Nanocrystalline TiO2 (anatase) was synthesized successfully by the direct conversion of TiO2-sol at 85 deg C. The as-prepared TiO2 at 85 deg C were calcined at different temperatures and time in ...order to optimize the system with best electrochemical performance. The particle sizes of the synthesized materials were found to be in the range of 15-20nm as revealed by the HR-TEM studies. Commercial TiO2 anatase (micron size) was also studied for its Li-insertion and deinsertion properties in order to compare with the nanocrystalline TiO2. The full cell studies were performed with LiCoO2 cathode with the best performing nano-TiO2 as anode. The specific capacity of the nanocrystalline TiO2 synthesized at 500 deg C/2h in a half-cell configuration was 169mAhg-1 while for the cell with LiCoO2 cathode, it was 95mAhg-1 in the 2V region. The specific reversible capacity and the cycling performance of the synthesized nano-TiO2 anode in full cell configuration across LiCoO2 cathode are superior to that reported in the literature. Cyclic voltammetry measurements showed a larger peak separation for the micro-TiO2 than the nano-TiO2, clearly indicating the influence of nano-particle size on the electrochemical performance.
Spinel-type novel compositions of mesoporous ternary metal oxides ZnFeNiO4 (ZFNO) and CoFeNiO4 (CFNO) microspheres were synthesized through a facile hydrothermal method with post calcination ...approach. X-ray powder diffraction and X-ray photoelectron spectroscopy studies reveal the phase pure spinel-type cubic crystal formation. Electron microscopic studies show the mesoporous microspheres were constructed by the porous nano-lamellae which are formed by the nanoparticles. Specific surface area of ZFNO and CFNO is found as 107 and 28 m2 g−1 with maximum pore diameter of 4 and 3 nm respectively. The optical Eg of ZFNO and CFNO is found to be 2.21 and 1.98 eV respectively. Impedance spectroscopy is used to study the electrical properties of the samples in the temperature range of 150–600 °C. The conductivity of CFNO is higher than that of ZFNO. The activation energy of conductivity is found to be 0.67 and 0.42 eV for ZFNO and CFNO respectively. Isothermal AC conductivity were analysed with Koops theory and Jonscher's power law. Frameworks of various theoretical models are considered in order to explain the frequency and temperature dependent conductivity. It is observed that the quantum mechanical tunnelling mechanism is consistent for conductivity's frequency exponent of ZFNO and only below 330 °C for CFNO.
•Novel porous ZnFeNiO4 and CoFeNiO4 microspheres fabricated by hydrothermal route.•Optical Eg of ZnFeNiO4 and CoFeNiO4 is found to be 2.21 and 1.98 eV respectively.•EA of conductivity is found as 0.66 & 0.41 eV for ZnFeNiO4 & CoFeNiO4 respectively.•AC conductivity were analysed with Koops theory and Jonscher's power law.•Quantum mechanism tunnelling is consistent for conductivity's frequency exponent.
A compact thin film-based multilayered YSZ oxygen sensor, configured as (RE)Pt|Cu,Cu2O|YSZ|O2,ITO(WE) with Cu-Cu2O as reference (RE) and ITO as the working electrode (WE) on (100) SrTiO3 substrate is ...realized and its performance is demonstrated. The sensor with ITO WE operates at temperatures as low as 623 K in contrast to 923 K for Pt-based oxygen sensors. The sensor responds to 10 to 824 ppm of oxygen in inert streams with a sensitivity of +40.0 and +44.8 mV/decade at 623 and 648 K without suffering any baseline drifts. Secondary ion mass spectrometry reveals a sharp ITO/YSZ interface. A high exchange current density of 10−3 A cm−2 is observed for the ITO/YSZ interface at 973 K which decreases only by an order to 10−4 A cm−2 at 523 K for a 450 K drop in temperature whereas it drops by four order from 10−5 to 10−9 A cm−2 for Pt/YSZ interface for the temperature interval of 973 to 623 K. The solubility of ITO in cubic zirconia gave rise to lower interfacial resistance and the enhanced chemisorption properties of ITO favoured a low-temperature operation. Below 723 K, the Pt/YSZ interface shows an anodic overpotential due to the formation of the platinum oxide layers causing non-Nerstain behaviour.
