Controlled-surfactant-directed solvothermal synthesis of γ-Al2O3 nanorods through a boehmite precursor route

Ceramic one-dimensional particles are fascinating nanomaterials for sustainable future industries. Nanorods of γ-Al₂O₃ with single crystallinity and 10 nm diameter regime were newly developed through solvothermal procedure between AlCl₃·6H₂O, NaOH, and sodium dodecylbenzene sulfonate at 200 °C for 24 h. Controlling the pH values, reaction time, temperature, and effect of surfactant during the solvothermal reaction was studied to control the morphology and structure of nanorods. The solvothermal procedure for preparing γ-AlOOH nanorods followed lamellar growth, assembly, and ripening routes. The γ-AlOOH nanorods were converted to γ-Al₂O₃ through calcination reaction at 500 °C for 3 h. The produced γ-Al₂O₃ nanorods were 10 nm average width, 100–200 nm average length, and exposed with [101] orientation and a linear structure. FTIR, HRTEM, FESEM, XRD, and X-ray photoelectron spectroscopy methods were used for characterizing the prepared nanomaterials. New features and applied fields are predictable for the designed γ-AlOOH and γ-Al₂O₃ nanorods.     

Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 enabled PEO-based solid composite electrolyte with high lithium ion transference number and cycling stability

Solid polymer electrolytes (SPEs) have attracted much attention because of their potential in improving energy density and safety. Vanadium doped ceramic matrix Li_6.7La₃Zr_1.7V_0.3O₁₂ (LLZVO) was synthesized by high-temperature annealing, and formed a composite electrolyte with polyethylene oxide (PEO). Compared with pure PEO electrolyte membrane, the composite electrolyte membrane exhibited better ionic conductivity (30 °C: 3.2 × 10^?5 S cm^?1; 80 °C: 3.6 × 10^?3 S cm^?1). The combination of LLZVO was beneficial to improve the lithium ion transference number (t_Li⁺) of SPE, which was as high as 0.81. The Li/SPE/LiFePO₄ battery shows good cycling ability, with a specific capacity of 142 mAh g^?1 after a stable cycle of 150 cycles. Meanwhile, the symmetrical lithium battery with composite electrolyte can work continuously for 1200 h without short circuit at the current density of 0.1 mA cm^?2 at 50 °C, and the capacity is 0.176 mAh. Vanadium doped ceramic matrix LLZVO as an active ionic conductor, improved the overall performance of solid electrolyte.     

Facile synthesis of nanorods of tetragonal barium titanate using ethylene glycol

Tetragonal barium titanate (BaTiO₃) nanorods were synthesized from hydroxide precursor by a hydrothermal/solvothermal method with 10 vol% ethylene glycol as solvent. The hydroxide precursor slurry was prepared by the addition of 10 M NaOH to a mixed solution of BaCl₂ and TiCl₄. When the above aqueous slurry was heated with water only at 200 °C, cubic BaTiO₃ nanocrystals formed, whereas tetragonal BaTiO₃ nanorods were obtained when heated with 10 vol% ethylene glycol. The crystallization of cubic BaTiO₃ via dissolution–reprecipitation of precursor could be suppressed by the addition of ethylene glycol, resulting in the formation of tetragonal BaTiO₃ under hydrothermal treatment at 200 °C.     

Preparation of spherical α-Al2O3 nanoparticles by microwave hydrothermal synthesis and addition of nano-Al seeds

Due to their special appearance, spherical α-Al₂O₃ nanoparticles play an important role for obtaining high-performance structural and functional ceramics. However, there are still problems such as easily agglomerates to form worm-like structures at high temperatures and difficult availability of spherical nanoparticles. In this study, spherical α-Al₂O₃ nanoparticles with high dispersion were prepared by a combination of a microwave hydrothermal method and an addition of nano-Al particles as seeds. First, spherical amorphous alumina precursors were synthesized by the microwave hydrothermal method at 100°C for 30 min using Al₂(SO₄)₃·18H₂O, Al(NO₃)₃·9H₂O, and urea, as raw materials, and then spherical α-Al₂O₃ nanoparticles with a diameter of about 66 nm were acquired after calcined the precursor at 1050°C for 90 min by adding nano-Al seeds, which reduced the calcination temperature by 50°C and holding time by 30 min compared to that without seeds. Kinetic analysis shows that 5 wt.% nano-Al seeds can reduce the activation energy of crystalline transition of γ-Al₂O₃ to α-Al₂O₃ from 516.51 to 474.37 kJ/mol. Moreover, the microscopic mechanism of nano-Al particles as seeds was investigated. The characterizations of sintering properties show that spherical α-Al₂O₃ nanoparticles facilitate the acquisition of uniform microstructure for resulting ceramic and the fracture modes include both intergranular and transgranular fractures.     

