Homogeneous Precursor Research Articles

A facile, low temperature spray pyrolysed tungsten oxide (WO3): an approach to antifouling coating by amalgamating scratch resistant and water repellent properties

In this study, a facile spray pyrolysed hydrophobic robust tungsten oxide (WO3) films were deposited at an annealing temperature of 400°C on inexpensive glass substrates, using clear and homogeneous precursor solution containing tungsten hexachloride and 2-methoxyethanol. The 10 and 15 times sprayed films were polycrystalline with the monoclinic crystal structure, uniform with the submicron-sized grain morphology (size ~320–420 nm), with an average surface roughness ranging from 12 to 17 nm and transparent above 60% in the visible region with a thickness of 380 and 550 nm, respectively. Elemental existence of tungsten and oxygen was recognized on the surface of the films possessing the highest lattice oxygen percentage of 91.1. Increment in the scratch hardness of the films with the number of sprays compared to uncoated glass was identified. The films were hydrophilic in nature (water contact angle 120°) by treating chemically with octadecyltrichlorosilane to form a self-assembled monolayer on the top and the hydrophobicity remained same (~120°) even after a year. These films with unique and combined properties of scratch hardness and hydrophobicity can serve in the potential application as antifouling coatings.

Atmospheric Modified Thiol-Based Solution Deposition for Cu2ZnSn(S,Se)4 Absorber Layer

Abandoning the traditional deposition of as-prepared Cu2ZnSnS4 (CZTS) thin films in a glove box, a modified thiol-based solution system suitable for deposition in air is described to further reduce device production costs. In this modified approach, metal salts and thiourea are used as the starting materials and are dissolved in a mixed solution of thioglycolic acid and 2-methoxyethanol, forming a homogeneous precursor solution. The as-deposited CZTS thin films are obtained by spin-coating the precursor solution in air, followed by the selenization process to form large-grained Cu2ZnSn(S,Se)4 thin films. Combining the microstructural results with compositional analyses, the optimal selenization conditions for the Cu2ZnSn(S,Se)4 absorber layer were found to be 540°C and 10 min.

Effect of nonmetal element dopants on photo- and electro-chemistry performance of ultrathin g-C3N4 nanosheets

Increased charge transfer and light absorption as well as large specific surface area are effective ways to improve the catalytic efficiency of photocatalysts. In this paper, barbituric acid, urea and thiourea were separately freeze-dried to form a homogeneous precursor with melamine, followed by thermal polymerization at 750 °C, g-C3N4 was doped successfully with C, N and S. Among them, C-doped g-C3N4 revealed well photocatalytic hydrogen production which reached to 2.45 mmol g−1 h−1. N-doped g-C3N4 exhibited enhanced photocatalytic degradation properties for organic dye (RhB) which is completely degraded within 8 min while the performance S-doped sample is not satisfied. The introduction of C resulted in planarized sample which has a larger specific surface area and provides more active sites. N doping makes the valence band position moving in the direction of high energy. Thus, holes have stronger oxidizing ability. Accordingly, the effect of C and N ratios in g-C3N4 photocatalysis was fully discussed for more comprehensive understanding of g-C3N4.

Fabrication of Nanoporous Metals through Thermal Decomposition of Transition Metal Dichalcogenides

Nanoporous metals (np-M) owing to their high surface area-to-volume ratio and electrical/thermal conductivity, have emerged as promising materials for catalysis. There exists a group of processing methodologies by which np-M are formed through a top-down nanostructure evolution driven by the selective removal of a sacrificial component, all of which are a variation of dealloying. The driving force for the traditional electrochemical/chemical dealloying is difference of redox potentials and dissolution tendencies amongst the constituent metals. This limits the process to few noble metals e.g. Pt, Pd, Au etc. More recently liquid metal dealloying and vapor phase dealloying have shown success in mimicking the process of traditional dealloying based on difference of affinities of thermal dissolution in a liquid metal, and vapor pressures of the constituent metals, respectively. Nanoporosity evolution through current dealloying methodologies, however, is governed by strict requirements including sufficient separation in “reactivity” of the participating components and a homogeneous solid solution precursor alloy. This limits the viable alloy systems that may be used and the range of np-M's that may be formed with reasonable porosity length scales. Here, we report thermal decomposition of crystalline transition metal dichalcogenides (TMDs) as a new processing methodology for np-M formation, adding to the spectrum of dealloying protocols. We demonstrate application of this process to the formation of a broader class of np-M including W, Re, Mo, and Ta with feature sizes below 100 nm. The presented facile thermal treatment of TMDs offers a new methodology for the evolution of nanoporosity in a broad range of metals.

