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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nanostructured rocksalt-type solid solution series (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} (n=4, 7, 12; 0≤x≤1): Thermal behavior and thermoelectric properties

Solid solutions (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} (n=4, 7, 12; 0≤x≤1) represent stable high-temperature phases and can be obtained as metastable compounds by quenching. High-resolution transmission electron microscopy reveals that the quenched (pseudo-)cubic materials exhibit parquet-like nanostructures comparable to, but especially for n=4 more pronounced than in (GeTe){sub n}Sb{sub 2}Te{sub 3} (GST materials). The temperature-dependent phase transitions are comparable; however, substitution with Sn significantly lowers the transition temperatures between cubic high-temperature phase and the long range ordered layered phases that are stable at ambient conditions. In addition, the metrics of the quenched Sn-containing materials remains closer to cubic, especially for samples with n=7 or 12. For samples with high defect concentrations (n=4, 7), Sn-substituted samples exhibit electrical conductivities up to 3 times higher than those of corresponding GST materials. Since the difference in thermal conductivity is much less pronounced, this results in a doubling of the thermoelectric figure of merit (ZT) at high temperatures for (Ge{sub 0.5}Sn{sub 0.5}Te){sub 4}Sb{sub 2}Te{sub 3} as compared to (GeTe){sub 4}Sb{sub 2}Te{sub 3}. Sn doping in (GeTe){sub 7}Sb{sub 2}Te{sub 3} increases the ZT value by a factor of up to 4 which is also due to an increased Seebeck coefficient. - Graphical abstract: High-resolution transmission electron micrographs of (GeTe){sub 4}Sb{sub 2}Te{sub 3} (top) and (Ge{sub 0.5}Sn{sub 0.5}Te){sub 4}Sb{sub 2}Te{sub 3} (bottom) with different nanostructures and thermoelectric figures of merit (ZT) of these samples. - Highlights: • Representative samples of solid solutions of (Ge{sub 1−x}Sn{sub x}Te){sub n}Sb{sub 2}Te{sub 3} were synthesized. • Sn substitution leads to more pronounced nanostructures in defect-rich compounds. • Phase transitions are comparable to (GeTe){sub n}Sb{sub 2}Te{sub 3} but occur at lower temperatures. • Sn substitution tends to increase electrical conductivity and Seebeck coefficient. • ZT of (GeTe){sub 7}Sb{sub 2}Te{sub 3} increases from 0.2 to 0.7 (at 400 °C) upon Sn substitution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Understanding the formation of nanocomposites consisting of silver sulfide and platinum hollow nanostructures

Highlights: • Reacting core-shell [email protected] particles with Na{sub 2}S leads to hollow Pt nanostructures. • Reacting core-shell [email protected] particles with sulfur leads to Ag{sub 2}S-hPt nanocomposites. • The mechanism determining the formation of Ag{sub 2}S-hPt nanocomposites was elucidated. • Additional experiments were designed to rationalize the formation mechanism. - Abstract: Structural conversion using core-shell silver (Ag)-platinum (Pt) nanoparticles as starting materials is a promising way to produce nanocomposites consisting of silver sulfide (Ag{sub 2}S) and hollow Pt nanostructures (Ag{sub 2}S-hPtNCs). However, the mechanism behind the structural conversion process is yet to be understood. In this study, we use transmission electron microscope (TEM) as a typical tool to characterize the products formed in different structural conversion processes, and interpret the experimental observations by proposing mechanisms behind the reactions between core-shell Ag-Pt nanoparticles and sulfur precursors from different sources. We then design additional experiments to rationalize the formation mechanism we proposed. The mechanistic understanding of the structural conversion from bimetallic core-shell nanostructures to heterogeneous nanocomposites may extend the fabrication of heterogeneous nanocomposites for a given technological application.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Nanostructured cobalt powders synthesised by polyol process and consolidated by Spark Plasma Sintering: Microstructure and mechanical properties