Crystal structure, morphological features, and hydrogen-sensing properties of thick film sensors of TiO2 nanotubes (NTs) impregnated with nanoparticles of elements of Group 10, viz., nickel, ...palladium, and platinum, having average grain size of about 25, 20, and 20 nm, respectively, are presented. The sensitivity is observed to be higher for Pd/TiO2 NTs than for Pt/TiO2 NTs. Ni/TiO2 NTs exhibited very poor sensitivity. X-ray photoelectron spectroscopy (XPS) studies confirm reduction of the oxide layer of palladium nanoparticles, which, in turn, is responsible for the generation of Ti3+ ion in TiO2 NTs through hydrogen spillover. For Pt/TiO2 NTs, only reduction of the oxide layer over Pt nanoparticles takes place without any spillover effect. For Ni/TiO2 NTs, neither NiO nor TiO2 undergoes any reduction. Changes in the Fermi level difference of PdO and TiO2 along with Ti3+ generation synergistically operate for Pd/TiO2 NTs, whereas the difference in Fermi levels of PtO and TiO2 alone operates for Pt/TiO2 NTs during sensing.
The structure and the electrochemical performance of mesoporous spinel-analogous Zn-Ni-Co-O (Zn1−xNixCo2O4; 0.2 ≤ x ≤ 0.8) nanorods are investigated. Cyclic voltammetry gives strong indication that ...the charge storage mechanism is governed by pore surface redox processes without significant contribution from the sub-surface charge storage. Since the size of the Zn1−xNixCo2O4 rods decreases with increasing Ni content x, the BET surface and thus the charge storage capacity increases with increasing x, namely from 266 C g−1 to 463 C g−1 at 3.12 A g−1 when increasing x from 0.2 to 0.8. Hybrid aqueous supercapacitors (HSC) are fabricated with Zn1−xNixCo2O4, activated carbon (AC) and 6 M KOH as positive electrode, negative electrode and electrolyte, respectively. The specific energy densities of HSC are in the range of 27–2 Wh kg−1 at the specific power densities range of 780–2240 W kg−1. Real-world usage of the aqueous HSC device is demonstrated by enlightening a red light-emitting diode. These outcomes show that the mesoporous spinel-analogous Zn-Ni-Co-O materials are potential candidates for next-generation electrochemical energy storage applications.
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•Mesoporous spinel-analogous Zn1−xNixCo2O4; 0.2 ≤ x ≤ 0.8nanorods prepared by Solvothermal route.•The size of the Zn1−xNixCo2O4 rods decreases with increasing Ni content.•The ES,HSC of HSC are in the range of 27–2 Wh kg−1 at the PS,HSC of 780–2240 W kg−1.•Real-world usage of the aqueous ASC device is demonstrated by enlightening a red light-emitting diode.
The negative electric potential difference observed in a YSZ-based thin film potentiometric sensor at a low operating temperature of 673 K is investigated. The multilayered sensor is grown ...sequentially using pulsed laser deposition at 998 K with Cu-Cu
2
O reference electrode, YSZ electrolyte and Pt as working electrode respectively. The thickness of the Cu-Cu
2
O reference layer is a critical factor in thin film sensors as the Pt
3
O
4
phase stabilized along with Cu-Cu
2
O can reach the YSZ interface. XRD, μ- Raman and XPS confirm the formation of the Pt
3
O
4
phase on the reference side along with the Cu-Cu
2
O layer. However, the pure Pt
3
O
4
phase could not be stabilized in the thin film without Cu-Cu
2
O. The presence of the Pt
3
O
4
phase on the reference side generates a Pt-Pt
3
O
4
reference couple with an equilibrium oxygen partial pressure of ~ 10
4
ppm higher than the sample oxygen pressure of 10-10
3
ppm giving rise to a negative electric potential difference with a sensitivity of -7.5 mV/decade.