Endurance degradation of solution-processed ZnO polycrystalline film-based resistive switching memory

Metal oxide-based resistive switching memory cell has potential applications in the next generation of nonvolatile memory devices due to its simple structure, fast reading/writing speed, and good endurance. Zinc oxide (ZnO) is one of excellent resistive switching candidate materials owing to its low-cost, simple preparation process and significant resistive switching characteristics. In this work, homogeneous ZnO precursor solution is spin-coated on indium tin oxide (ITO)-coated glass substrate to deposit a smooth and dense film composed by ZnO nanoparticles with the hexagonal wurtzite structure. Atomic force microscopy images reveal the average grain size of ZnO polycrystalline nanoparticle is about 23.7 nm. An optical band gap of about 3.3 eV is derivate from the ultraviolet-visible light absorption spectra. Current-voltage ( I - V ) curves of Ag/ZnO/ITO memory cells exhibit reversible low-voltage bipolar resistive switching characteristics. Their switching voltages ( V Set/ V Reset) are lower than ± 0.4 V, and the ON/OFF resistance ratio is 103–104 at the read voltage of −0.1 V, which are superior to resistive switching performance of other ZnO polycrystalline films prepared via similar solution methods. However, the memory cell can only maintain 60 stable I - V cycles. After that, the low resistance state gradually degrades to the high resistance state, and the resistive switching memory window completely disappears after 100 I - V cycles. X-ray photoelectron spectra of Zn 2p and O 1s core-levels for ZnO film before and after I - V measurement demonstrate that as-grown film is oxygen-defective ZnO x I - V measurement. Under sustained electric field stress, some drifted oxygen ions combine with oxygen vacancies and change to localized lattice oxygen atoms, this partially remedies the oxygen-deficiency of as-grown non-stoichiometric ZnO x

Reductive amination of levulinic acid to N-substituted pyrrolidones over RuCl3 metal ion anchored in ionic liquid immobilized on graphene oxide

Reductive amination of biomass derived Levulinic acid (LA) for the synthesis of N-substituted pyrrolidones is one of the highly attractive routes for biomass valorization. The supported homogeneous metal precursor into the solid surface is an important context in the field of catalysis because these types of catalysts provide the heterogeneous nature and meet the needs of recyclability. Herein, we have reported a synthesis of catalyst with ruthenium ion supported on ionic liquid immobilized into graphene oxide (Ru@GOIL) and its application for reductive amination reaction. Synthesized catalyst is characterized using different analytical techniques such as FT-IR, XRD, XPS, TGA, FEG-SEM, TEM and EXAFS analysis. The prepared Ru@GOIL found to be highly effective for reductive amination of LA and under these optimized conditions various N-substituted pyrrolidones derivatives were synthesized in excellent yield (78–93%). Ru@GOIL catalyst demonstrated great catalytic performance for reductive amination reaction of LA giving good turnover frequency (TOF = 62 h−1) value in comparison with other catalysts. The Ru@GOIL catalyst was recycled for six reaction runs with slight drop-in activity after 4th cycle. Practical applicability of the developed catalyst was successfully demonstrated by direct transformation of biomass waste (rice husk and wheat straw) derived LA to N-substituted pyrrolidones.

Facile Synthesis of Hierarchical Nanosized Single-Crystal Aluminophosphate Molecular Sieves from Highly Homogeneous and Concentrated Precursors.

The synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single-crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8-rings), AEL (10-rings), AFI (12-rings), and -CLO (20-rings) topologies, ranging from small to extra-large pores, were synthesized. These materials show exceptional properties, including small crystallites (30-150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time-dependent study revealed a non-classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism.

