Variations In Oxidation State Research Articles

Mining for Metal-Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials.

The conceptual framework presented in this Perspective overviews the design principles of innovative thorium-based materials that could address urgent needs of the medicinal, nuclear energy, and waste remediation sectors from the lens of zirconium and uranium analogs. We survey the intersections of Zr, Th, and U chemistry with a focus on how the intrinsic behavior of each metal translates to broader material properties, including, but not limited to, structural and topological diversity, preferential metal-ligand binding, and reactivity. On the example of several classes of materials, including organometallic complexes, polyoxometalates, and the primary focus of this Perspective, metal-organic frameworks (MOFs), the design principles that govern the preparation of Zr-, Th-, and U-compounds, including oxophilicity, variation in oxidation states, and stable coordination environments have been considered. Further, we highlight how the impact of the mentioned variables may shift throughout the progression from discrete molecular systems to extended structures. We discuss the common assumption that zirconium-organic materials are typically considered a close analog of thorium-based congeners in areas such as material design and preparation. Through consideration of fundamental chemistry principles, we shed light on the relationships between Zr-, Th-, and U-based materials and highlight how a critical analysis of their distinct properties can be used to target a desired material performance. As a result, we provide a detailed understanding of Th-based materials chemistry by anchoring their fundamental properties between two well-studied reference points, zirconium- and uranium-containing analogs.

Base-free synthesis of renewable furan-2,5-dicarboxylic acid (FDCA) over an earth-abundant magnetic catalyst

Being a biobased alternative to petroleum-based terephthalic acid (TPA), furan-2,5-dicarboxylic acid (FDCA) requires a low-cost and efficient catalytic system for its commercialization. This study describes FDCA production using whey permeate powder (WPP)-derived 5-(hydroxymethyl)furfural (HMF) in a base-free system over a magnetically recyclable catalyst composed of earth-abundant metals (Mn and Fe). The impact of MnCl2·4 H2O loading on the iron core was studied at different levels and found optimal at the ratio of 1:1. The in-situ oxidation of HMF was carried out using ozone and t-BuOOH as the oxidants in a γ-valerolactone (GVL) -water solvent system. It was observed that the ozone pre-treatment (3 h at room temperature) of HMF increased the FDCA yield from 39.7 % (without ozonation) to 60 % at a reaction condition of 130 °C for 2 h. The concentration profiles for the intermediates formed during HMF to FDCA oxidation i.e., 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), furan-2,5-dicarbaldehyde (DFF), and 5-formyl-2-furancarboxylic acid (FFCA) were analyzed at different reaction temperatures to evaluate the reaction kinetics. The kinetic study revealed that the present solvent-catalytic system favored HMFCA formation over DFF due to the requirement of higher activation energy for the latter. The HMF to FDCA catalytic solvent was tested for WPP, which afforded an overall FDCA yield of 14.6 % at 130 °C in 120 min. In addition, the Mn1Fe1 consisted of mixed phases of Mn3O4, Mn2O3, MnO2, Fe2O3, and Fe3O4 and demonstrated variation in oxidation states for Mn (Mn3+↔Mn2+) and Fe (Fe2+↔Fe3+) species.

Revisiting the metal sites of nitrous oxide reductase in a low-dose structure from Marinobacter nauticus

Copper-containing nitrous oxide reductase catalyzes a 2-electron reduction of the green-house gas N2O to yield N2. It contains two metal centers, the binuclear electron transfer site CuA, and the unique, tetranuclear CuZ center that is the site of substrate binding. Different forms of the enzyme were described previously, representing variations in oxidation state and composition of the metal sites. Hypothesizing that many reported discrepancies in the structural data may be due to radiation damage during data collection, we determined the structure of anoxically isolated Marinobacter nauticus N2OR from diffraction data obtained with low-intensity X-rays from an in-house rotating anode generator and an image plate detector. The data set was of exceptional quality and yielded a structure at 1.5 Å resolution in a new crystal form. The CuA site of the enzyme shows two distinct conformations with potential relevance for intramolecular electron transfer, and the CuZ cluster is present in a [4Cu:2S] configuration. In addition, the structure contains three additional types of ions, and an analysis of anomalous scattering contributions confirms them to be Ca2+, K+, and Cl–. The uniformity of the present structure supports the hypothesis that many earlier analyses showed inhomogeneities due to radiation effects. Adding to the earlier description of the same enzyme with a [4Cu:S] CuZ site, a mechanistic model is presented, with a structurally flexible CuZ center that does not require the complete dissociation of a sulfide prior to N2O binding.Graphical The [4Cu:2S] CuZ site in M. nauticus N 2O reductase. The electron density map shown is contoured at the 5 σ level, highlighting the presence of two sulfide ligands. 705x677mm (72 x 72 DPI)

