhanced air-exposure and thermal stability. A 30-day air-stored B-NC delivers a discharge capacity of 125 mA h g -1 at 10C rate, in sharp contrast to 65 mA h g -1 for the stored NC. Finally, this work advances the understanding of the effect boron-based polyanion insertion into layered oxides has on battery performance and offers a viable strategy for developing practically viable ultra-high-Ni cathodes with high-energy density.
Tuning Fe-Se Tetrahedral Frameworks by a Combination of [Fe(en)[subscript 3]][superscript 2+] Cations and Cl[superscript -] Anions
Abstract not provided
Tuning Electrogenerated Chemiluminescence Intensity Enhancement Using Hexagonal Lattice Arrays of Gold Nanodisks
Electrogenerated chemiluminescence (ECL) microscopy shows promise as a technique for mapping chemical reactions on single nanoparticles. The technique’s spatial resolution is limited by the quantum yield of the emission and the diffusive nature of the ECL process. To improve signal intensity, ECL dyes have been coupled with plasmonic nanoparticles, which act as nanoantennas. Here, we characterize the optical properties of hexagonal arrays of gold nanodisks and how they impact the enhancement of ECL from the coreaction of tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate and tripropylamine. Here, we find that varying the lattice spacing results in a 23-fold enhancement of ECL intensity because of increased dye-array near-field coupling as modeled using finite element method simulations.
Li Intercalation in MoS 2 : In Situ Observation of Its Dynamics and Tuning Optical and Electrical Properties
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Tuning the Number of Active Sites and Turnover Frequencies by Surface Modification of Supported ReO4/(SiO2-Al2O3) Catalysts for Olefin Metathesis
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Tuning Noncollinear Spin Structure and Anisotropy in Ferromagnetic Nitride MXenes
Recent experimental success in the realization of two-dimensional magnetism has invigorated the search for low-dimensional material systems with tunable magnetic anisotropy that exhibit intrinsic long-range ferromagnetic order. Here in this paper, we report that modifying the surface termination and transition metal in monolayer M 2 NT x nitride MXenes gives rise to a rich diversity of noncollinear spin structures and finely tunable magnetocrystalline anisotropy. Based on first-principles simulations, we predict that manipulating the strength of the spin–orbit interaction and electron localization via the chemical degrees of freedom can induce sufficient anisotropy to counteract thermal fluctuations that suppress long-range magnetic order. We find that Ti 2 NO 2 and Mn 2 NF 2 MXenes have continuous O(3) and O(2) spin symmetries, respectively, that may be broken by an applied field, while Cr 2 NO 2 and Mn 2 NO 2 are intrinsic Ising ferromagnets with out-of-plane easy axes and magnetic anisotropy energies up to 63 μeV/atom. These systems also exhibit both gapped and gapless Dirac points near the Fermi level. Our study suggests that nitride MXenes offer a promising avenue for achieving both practical spintronic devices and investigating fundamental spin processes in two-dimensional materials.
Improved Performances in Polymer BHJ Solar Cells Through Frontier Orbital Tuning of Small Molecule Additives in Ternary Blends
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Tuning the Formations of Metal-Organic Frameworks by Modification of Ratio of Reactant, Acidity of Reaction System, and Use of a Secondary Ligand
Four porous coordination networks (PCNs), {[Zn3O(H2O)(3)(adc)(3)]center dot 2(C2H6NH2)center dot 2(DMF)center dot 3(H2O)}(n) (PCN-131), Zn-2(DMA)(2)(adc)(2)]center dot 2(DMA)}(n) (PCN-132), {[Zn3O(DMF)(adc)(3)(4,4'-bpy)]center dot 2(C2H6NH2)center dot S}(n) (PCN-131'), and {[Zn(adc)(4,4'-bpy)(0.5)]center dot S}(n) (PCN-132'), have been synthesized by the assembly of anthrancene-9,10-dicarboxylic acid (H(2)adc) with Zn(II) under different reaction conditions, including modifications of reactant ratio, acidity variations, and the use of a secondary ligand. Single-crystal X-ray diffraction studies reveal that PCN-131, obtained from the dimethylformamide (DMF) solution under acid condition, has a three-dimentional (3D) framework structure with one-dimensional (1D) honeycomb channels. PCN-132 isolated from dimethylacetamide (DMA) solution without adding acid in synthesis is a two-dimensional (2D) layer compound. By employing 4,4'-bipyridyl (4,4'-bpy) as a secondary ligand, PCN-131' and PCN-132' were synchronously synthesized as a mixture outcome with more PCN-131' than PCN-132'. In PCN-131', 4,4'-bpy acting as a secondary ligand is arranged inside the honeycomb channel of the 3D PCN-131, resulting in an effective improvement of thermal stability of the network, while in PCN-132', 4,4'-bpy ligands link 2D layers of PCN-132 to form a pillared-layer 3D framework Gas adsorption has been performed for selected materials. The results show that the framework of PCN-131 is thermally unstable after removing the solvent molecules coordinated to their metal sites. While PCN-131' is stable for gas uptake, with an evaluated Langmuir surface area of 199.04 m(2) g(-1), it shows a selective adsorption of CO2 over CH4.
Tuning the Moisture and Thermal Stability of Metal–Organic Frameworks through Incorporation of Pendant Hydrophobic Groups
An isostructural series of NbO-type porous metal–organic frameworks (MOFs) with different dialkoxy-substituents of formula Cu 2 (TPTC-OR) (TPTC-OR = 2',5'-di{alkyl}oxy-[1,1':4',1"-terphenyl]-3,3",5,5"-tetracarboxylate, R = Me, Et, n Pr, n Hex) has been synthesized and characterized. The moisture stability of the materials has been evaluated, and a new superhydrophobic porous MOF has been identified. The relationship between pendant side chain length and thermal stability has been analyzed by in situ synchrotron powder X-ray diffraction, showing decreased thermal stability as the side chain length is increased, contradictory to thermogravimetric decomposition studies. Additionally, the four materials exhibit moderate Brunauer–Emmett–Teller (BET) and Langmuir surface areas (1127–1396 m 2 g –1 and 1414–1658 m 2 g –1 ) and H 2 capacity up to 1.9 wt % at 77 K and 1 bar.
Tuning P2-Structured Cathode Material by Na-Site Mg Substitution for Na-Ion Batteries
Abstract not provided
Electrostatically Tuned Self-Assembly of Branched Amphiphilic Peptides
Electrostatics plays an important role in the self-assembly of amphiphilic peptides. To develop a molecular understanding of the role of the electrostatic interactions, we develop a coarse-grained model peptide and apply self-consistent field theory to investigate the peptide assembly into a variety of aggregate nanostructures. We find that the presence and distribution of charged groups on the hydrophilic branches of the peptide can modify the molecular configuration from extended to collapsed. This change in molecular configuration influences the packing into spherical micelles, cylindrical micelles (nanofibers), or planar bilayers. The effects of charge distribution therefore has important implications for the design and utility of functional materials based on peptides.