Facile Synthesis of Hierarchical Nanosized Single‐Crystal Aluminophosphate Molecular Sieves from Highly Homogeneous and Concentrated Precursors

AbstractThe synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single‐crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8‐rings), AEL (10‐rings), AFI (12‐rings), and ‐CLO (20‐rings) topologies, ranging from small to extra‐large pores, were synthesized. These materials show exceptional properties, including small crystallites (30–150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time‐dependent study revealed a non‐classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism.

Cellulose Nanocrystal-Templated Tin Dioxide Thin Films for Gas Sensing.

Porous tin dioxide is an important low-cost semiconductor applied in electronics, gas sensors, and biosensors. Here, we present a versatile template-assisted synthesis of nanostructured tin dioxide thin films using cellulose nanocrystals (CNCs). We demonstrate that the structural features of CNC-templated tin dioxide films strongly depend on the precursor composition. The precursor properties were studied by using low-temperature nuclear magnetic resonance spectroscopy of tin tetrachloride in solution. We demonstrate that it is possible to optimize the precursor conditions to obtain homogeneous precursor mixtures and therefore highly porous thin films with pore dimensions in the range of 10-20 nm (ABET = 46-64 m2 g-1, measured on powder). Finally, by exploiting the high surface area of the material, we developed a resistive gas sensor based on CNC-templated tin dioxide. The sensor shows high sensitivity to carbon monoxide (CO) in ppm concentrations and low cross-sensitivity to humidity. Most importantly, the sensing kinetics are remarkably fast; both the response to the analyte gas and the signal decay after gas exposure occur within a few seconds, faster than in standard SnO2-based CO sensors. This is attributed to the high gas accessibility of the very thin porous film.

Modus Operandi of Simultaneous Covering Synthesis from Precursor Heterogeneity for Shelled Nanorods for Multipotent Cancer Theranostics

AbstractThe synthesis of nanostructures using homogeneous precursors in the solution phase is widely used to achieve uniformity and well‐defined morphological control. However, drawbacks such as the lack of diversity due to the limited reaction rate modulation exist. One‐step, core–shell nanorod formation using simultaneous covering synthesis using solid and ionic heterogeneous precursors is proposed in this study. A Te‐Bi2Te3/TeO2 core–shell structure is successfully synthesized by precisely controlling various influencing factors, including concentration, temperature, and pH, and its physicochemical and photochemical properties are thoroughly investigated. The proposed nanostructure overcomes the oxidation susceptibility of Te and can be applied to multipotent cancer theranostics in vitro and in vivo in combination with computed tomography imaging.

Activation of homogeneous precursors for formation of uniform and refined α precipitates in a high-strength β-Ti alloy

The influence of heating rates and interrupted aging treatments on α precipitation in the β-quenched Ti-6Cr-5Mo-5V-4Al alloy has been investigated. Microstructure observations reveal that slow heating rates and low temperature pre-aging produce much refined and uniform distributions of intragranular α precipitates in comparison to aging using fast heating rates at a high temperature only. For interrupted aging treatments, the nucleation rate and refinement of α are gradually enhanced with increasing pre-aging time, but this is dependent on the final aging temperature: at high final aging temperatures, the distribution of α precipitates is similar to single aging at the same temperature. The kinetics of phase transformation was analyzed by thermal mechanical analysis (TMA) under the framework of the Johnson–Mehl–Avrami (JMA) theory. Coupled with microstructural observations, it is suggested that epitaxial growth of pre-existing α phase formed during heating to the aging temperature is the governing mechanism under slow heating rate conditions, while for interrupted aging treatments, the mechanism for intergranular α precipitation is consistent with that of fast heating rate single temperature aging treatments. For interrupted aging, the formation of uniform and refined α precipitates essentially relies on activation of homogeneous precursors associated with chemical partitioning and structural modulation which provide a strong driving force for nucleation of α.