Optical storage and encryption via efficient reversible luminescence modulation based on copper-doped borate glass

Transparent glass is a promising candidate for optical storage media due to its large capacity and high stability advantages. Previously reported optical storage glass systems meet various problems, such as high manufacturing costs, low security levels, etc. Herein, a kind of copper-contained borate glass was designed and fabricated, emitting tunable broadband upon various ultraviolet light excitations. By alternating 360 nm laser (10.7 W/cm2) irradiation for 15 s and thermal treatment at 400 ℃ for 2 h, the emission intensity of the glass can be reversibly regulated, which is associated with the variation of oxidation states of the copper element. Relying on their efficient reversible luminescence modulation behaviors, the potential application of this glass as an optical storage and encryption media is developed, exhibiting the high performances of repeatable writing and erasing, dual mode readout, high-level safety, and good writing resolution for the Cu-doped borate glass.

Cerium oxide nanoparticles: Chemical properties, biological effects and potential therapeutic opportunities (Review).

The chemistry of pure cerium oxide (CeO2-x) nanoparticles has been widely studied since the 1970s, especially for chemical catalysis. CeO2-x nanoparticles have been included in an important class of industrial metal oxide nanoparticles and have been attributed a range of wide applications, such as ultraviolet absorbers, gas sensors, polishing agents, cosmetics, consumer products, high-tech devices and fuel cell conductors. Despite these early applications in the field of chemistry, the biological effects of CeO2-x nanoparticles were only explored in the 2000s. Since then, CeO2-x nanoparticles have gained a spot in research related to various diseases, especially the ones in which oxidative stress plays a part. Due to an innate oxidation state variation on their surface, CeO2-x nanoparticles have exhibited redox activities in diseases, such as cancer, acting either as an oxidizing agent, or as an antioxidant. In biological models, CeO2-x nanoparticles have been shown to modulate cancer cell viability and, more recently, cell death pathways. However, a deeper understanding on how the chemical structure of CeO2-x nanoparticles (including nanoparticle size, shape, suspension, agglomeration in the medium used, pH of the medium, type of synthesis and crystallite size) influences the cellular effects observed remains to be elucidated. In the present review, the chemistry of CeO2-x nanoparticles and their impact on biological models and modulation of cell signalling, particularly focusing on oxidative and cell death pathways, were investigated. The deeper understanding of the chemical activity of CeO2-x nanoparticles may provide the rationale for further biomedical applications towards disease treatment and drug delivery purposes.

Zircons reveal the history of fluctuations in oxidation state of crustal magmatism and supercontinent cycle

We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxidation state, expressed as ΔFMQ, through Earth’s history. Those from I-type rocks, which comprise mantle and crustal igneous protoliths, including tonalite–trondhjemite–granodiorites (TTGs), generally have a high oxidation state (ΔFMQ > 0). In contrast, zircons from igneous rocks derived from supracrustal source rocks (S-type) are commonly reduced (ΔFMQ < 0). With the probability density function derived from the Gaussian-Kernel-Density-Estimation, we use the maximum likelihood estimation (MLE) to distinguish S-type from I-type zircons through Earth’s history using zircon redox. Voluminous S-type magma production shows a ca. 600 Ma cyclicity that is closely related to the supercontinent cycle. We link a cyclic drop in redox values after 2.6 Ga to periodic S-type magma generation associated with burial and melting of metasedimentary rocks during supercontinent assembly and amalgamation. The ΔFMQ of the detrital zircons rise at ∼3.5 Ga followed by a consistent average ΔFMQ > 0 over the last 3 Ga. Given that the redox state of magmas is independent of crustal thickness and silica variation, and elevated values are likely more closely related to tectonic setting, we suggest that the consistent average ΔFMQ > 0 from ca. 3.5 Ga onwards relates to recycling of oceanic lithosphere back into the mantle in what eventually became established as subduction zones. The more reduced magmas associated with sedimentary sources, became established at 2.6 Ga, presumably in response to continental rocks rising above sea-level, and follow peaks of productivity associated with the supercontinent cycle.