Composite polymer electrolyte incorporating WO3 nanofillers with enhanced performance for dendrite-free solid-state lithium battery

All solid-state lithium batteries (ASS-LBs) with polymer-based solid electrolytes are a prospective contender for the next-generation batteries because of their high energy density, flexibility, and safety. Among all-polymer electrolytes, PEO-based solid polymer electrolytes received huge consideration as they can dissolve various Li salts. However, the development of an ideal PEO-based solid polymer electrolyte is hindered by its insufficient tensile strength and lower ionic conductivity due to its semi-crystalline and soft chain structure. In order to lower the crystallization and improve the performance of PEO-based solid polymer electrolyte, tungsten trioxide (WO₃) nanofillers were introduced into PEO matrix. Herein, a PEO₂₀/LiTFSI/x-WO₃ (PELI-xW) (x = 0%, 2.5%, 5%, 10%) solid composite polymer electrolyte was prepared by the tape casting method. The solid composite polymer electrolyte containing 5 wt% WO₃ nanofillers achieved the highest ionic conductivity of 7.4 × 10^-4 S cm^-1 at 60 °C. It also confirms a higher Li-ion transference number of 0.42, good electrochemical stability of 4.3V, and higher tensile strength than a PEO/LiTFSI (PELI-0W) fillers-free electrolyte. Meanwhile, the LiFePO₄│PELI-xW│Li ASS-LBs demonstrated high performance and cyclability. Based on these findings, it can be considered a feasible strategy for the construction of efficient and flexible PEO-based solid polymer electrolytes for next-generation solid-state batteries.     

Polymer-derived mullite–SiC-based nanocomposites

Ceramic mullite–SiC nanocomposites were successfully produced at temperatures below 1500 °C by the polymer pyrolysis technique. An alumina-filled poly(methylsilsesquioxane) compound was prepared by mechanically mixing and cross-linking via a catalyst prior to pyrolysis. Heat treatment of warm pressed alumina/polymer bulk samples under the exclusion of oxygen (inert argon atmosphere) up to 1500 °C initiated crystallization of mullite even at pyrolysis temperatures as low as 1300 °C. The influence of the filler and of the pyrolysis temperature on the crystallization behavior of the materials has been investigated. Based on thermal analysis in combination with elemental analysis and X-ray powder diffraction studies four polymer mixtures differing in type and content of nano-alumina powders were examined. Nano-sized γ-Al₂O₃ powders functionalized at the surface by octylsilane groups proved to be more reactive towards the preceramic polymer leading to the formation of a larger weight fraction of mullite crystals at lower processing temperatures (1300 °C) as compared to native nano-γ-Al₂O₃ filler. Moreover, the functionalized nano-alumina particles offer an enhanced homogeneity of the distribution of alumina nano-particles in the starting polysiloxane system. In consequence, the received ceramic samples exhibited a nano-microstructure consisting of crystals of mullite with an average dimension in the range of 60–160 nm and silicon carbide crystals in the range of 1–8 nm.     

Boosting lithium-ion transport capability of LAGP/PPO composite solid electrolyte via component regulation from ‘Ceramics-in-Polymer’ to ‘Polymer-in-Ceramics'