TBX2-positive cells represent a multi-potent mesenchymal progenitor pool in the developing lung

BackgroundIn the embryonic mammalian lung, mesenchymal cells act both as a signaling center for epithelial proliferation, differentiation and morphogenesis as well as a source for a multitude of differentiated cell types that support the structure of the developing and mature organ. Whether the embryonic pulmonary mesenchyme is a homogenous precursor pool and how it diversifies into different cell lineages is poorly understood. We have previously shown that the T-box transcription factor gene Tbx2 is expressed in the pulmonary mesenchyme of the developing murine lung and is required therein to maintain branching morphogenesis.MethodsWe determined Tbx2/TBX2 expression in the developing murine lung by in situ hybridization and immunofluorescence analyses. We used a genetic lineage tracing approach with a Cre line under the control of endogenous Tbx2 control elements (Tbx2cre), and the R26mTmG reporter line to trace TBX2-positive cells in the murine lung. We determined the fate of the TBX2 lineage by co-immunofluorescence analysis of the GFP reporter and differentiation markers in normal murine lungs and in lungs lacking or overexpressing TBX2 in the pulmonary mesenchyme.ResultsWe show that TBX2 is strongly expressed in mesenchymal progenitors in the developing murine lung. In differentiated smooth muscle cells and in fibroblasts, expression of TBX2 is still widespread but strongly reduced. In mesothelial and endothelial cells expression is more variable and scattered. All fetal smooth muscle cells, endothelial cells and fibroblasts derive from TBX2+ progenitors, whereas half of the mesothelial cells have a different descent. The fate of TBX2-expressing cells is not changed in Tbx2-deficient and in TBX2-constitutively overexpressing mice but the distribution and abundance of endothelial and smooth muscle cells is changed in the overexpression condition.ConclusionThe fate of pulmonary mesenchymal progenitors is largely independent of TBX2. Nevertheless, a successive and precisely timed downregulation of TBX2 is necessary to allow proper differentiation and functionality of bronchial smooth muscle cells and to limit endothelial differentiation. Our work suggests expression of TBX2 in an early pulmonary mesenchymal progenitor and supports a role of TBX2 in maintaining the precursor state of these cells.

Xantphos‐ligated palladium dithiolates: An unprecedented and convenient catalyst for the carbonylative Suzuki–Miyaura cross‐coupling reaction with high turnover number and turnover frequency

Xantphos‐ and dithiolate‐ligated macrocyclic palladium complexes as an efficient and stable catalyst for the carbonylative Suzuki–Miyaura cross‐coupling reaction have been synthesized. The catalysts were characterized by 1H‐nuclear magnetic resonance (NMR), CHNS (carbon, hydrogen, nitrogen, and sulfur) analysis, melting point analysis, and 31P‐NMR spectroscopy. Several sensitive functional groups (e.g., –NO2, –F, –Cl, –Br, –NH2, and –CN) on the aromatic ring were well tolerated in the carbonylative Suzuki–Miyaura coupling reaction. The present palladium complexes produce six times higher turnover number (TON) and five times higher turnover frequency (TOF) compared with conventional homogeneous palladium precursors. Maximum TONs in the range of 105 to 106 and TOF in the range of 104 to 105 could be generated by a very low amount of catalyst loading (10–5 mol%).

Nanoporous metals from thermal decomposition of transition metal dichalcogenides

Nanoporous metals (np-M) have emerged as promising materials owing to their high surface area-to-volume ratio and electrical/thermal conductivity. There exists a group of processing methodologies by which np-M are formed through a top-down nanostructure evolution driven by the selective removal of a sacrificial component, all of which are a variation of dealloying. Nanoporosity evolution through current dealloying methodologies, however, is governed by strict requirements including sufficient separation in “reactivity” of the participating components and a homogeneous solid solution precursor alloy. This limits the viable alloy systems that may be used and the range of np-M's that may be formed. Here, we report thermal decomposition of crystalline transition metal dichalcogenides (TMDs) as a new processing methodology for np-M formation, adding to the spectrum of dealloying protocols. We demonstrate application of this process to the formation of a broader class of np-M including W, Re, Mo, and Ta with feature sizes below 100 nm. The presented facile thermal treatment of TMDs offers a new methodology for the evolution of nanoporosity in a broad range of metals.