Lanthanides: The Key to Durable and Sustainable Corrosion Protection

Lanthanides (Ln), as an important class of materials, have recently generated global interest in modern technology due to their unique metallurgical, ceramic, catalytic, electronic, nuclear, and mechanical properties. Here, 12 Ln (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y, and Lu) elements are outlined based on their impacts on the structural and functional properties of alloys that have tremendous applications in both the chemical and industrial sectors. Owing to the particular position in the lanthanides series, although each element possesses similar oxidation state variation in the number of unpaired electrons in the outermost shell, it is responsible for imparting unique features such as electrochemical characteristics, mechanical strength, and improvement in magnetic properties. This review starts with an introduction of every Ln element, followed by a detailed description of the element-based conversion coatings, which includes the morphology and composition of these Ln-based coatings along with their mechanism of formation and competence for the corrosion control process.

Surface Oxidation State Variations and Insulator–Metal Transition Modulations in Vanadium Oxides with Pulsed Hydrogen Plasma

AbstractSurface often determines the formation and function of nanoscale thin films and nanomaterials. In correlated vanadium oxides, oxidation states and stoichiometry play important roles in regulating reversible insulator–metal transition (IMT) behaviors. This study presents the surface oxidation state reductions and IMT modulations in vanadium oxides. Oxidation states of vanadium in the surface layer are changed in the nanostructures of vanadium oxides through pulsed hydrogen plasma (PHP). The thickness‐dependent variations are also observed with Raman and X‐ray photoelectron spectroscopy (XPS), and verified in vanadium oxides with different oxidation states. Obvious modulations on IMT behaviors are then demonstrated and related to such variation of surface oxidation states in the VO2 thin film and nanobeam. It is expected that such surface manipulations are beneficial to a better understanding of the IMT in correlated vanadium oxides and the fabrication of advanced functional electronic and photoelectronic devices.

Atomic structure and physical properties of peridotite glasses at 1 bar

Earth’s mantle, whose bulk composition is broadly peridotitic, likely experienced periods of extensive melting in its early history that formed magma oceans and led to its differentiation and formation of an atmosphere. However, the physical behaviour of magma oceans is poorly understood, as the high liquidus temperatures and rapid quench rates required to preserve peridotite liquids as glasses have so far limited their investigation. In order to better characterize the atomic structure and estimate the physical properties of such glasses, we examined the Raman spectra of quenched peridotite melts, equilibrated at 1900 °C ± 50 °C at ambient pressure under different oxygen fugacities (fO2), from 1.9 log units below to 6.0 log units above the Iron-Wüstite buffer. Fitting the spectra with Gaussian components assigned to different molecular entities (Q-species) permits extraction of the mean state of polymerisation of the glass. We find that the proportions of Q1 (0.36–0.32), Q2 (0.50–0.43), and Q3 (0.16–0.23) vary with Fe3+/FeTOT (FeTOT = Fe2+ + Fe3+), where increasing Fe3+/FeTOT produces an increase in Q3 at the expense of Q2 at near-constant Q1. To account for the offset between Raman-derived NBO/T (2.06–2.27) with those determined by assuming Fe2+ exists entirely as a network modifier and Fe3+ a network former (2.10–2.44), ∼2/3 of the ferric iron and ∼90% of the ferrous iron in peridotite glasses must behave as network modifiers. We employ a deep neural network model, trained to predict alkali and alkaline-earth aluminosilicate melts properties, to observe how small variations in the atomic structure of peridotite-like melts affect their viscosity. For Fe-free peridotite-like melts, the model yields a viscosity of ∼ −1.75 log Pa s at 2000 °C, similar to experimental determinations for iron-bearing peridotite melts. The model predicts that changes in the peridotite melt atomic structure with Fe3+/FeTOT yield variations in melt viscosity lower than 0.1 log Pa s, barely affecting the Rayleigh number. Therefore, at the high temperatures typical of magma oceans, at least at 1 bar, small changes in melt structure from variations in oxidation state are unlikely to affect magma ocean fluid dynamics.

