Synthesis of flexible Co nanowires from bulk precursors.

This work reports a method of producing flexible cobalt nanowires (NWs) directly from the chemical conversion of bulk precursors at room temperature. Chemical reduction of LiCoCl produces a nanocomposite of Co and LiCl, of which the salt is subsequently removed. The dilute concentration of Co in the precursor combined with the anisotropic crystal structure of the hcp phase leads to 1D growth in the absence of any templates or additives.

Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries.

Lithium (Li) metal serving as an anode has the potential to double or triple stored energies in rechargeable Li batteries. However, they typically have short cycling lifetimes due to parasitic reactions between the Li metal and electrolyte. It is critically required to develop early fault-detection methods for different failure mechanisms and quick lifetime-prediction methods to ensure rapid development.

Selectivity in Yttrium Manganese Oxide Synthesis via Local Chemical Potentials in Hyperdimensional Phase Space.

In sharp contrast to molecular synthesis, materials synthesis is generally presumed to lack selectivity. The few known methods of designing selectivity in solid-state reactions have limited scope, such as topotactic reactions or strain stabilization. This contribution describes a general approach for searching large chemical spaces to identify selective reactions.

Anisotropic nanoporous morphology of ZnO-supported Co that enhances catalytic activity.

A novel conversion reaction synthesis (CRS) method is used to synthesize ZnO-supported Co nanoporous metal hybrid structures from a co-precipitated nanocomposite precursor of ZnO and CoO. After removal of LiO with water, the resulting material consists of ZnO-supported Co nanoparticles that are interconnected to form anisotropic micro-particles. Additionally, individual ZnO nanoparticles have an anisotropic morphology, as revealed by synchrotron XRD analysis.

When Do Anisotropic Magnetic Susceptibilities Lead to Large NMR Shifts? Exploring Particle Shape Effects in the Battery Electrode Material LiFePO.

Materials used as electrodes in energy storage devices have been extensively studied with solid-state NMR spectroscopy. Due to the almost ubiquitous presence of transition metals, these systems are also often magnetic. While it is well known that the presence of anisotropic bulk magnetic susceptibility (ABMS) leads to broadening of resonances under magic angle spinning, we show that for monodisperse and nonspherical particle morphologies the ABMS can also lead to considerable shifts, which vary substantially as a function of particle shape.

Extending the limits of powder diffraction analysis: Diffraction parameter space, occupancy defects, and atomic form factors.

Although the determination of site occupancies is often a major goal in Rietveld refinement studies, the accurate refinement of site occupancies is exceptionally challenging due to many correlations and systematic errors that have a hidden impact on the final refined occupancy parameters. Through the comparison of results independently obtained from neutron and synchrotron powder diffraction, improved approaches capable of detecting occupancy defects with an exceptional sensitivity of 0.1% (absolute) in the class of layered NMC (Li[NiMnCo]O) Li-ion battery cathode materials have been developed.

Impact of stereochemistry on rheology and nanostructure of PLA-PEO-PLA triblocks: stiff gels at intermediate l/d-lactide ratios.

We report rheology and structural studies of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer gels with various ratios of l-lactide and d-lactide in the PLA blocks. These materials form associative micellar gels in water, and previous work has shown that stereoregular triblocks with a l/d ratio of 100/0 form much stiffer gels than triblocks with a 50/50 l/d ratio. Our systems display an unexpected maximum in the storage modulus, G', of the hydrogels at intermediate l/d ratio.

Observation of Vacancies, Faults, and Superstructures in LnMoO (Ln = La, Y, and Lu) Compounds with Direct Mo-Mo Bonding.

Among oxide compounds with direct metal-metal bonding, the YMoO (ABO) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral BO dimers arranged in one-dimensional edge-sharing chains along the direction of the metal-metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal-metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal-metal bonding.

In Situ Neutron Diffraction Studies of the Ion Exchange Synthesis Mechanism of LiMgPON: Evidence for a Hidden Phase Transition.

Motivated by predictions made using a bond valence sum difference map (BVS-DM) analysis, the novel Li-ion conductor LiMgPON was synthesized by ion exchange from a NaMgPON precursor. Impedance spectroscopy measurements indicate that LiMgPON has a room temperature Li-ion conductivity of about 10 S/cm (comparable to LiPON), which is 6 orders of magnitude higher than the extrapolated Na-ion conductivity of NaMgPON at this temperature. The structure of LiMgPON was determined from ex situ synchrotron and time-of-flight neutron diffraction data to retain the P23 space group, though with a cubic lattice parameter of a = 9.

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na3Ni2BiO6 Cathodes for Na-Ion Batteries.

Ordered and disordered samples of honeycomb-lattice Na3Ni2BiO6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na(+)/Na) with minimal capacity fade during extended cycling.

Molybdenum nitrides as oxygen reduction reaction catalysts: structural and electrochemical studies.

Monometallic (δ-MoN, Mo5N6, and Mo2N) and bimetallic molybdenum nitrides (Co0.6Mo1.4N2) were investigated as electrocatalysts for the oxygen reduction reaction (ORR), which is a key half-reaction in hydrogen fuel cells.

Charge disproportionation in tetragonal La2MoO5, a small band gap semiconductor influenced by direct Mo-Mo bonding.

The structure of the novel compound La2MoO5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.

Structures of delithiated and degraded LiFeBO(3), and their distinct changes upon electrochemical cycling.