Solid Nano-Composite Electrolytes (nano-SCE) with Ion Conductivity Promotion at an Interfacial Ice Layer on the Mesoporous Silica Matrix

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Comparison with ILE-based composite electrolytes with solid and mesoporous oxide particles will be made, showing that enhancement exist only in the monolith structures and not in the particle systems where percolation limits the conductivity.

High Active Ultra-Low Pt Content Oxygen Reduction Reaction Catalyst Derived from Metal Organic Framework for PEMFC

Proton exchange membrane fuel cell (PEMFC) has been demonstrated as a highly efficient energy conversion technology. The sluggish oxygen reduction reaction (ORR) at the fuel cell cathode requires 3 to 5 times more catalysts than the hydrogen oxidation reaction at the anode.(1) Currently, platinum is still the catalyst material of choice. However, the heavy use of scarce Pt in the electrodes represents a major cost barrier to the commercialization of PEMFCs. Tremendous efforts have been dedicated to reduce or remove Pt usage through the development of Pt-transition metal catalysts, as highlighted recently by dealloyed PtNi (2), Mo-doped PtNi(3), and ordered PtCo(4); or through the development of transition metals-nitrogen-carbon based PGM-free catalysts (5, 6). In the fuel cell, catalysts should be highly dispersed over the electrode surface to be easily accessible by the reactants, especially at the high fuel cell current density where a large influx of O2 must be converted. For the Pt alloy catalyst of large crystallites, there won’t be enough crystallites available to spread over the electrode surface to encounter the incoming O2 if the total loading of platinum has to be maintained ultralow. Furthermore, unprotected Pt nano-alloys may lose their nanostructure and crystallinity from the dissolution and agglomeration during the ORR process. The PGM-free catalysts, on the other hand, have high catalytic site density with uniform distribution when prepared by homogenous precursors such as metal-organic framework or porous organic polymer, rendering them highly efficient in interacting with O2 flux. Their key drawback, however, is the poor stability operated under PEMFC condition. In this presentation, we will describe a method of preparing highly active yet stable electrocatalysts containing ultralow Pt content using Co or Co/Zn zeolitic imidazolate frameworks as precursors. The new catalysts contain Pt-Co core-shell nanoparticles (NPs) situated over the PGM-free catalytically active support (7). The ORR activities of the new catalysts were first tested in the O2 saturated acidic electrolyte by rotating ring disk electrode (RRDE) before fabricated into the membrane electrode assembly (MEA) and evaluated under fuel cell operating condition. The synergistic catalysis between Pt-Co NPs and PGM-free active substrate led to an unprecedented ORR performance in both RRDE and fuel cell. For example, the fuel cell test demonstrated a mass activity of 1.77 A/mgPt for the new catalysts and > 60% retention of the initial mass activity after 30,000 continuous voltage cycles from 0.6V – 1.0V. The characterizations of the fresh and the post-electrochemical test samples were investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT calculation on the ORR thermodynamic barriers over both Pt-Co NPs and PGM-free site as the descriptors for reaction pathway. The results reveal that the synergistic interaction between Pt-Co and PGM active substrate contribute significantly to both activity and durability enhancements. Acknowledgments: This work was supported by U.S. Department of Energy, Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy. LC wishes to thank Argonne National Laboratory for Maria Goeppert Mayer Fellowship. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source, U.S. Department of Energy Office of Science User Facilities, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. H. A. Gasteiger, N. M. Markovic, Just a Dream-or Future Reality? Science 324, 48-49 (2009).B. Han et al., Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells. Energy & Environmental Science 8, 258-266 (2015).X. Huang et al., High-performance transition metal–doped Pt3Ni octahedra for oxygen reduction reaction. Science 348, 1230-1234 (2015 ).D. Wang et al., Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nat Mater 12, 81-87 (2013).L. Chong et al., Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells. ChemElectroChem 3, 1541-1545 (2016).J. Shui, C. Chen, L. Grabstanowicz, D. Zhao, D. J. Liu, Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network. Proc Natl Acad Sci U S A 112, 10629-10634 (2015).L. Chong et al., Ultralow-loading platinum-cobalt fuel cell catalysts derived from imidazolate frameworks. Science, (2018).