CuO Nanowires Fabricated by Thermal Oxidation of Cu Foils towards Electrochemical Detection of Glucose

In view of the various stability issues and high cost of enzymatic glucose biosensors, non-enzymatic biosensors have received great attention in recent research and development. Copper oxide (CuO) nanowires (NWs) were fabricated on Cu foil substrate using a simple thermal oxidation method. The phase and morphology of the CuO NWs could be controlled by synthesis temperature. Variation in oxidation states enables CuO NWs to form Cu (III) species, which is crucial in catalysing the eletro-oxidation of glucose. The Cu-based metal/oxide composite electrode works as a non-enzymatic biosensor that adapts to the fast, dynamic change in glucose concentration, with a low saturation concentration (~0.7 mM) and a lower detection limit of 0.1 mM, making CuO NWs an excellent sensor towards impaired fasting glucose. The simplicity, cost-effectiveness and non-toxicity features of this study might make a way for potentially scalable application in glucose biosensing.

Interplay of valence states and magnetic interactions in the perovskite system LaNi1–xRhxO3

We report on the structural, magnetic and electronic properties of Rh substituted LaNiO3, LaNi1–xRhxO3 (0 ​≤ ​x ​≤ ​1). Increased Rh contents are associated with increased structural distortion, and we observe a phase transformation and an immiscibility gap between 0.15 ​≤ ​x ​≤ ​0.25, separating the R-3c and Pnma perovskite structure regimes. Structural evaluation by synchrotron X-ray diffraction, X-ray absorption spectroscopy and DC magnetic measurements suggest variations in oxidation state for the B-site cations, with Ni(II)/Rh(IV), in addition to Rh(III), dominating for high Rh-contents. Although ordering of Ni(II)/Rh(IV) is possible, no B-site ordering between Ni and Rh is observed for any composition. A metal-to-insulator transition occurs upon Rh-substitution, correlating with the structural transition. DC- and AC magnetic measurements reveal that several of the compositions are magnetically frustrated with both antiferro- and ferromagnetic behaviour at low temperatures. The antiferromagnetic interactions are dominating, while the ferromagnetic interactions increase with increasing Rh-content, to a maximum at x ​= ​0.80 and x ​= ​0.90 in LaNi1–xRhxO3. The mixed valence states are assumed to contribute with a ferromagnetic super-exchange interaction between Ni(II) and Rh(IV).

Operando XAS/SAXS: Guiding Design of Single-Atom and Subnanocluster Catalysts.

Single-atom and subnanocluster catalysts (SSCs) represent a highly promising class of low-cost materials with high catalytic activity and high atom-utilization efficiency. However, SSCs are susceptible to undergo restructuring during the reactions. Exploring the active sites of catalysts through in situ characterization techniques plays a critical role in studying reaction mechanism and guiding the design of optimum catalysts. In situ X-ray absorption spectroscopy/small-angle X-ray scattering (XAS/SAXS) is promising and widely used for monitoring electronic structure, atomic configuration, and size changes of SSCs during real-time working conditions. Unfortunately, there is no detailed summary of XAS/SAXS characterization results of SSCs. The recent advances in applying in situ XAS/SAXS to SSCs are thoroughly summarized in this review, including the atomic structure and oxidation state variations under open circuit and realistic reaction conditions. Furthermore, the reversible transformation of single-atom catalysts (SACs) to subnanoclusters/nanoparticles and the application of in situ XAS/SAXS in subnanoclusters are discussed. Finally, the outlooks in modulating the SSCs and developing operando XAS/SAXS for SSCs are highlighted.