The design and regulation of the ion transport channels in the polymer electrolyte is an important means to improve the lithium ion transport behavior of the electrolyte. In this work, we for the first time combined the high ionic conductive inorganic ceramic electrolyte Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) with flexible polypropylene oxide (PPO) polymer electrolyte to synthesize a high-filling LAGP/PPO composite solid electrolyte film and regulated the ion transport channels from ‘Ceramics-in-Polymer’ mode to ‘Polymer-in-Ceramics' mode by optimizing the ratio of LAGP vs. PPO. The results reveal that when the LAGP content <40%, the electrolyte belongs to ‘LAGP-in-PPO’, and then changes to ‘PPO-in-LAGP’ when the LAGP content exceeds 40%. Compared with ‘LAGP-in-PPO’, the ‘PPO-in-LAGP’ shows better comprehensive properties, especially for the 75% LAGP-filled PPO electrolyte, the room-temperature ionic conductivity is as high as 3.46 × 10^?4 Scm^?1, the ion migration number and voltage stable window reach 0.83 and 4.78 V respectively. This high-filled composite electrolyte possesses high tensile stress of 40 MPa with a strain of 46% and withstands working environment up to 200 °C. The NCM622/Li solid-state battery composed of this electrolyte also presents good rate and cycle performances with a capacity retention of 80% after 230 cycles at 0.3C because of its high ion transport capability and good inhibition of lithium dendrites. This composite structural design is expected to develop high-performance solid-state electrolytes suitable for high-voltage solid-state lithium batteries.     

Al-doping induced superior lithium ion storage capability of LiNiO2 spheres

To optimize the performance of LiNiO₂ with minimal modification of the pristine structure, a facile solid-state approach, based on the interdiffusion of elements at the solid/solid interface, is developed to achieve uniformly Al-doped LiNiO₂ using alumina coated Ni(OH)₂ spheres as the precursor. The resulting LiNi_0.95Al_0.05O₂ material exhibits excellent discharge capacity (209.9 mAh g⁻¹ at 0.1 C) and cycling stability with a capacity retention of 85.10% after 200 cycles at 0.5 C. This is ascribed to the improved reversibility of the phase transitions by Al-doping as revealed by in-situ XRD characterization. The Al-doping also endows the material with superior rate capability due to the enlarged interlayer spacing in the structure and alleviation of the side reactions at the electrode/electrolyte interface, favorable for lithium ion diffusion. An optimal amount of doped Al is necessary for ensuring the structure stability and interface ionic conductivity of the LiNiO₂ spheres. Thus, the present strategy may provide an opportunity to optimize the performance of LiNiO₂, with uniform doping of a small amount of Al, producing a promising cathode material for advanced lithium ion batteries.     

Electrophoretic Deposition of Zirconia Thin Film on Nonconducting Substrate for Solid Oxide Fuel Cell Application

Electrophoretic deposition (EPD) of 8 mol% yttria‐stabilized zirconia (YSZ) electrolyte thin film has been carried out onto nonconducting porous NiO‐YSZ cermet anode substrate using a fugitive and electrically conducting polymer interlayer for solid oxide fuel cell (SOFC) application. Such polymer interlayer burnt out during the high‐temperature sintering process (1400°C for 6 h) leaving behind a well adhered, dense, and uniform ceramic YSZ electrolyte film on the top of the porous anode substrate. The EPD kinetics have been studied in depth. It is found that homogeneous and uniform film could be obtained onto the polymer‐coated substrate at an applied voltage of 15 V for 1 min. After the half‐cell (anode + electrolyte) is co‐fired at 1400°C, a suitable cathode composition (La_0.65Sr_0.3MnO₃) thick film paste is screen printed on the top of the sintered YSZ electrolyte. A second stage of sintering of such cathode thick film at 1100°C for 2 h finally yield a single cell SOFC. Such single cell produced a power output of 0.91 W/cm² at 0.7 V when measured at 800°C using hydrogen and oxygen as fuel and oxidant, respectively.     

Hydrothermally grown ZnO nanorods arrays for selective NO2 gas sensing: Effect of anion generating agents

Vertically aligned ZnO nanorods (ZNRs) arrays with various aspect ratios were deposited by using a simple and inexpensive hydrothermal route at relatively low temperature of 90 °C. The influence of hydroxide anion generating agents in the solution on the growth of ZNRs arrays was studied. Hexamethylenetetramine (HMTA) and ammonia were used as hydroxide anion generating agents while polyethyleneimine (PEI) as structure directing agent. The combined effect of these three agents plays a crucial role in the growth of ZNRs arrays with respect to their rod length and diameter, which controls the aspect ratio. The deposited ZNRs exhibited hexagonal wurtize crystal structure with preferred orientation along (002) plane. The highly crystalline nature and pure phase formation of ZNRs was confirmed from FT-Raman studies. The maximum gas response (R_g/R_a) of 67.5 was observed for high aspect ratio ZNRs, deposited with combination of HMTA, ammonia as well as PEI. The enhancement in gas response can be attributed to high surface area (45 cm²/g) and desirable surface accessibility in high aspect ratio ZNRs. Fast response–recovery characteristics, especially a much quicker gas response time of 32 s and recovery time of 530 s were observed at 100 ppm NO₂ gas concentration.     

