Enhanced Activity of Chemically Synthesized Nanorod Mn3O4 Thin Films for High Performance Supercapacitors

The present study addresses a cost effective method for fabricating high performance and flexible supercapacitor based on the transition metel oxides of Mn3O4 thin films. The Mn3O4 prepared by SILAR method at different cycles such as 25, 50, 75 and 100 cycles. The prepared Mn3O4 thin films were characterized by means of structural, morphological and electrochemical studies. The structural studies of X-ray diffraction (XRD) reveal that 75 cycles have good crystalline nature with tetrahedral structure. Fourier transform infrared spectroscopy (FTIR) indicates the functional group of Mn-O. Raman spectra indicate the formation of Mn3O4 thin films. SEM analysis depicted that Mn3O4 thin films have a rod-like structure. TEM images show the SAED pattern and lattice fringes of Mn3O4. The electrochemical measurements of CV, GCD and impedance measurements are investigated using 1M Na2SO4 electrolyte. In the electrochemical measurement Mn3O4 thin films exhibit the maximum specific capacitance value of 295 Fg-1 at the scan rate of 2 mVs-1

Advanced Instrumentation of Frequency Modulation AFM for Subnanometer-Scale 2D/3D Measurements at Solid-Liquid Interfaces

Since the first demonstration of true atomic-resolution imaging by frequency modulation atomic force microscopy (FM-AFM) in liquid, the method has been used for imaging subnanometer-scale structures of various materials including minerals, biological systems and other organic molecules. Rencetly, there have been further advancements in theFM-AFMinstrumentation. Three-dimensional (3D) force measurement techniques are proposed for visualizing 3D hydration structures formed at a solid-liquid interface. Thesemethods further enabled to visualize 3D distributions of flexible surface structures at interfaces between soft materials andwater. Furthermore, the fundamental performance such as force sensitivity and operation speed have been significantly improved using a small cantilever and high-speed phase detector. These technical advancements enabled direct visualization of atomic-scale interfacial phenomena at 1 frame/s. In this chapter, these recent advancements in the FM-AFM instrumentation and their applications to the studies on various interfacial phenomena are presented. © Springer International Publishing Switzerland 201

Titanium(III) sulfate as new negative electrode for sodium-ion batteries

A straightforward synthesis of Ti2(SO4)3 and reversible intercalation of 1.7 sodium ions via a two step process with formation of an intermediate phase was reported. The product was then washed with ethyl acetate and dried at 80°C overnight under vacuum. Electrochemical measurements were carried out in Swagelok cells using sodium metal as counter electrode and Whatman GF/D borosilicate glass fiber soaked in the electrolyte as separator. For the sample manually milled, a pseudo-plateau is observed at ca. 1.5 V vs Na+/Na followed by a sloping region to 1.0 V and another pseudo-plateau at ca. 1.0 V. Ball-milled samples exhibit similar profiles but with substantially enhanced capacity, even above 1.5 V. Upon oxidation, two well-defined plateaus at 1.10 and 1.64 V are observed in all samples. The number of electrons exchanged per mol of Ti2(SO4)3 increases with milling time to reach 3.4, which is above the theoretical expected capacity, but only 1.7 are reversible

A low temperature TiP2O7 polymorph exhibiting reversible insertion of lithium and sodium ions

A new TiP2O7 form has been prepared by low temperature synthesis, which does not exhibit the superstructure reported when TiP2O7 is prepared via a conventional ceramic route. This LT-TiP2O7 polymorph presents linear P2O 7 pyrophosphate groups, connected through a pivotal oxygen which ensure the flexibility of the structure. Therefore it can reversibly take up both Li and Na ions, contrary to the high temperature polymorph that can only take up Li. © 2013 The Royal Society of Chemistry

Na2Ti3O7: Lowest voltage ever reported oxide insertion electrode for sodium ion batteries

Na2Ti3O7 is found to reversibly uptake 2 Na ions per formula unit (200 mA h/g) at an average potential of 0.3 V and is hence a very promising negative electrode material for building sodium ion batteries working at room temperature. © 2011 American Chemical Society

Synthesis of ZnTe Nanoparticles by Microwave Irradiation Technique, and Their Characterization