Electrochemical Zinc Ion Capacitors Enhanced by Redox Reactions of Porous Carbon Cathodes

AbstractAqueous electrochemical zinc ion capacitors (ZICs) are promising next‐generation energy storage devices because of their high safety, inexpensive raw materials, and long cycle life. Herein, an aqueous ZIC with superior performance is fabricated by employing an oxygen‐rich porous carbon cathode. Excellent capacitance and energy density are obtained thanks to the electric double‐layer capacitance of porous carbon, and additional pseudocapacitances originating from the variation in oxidation states of oxygen functional groups and the reversible electrochemical hydrogen adsorption and desorption during each round‐trip charge–discharge cycle. Moreover, the cycling stability of ZIC is effectively prolonged by suppressing zinc dendrite growth with a simple surface carbon coating strategy. The assembled ZIC delivers a high capacitance of 340.7 F g−1, a high capacity of 179.8 mAh g−1 in a wide voltage window of 0–1.9 V, a maximum energy density of 104.8 Wh kg−1, and an ultrahigh power density of 48.8 kW kg−1. Furthermore, the as‐fabricated aqueous ZIC exhibits an ultralong cycle life of 30 000 cycles with a high capacity retention of 99.2%. This work provides a novel design strategy by incorporating reversible hydrogen and oxygen redox reactions to enhance the energy storage capability of aqueous ZICs toward practical energy storage applications.

Understanding the Overlithiation Properties of LiNi0.6Mn0.2Co0.2O2 Using Electrochemistry and Depth-Resolved X-ray Absorption Spectroscopy

One known drawback of Ni-containing layered cathodes is their poor first cycle efficiency of 85%–90%, upon cycling in a practical potential window. The poor first cycle efficiency is likely a result of surface overlithiation due to significant lithium ion diffusion limitation at this bulk state of charge, but the overlithiation properties of Ni-containing cathodes are currently insufficiently understood. This work focuses on one Ni-containing cathode, LixNi0.6Mn0.2Co0.2O2, and performs detailed characterization of its intercalation properties both in the poor cycling efficiency region as well as in the overlithiation region, where the bulk lithium ion content rises above the value of 1. The results of the study first demonstrate that it is possible to recover the capacity this cathode “loses” in the first cycle by lowering the applied potential. Then, they establish the possibility to overlithiate LixNi0.6Mn0.2Co0.2O2 cathodes by as much as 300 mAhg−1 relative to the pristine electrode. Through complementary characterization using ex situ X-ray diffraction and X-ray absorption spectroscopy both the structural changes and the oxidation state variations in the material throughout the overlithiation process are elucidated. The generated knowledge can be used in developing more accurate physics-based models of industrially-relevant batteries.

Influence of redox processes on the germanium isotopic composition of ordinary chondrites

