Uncovering the Size-Dependent Thermal Solid Transformation of Akaganéite.

Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, in-situ heating techniques are employed in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite 1D nanostructures with varying diameters. These findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (γ-Fe2O3) and subsequent crystal growth. Specifically, it is observed that akaganéite nanorods with a diameter of ∼50 nm transformed into hollow polycrystalline maghemite nanorods, which demonstrated remarkable stability without arresting crystal growth under continuous heating. In contrast, smaller akaganéite nanoneedles or nanowires with a diameter ranging from 20 to 8 nm displayed a propensity for forming single-crystal nanoneedles or nanowires through phase transformation and densification. By manipulating the size of the precursors, a straightforward method is developed for the synthesis of single-crystal and polycrystalline maghemite nanowires through solid-phase transformation. These significant findings provide new insights into the size-dependent structural evolution and phase transformation of iron oxides at the nanoscale.

Spontaneous Lithiation of Binary Oxides during Epitaxial Growth on LiCoO2.

Epitaxial growth is a powerful tool for synthesizing heterostructures and integrating multiple functionalities. However, interfacial mixing can readily occur and significantly modify the properties of layered structures, particularly for those containing energy storage materials with smaller cations. Here, we show a two-step sequence involving the growth of an epitaxial LiCoO2 cathode layer followed by the deposition of a binary transition metal oxide. Orientation-controlled epitaxial synthesis of the model solid-state-electrolyte Li2WO4 and anode material Li4Ti5O12 occurs as WO3 and TiO2 nucleate and react with Li ions from the underlying cathode. We demonstrate that this lithiation-assisted epitaxy approach can be used for energy materials discovery and exploring different combinations of epitaxial interfaces that can serve as well-defined model systems for mechanistic studies of energy storage and conversion processes.

Single-Crystal to Single-Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes.

Mechanistic studies of substrate insertion into dimeric [(NHC)CuH]2 (NHC=N-heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)Cu-H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway of stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 (IPr*OMe=N,N'-bis(2,6-bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2-ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu]2 (µ-1,3-O2 CH)(µ-H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu]2 (µ-1,3-O2 CH)(µ-1,1-O2 CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.

Multi-Step Nucleation of a Crystalline Silicate Framework via a Structurally Precise Prenucleation Cluster.

Hierarchical nucleation pathways are ubiquitous in the synthesis of minerals and materials. In the case of zeolites and metal-organic frameworks, pre-organized multi-ion "secondary building units" (SBUs) have been proposed as fundamental building blocks. However, detailing the progress of multi-step reaction mechanisms from monomeric species to stable crystals and defining the structures of the SBUs remains an unmet challenge. Combining in situ nuclear magnetic resonance, small-angle X-ray scattering, and atomic force microscopy, we show that crystallization of the framework silicate, cyclosilicate hydrate, occurs through an assembly of cubic octameric Q3 8 polyanions formed through cross-linking and polymerization of smaller silicate monomers and other oligomers. These Q3 8 are stabilized by hydrogen bonds with surrounding H2 O and tetramethylammonium ions (TMA+ ). When Q3 8 levels reach a threshold of ≈32 % of the total silicate species, nucleation occurs. Further growth proceeds through the incorporation of [(TMA)x (Q3 8 )⋅n H2 O](x-8) clathrate complexes into step edges on the crystals.

Understanding the Electronic Structure Evolution of Epitaxial LaNi1-xFexO3 Thin Films for Water Oxidation.

Rare earth nickelates including LaNiO3 are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO3. However, the role of Fe in increasing the activity remains ambiguous, with potential origins that are both structural and electronic in nature. On the basis of a series of epitaxial LaNi1-xFexO3 thin films synthesized by molecular beam epitaxy, we report that Fe substitution tunes the Ni oxidation state in LaNi1-xFexO3 and a volcano-like OER trend is observed, with x = 0.375 being the most active. Spectroscopy and ab initio modeling reveal that high-valent Fe3+δ cationic species strongly increase the transition-metal (TM) 3d bandwidth via Ni-O-Fe bridges and enhance TM 3d-O 2p hybridization, boosting the OER activity. These studies deepen our understanding of structural and electronic contributions that give rise to enhanced OER activity in perovskite oxides.

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species.