Bulk nanostructured cobalt was processed using a bottom-up strategy. Nanostructured particle agglomerates of about 50 and 240 nm in diameter were synthesised using a polyol route and subsequently consolidated by Spark Plasma Sintering (SPS). The microstructure of the starting powders and of the processed bulk samples was studied and characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of the as-prepared powders showed predominantly a face centred cubic (fcc) crystalline phase, whereas both fcc and hexagonal close packed (hcp) phases were found within the consolidated samples. A sample with the highest relative mass density (94.5%) was obtained from the small powder particles. TEM observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain in the sample with the highest density. Brillouin light scattering (BLS) and quasistatic compression tests were used to investigate the mechanical properties of the consolidated samples. The two techniques yielded Young modulus values of 168 GPa and 130 GPa, respectively, in the sample with the highest density. This sample also exhibited a yield stress higher than 1 GPa after the compression test, which is mainly attributed to the lamellar-like structure occurring in almost every grain of the polycrystalline aggregate. - Highlights: Black-Right-Pointing-Pointer Cobalt nanoparticles produced by the polyol process present mainly the fcc metastable phase. Black-Right-Pointing-Pointer Bulk nanostructured cobalt is obtained from the nano-particles by Spark Plasma Sintering consolidation. Black-Right-Pointing-Pointer Nanotwins and stacking faults are present in every grain of the more dense sample. Black-Right-Pointing-Pointer Yield strength and plastic domain may be varied depending on the nanoparticle size and the porosity of the consolidated material.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Retained austenite thermal stability in a nanostructured bainitic steel

The unique microstructure of nanostructured bainite consists of very slender bainitic ferrite plates and high carbon retained austenite films. As a consequence, the reported properties are opening a wide range of different commercial uses. However, bainitic transformation follows the T{sub 0} criteria, i.e. the incomplete reaction phenomena, which means that the microstructure is not thermodynamically stable because the bainitic transformation stops well before austenite reaches an equilibrium carbon level. This article aims to study the different microstructural changes taking place when nanostructured bainite is destabilized by austempering for times well in excess of that strictly necessary to end the transformation. Results indicate that while bainitic ferrite seems unaware of the extended heat treatment, retained austenite exhibits a more receptive behavior to it. - Highlights: • Nanostructured bainitic steel is not thermodynamically stable. • Extensive austempering in these microstructures has not been reported before. • Precipitation of cementite particles is unavoidable at longer austempering times. • TEM, FEG-SEM and XRD analysis were used for microstructural characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure and mechanical properties of bulk highly faulted fcc/hcp nanostructured cobalt microstructures

Nanostructured cobalt powders with an average particle size of 50 nm were synthesized using a polyol method and subsequently consolidated by spark plasma sintering (SPS). SPS experiments performed at 650 °C with sintering times ranging from 5 to 45 min under a pressure of 100 MPa, yielded to dense bulk nanostructured cobalt (relative density greater than 97%). X-ray diffraction patterns of the as-prepared powders showed only a face centered cubic (fcc) crystalline phase, whereas the consolidated samples exhibited a mixture of both fcc and hexagonal close packed (hcp) phases. Transmission electron microscopy observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain of the sintered samples. Room temperature compression tests, carried out at a strain rate of 10{sup −3} s{sup −1}, yielded to highest strain to fracture values of up to 5% for sample of holding time of 15 min, which exhibited a yield strength of 1440 MPa, an ultimate strength as high as 1740 MPa and a Young's modulus of 205 GPa. The modulus of elasticity obtained from the nanoindentation tests, ranges from 181 to 218 GPa. The lowest modulus value of 181 GPa was obtained for the sample with the highest sintering time (45 min), which could be related to mass density loss as a consequence of trapped gases releasing. - Highlights: • Co nanopowder (50 nm) was prepared by reduction in polyol medium. • SPS was used to process bulk nanostructured Co specimens. • Microstructures were made of intricate fcc/hcp, along with nanotwins and SFs. • High strengths and moderate compressive ductility were obtained. • Deformation mechanisms related to complex interplay of different length scales.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Synthesis, deposition and characterization of magnesium hydroxide nanostructures on zeolite 4A

Research highlights: {yields} Reports a simple precipitation-growth method to produce nanostructures of Mg(OH){sub 2} on the surface of zeolite 4A. {yields} Able to control the growth of the nanostructures by manipulating the experimental procedure. {yields} Able to deposit Mg(OH){sub 2} onto specific sites namely bridging hydroxyl protons (SiOHAl) on the surface of zeolite 4A. -- Abstract: The precipitation and self-assembly of magnesium hydroxide Mg(OH){sub 2} nanopetals on dispersed zeolite 4A particles was investigated. Mg(OH){sub 2}/zeolite nanocomposites were produced from magnesium chloride solutions and characterized via X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared analysis (FTIR), and solid state NMR. It was determined that Mg(OH){sub 2} interacted with bridging hydroxyl protons (SiOHAl) on the zeolite surface, but not with silanol or aluminol groups. NMR analysis showed that 13% of the tetrahedral Al sites on the zeolite were converted to octahedral Al. The zeolite structure and crystallinity remained intact after treatment, and no dealumination reactions were detected. This suggests that the deposition-precipitation process at ambient conditions is a facile method for controlling Mg(OH){sub 2} nanostructures on zeolites.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Facile and template-free preparation of {alpha}-MnO{sub 2} nanostructures and their enhanced adsorbability