Ordinary chondrites (OCs) are classified into three groups, according to their oxidation state, which increases from the H to L to LL groups. This is demonstrated by the decrease in metal content (H = ∼8 vol%, L = ∼4 vol%, and LL = ∼2 vol%), and by a positive correlation between Δ17O and %Fa through the OC sequence. Compared to other chondrites, OCs exhibit the largest variation in oxidation state, but there is an ongoing debate on the processes that control this variation. To constrain the causes of the variations in the oxidation state with respect to the associated nebular versus parent bodies processes, we investigated the elemental and isotopic variations of germanium (moderately siderophile and volatile) in the bulk sample, as well as in the metal, silicate and sulfide phases, over a range of petrographic types for the H, L, and LL ordinary chondrites.We found that δ74/70Gemetal is a proxy for the δ74/70Gebulk composition and that each OC group is distinguishable by their δ74/70Gemetal, which increases from −0.51 ± 0.09‰ for H chondrites, −0.31 ± 0.06‰ for L chondrites, and, finally, to −0.26 ± 0.09‰ for LL chondrites (2σ SD). Additionally, the OC sequence exhibited a positive correlation, from H to L to LL, between δ74/70Gemetal and %Fa, as well as oxygen isotopes (δ17O, δ18O and Δ17O), that was not a consequence of a “size sorting effect” on chondrules (i.e., chondrule mixing) or metamorphic processes in the parent bodies but, rather, was the result of nebular processes. We propose that the correlation between the δ74/70Ge values and %Fa, Δ17O, δ18O can be explained by an increasing proportion of accreted hydrated phyllosilicates, from the H, L to LL groups, with high δ74/70Ge and Δ17O. We found that 10 to 15% of phyllosilicates, with a composition of [Ge] = 4–7 ppm and δ74/70Ge = 3–2.5‰, is needed to change the δ74/70Ge from H to LL, which corresponds to a Δ17O ≈ 8–7‰. This value agrees with the Δ17O ≈ 7‰ composition of the accreted nebular component reported by Choi et al. (1998). During thermal metamorphism, phyllosilicates destabilize, liberating germanium that will be incorporated in the metal, then leading to its high δ74/70Ge signature.High-temperature metamorphism can explain the lack of δ74/70Gemetal variation with the petrologic type in the OC, even for the type 3 chondrites (T ≈ 675 °C), implying a complete reaction even at low petrologic types. In addition, metal-silicate re-equilibration in response to thermal metamorphism results in a decrease in Δ74/70Gemetal-silicate from 0.33‰ to 0.06‰, within the H chondrite group, which is interpreted as the result of δ74/70Gesilicate variation. The mean positive Δ74/70Gemetal-silicate fractionation factor of +0.22 ± 0.36‰ (error propagation on individual error) also displays a remarkable similarity to the direction of isotopic fractionation with other germanium isotopic metal-silicate datasets, such as the magmatic iron meteorites, the Earth silicate reservoirs. We propose that the Δ74/70Gemetal-silicate and the negative δ74/70Ge values of OCs are inherited from metal-silicate melting and partial exchange before planetesimal accretion in a light isotope-enriched gas. Finally, the δ74/70Gemetal-Δ17Osilicate correlation between the IIE iron meteorites and OCs, provides new evidence for the existence of a highly reduced HH group.

Interfacial Engineering of SeO Ligands on Tellurium Featuring Synergistic Functionalities of Bond Activation and Chemical States Buffering toward Electrocatalytic Conversion of Nitrogen to Ammonia.

Ammonia (NH3) production from electrochemical nitrogen (N2) reduction reaction (NRR) under ambient conditions represents a sustainable alternative to the traditional Haber–Bosch process. However, the conventional electrocatalytic NRR process often suffers from low selectivity (competition with the hydrogen evolution reaction (HER)) and electron transfer bottleneck for efficient activation and dissociation. Herein, a strategy to simultaneously promote selectivity and activity through dual‐incorporation of Se and O elements onto the shell of HER‐inactive Te nanorods is reported. It is theoretically and experimentally verified that the exposure of lone‐pair electrons in the TeO2 shell of Se, O dual‐doped Te nanorods can maximize orbits overlap between N2 and Te for N‐N bond activation via π‐backdonation interactions. Further, the Gibbs free energy change indicates that the Lewis‐basic anchor ‐SeO ligand with strong electron‐donating characteristics serves as an electron reservoir and is capable of buffering the oxidation state variation of Te, thereby improving the thermodynamics of desorption of the intermediates in the N2‐to‐NH3 conversion process. As expected, a high faradaic efficiency of 24.56% and NH3 yield rate of ≈21.54 µg h−1 mg−1 are obtained under a low overpotential of ≈0.30 V versus reversible hydrogen electrode in an aqueous electrolyte under ambient conditions.