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH)4-) or dimeric (Al2O(OH)62-) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH)4- and Al2O(OH)62- anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K2[Al2O(OH)6], Rb2[Al2O(OH)6], and Cs[Al(OH) 4]·2H2O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al2O(OH)62- anions, while the third contains the monomeric Al(OH)4- anion. Comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

Molecular Intermediate in the Directed Formation of a Zeolitic Metal-Organic Framework.

Directed synthesis promises control over architecture and function of framework materials. In practice, however, designing such syntheses requires a detailed understanding of the multistep pathways of framework formations, which remain elusive. By identifying intermediate coordination complexes, this study provides insights into the complex role of a structure-directing agent (SDA) in the synthetic realization of a promising material. Specifically, a novel molecular intermediate was observed in the formation of an indium zeolitic metal-organic framework (ZMOF) with a sodalite topology. The role of the imidazole SDA was revealed by time-resolved in situ powder X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS).

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair.

We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis(pentafluorophenyl)boryl]phenyl}-2,2,6,6-tetramethylpiperidine (KCAT). The gas-solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 h at 300 K under a flow of H2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4-200 K did not provide evidence for the formation of polarized H2 in a precursor complex within the crystal at low temperatures and high pressures. However, at 300 K, the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Calculations suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2, and a possible precursor complex of H2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H2 diffusion into the FLP crystal with a rate-limiting movement of H2 from inactive positions to reactive sites.

Structural and reorientational dynamics of tetrahydroborate (BH4-) and tetrahydrofuran (THF) in a Mg(BH4)2·3THF adduct: neutron-scattering characterization.

Metal borohydrides are considered promising materials for hydrogen storage applications due to their high volumetric and gravimetric hydrogen density. Recently, different Lewis bases have been complexed with Mg(BH4)2 in efforts to improve hydrogenation/dehydrogenation properties. Notably, Mg(BH4)2·xTHF adducts involving tetrahydrofuran (THF; C4H8O) have proven to be especially interesting. This work focuses on exploring the physicochemical properties of the THF-rich Mg(BH4)2·3THF adduct using neutron-scattering methods and molecular DFT calculations. Structural analysis, based on neutron diffraction measurements of Mg(11BH4)2·3TDF (D - deuterium), has confirmed a lowering of the symmetry upon cooling, from monoclinic C2/c to P1[combining macron] via a triclinic distortion. Vibrational properties are strongly influenced by the THF environment, showing a splitting in spectral features as a result of changes in the bond lengths, force constants, and lowering of the overall symmetry. Interestingly, the orientational mobilities of the BH4- anions obtained from quasielastic neutron scattering (QENS) are not particularly sensitive to the presence of THF and compare well with the mobilities of BH4- anions in unsolvated Mg(BH4)2. The QENS data point to uniaxial 180° jump reorientations of the BH4- anions around a preferred C2 anion symmetry axis. The THF rings are also found to be orientationally mobile, undergoing 180° reorientational jumps around their C2 molecular symmetry axis with jump frequencies about an order of magnitude lower than those for the BH4- anions. In contrast, no dynamical behavior of the THF rings is observed with QENS for a more THF-deficient 2Mg(BH4)2·THF adduct. This lack of comparable THF mobility may reflect a stronger Mg2+-THF bonding interaction for lower THF/Mg(BH4)2 stoichiometric ratios, which is consistent with DFT calculations showing a decrease in the binding energy with each additional THF ring in the adduct. Based on the combined experimental and computational results, we propose that combining THF and Mg(BH4)2 is beneficial to (i) preventing weakly bound THF from coming free from the Mg2+ cation and reducing the concentration of any unwanted impurity in the hydrogen and (ii) disrupting the stability of the crystalline phase, leading to a lower melting point and enhanced kinetics for any potential hydrogen storage applications.

Isolation of Tryptanthrin and Reassessment of Evidence for Its Isobaric Isostere Wrightiadione in Plants of the Wrightia Genus.