Graphical abstract: . The as-obtained ({alpha}-MnO{sub 2}) nanomaterials could act as an adsorbent to remove Conge red. More significantly, the nanomaterials are nontoxic and environmentally friendly though a biological MTT assay experiment. Plots of the capacity to remove Conge red with time by the commercial and new-prepared {alpha}-MnO{sub 2}. Inset shows absorption of Congo Red with time by new-prepared rod-clusters {alpha}-MnO{sub 2} (0, 10, 20, 40 and 60 min, respectively). Highlights: {yields} Nanostructured {alpha}-MnO{sub 2} was prepared through a template-free hydrothermal method. {yields} The obtained {alpha}-MnO{sub 2} could act as effective adsorbents to remove organic dyes. {yields} The obtained adsorbents are environmentally friendly. -- Abstract: In this paper, nanostructured MnO{sub 2} materials were successfully prepared through a simple and template-free hydrothermal method. X-ray diffraction pattern indicates that the as-prepared nanomaterials are {alpha}-MnO{sub 2}. Transmission Electron Microscopy and Scanning Electron Microscopy images demonstrate that nanostructured rod-clusters {alpha}-MnO{sub 2} could be evolved from the nanorods. Brunauer-Emmett-Teller (BET) surface area measurement was employed to characterize the surface property. Moreover, the as-obtained ({alpha}-MnO{sub 2}) nanomaterials could act as an efficient adsorbent to remove Congo Red and Methlylene Blue. More significantly, the nanomaterials are nontoxic and environmentally friendly via biological methylthiazolyldiphenyltetrazoliumbromide assay experiments. Its nontoxic and enhanced adsorbability properties guarantee their safe applications in environmental protection and industrial aspects.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Photocatalytic activity of nanostructured {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} composite powder formed via a polyelectrolyte-multilayer-assisted sol-gel reaction

Highlights: Black-Right-Pointing-Pointer PEM assisted synthesis for {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} composite powder is developed. Black-Right-Pointing-Pointer Nanoparticulate TiO{sub 2} layer results in high specific surface area composite powder. Black-Right-Pointing-Pointer {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} composite powder exhibit enhanced photocatalytic activity. -- Abstract: Nanostructured, {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} composite powder was fabricated via an in situ, sol-gel reaction of titanium iso-propoxide in a self-assembled, polyelectrolyte multilayer (PEM) formed on the surface of high-specific-area, polycrystalline, {gamma}-Al{sub 2}O{sub 3} lamellas. The infiltration of the titanium precursor into the PEM, followed by the hydrolysis and condensation reactions with the water absorbed in the PEM after annealing, resulted in the formation of a nanostructured TiO{sub 2} layer on the surface of the {gamma}-Al{sub 2}O{sub 3} lamellas. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were employed to evaluate the morphology, the chemical composition and the crystallinity of the {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} particles of the composite powder. The as-formed, nanostructured, {gamma}-Al{sub 2}O{sub 3}/TiO{sub 2} composite powder exhibited a 2.7-times-higher photo-activity in the near-UV region compared to commercially available TiO{sub 2} (Degusa P25), as monitored by the photo-decomposition of a methylene blue (MB) dye.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Hydrothermal synthesis of nanostructured zinc oxide and study of their optical properties

Highlights: Black-Right-Pointing-Pointer Nanostructured ZnO were successfully obtained by a hydrothermal route. Black-Right-Pointing-Pointer Inorganic precursor and molar ratio are key factors for morphology and particle size. Black-Right-Pointing-Pointer Optical properties were also studied. -- Abstract: Nanostructured ZnO (nanorods, nanoshuttles) have been synthesized by hydrothermal approach using ZnCl{sub 2} or Zn(NO{sub 3}){sub 2}{center_dot}6H{sub 2}O as zinc sources and cetyltrimethylammonium bromide as structure-directing agent. Techniques X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible absorption, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy have been used to characterize the structure, morphology and composition of the nanostructured zinc oxide. The optical properties of the as-obtained materials were also studied and showing that it is possible to apply the ZnO nanoshuttles and nanorods on the UV filter, photocatalysis, and special optical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis, surface group modification of 3D MnV{sub 2}O{sub 6} nanostructures and adsorption effect on Rhodamine B