New insight on the mechanism of electrochemical cycling effects in MnO2-based aqueous supercapacitor

The investigation of mechanism for electrochemical cycling process has become ever more important in supercapacitor electrode material for achieving higher stability and electrochemical performance. Herein, an electrochemical cycling effect has been demonstrated basing on the comprehensive study on the morphological and electronic evolution, which provides an insight into the capacity fluctuation mechanism in a typical MnO2-based supercapacitor. The results reveal that the significant changes of morphologies and chemical valence state of MnO2 take place accompanying with the intercalation of electrolyte ions (i.e. Na+) during the electrochemical cycling process. A structural reconstruction model is established to unravel the origin of microscopic changes of MnO2@carbon nanotubes (MnO2@CNTs) composites electrode and their relationships with the capacity at different electrochemical stages. It was found that the morphological and structural evolution of the electrode should be attributed to the dissolution-redeposition process of MnO2, which governed by the cation distribution near the interface between electrode and electrolyte. The ion intercalation-deintercalation process is evidenced by the oxidation state variations of Mn with the Na+ intercalation amount. Therefore, the capacity performance of MnO2@CNTs was strongly correlated with its structural and chemical states. This work will open up new perspectives for the capacity performance improvement of MnO2-based electrode materials.

N2Reduction on Fe‐Based Complexes with Different Supporting Main‐Group Elements: Critical Roles of Anchor and Peripheral Ligands

AbstractDue to the enigmatic existence of the carbon atom in the MoFeS cluster of iron‐molybdenum cofactor (FeMoco), the design of biomimetic model catalysts featuring a dative bond between a transition metal and a main group atom is an important topic for efficient reduction of N2to NH3at ambient conditions. Different anchor atoms (X) for the trigonal bipyramidal (XPiPr3)Fe (X = B, C, N) catalyst scaffold are investigated by theory. The calculations show that from Lewis acidic B anchor to Lewis basic N or P anchor, the molecular orbital energy levels consisting mainly of Fe 3d orbitals are pushed higher, thus causing stronger backdonation bonding with theπ*orbitals of N2, which promotes activation of N2but impedes reduction of N2. The redox‐flexible bonding can act as an electron reservoir and buffer the oxidation state variation of Fe. However, when the FeX bond is less flexible, the peripheral ligands can serve as an extra electron reservoir in the model with Lewis basic anchor. Thus, engineering the peripheral ligand with proper electron‐withdrawing substituent groups can promote reduction of N2. The ability to balance well the electron‐donating ability of anchor and electrophilicity of the peripheral ligand is a promising direction toward novel efficient catalysts for N2fixation.

Scalable Room-Temperature Synthesis of Multi-shelled Na3(VOPO4)2F Microsphere Cathodes

Summary The large-scale application of rechargeable batteries in electric vehicles and energy-storage systems is still hindered by their high cost, particularly from the active materials. Here we proposed a concept of integration of extraction-separation and materials-preparation to further reduce the materials' cost. The power of this concept was demonstrated by the large-scale room-temperature synthesis (150 g per batch) of multi-shelled Na3(VOPO4)2F microspheres based on in situ generated bubbles as soft templates. The as-prepared Na3(VOPO4)2F shows superior rate capability with discharge capacity of 81 mAh g−1 at 15 C current rate and capacity retention of 70% after 3,000 cycles. Ex situ UV-vis was first employed to characterize the variation of oxidation state for vanadium during the charging and discharging process. This is the first report of a rapid and facile large-scale room-temperature controllable synthesis of Na3(VOPO4)2F microspheres, and this approach could be extended to synthesize other similar compounds.

Investigation of the Active Site for the Oxygen Reduction Reaction on the Oxide Surface Using by In-Situ XAFS Method

In this study, the oxidation state of Rh2O3, RuO2, and IrO2 during the oxygen reduction reaction (ORR) was investigated using in-situ x-ray adsorption fine structure measurement in order to understand the influence of oxygen adsorption on the oxide surface as the first step of ORR. In case of Rh2O3, the oxidation state was changed by the applied potential and kind of saturated gas. It is thought that this phenomenon attributes to the oxygen molecules adsorbing to the low valence rhodium atom. Our results indicate that The ORR activity seems to relate to the variation of oxidation state by the saturated gas at the low potential region. In addition, we observed the variation of oxidation state in noble oxide at the first.