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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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Unravelling the Proton Conduction Mechanism from Room Temperature to 553 K in a 3D Inorganic Coordination Framework
We report the preparation of proton-conducting materials that are functional and stable at intermediate temperatures (393–573 K) is a focal point of fuel cell development. The purely inorganic material, HNd(IO 3 ) 4 , which possesses a dense 3D framework structure, can reach a maximum of 4.6 × 10 –4 S·cm –1 at 353 K and 95% relative humidity and exhibit a high conductivity of 8.0 × 10 –5 S·cm –1 from 373 to 553 K under the flow of wet N 2 . HNd(IO 3 ) 4 exhibits a variety of improvements including high thermal stability, low solubility in water, and resistance to reducing atmosphere. The proton conductivity in such a wide temperature range originates from the intrinsic liberated protons in the structure and the resulting 1D hydrogen-bonding network confirmed by bond valence sum calculation and solid-state NMR analysis. Moreover, two different activation energies are observed in different temperature regions (0.23 eV below 373 K and 0.026 eV from 373 to 553 K), indicating that two types of proton motion are responsible for proton diffusion, as further domenstrated by temperature-dependent open-circuit voltage hysteresis in a tested fuel cell assembly as well as variable-temperature and double quantum filtered solid-state NMR measurements.
Hydrogenation of CO2 at Room Temperature and Low Pressure with a Cobalt Tetraphosphine Catalyst
Large-scale implementation of carbon neutral energy sources such as solar and wind will require the development of energy storage mechanisms. The hydrogenation of CO2, a potent greenhouse gas, into formic acid or methanol could function as means to store energy in a chemical bond. Here we report hydrogenation of CO2 to formate under low pressure conditions using a Co(I) tetraphosphine complex, [Co(L3)(CH3CN)]BF4, where L3 = 1,5-diphenyl-3,7-bis(diphenylphosphino)-propyl)-1,5-diaza-3,7-diphosphacyclooctane. [Co(L3)(CH3CN)]+ (0.31 mM) catalyzes CO2 hydrogenation with an initial turnover frequency (TOF) of 150(20) h-1 at 25 °C, 1.7 atm of a 1:1 mixture of H2 and CO2, and 0.6 M tBuTMG (2-tert-Butyl-1,1,3,3-tetramethylguanidine). This research was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
Single-Crystal Growth and Room-Temperature Magnetocaloric Effect of X-Type Hexaferrite Sr 2 Co 2 Fe 28 O 46
X-type hexaferrites have been receiving considerable attention due to their promising applications in many magnetic-electronic fields. However, the growth of single-crystal X-type hexaferrite is still a challenge. Herein we reported, for the first time, the preparation of single crystal X-type hexaferrite Sr 2 Co 2 Fe 28 O 46 (Sr 2 Co 2 X) with high-quality and large size using floating-zone method with laser as the heating source. The crystals show rhombohedral symmetry with space group of R-3m (No. 166, a = 5.8935(1) Å and c = 83.7438(17) Å). Co 2+ and Fe 3+ oxidation states were confirmed by the X-ray absorption near-edge spectroscopy. The prepared Sr 2 Co 2 X exhibits a spin reorientation transition from easy-cone to easy-axis at T 2 of 343 K and a ferrimagnetism–paramagnetism transition at Curie temperature (TC) of ~743 K. The spin reorientation transition was accompanied by magnetocaloric effect (MCE). Both conventional and inverse MCEs were observed near T 2 with a magnetic field applied along the c-axis. The maximum value of the magnetic entropy change along the c-axis was evaluated to be 1.1 J/kg·K for a magnetic field change of 5 T.
Evidence for Nanostructures of at Least 20 nm in a Phosphonium Ionic Liquid at Room Temperature Using Fluorescence Correlation Spectroscopy
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Structure of the Oxygen Evolving Complex of Photosystem II at Room Temperature
Abstract not provided
Computational Modeling of Exciton-Bath Hamiltonians for Light Harvesting 2 and Light Harvesting 3 Complexes of Purple Photosynthetic Bacteria at Room Temperature
Light harvesting 2 (LH2) complex is the primary component of the photosynthetic unit of purple bacteria that is responsible for harvesting and relaying excitons. The electronic absorption line shape of LH2 contains two major bands at 800 and 850 nm wavelength regions. Under low light conditions, some species of purple bacteria replace LH2 with light harvesting 3 (LH3), a variant form with almost the same structure as the former but with distinctively different spectral features. The major difference between the absorption line shapes of LH2 and LH3 is the shift of the 850 nm band of the former to a new 820 nm region. The microscopic origin of this difference has been the subject of some theoretical/computational investigations. However, the genuine molecular level source of such a difference is not clearly understood yet. This work reports a comprehensive computational study of LH2 and LH3 complexes so as to clarify different molecular level features of LH2 and LH3 complexes and to construct simple exciton-bath models with a common form. All-atomistic molecular dynamics simulations of both LH2 and LH3 complexes provide detailed molecular level structural differences of bacteriochlorophylls (BChls) in the two complexes, in particular, in their patterns of hydrogen bonding (HB) and torsional angles of the acetyl group. Time-dependent density functional theory calculation of the excitation energies of BChls for structures sampled from the MD simulations suggests that the observed differences in the HB and torsional angles cannot fully account for the experimentally observed spectral shift of LH3. Potential sources that can explain the actual spectral shift of LH3 are discussed, and their magnitudes are assessed through fitting of experimental line shapes. Furthermore, these results demonstrate the feasibility of developing simple exciton-bath models for both LH2 and LH3, which can be employed for large-scale exciton quantum dynamics in their aggregates.
High-Pressure Tetrahedral Amorphous Carbon Synthesized by Compressing Glassy Carbon at Room Temperature
Abstract not provided
Ultrafast Spin Crossover in a Room-Temperature Ferrimagnet: Element-Specific Spin Dynamics in Photoexcited Cobalt Ferrite
Transition metal complexes capable of photoinduced spin crossover have been greatly investigated because of their potential to enable ultrafast optical control of information processing. Yet, any real application of photoswitchable molecules requires that spin crossover be paired with additional functionality such as long-range magnetic order. Important advances combining these functions are notably reported for a number of bimetallic Prussian Blue analogues; however, to date, PBA-based magnetic photoswitches can only operate below 150 K due to loss of magnetic order. In contrast, cobalt ferrite is a ferrimagnetic semiconductor with a Curie temperature of 790 K and extremely favorable magnetic properties by comparison to state-of-the-art PBAs. The mixed valence electronic structure of cobalt ferrite is reminiscent of cobalt–iron PBA, which is a well-known photoswitch. To investigate the potential for photoswitching in this material, we employ transient XUV spectroscopy to probe charge and spin dynamics with element-specific resolution on the femtosecond time scale. Results show that 400 nm light excites a metal-to-metal charge transfer transition, which drives the crossover of high-spin Co 2+ to low-spin Co 3+ with a time constant of 405 ± 29 fs and an internal quantum efficiency of unity. This result establishes the existence of efficient photoswitching in a new class of robust ferrimagnetic spinel ferrites.
X-ray Spectroscopy of a Rare-Earth Molecular System Measured at the Single Atom Limit at Room Temperature
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