The solid state syntheses of cubic Zinc Telluride nanoparticles were successesfully achieved for the first time by microwave irradiation technique within ∼25 min as per the author's knowledge. The crystalline phase was confirmed by powder X-ray diffraction. The crystallite size was calculated and found to be ∼40 nm. Scanning electron microscope was also used to determine the size and shape of the nanoparticles, and the average particle size was found to be ∼60 nm with spherical shapes. The particle size distribution was in range of ∼50 to 70 nm. One transverse optic (TO) and two longitudinal optic (1LO and 2LO) phonon modes were observed at 167 and 205, 408 cm–1 in the FT-Raman spectrum. The optical band gap was calculated which has found to be 2.51 eV higher than the bulk ZnTe (E g = 2.26 eV), it reveals a clear blue shift with an energy difference 0.25 eV, this may be due to the crystallite size, exciton or charge carrier confinement

Enhancement in Figure of Merit (ZT) by Annealing of BiTe Nanostructures Synthesized by Microwave-Assisted Flash Combustion

Uniform polycrystalline bismuth telluride (BiTe) nanowires of diameter 100 nm to 150 nm and hexagonal nanoplates with thickness of 50 nm to 100 nm have been successfully synthesized by the microwave-assisted flash combustion technique. The formation of BiTe nanostructures depends on the type of fuel and the oxidant-to-fuel ratio, which in turn affect the reaction time and reaction temperature. Spark plasma sintering has been employed for compaction and sintering of both as-synthesized as well as annealed BiTe powders. Increasing the sintering temperature while using faster sintering cycles reduced the porosity, resulting in high densification while preserving the nanostructures. The dimensionless figure of merit (ZT) was evaluated from the Seebeck coefficient, electrical resistivity, and thermal conductivity values over the range from 300 K to 600 K. The effect of annealing on the enhancement of ZT is discussed. These evaluations suggest that the rarely studied BiTe is a potential candidate for thermoelectric applications at low temperatures

Panoscopically optimized thermoelectric performance of a half-Heusler/full-Heusler based in situ bulk composite Zr0.7Hf0.3Ni1+xSn: an energy and time efficient way

All scale hierarchical architecturing, matrix/inclusion band alignment and intra-matrix electronic structure engineering, the so called panoscopic approach for thermoelectric materials has been demonstrated to be an effective paradigm for optimizing high ZT. To achieve such hierarchically organized microstructures, composition engineering has been considered to be an efficient strategy. In this work, such a panoscopic concept has been extended to demonstrate for the first time in the case of half-Heusler based thermoelectric materials via a composition engineering route. A series of new off-stoichiometric n-type Zr0.7Hf0.3Ni1+xSn (0 <= x <= 0.10) HH compositions have been modified to derive HH(1 - x)/full-Heusler (FH)(x) composite with an all scale hierarchically modified microstructure with FH inclusions within the matrix to study the temperature dependent thermoelectric properties. The structural analysis employing XRD, FE-SEM and HR-TEM of these materials reveal a composite of HH and FH, with hierarchically organized microstructures. In such a submicron/nano-composite, the electronic properties are observed to be well optimized yielding a large power factor; alpha(2)sigma (similar to 30.7 x 10(-4) W m(-1) K-2 for Zr0.7Hf0.3Ni1.03Sn) and reduced thermal conductivity (similar to 2.4 W m(-1) K-1 for Zr0.7Hf0.3Ni1.03Sn) yielding a high ZT similar to 0.96 at 773 K for composition Zr0.7Hf0.3Ni1.03Sn which is similar to 250% larger than the normal HH Zr0.7Hf0.3NiSn (ZT B 0.27 at 773 K). The enhancement in ZT of these composites has been discussed in terms of primary electron filtering, electron injection and several phonon scattering mechanisms such as alloy scattering, point defect scattering, and grain boundary scattering. The Bergman and Fel model is used to calculate effective thermoelectric parameters of these composites for comparing the experimental results

Low-potential sodium insertion in a nasicon-type structure through the Ti(III)/Ti(II) redox couple

We report the direct synthesis of powder Na3Ti 2(PO4)3 together with its low-potential electrochemical performance and crystal structure elucidation for the reduced and oxidized phases. First-principles calculations at the density functional theory level have been performed to gain further insight into the electrochemistry of Ti(IV)/Ti(III) and Ti(III)/Ti(II) redox couples in these sodium superionic conductor (NASICON) compounds. Finally, we have validated the concept of full-titanium-based sodium ion cells through the assembly of symmetric cells involving Na3Ti2(PO4) 3 as both positive and negative electrode materials operating at an average potential of 1.7 V. © 2013 American Chemical Society