Lithium iron borate (LiFeBO3) has a high theoretical specific capacity (220 mAh/g), which is competitive with leading cathode candidates for next-generation lithium-ion batteries. However, a major factor making it difficult to fully access this capacity is a competing oxidative process that leads to degradation of the LiFeBO3 structure. The pristine, delithiated, and degraded phases of LiFeBO3 share a common framework with a cell volume that varies by less than 2%, making it difficult to resolve the nature of the delithiation and degradation mechanisms by conventional X-ray powder diffraction studies.

Thin-film and bulk investigations of LiCoBO₃ as a Li-ion battery cathode.

The compound LiCoBO3 is an appealing candidate for next-generation Li-ion batteries based on its high theoretical specific capacity of 215 mAh/g and high expected discharge voltage (more than 4 V vs Li(+)/Li). However, this level of performance has not yet been realized in experimental cells, even with nanosized particles. Reactive magnetron sputtering was therefore used to prepare thin films of LiCoBO3, allowing the influence of the particle thickness on the electrochemical performance to be explicitly tested.

Mixed close-packed cobalt molybdenum nitrides as non-noble metal electrocatalysts for the hydrogen evolution reaction.

A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density of 10 mA cm(-2) at -0.20 V vs RHE at low catalyst loadings of 0.24 mg/cm(2) in rotating disk experiments under a H2 atmosphere.

Design of medium band gap Ag-Bi-Nb-O and Ag-Bi-Ta-O semiconductors for driving direct water splitting with visible light.

Two new metal oxide semiconductors belonging to the Ag-Bi-M-O (M = Nb, Ta) chemical systems have been synthesized as candidate compounds for driving overall water splitting with visible light on the basis of cosubstitution of Ag and Bi on the A-site position of known Ca2M2O7 pyrochlores. The low-valence band edge energies of typical oxide semiconductors prevents direct water splitting in compounds with band gaps below 3.0 eV, a limitation which these compounds are designed to overcome through the incorporation of low-lying Ag 4d(10) and Bi 6s(2) states into compounds of nominal composition "AgBiM2O7".

Synthesis and characterization of visible light absorbing (GaN)(1-x)(ZnO)x semiconductor nanorods.

Although the (GaN)(1-x)(ZnO)x solid solution is one of the most effective systems for driving overall solar water splitting with visible light, its quantum yield for overall water splitting using visible light photons has not yet reached ten percent. Understanding and controlling the nanoscale morphology of this system may allow its overall conversion efficiency to be raised to technologically relevant levels. We describe the use a Ga2O3(ZnO)16 precursor phase in the synthesis of this phase which naturally results in the production of arrays of nanorods with favorable diameters (∼100 nm) and band gaps (∼2.

Thermally stable N2-intercalated WO3 photoanodes for water oxidation.

We describe stable intercalation compounds of the composition xN(2)·WO(3) (x = 0.034-0.039), formed by trapping N(2) in WO(3).

Structural modulation in the high capacity battery cathode material LiFeBO3.

The crystal structure of the promising Li-ion battery cathode material LiFeBO(3) has been redetermined based on the results of single crystal X-ray diffraction data. A commensurate modulation that doubles the periodicity of the lattice in the a-axis direction is observed. When the structure of LiFeBO(3) is refined in the 4-dimensional superspace group C2/c(α0γ)00, with α = 1/2 and γ = 0 and with lattice parameters of a = 5.

Substitutional mechanism of Ni into the wide-band-gap semiconductor InTaO4 and its implications for water splitting activity in the wolframite structure type.

The mechanism of Ni substitution into the oxide semiconductor InTaO(4) has been studied through a combination of structural and spectroscopic techniques, providing insights into its previously reported photoactivity. Magnetic susceptibility and X-ray absorption near-edge spectroscopy (XANES) measurements demonstrate that nickel is divalent within the host lattice. The combined refinement of synchrotron X-ray and neutron powder diffraction data indicates that the product of Ni doping has the stoichiometry of (In(1-x)Ni(2x/3)Ta(x/3))TaO(4) with a solubility limit of x ≈ 0.

Design and characterization of a calixarene inclusion compound for calibration of long-range carbon-fluorine distance measurements by solid-state NMR.

An inexpensive, easily synthesized calixarene:fluorotoluene host:guest inclusion complex has been designed for optimization and calibration of solid-state NMR measurements of carbon-fluorine distances using Rotational Echo DOuble Resonance (REDOR). Complexation of the fluorotoluene with the calixarene host separates the molecules such that simple two-spin behavior is observed for one site with a 4.08 Å carbon-fluorine distance.

Fluorescent detection of nitroaromatics and 2,3-dimethyl 2,3-dinitrobutane (DMNB) by a zinc complex: (salophen)Zn.

Fluorescent sensors for the detection of chemical explosives are in great demand. It is shown herein that the fluorescence of ZnL* (H2L=N,N'-phenylene-bis-(3,5-di-tert-butylsalicylideneimine)) is quenched in solution by nitroaromatics and 2,3-dimethyl-2,3-dinitrobutane (DMNB), chemical signatures of explosives. The relationship between the structure and fluorescence of ZnL is explored, and crystal structures of three forms of ZnL(base), (base=ethanol, tetrahydrofuran, pyridine) are reported, with the base=ethanol structure exhibiting a four-centered hydrogen bonding array.