A series of Wrightia hanleyi extracts was screened for activity against Mycobacterium tuberculosis H37Rv. One active fraction contained a compound that initially appeared to be either the isoflavonoid wrightiadione or the alkaloid tryptanthrin, both of which have been previously reported in other Wrightia species. Characterization by NMR and MS, as well as evaluation of the literature describing these compounds, led to the conclusion that wrightiadione (1) was misidentified in the first report of its isolation from W. tomentosa in 1992 and again in 2015 when reported in W. pubescens and W. religiosa. Instead, the molecule described in these reports and in the present work is almost certainly the isobaric (same nominal mass) and isosteric (same number of atoms, valency, and shape) tryptanthrin (2), a well-known quinazolinone alkaloid found in a variety of plants including Wrightia species. Tryptanthrin (2) is also accessible synthetically via several routes and has been thoroughly characterized. Wrightiadione (1) has been synthesized and characterized and may have useful biological activity; however, this compound can no longer be said to be known to exist in Nature. To our knowledge, this misidentification of wrightiadione (1) has heretofore been unrecognized.

Direct Visualization of Li Dendrite Effect on LiCoO2 Cathode by In Situ TEM.

Nonuniform and highly localized Li dendrites are known to cause deleterious and, in many cases, catastrophic effects on the performance of rechargeable Li batteries. However, the mechanisms of cathode failures upon contact with Li metal are far from clear. In this study, using in situ transmission electron microscopy, the interaction of Li metal with well-defined, epitaxial thin films of LiCoO2 , the most widely used cathode material, is directly visualized at an atomic scale. It is shown that a spontaneous and prompt chemical reaction is triggered once Li contact is made, leading to expansion and pulverization of LiCoO2 and ending with the final reaction products of Li2 O and Co metal. A topotactic phase transition is identified close to the reaction front, resulting in the formation of CoO as a metastable intermediate. Dynamic structural and chemical imaging, in combination with ab initio simulations, reveal that a high density of grain and antiphase boundaries is formed at the reaction front, which are critical for enabling the short-range topotactic reactions and long-range Li propagation. The fundamental insights are of general importance in mitigating Li dendrites related issues and guiding the design principle for more robust energy materials.

In Situ 27Al NMR Spectroscopy of Aluminate in Sodium Hydroxide Solutions above and below Saturation with Respect to Gibbsite.

Aluminum hydroxide (Al(OH)3, gibbsite) dissolution and precipitation processes in alkaline environments play a commanding role in aluminum refining and nuclear waste processing, yet mechanistic aspects underlying sluggish kinetics during crystallization have remained obscured due to a lack of in situ probes capable of isolating incipient ion pairs. At a molecular level Al is cycling between tetrahedral ( T d) coordination in solution to octahedral ( O h) in the solid. We explored dissolution of Al(OH)3 that was used to produce variably saturated aluminate (Al(OH)4-)-containing solutions under alkaline conditions (pH >13) with in situ 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, and interrogated the results with ab initio molecular dynamics (AIMD) simulations complemented with chemical shift calculations. The collective results highlight the overall stability of the solvation structure for T d Al in the Al(OH)4- oxyanion as a function of both temperature and Al concentration. The observed chemical shift did not change significantly even when the Al concentration in solution became supersaturated upon cooling and limited precipitation of the octahedral Al(OH)3 phase occurred. However, subtle changes in Al(OH)4- speciation correlated with the dissolution/precipitation reaction were found. AIMD-informed chemical shift calculations indicate that measurable perturbations should begin when the Al(OH)4-···Na+ distance is less than 6 Å, increasing dramatically at shorter distances, coinciding with appreciable changes to the electrostatic interaction and reorganization of the Al(OH)4- solvation shell. The integrated findings thus suggest that, under conditions incipient to and concurrent with gibbsite crystallization, nominally expected contact ion pairs are insignificant and instead medium-range (4-6 Å) solvent-separated Al(OH)4-···Na+ pairs predominate. Moreover, the fact that these medium-range interactions bear directly on resulting gibbsite characteristics was demonstrated by detailed microscopic and X-ray diffraction analysis and by progressive changes in the fwhm of the O h resonance, as measured by in situ NMR. Sluggish gibbsite crystallization may arise from the activation energy associated with disrupting this robust medium-range ion pair interaction.

Tunable Manipulation of Mineral Carbonation Kinetics in Nanoscale Water Films via Citrate Additives.