Highlights: ► Fabrication of urchin-like MnV{sub 2}O{sub 6} with oxygen-containing surface groups. ► Mn{sub 0.5}V{sub 2}O{sub 5}·nH{sub 2}O as an intermediate product holds the key to the final products. ► 3D architectures of MnV{sub 2}O{sub 6} with oxygen-containing surface groups as sorbent. ► The sorbent shows a good adsorption ability. -- Abstract: Highly uniform 3D MnV{sub 2}O{sub 6} nanostructures modified by oxygen functional groups (-COO-) were successfully prepared in large quantities by an approach involving preparation of vanadyl ethylene glycolate as the precursor. The growth and self-assembly of MnV{sub 2}O{sub 6} nanobelts and nanorods could be readily tuned by additive species and quantities, which brought different morphologies and sizes to the final products. With a focus on the regulation of structure, the formation process of 3D architectures of MnV{sub 2}O{sub 6} by self-assembly of nanobelts was followed by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The consecutive processes of vanadyl ethylene glycolate and benzoyl peroxide assisted formation of layered structure Mn{sub 0.5}V{sub 2}O{sub 5}·nH{sub 2}O, growth of aligned MnV{sub 2}O{sub 6} nanobelts, and oriented assembly were proposed for the growth mechanism. The band gap vs. different morphology was also studied. Optical characterization of these MnV{sub 2}O{sub 6} with different morphologies showed direct bandgap energies at 1.8–1.95 eV. The adsorption properties of 3D MnV{sub 2}O{sub 6} nanostructures synthesized under different conditions were investigated through the removal test of Rhodamine B in aqueous water, and the 3D nanostructures synthesized with 30 g L{sup −1} benzoyl peroxide showed good adsorption capability of Rhodamine B.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Ultrasound-assisted synthesis of CuO nanostructures templated by cotton fibers

Highlights: ► Flower-like and corn-like CuO nanostructures were synthesized by a simple method. ► Cotton fibers purchased from commercially are used as template. ► The concentration of Cu(NO{sub 3}){sub 2} solution is an important parameter. -- Abstract: Flower-like and corn-like CuO nanostructures composed of CuO nanoparticles were successfully synthesized via ultrasound-assisted template method, respectively, by controlling the initial concentration of Cu(NO{sub 3}){sub 2} solution. Here, cotton fibers were used as template agent. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM) and energy-dispersive spectroscopy (EDS), respectively. The results demonstrated that the initial concentration of Cu(NO{sub 3}){sub 2} solution was an important parameter for determining whether CuO nanoparticles assembled into flower-like structures or corn-like structures. The mechanism of forming different nanostructures of CuO was discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Crystallization control of SrCO{sub 3} nanostructure in imidazolium-based temperature ionic liquids

Highlights: ► Nanowhisker, nanospindle, nanosphere, sphere, spindle, rodlike SrCO{sub 3} were obtained. ► Nanowhisker, nanospindle SrCO{sub 3} were auto-assembled in [C{sub 8}mim]BF{sub 4} and [HOEtMIm]NT{sub f2}. ► Small size and rough surface particle show low starting decomposition temperature. ► This method is simple, easy to control in large-scale producing SrCO{sub 3} nanostructure. -- Abstract: Strontium carbonate nanostructures, with unique nanowhisker, nanospindle, nanosphere, sphere, spindle, and rodlike hierarchical structure, were synthesized in imidazolium-based room temperature ionic liquids [C{sub 4}mim]PF{sub 6}, [C{sub 4}mim]Cl, [C{sub 8}mim]Br, [C{sub 8}mim]BF{sub 4}, and [HOEtMIm]NT{sub f2}. The nanostructures were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The results show that the morphologies of SrCO{sub 3} were strongly dependent on the nature of the corresponding RILs, its content, and the reaction temperature. RILs can act as structure-directing agent, leading the auto-assembly of SrCO{sub 3} crystal. [C{sub 8}mim]BF{sub 4} and [HOEtMIm]NT{sub f2} favored the production of nanowhisker and nanospindle SrCO{sub 3}, respectively, whereas [C{sub 4}mim]PF{sub 6} favored the production of nanosphere. Small particles were obtained at high reaction temperature. Low starting decomposition temperature was observed. Finally, the formation mechanism of the SrCO{sub 3} crystal was preliminary presented.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Sensing performances of ZnO nanostructures grown under different oxygen pressures to hydrogen