Influence of hydrothermal treatment conditions on the structure and catalytic activity of alumina during the skeletal isomerization of <Emphasis Type="Italic">n</Emphasis>-butenes

In order to obtain an efficient alumina catalyst for skeleton isomerization of n-butenes with a high catalytic activity, we study the influence of hydrothermal treatment (HTT) of alumina systems at 150–200°C on the parameters of the crystalline and pore structure, and acid-base properties of industrial γ-Al₂O₃. It is shown that the HTT of aluminum hydroxide increases the sizes of microcrystallites and reduces the alumina’s specific surface area and the number of acid-base centers. This reduces the activity in the reaction of skeletal isomerization of n-butenes. HTT of the two-phase alumina-aluminum hydroxide system produces smaller crystallites of γ-Al₂O₃ and raises the acidity of the alumina obtained after calcination at 550°C; as a result, the catalytic activity increases. This method can be used to enhance the activity of industrial samples of alumina in the reaction of skeletal isomerization of n-butenes.     

Microwave‐assisted Hydrothermal Synthesis of Single‐crystal Nanorods of Rhabdophane‐type Sr‐doped LaPO4·nH2O

A novel, simple, soft, and fast microwave‐assisted hydrothermal method was used for the preparation of single‐crystal nanorods of hexagonal rhabdophane‐type La_1?xSr_xPO_4?x/2·nH₂O (x = 0 or 0.02) from commercially available La(NO₃)₃·6H₂O, Sr(NO₃)₂, and H₃PO₄. The synthesis was conducted at 130°C for 20 min in a sealed‐vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized using a wide battery of analytical techniques. Highly uniform, well‐shaped nanorods of LaPO₄·nH₂O and La_0.98Sr_0.02PO_3.99·nH₂O were readily obtained, with average length of 213 ± 41 nm and 102 ± 25 nm, average aspect ratio (ratio between length and diameter) of 21 ± 9 and 12 ± 5, and specific surface area of 45 ± 2 and 51 ± 1 m²/g, respectively. In both cases, the single‐crystal nanorods grew anisotropically along their c crystallographic‐axis direction. At 700°C, the hexagonal rhabdophane‐type phase has already transformed into the monoclinic monazite‐type structure, although the undoped and Sr‐doped nanorods retain their morphological features and specific surface area during calcination.     

Modified polysulfides conversion catalysis and confinement by employing La2O3 nanorods in high performance lithium-sulfur batteries

The development of lithium-sulfur batteries (LSB) was hindered due to the shuttling of Li-polysulfides in electrolytes and sluggish electrochemical kinetics of polysulfides. To address these stumbling blocks, we introduced La₂O₃ nanorods modification of ketjen black@sulfur (La₂O₃/KB@S) composite that adsorbs and provides sufficient sites with Li-polysufides interaction. The La₂O₃ nanorods play a key role in the adsorption and catalysis performance of the polysulfides, which further accelerate the redox kinetics. Consequently, the La₂O₃/KB@S cathode with sulfur loading of 3.1 mg cm⁻² attained a high initial discharge capacity of 833 mAh g⁻¹ at a 0.5C rate and displayed excellent cyclic stability with reversible capacity of 380 mAh g⁻¹ after 500 cycles with an average of 98% coulombic efficiency. Further, even with high sulfur loading of 5 mg cm⁻², the La₂O₃/KB@S cathode also presents a capacity of 4.9 mAh at 0.3C and still maintains a stable value of 3.87 mAh after 150 cycles. The results suggest the multifunction La₂O₃ nanorods anchoring effectively and catalyzing are beneficial to realize the goal of the large-scale application with high load active materials and high-performance LSB.     