Role of Coprecipitation and Calcination of Precursors on Phase Homogeneity and Electrochemical Properties of Battery Active Materials

Coprecipitation is generally expected to produce particles with atomic level mixing between different cations, and thus has been extensively used to synthesize homogeneous and phase pure multi-component transition metal precursors that are converted to oxides for use as lithium-ion battery active materials. However, very few studies have attempted to quantitatively confirm the mixing level of ions by coprecipitation reactions, and neither have shown the superiority of local mixing for the homogeneity of final materials compared to alternative routes to producing battery active materials. In this talk, we will present experimental results from systematically comparing the phase purity and crystallinity of oxide powders that were either from a solution mixed multicomponent transition metal precursor via coprecipitation or from physically mixed single transition metal salts after calcination at the same conditions. A simple model was also applied to understand the diffusion limitations during the calcination process under various conditions. High voltage spinel LiMn1.5Ni0.5O4 was used as the target final oxide material composition and phase in this study, and electrochemical data will be provided to show the role that local mixing via coprecipitation plays in forming high crystallinity battery active materials with the desired phase.

Solid Nano-Composite Electrolytes (nano-SCE) with Ion Conductivity Promotion at an Interfacial Ice Layer on the Mesoporous Silica Matrix

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Figure caption: Ball-and-stick model for the adsorbed mesophase layer on silica with an interfacial ice water layer. The strong H-bonding between TFSI anions and OH surface groups result in polarization of the adsorbed ILE layer and the dissociation of Li+ from TFSI- anion. The free Li-ions can move faster through the liquid-like layer just above the adsorbed mesophase layer resulting in enhanced ion conductivity. Figure 1

Fabrication of superconducting YBCO agglomerated particles (ANPs) by electrospinning

Superconducting YBa2Cu3O7-δ (YBCO) agglomerated nanoparticle (ANPs) was fabricated by electrospinning technique and sol-gel of a homogeneous precursor of Y-Ba-Cu acetate and Poly (vinyl pyrrolidone) (PVP). The sol-gel solution of YBCO is conducted by adding 4.0 g of (Y-Ba-Cu) metal acetate according to a stoichiometric ratio of 1:2:3 molar mass and 5.0 g of PVP powder in 25.0 ml solution contains propionic acid 10 ml, acetic acid 5 ml and methanol 10 ml. By optimizing electrospinning process, sol-gel parameters and heat treatment, YBCO ANPs were obtained with a transition temperature of Tc ~90 K using the AC susceptibility. YBCO ANPs was found with high surface area 6.8310 m2/g, and not affected by high calcination temperature at 950 oC in comparison with bulk YBCO sample. XRD Characterization of YBCO was demonstrated YBCO has orthorhombic phase, FESEM images of the electrospun YBCO sample showed ANPs of size in the 200 – 400 nm range. A closer examination revealed that agglomerates contain finer particles of size ~50 nm. Electrospinning is an effective technique can produce various morphologies of YBCO superconductor at the nanoscale with unique properties for practical applications.

Characteristics of Nanosized Ni, NiCo-Y₂O₃ Powders Synthesized by a PVA Solution Route at Low Temperature.

Nanosized Ni, NiCo-Y₂O₃ powders were successfully synthesized at low temperature via a simple polymer solution route. As an organic carrier, polyvinyl alcohol (PVA) afforded an atom-scale homogeneous precursor gel, which in turn gave fully crystallized nanosized Ni, NiCo-Y₂O₃ powder upon calcination at a low temperature under an Ar-4% H₂ atmosphere. The PVA content, calcination temperature, heating time, and reduction conditions affected the microstructure and crystallization behavior of the as-synthesized powders. The PVA content also influenced the synthesis behavior and microstructure of the final powder. The particle size increased with an increase in the calcination temperature and decrease in the PVA content. At a PVA-metal ion ratio of 4:1, the measured particle size was about 20 nm. The results of TEM mapping on the NiCo-Y (0.6 wt%) powders revealed a well-dispersed Y₂O₃ phase in the NiCo crystalline matrix.