Graphical abstract: Display Omitted Highlights: ► Surface morphology depends on the oxygen pressure. ► Structural degradation was observed for the ZnO samples when oxygen pressure was overhigh. ► The sensitivity of the ZnO-based sensors increase with grown oxygen pressure. -- Abstract: For extensive use in an industrialized process of individual ZnO nanostructures applied in gas sensors, a simple, inexpensive, and safe synthesis process is required. Here, nanostructured ZnO films were grown by a pulsed laser deposition technique under different oxygen pressures. Scanning electron microscopy images show nanopores, nanotips, and nanoparticles are obtained and energy dispersive X-ray spectroscopy data indicate oxygen concentration of the synthesized samples increases monotonously with oxygen pressure. The sensor based on ZnO with high oxygen concentration has high sensitivity, rapid response (9 s) and recovery (80 s) behavior to 500 ppm hydrogen below 150 °C. Experimental data indicate that high oxygen concentration effectively improves the sensing properties of nanostructured ZnO.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Rapid preparation of α-FeOOH and α-Fe{sub 2}O{sub 3} nanostructures by microwave heating and their application in electrochemical sensors

Graphical abstract: - Highlights: • Simple microwave method leads to the rapid formation of the goethite and hematite. • Homogenous nucleation and growth of particles are controlled by synthesis time. • Modified electrode with α-FeOOH nanoplates improved the electrochemical response. • The sample is directly heated by microwaves and its crystallization is accelerated. • Fe{sup 3+} nanostructures are promising for development of electrochemical sensors. - Abstract: α-FeOOH (goethite) and α-Fe{sub 2}O{sub 3} (hematite) nanostructures have been successfully synthesized using the microwave-assisted hydrothermal (MAH) method and by the rapid burning in a microwave oven of the as-prepared goethite, respectively. The orthorhombic α-FeOOH to rhombohedralα-Fe{sub 2}O{sub 3} structural transformation was observed by X-ray diffraction (XRD) and Raman spectroscopy results. Plates-like α-FeOOH prepared in 2 min and rounded and quasi-octahedral shaped α-Fe{sub 2}O{sub 3} particles obtained in 10 min were observed using field emission gun scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The use of microwave heating allowed iron oxides to be prepared with shorter reaction times when compared to other synthesis methods. α-FeOOH nanoplates were incorporated into graphite-composite electrodes, which presented electrocatalytic properties towards the electrochemical oxidation of ascorbic acid in comparison with unmodified electrodes. This result demonstrates that such α-FeOOH nanostructures are very promising chemical modifiers for the development of improved electrochemical sensors.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Methanol conversion to light olefins over nanostructured CeAPSO-34 catalyst: Thermodynamic analysis of overall reactions and effect of template type on catalytic properties and performance

Graphical abstract: In this research nanostructured CeAPSO-34 was synthesized to explore the effect of TEAOH and morpholine on its physiochemical properties and MTO performance. Prepared catalysts were characterized with XRD, FESEM, BET, FTIR and NH3-TPD techniques. The results indicated that the nature of the template determines the physiochemical properties of CeAPSO-34 due to different rate of crystal growth. The catalyst obtained by using morpholine showed longer life time as well as sustaining light olefins selectivity at higher values. Furthermore, a comprehensive thermodynamic analysis of overall reactions network was carried out to address the major channels of methanol to olefins conversion. - Highlights: • Introduction of Ce into SAPO-34 framework. • Comparison of CeAPSO-34 synthesized using morpholine and TEAOH. • The nature of the template determines the physiochemical properties of CeAPSO-34. • Morpholine enhances catalyst lifetime in MTO process. • Presenting a complete reaction network for MTO process. - Abstract: TEAOH and morpholine were employed in synthesis of nanostructured CeAPSO-34 molecular sieve and used in methanol to olefins conversion. Prepared samples were characterized by XRD, FESEM, EDX, BET, FTIR and NH{sub 3}-TPD techniques. XRD patterns reflected the higher crystallinity of the catalyst synthesized with morpholine. The FESEM results indicated that the nature of the template determines the morphology of nanostructured CeAPSO-34 due to different rate of crystal growth. There was a meaningful difference in the strength of both strong and weak acid sites for CeAPSO-34 catalysts synthesized with TEAOH and morpholine templates. The catalyst synthesized with morpholine showed higher desorption temperature of both weak and strong acid sites evidenced by NH{sub 3}-TPD characterization. The catalyst obtained using morpholine template had the longer lifetime and sustained desired light olefins at higher values. A comprehensive thermodynamic analysis of overall reactions network was carried out to address the major channels of methanol to olefins conversion.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrodeposited manganese dioxide nanostructures on electro-etched carbon fibers: High performance materials for supercapacitor applications