We explored the influence of a model organic ligand on mineral carbonation in nanoscale interfacial water films by conducting five time-resolved in situ X-ray diffraction (XRD) experiments at 50 °C. Forsterite was exposed to water-saturated supercritical carbon dioxide (90 bar) that had been equilibrated with 0-0.5 m citrate (C6H5O7-3) solutions. The experimental results demonstrated that greater concentrations of citrate in the nanoscale interfacial water film promoted the precipitation of magnesite (MgCO3) relative to nesquehonite (MgCO3·3H2O). At the highest concentrations tested, magnesite nucleation and growth were inhibited, lowering the carbonation rate constant from 9.1 × 10-6 to 3.6 × 10-6 s-1. These impacts of citrate were due to partial dehydration of Mg2+(aq) and the adsorption of citrate onto nuclei and magnesite surfaces. This type of information may be used to predict and tailor subsurface mineralization rates and pathways.

Cr(VI) Effect on Tc-99 Removal from Hanford Low-Activity Waste Simulant by Ferrous Hydroxide.

Here, Cr(VI) effects on Tc-immobilization by Fe(OH)2(s) are investigated while assessing Fe(OH)2(s) as a potential treatment method for Hanford low-activity waste destined for vitrification. Batch studies using simulated low-activity waste indicate that Tc(VII) and Cr(VI) removal is contingent on reduction to Tc(IV) and Cr(III). Furthermore, complete removal of both Cr and Tc depends on the amount of Fe(OH)2(s) present, where complete Cr and Tc removal requires more Fe(OH)2(s) (∼200 g/L of simulant), than removing Cr alone (∼50 g/L of simulant). XRD analysis suggests that Fe(OH)2(s) reaction and transformation in the simulant produces mostly goethite (α-FeOOH), where Fe(OH)2(s) transformation to goethite rather than magnetite is likely due to the simulant chemistry, which includes high levels of nitrite and other constituents. Once reduced, a fraction of Cr(III) and Tc(IV) substitute for octahedral Fe(III) within the goethite crystal lattice as supported by XPS, XANES, and/or EXAFS results. The remaining Cr(III) forms oxide and/or hydroxide phases, whereas Tc(IV) not fully incorporated into goethite persists as either adsorbed or partially incorporated Tc(IV)-oxide species. As such, to fully incorporate Tc(IV) into the goethite crystal structure, additional Fe(OH)2(s) (>200 g/L of simulant) may be required.

Complete Decomposition of Li2CO3 in Li-O2 Batteries Using Ir/B4C as Noncarbon-Based Oxygen Electrode.

Instability of carbon-based oxygen electrodes and incomplete decomposition of Li2CO3 during charge process are critical barriers for rechargeable Li-O2 batteries. Here we report the complete decomposition of Li2CO3 in Li-O2 batteries using the ultrafine iridium-decorated boron carbide (Ir/B4C) nanocomposite as a noncarbon based oxygen electrode. The systematic investigation on charging the Li2CO3 preloaded Ir/B4C electrode in an ether-based electrolyte demonstrates that the Ir/B4C electrode can decompose Li2CO3 with an efficiency close to 100% at a voltage below 4.37 V. In contrast, the bare B4C without Ir electrocatalyst can only decompose 4.7% of the preloaded Li2CO3. Theoretical analysis indicates that the high efficiency decomposition of Li2CO3 can be attributed to the synergistic effects of Ir and B4C. Ir has a high affinity for oxygen species, which could lower the energy barrier for electrochemical oxidation of Li2CO3. B4C exhibits much higher chemical and electrochemical stability than carbon-based electrodes and high catalytic activity for Li-O2 reactions. A Li-O2 battery using Ir/B4C as the oxygen electrode material shows highly enhanced cycling stability than those using the bare B4C oxygen electrode. Further development of these stable oxygen-electrodes could accelerate practical applications of Li-O2 batteries.

Trace Uranium Partitioning in a Multiphase Nano-FeOOH System.