Novel silica-modified boehmite aerogels and fiber-reinforced insulation composites with ultra-high thermal stability and low thermal conductivity

Alumina–silica composite aerogels have drawn vast attention due to their enhanced thermal stability compared to pristine alumina aerogels. However, they are generally weakly-crystallized and tend to experience inevitable sintering and significant surface area loss especially above 1200 °C. In this study, we developed a hydrothermal treatment and supercritical drying strategy for synthesizing novel, well-crystallized, silica-modified boehmite aerogels and fiber-reinforced composites. For the prepared aerogel, network coarsening was significantly hindered and the α-Al₂O₃ transition was completely prevented even at 1400 °C. As a result, the aerogel exhibits extremely high surface area maintenance (87 % and 53 % after 1300 °C and 1400 °C calcination, respectively) and low linear shrinkage (14 % after 1300 °C calcination) at elevated temperatures. The composite with good toughness shows excellent heat resistance and thermal insulating performance up to 1500 °C. These findings provide a general, direct new idea to improve the thermal tolerance of alumina-based aerogels and extend their applications to higher temperatures.     

Effect of additives in PEO/PAA/PMAA composite solid polymer electrolytes on the ionic conductivity and Li ion battery performance

Polyethylene oxide (PEO) based-solid polymer electrolytes were prepared with low weight polymers bearing carboxylic acid groups added onto the polymer backbone, and the variation of the conductivity and performance of the resulting Li ion battery system was examined. The composite solid polymer electrolytes (CSPEs) were composed of PEO, LiClO_4, PAA (polyacrylic acid), PMAA (polymethacrylic acid), and Al₂O₃. The addition of additives to the PEO matrix enhanced the ionic conductivities of the electrolyte. The composite electrolyte composed of PEO:LiClO₄:PAA/PMAA/Li_0.3 exhibited a low polarization resistance of 881.5 ohms in its impedance spectra, while the PEO:LiClO₄ film showed a high value of 4,592 ohms. The highest ionic conductivity of 9.87 × 10⁻⁴ S cm⁻¹ was attained for the electrolyte composed of PEO:LiClO₄:PAA/PMAA/Li_0.3 at 20 °C. The cyclic voltammogram of Li⁺ recorded for the cell consisting of the PEO:LiClO₄:PAA/PMAA/Li_0.3:Al₂O₃ composite electrolyte exhibited the same diffusion process as that obtained with an ultra-microelectrode. Based on this electrolyte, the applicability of the solid polymer electrolytes to lithium batteries was examined for an Li/SPE/LiNi_0.5Co_0.5O₂ cell.     

Preparation and performance of poly(ethylene oxide)-based composite solid electrolyte for all solid-state lithium batteries

Poly(ethylene oxide)-based solid electrolyte is attractive for using in all solid-state lithium batteries. However, the polymer has a certain degree of crystallization, which is adverse to the conduction of lithium ions. In order to overcome this drawback, a flexible composite polymer electrolyte (CPE) containing TiO₂ nanoparticles is elaborately designed and synthesized by tape casting method. The effects of different molar ratios of EO: Li and mass fraction of TiO₂ on the physical and electrochemical performances are carefully studied. The results show the CPE10 having 10 wt % TiO₂ has the lowest degree of crystallinity of 9.04%, the lowest activation energy of 8.63 × 10⁻⁵ eV mol⁻¹. Besides, the CPE10 shows a lower polarization and higher decomposition voltage. Thus, prepared all solid-state battery LiFePO₄/CPE10/Li shows a high initial capacity of 160 mAh g⁻¹ at 0.1 C, 134 mAh g⁻¹ at 0.5 C and higher capacity retention of 93.2% after 50 cycles at 0.5 C (1 C = 170 mAh g⁻¹). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47498.     

Additive‐Free Synthesis of Cerium Oxide Nanorods with Reaction Temperature‐Tunable Aspect Ratios

The ability to control the morphology of fluorite‐structured cerium oxide nanomaterials is an important step in the design of cerium oxide‐based catalysts. Herein, we report an additive‐free synthesis of cerium oxide nanorods with highly tunable aspect ratios from ~6:1 to 40:1. The use of a microwave hydrothermal method allows for both rapid synthesis and temperature control. The ability to control the length of the nanorods from <51 nm to >1.7 μm by varying only the reaction temperature was demonstrated over a temperature range of 80°C to 200°C. The formation of the resulting nanorods was investigated using selected‐area electron‐diffraction and high‐resolution transmission electron microscopy. The surface area of nanorod products was found to decrease from 117 to 22 m²/g as the reaction temperature increased from 80°C to 200°C, complementing the general trend of the increasing aspect ratios of these products.     