Highlights: • We report a facile method for fabrication of MnO{sub 2} nanostructures on electro-etched carbon fiber. • MnO{sub 2}-ECF electrode shows outstanding supercapacitive behavior even at high discharge rates. • Exceptional cycle stability was achieved for MnO{sub 2}-ECF electrode. • The coulombic efficiency of MnO{sub 2}-ECF electrode is nearly 100%. - Abstract: In this article we introduce a facile, low cost and additive/template free method to fabricate high-rate electrochemical capacitors. Manganese oxide nanostructures were electrodeposited on electro-etched carbon fiber substrate by applying a constant anodic current. Nanostructured MnO{sub 2} on electro-etched carbon fiber was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive X-ray analysis. The electrochemical behavior of MnO{sub 2} electro-etched carbon fiber electrode was investigated by electrochemical techniques including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. A maximum specific capacitance of 728.5 F g{sup −1} was achieved at a scan rate of 5 mV s{sup −1} for MnO{sub 2} electro-etched carbon fiber electrode. Also, this electrode showed exceptional cycle stability, suggesting that it can be considered as a good candidate for supercapacitor electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mesoporous wormholelike carbon with controllable nanostructure for lithium ion batteries application

Highlights: • Wormholelike carbon (WMC) with controllable nanostructure is prepared by sol–gel method. • The reversible capacity of WMC is much higher than that of many other reported nanocarbons. • The effect of pore diameter on Li storage capacity is investigated. - Abstract: A class of mesoporous wormholelike carbon (WMC) with controllable nanostructure was prepared by sol–gel method and then used as the anode material of lithium-ion batteries. Based on the experimental results, it is found that the nanostructure of the as-prepared WMC plays an important role in the electrochemical performances. A suitable mesopore size is necessary for a high performance carbon-based anode material since it can not only guarantee effective mass transport channels but also provide large surface area. As a result, F30 with a mesopore size of 4.4 nm coupled with high surface area of 1077 m{sup 2} g{sup −1} shows a reversible capacity of 630 mAh g{sup −1}, much higher than commercial graphite and many other reported nanocarbons.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Mn-substituted cerium oxide nanostructures and their magnetic properties

Highlights: • Mn{sub x}Ce{sub 1-x}O{sub 2} (0.1 ≤ x ≤ 0.5) nanostructures were prepared by one step microwave refluxing method. • The saturation magnetization values for the samples rose with increased Mn content. • The oxygen vacancies inherently played crucial role in increasing the magnetization values. - Abstract: In this study, we report the magnetic properties of nanostructured Mn{sub x}Ce{sub 1-x}O{sub 2} (0 0.1 ≤ x ≤ 0.5) materials, synthesized via microwave refluxing technique. Phase purity of the samples was investigated using the structural characterization techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses indicated the substitution of Ce-ions with Mn-ions in the lattice. The progressive increase in the oxygen vacancies with increased dopant concentration was demonstrated by Raman, UV–vis and photoluminescence spectroscopic studies. X-ray photoelectron spectroscopy analysis further supported the presence of Mn{sup 2+}, Ce{sup 3+} and Ce{sup 4+} ions as well as oxygen vacancies in the samples. The Mn substituted CeO{sub 2} nanostructures were found to exhibit room temperature ferromagnetism (RTFM). There was a continuous improvement in the saturation magnetization (M{sub S}) values with increased Mn concentration. This might be due to the prevalence of surface oxygen vacancies and the systematic rise in their concentration with increased dopant content.

77 NANOSCIENCE AND NANOTECHNOLOGY↗