Electrical conductivity and gas sensing properties of MoO3 are investigated. The electrical conductivity is found to be independent of oxygen partial pressure in the temperature range 510–773K. Two ...distinct conduction processes were identified from the conductivity experiments carried out under ambient air, moist oxygen, and moist argon. The conductivity in the low temperature range (510–578K) are attributed to species arising from the reversibly inserted water molecules into MoO3 lattice. The conduction process in the high temperature region (578–773K) are attributed to the non-stoichiometry existing in the sample due to the presence of Mo5+ ions which was confirmed by EPR and XPS investigations. Sensing characteristics of MoO3 towards NH3, H2, and LPG were studied. Experiments showed that the ammonia sensing mechanism of MoO3 involved the formation of molybdenum suboxides and nitride.
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•Thin films of PbS deposited by pulsed laser deposition under in-situ argon pressure.•Oxygen-free PbS thin film confirmed by X-ray photoelectron spectroscopy.•Hall studies show p-type ...conductivity with a carrier concentration of 1011 cm−3 at 298 K.
Thin films of PbS were grown on (0 1 2) LaAlO3 by pulsed laser deposition and the deposition parameters were optimized. Films deposited at 553 K under the in-situ argon pressure of 10−1 mbar were granular having an average crystallite size of 25 nm with a texturing along (2 0 0) direction. Pb 4f and S 2p levels of PbS reveal Lead in +2 and Sulphur in −2 state and there was no evidence for oxygen contamination. Hall results revealed p-type conductivity with the carrier concentration of about 1011 cm−3 and a four-probe conductivity of 2 × 10−4 Ω−1 cm−1 at room temperature. The use of PLD for growing thin films of a non-oxide based material is demonstrated.
A highly crystalline tetragonal PtO not reported in phase diagrams is stabilized as a thin film in the narrow temperature window of 673–723 K under the in-situ oxygen partial pressure of 2 × 10
–1
... mbar using pulsed laser deposition. Raman spectra confirm the formation of PtO without any amorphous content or impurities. Our results show that PtO is a semiconductor in accordance with most of the theoretical predictions and not metallic. The room temperature conductivity and mobility of PtO are about 3.24 × 10
2
S cm
−1
and 1.6 cm
2
V
−1
s
−1
respectively. Hall studies confirm p-type conductivity with a carrier concentration of about 1.2 × 10
21
cm
−3
which is about three orders of magnitude higher than the value reported hitherto. XPS studies show that the majority of Pt exists as Pt
2+
along with a small fraction of Pt
4+
. The experimental result validates the theoretical work that predicts a semiconducting behaviour for PtO.
Owing to a wide range of industrial applications and fundamental importance, delafossite compounds have gathered tremendous interest in research community. In this study, the formation of hexagonal ...nanoplates of AgInO2 mainly dominated by (00l) facets with no metallic Ag impurity, reported using a facile hydrothermal route at 180 °C using KOH as mineralizer by adopting a factorial design approach. Rietveld analysis of the powder XRD pattern and SAED confirms the rhombohedral system of AgInO2. FE‐SEM image shows a uniform hexagonal plate‐like morphology with an average width of about 300 nm and thickness of 70 nm. XPS and EDX analysis confirm potassium ion free AgInO2. A specific surface area of about 48.5 m2 g−1 is arrived from N2 adsorption studies. Temperature‐dependent AC impedance measurements revealed an activation energy of 0.24 eV/f.u. Further, TG‐DTA studies found that the compound is stable in air up to 595 °C.
Design! The factorial design approach was adopted for synthesizing phase‐pure AgInO2 using a hydrothermal route. Silver nitrate and indium nitrate with KOH as a mineralizer promote the formation of AgInO2 in the form of hexagonal nanoplates. The optimum condition of 180 °C and 4 m KOH was the crucial combination to obtain the pure phase.
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