The characterization of trace elements in minerals using extended X-ray absorption fine structure (EXAFS) spectroscopy constitutes a first step toward understanding how impurities and contaminants interact with the host phase and the environment. However, limitations to EXAFS interpretation complicate the analysis of trace concentrations of impurities that are distributed across multiple phases in a heterogeneous system. Ab initio molecular dynamics (AIMD)-informed EXAFS analysis was employed to investigate the immobilization of trace uranium associated with nanophase iron (oxyhydr)oxides, a model system for the geochemical sequestration of radiotoxic actinides. The reductive transformation of ferrihydrite [Fe(OH)3] to nanoparticulate iron oxyhydroxide minerals in the presence of uranyl (UO2)2+(aq) resulted in the preferential incorporation of U into goethite (α-FeOOH) over lepidocrocite (γ-FeOOH), even though reaction conditions favored the formation of excess lepidocrocite. This unexpected result is supported by atomically resolved transmission electron microscopy. We demonstrate how AIMD-informed EXAFS analysis lifts the strict statistical limitations and uncertainty of traditional shell-by-shell EXAFS fitting, enabling the detailed characterization of the local bonding environment, charge compensation mechanisms, and oxidation states of polyvalent impurities in complex multiphase mineral systems.

Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone.

Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important sources of electron equivalents limiting the transport of redox-active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from the RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) natural content, but FeTOTAL remains constant, demonstrating no Fe loss during its reduction-oxidation cyclings. At native pH of 8.6, the anoxic fraction, despite its significant Fe(II), ∼23% of FeTOTAL, exhibits minimal reactivity with TcO4- and CrO42- and much slower reaction kinetics than those measured in studies with biologically/chemically reduced model clays. Reduction capacity is enhanced by added/sorbed Fe(II) (if Fe(II)SORBED > 8% clay Fe(II)LABILE); however, the kinetics of this conceptually surface-mediated reaction remain sluggish. Surface-sensitive Fe L-edge X-ray absorption spectroscopy shows that Fe(II)SORBED and the resulting reducing equivalents are not available in the outermost few nanometers of clay surfaces. Slow kinetics thus appear related to diffusion-limited access to electron equivalents retained within the clay mineral structure.

Reduction and Simultaneous Removal of 99Tc and Cr by Fe(OH)2(s) Mineral Transformation.

Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)2(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (Fe3O4). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, Cr2O3, and Cr(OH)3 phases. Spinel (modeled as Fe3O4), goethite (α-FeOOH), and feroxyhyte (δ-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)2(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (Fe3O4) and chromite (FeCr2O4).

Electrochemically Formed Ultrafine Metal Oxide Nanocatalysts for High-Performance Lithium-Oxygen Batteries.

Lithium-oxygen (Li-O2) batteries have an extremely high theoretical specific energy density when compared with conventional energy-storage systems. However, practical application of the Li-O2 battery system still faces significant challenges. In this work, we report a new approach for synthesis of ultrafine metal oxide nanocatalysts through an electrochemical prelithiation process. This process reduces the size of NiCo2O4 (NCO) particles from 20-30 nm to a uniformly distributed domain of ∼2 nm and significantly improves their catalytic activity. Structurally, the prelithiated NCO nanowires feature ultrafine NiO/CoO nanoparticles that are highly stable during prolonged cycles in terms of morphology and particle size, thus maintaining an excellent catalytic effect to oxygen reduction and evolution reactions. A Li-O2 battery using this catalyst demonstrated an initial capacity of 29 280 mAh g(-1) and retained a capacity of >1000 mAh g(-1) after 100 cycles based on the weight of the NCO active material. Direct in situ transmission electron microscopy observations conclusively revealed the lithiation/delithiation process of as-prepared NCO nanowires and provided in-depth understanding for both catalyst and battery chemistries of transition-metal oxides. This unique electrochemical approach could also be used to form ultrafine nanoparticles of a broad range of materials for catalyst and other applications.

Abiotic Protein Fragmentation by Manganese Oxide: Implications for a Mechanism to Supply Soil Biota with Oligopeptides.

The ability of plants and microorganisms to take up organic nitrogen in the form of free amino acids and oligopeptides has received increasing attention over the last two decades, yet the mechanisms for the formation of such compounds in soil environments remain poorly understood. We used Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies to distinguish the reaction of a model protein with a pedogenic oxide (Birnessite, MnO2) from its response to a phyllosilicate (Kaolinite). Our data demonstrate that birnessite fragments the model protein while kaolinite does not, resulting in soluble peptides that would be available to soil biota and confirming the existence of an abiotic pathway for the formation of organic nitrogen compounds for direct uptake by plants and microorganisms. The absence of reduced Mn(II) in the solution suggests that birnessite acts as a catalyst rather than an oxidant in this reaction. NMR and EPR spectroscopies are shown to be valuable tools to observe these reactions and capture the extent of protein transformation together with the extent of mineral response.