Effect of Tb3+ doping and self-generated pressure on the crystallographic/morphological features and thermal stability of LaPO4·nH2O single-crystal nanorods obtained by microwave-assisted hydrothermal synthesis

The effect of Tb³⁺-doping content (in the range 0–20 mol%) and autogeneous/self-generated pressure (in the range 2.3–3.4±0.1 bar) on the crystallographic/morphological features and thermal stability of single-crystal nanorods of LaPO₄·nH₂O obtained by a simple and fast microwave-assisted hydrothermal synthesis was investigated. It is shown that high-quality (that is, well-shaped and linear/planar defect free) rhabdophane-type single-crystal La_1-xTb_xPO₄·nH₂O (x=0–0.20) nanorods, with a high morphological uniformity, are obtained in all cases. In addition, it is shown that the Tb³⁺ solutes are incorporated into the LaPO₄·nH₂O host, forming substitutional solid solutions (i.e., partial substitution of La³⁺ by Tb³⁺) with progressively smaller unit-cell volume but with identical thermal stability. Morphologically Tb³⁺ doping however results in the formation of nanorods with lower aspect ratio. With respect to the self-generated pressure during the microwave synthesis, it is shown that its increase does not affect to crystallographic aspects, but however results again in nanorods with lower aspect ratio. It is also demonstrated that monazite-type single-crystal La_1-xTb_xPO₄ nanorods can be obtained by calcining their rhabdophane-type La_1-xTb_xPO₄·nH₂O counterparts at ~700 °C in air. Consequently, in the present study important guidelines have been identified for the controlled synthesis of functional La_1-xTb_xPO₄·nH₂O nanorods with tailored morphology.     

Preparation of ultrafine metal particles supported on alumina by pyrolysis of polymer complex/alumina composites

Ultrafine metal particles supported on alumina were prepared by pyrolysis of poly(vinylferrocene) (Poly(VFc))/alumina or sodium polyacrylate-Pd(II) (Poly(AANa)-Pd(II))/alumina precursors at 800 ～ 1200°C. α-Fe particles produced on k-Al₂O₃ was obtained by pyrolysis of the mixture of Poly(VFc)/alumina(5/5) at 1000°C. Crystalline Pd supported on alumina was also obtained from Poly(AANa)-Pd(II)/alumina precursor. The size of metal particles formed increased with increasing mixing ratio of polymer complex with alumina. © 1994 John Wiley & Sons, Inc.     

Green hydrothermal synthesis of high aspect ratio wollastonite nanofibers: Effects of reaction medium,temperature and time

Wollastonite 1D nanostructures have attracted widespread concern for their wide applications in biomedical, constructions and many more, which however have been synthesized via high temperature solid state method or wet precipitation method which required organic template. Herein, a controllable green hydrothermal route is used to produce high aspect ratio wollastonite nanofibers. The effect of hydrothermal synthesis parameters on the aspect ratio of synthetic wollastonite nanofibers (SWN) were investigated and the hydrothermal formation mechanism was proposed. The formation of nanofiber starts from the nuclei formation in supersaturated solution then followed by the crystal growth. The synthesis reactions were conducted under different conditions with reaction medium containing different ethanol composition and temperature from 160 °C to 240 °C for 8 h to 32 h. The SWN produced was characterized using XRD, FTIR, TGA and FESEM analysis techniques. It is proven that all wollastonite produced were in nanofiber form with the average aspect ratio ranging from 10 to 20, except for those synthesized at 160 °C which mainly has irregular grain shape. The reaction medium consisting of 80% water and 20% ethanol, which was heated at 200 °C for 16 h, resulted in SWN with the highest aspect ratio of 20.15. The study demonstrated that the hydrothermal synthesis parameters can be manipulated to produce SWN with various aspect ratios to meet its demand in different applications.