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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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Toward Computation-Guided Design of Tunable Organic-Inorganic CdS Quantum Dot Binary Superlattices
Combining the advantages of structural programmability in sequence-defined biomimetic molecules and the controllable packing geometry in nanoparticle superlattices, we demonstrate a self-assembled organic-inorganic superlattice whose structure can be altered with the slightest change in the sequence of the organic counterpart. Here, oleate-coated CdS quantum dots (QDs) form a square-packed superlattice with a 1:1 molar equivalence of a di-block amphiphilic peptoid (Nbrpe6Dig) in chloroform. In contrast, no apparent structure is observed in the organic solvent alone. Based on theoretical evidence, we show that the assembly is a binary superlattice where both the CdS QDs and the peptoids serve as building blocks and further predict a correlation between the superlattice structure and the peptoid sequence. The computationally guided prediction is validated by experiments where superlattice transformation is observed with modified peptoids. The mechanism identified in our work inspires new ways to control and tune organic-inorganic hybrid nanomaterial self-assembly.
Designing Nanoplatelet Alloy/Nafion Catalytic Interface for Optimization of PEMFCs: Performance, Durability, and CO Resistance
We have adapted the two phase Brust method to synthesize large quantities of AuPd alloy nanoparticles with diameter of 1.86 ± 0.40 nm. When the particles were spread at the air water interface of a Langmuir Blodgett (LB) trough, they exhibited a distinct pressure area isotherm curve. The X-ray reflectivity (XRR) shows the formation of an incompressible monolayer with uniform thickness of 1.16 ± 0.02 nm at low pressures which collapses to form a second layer with 2.13 nm thick at higher pressures. High resolution transmission electron microscopy (HRTEM) imaging of the monolayer indicates that the particles are highly crystalline, with well-defined atomic planes and self-assembly into a hexagonal structure. Extended X-ray absorption fine structure (EXAFS) analysis of the LB lift-off films only shows Au-Au and Au-Pd configurations, consistent with the formation of random alloy rather than core shell structure. When the particle monolayer was lifted onto the Nafion membrane of a proton exchange membrane fuel cell (PEMFC), a maximum power output of 0.54 W/cm 2 was obtained with a Pt loading of only 0.15 mg/cm 2 and 0.05 mg/cm 2 at the cathode and anode, respectively. This represents a 15% enhancement, which persists even after 30k cycles, relative to a membrane electrode assembly (MEA) using a non-coated membrane. Density function theory (DFT) modeling of the hexagonally packed platelet nanoparticle alloy structure deposited on Nafion predicted that the SO 3 functionality serves a similar function to metal oxide supports in reducing the activation barrier for the CO oxidation reaction. This was confirmed by measuring the power output of a PEMFC when 0.1% CO was mixed either into the input H 2 stream at the anode or with O 2 at the cathode. In the uncoated MEAs, a significant decrease of 72% and 61% was measured when CO was introduced at the anode and cathode, respectively, while MEAs with coated particle membranes only experienced a decrease of 21% and 17%, respectively. These results indicate that a synergy can be established between the nanoparticle platelets and the surface of the Nafion membrane which can produce CO resistant PEMFC that could operate at ambient temperatures on impure, but abundant hydrogen gas such as those produced by reformate or electrolysis processes. Furthermore the availability of inexpensive H 2 opens opportunities for gas distribution and greatly facilitates the commercialization of PEMFCs, which will conform to the ambitious goals set by the Department of Energy (DOE) for 2020.
A New Magnetic Topological Quantum Material Candidate by Design
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Designing Higher Resolution Self-Assembled 3D DNA Crystals via Strand Terminus Modifications
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Testing the Substrate-Envelope Hypothesis with Designed Pairs of Compounds
Abstract not provided
Protein Arginine Deiminase 2 Binds Calcium in an Ordered Fashion: Implications for Inhibitor Design
Abstract not provided
Solvation Structure Design for Aqueous Zn Metal Batteries
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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.
Enhanced Out-of-Plane Conductivity and Photovoltaic Performance in n = 1 Layered Perovskites through Organic Cation Design
Layered perovskites with the formula (R–NH 3 ) 2 PbI 4 have excellent environmental stability but poor photovoltaic function due to the preferential orientation of the semiconducting layer parallel to the substrate and the typically insulating nature of the R–NH 3 + cation. Here, we report a series of these n = 1 layered perovskites with the form (aromatic-O-linker-NH 3 ) 2 PbI 4 where the aromatic moiety is naphthalene, pyrene, or perylene and the linker is ethyl, propyl, or butyl. These materials achieve enhanced conductivity perpendicular to the inorganic layers due to better energy level matching between the inorganic layers and organic galleries. The enhanced conductivity and visible absorption of these materials led to a champion power conversion efficiency of 1.38%, which is the highest value reported for any n = 1 layered perovskite, and it is an order of magnitude higher efficiency than any other n = 1 layered perovskite oriented with layers parallel to the substrate. Furthermore, these findings demonstrate the importance of leveraging the electronic character of the organic cation to improve optoelectronic properties and thus the photovoltaic performance of these chemically stable low n layered perovskites.
Design and Validation of a High-Throughput Reductive Catalytic Fractionation Method
Reductive catalytic fractionation (RCF) is a promising method to extract and depolymerize lignin from biomass, and bench-scale studies have enabled considerable progress in the past decade. RCF experiments are typically conducted in pressurized batch reactors with volumes ranging between 50 and 1000 mL, limiting the throughput of these experiments to one to six reactions per day for an individual researcher. Here, we report a high-throughput RCF (HTP-RCF) method in which batch RCF reactions are conducted in 1 mL wells machined directly into Hastelloy reactor plates. The plate reactors can seal high pressures produced by organic solvents by vertically stacking multiple reactor plates, leading to a compact and modular system capable of performing 240 reactions per experiment. Using this setup, we screened solvent mixtures and catalyst loadings for hydrogen-free RCF using 50 mg poplar and 0.5 mL reaction solvent. The system of 1:1 isopropanol/methanol showed optimal monomer yields and selectivity to 4-propyl substituted monomers, and validation reactions using 75 mL batch reactors produced identical monomer yields. To accommodate the low material loadings, we then developed a workup procedure for parallel filtration, washing, and drying of samples and a 1H nuclear magnetic resonance spectroscopy method to measure the RCF oil yield without performing liquid-liquid extraction. As a demonstration of this experimental pipeline, 50 unique switchgrass samples were screened in RCF reactions in the HTP-RCF system, revealing a wide range of monomer yields (21-36%), S/G ratios (0.41-0.93), and oil yields (40-75%). These results were successfully validated by repeating RCF reactions in 75 mL batch reactors for a subset of samples. We anticipate that this approach can be used to rapidly screen substrates, catalysts, and reaction conditions in high-pressure batch reactions with higher throughput than standard batch reactors.
All-optical materials design of chiral edge modes in transition-metal dichalcogenides
Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping—instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. As a result, we develop an ab initio strategy to understand non-equilibrium Floquet–Bloch bands and topological transitions, and illustrate for WS 2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.
Anomalous metal segregation in lithium-rich material provides design rules for stable cathode in lithium-ion battery
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