Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

1D metal-oxide nanostructures have attracted much attention because metal oxides are the most fascinating functional materials. The 1D morphologies can easily enhance the unique properties of the metal-oxide nanostructures, which make them suitable for a wide variety of applications, including gas sensors, electrochromic devices, light-emitting diodes, field emitters, supercapacitors, nanoelectronics, and nanogenerators. Therefore, much effort has been made to synthesize and characterize 1D metal-oxide nanostructures in the forms of nanorods, nanowires, nanotubes, nanobelts, etc. Various physical and chemical deposition techniques and growth mechanisms are exploited and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the 1D metal-oxide nanostructures. Here a comprehensive review of recent developments in novel synthesis, exceptional characteristics, and prominent applications of one-dimensional nanostructures of tungsten oxides, molybdenum oxides, tantalum oxides, vanadium oxides, niobium oxides, titanium oxides, nickel oxides, zinc oxides, bismuth oxides, and tin oxides is provided.

One-Dimensional Metal-Oxide Nanostructures: Recent Developments in Synthesis, Characterization, and Applications

Graphene, a monolayer of graphite sheet consisting of sp2 hybridized carbon atoms covalently bonded to three other atoms (discovered in 2004), has recently attracted the attention of chemical sensor researchers owing to its unprecedented structural, mechanical and electrical properties. Excellent mechanical strength (Young modulus ∼0.05 TPa), potentiality of ultrafast electron transport (highest mobility ∼200,000 cm 2 /V s) along with the best surface to volume ratio has opened up the opportunity to use the material for future gas and vapor sensors with ultra fast speed and long-term durability. Since it is a two dimensional material, every atom of graphene may be considered a surface atom and as a result every atom site may be involved in the gas interactions. This feature of graphene can eventually be responsible for its ultra sensitive sensor response with the lowest detection capability approaching even a single molecule. Further, the ease of functionalization of the material either by chemical means (absorption of many molecules like oxygen or hydrogen) or by application of voltage or pressure, facilitates bandgap-engineering which in turn may lead to a possible solution to the selectivity issues, the perennial problems of chemical sensors. In this review, the latest advancement and new perspectives of graphene based gas and vapor sensors have been discussed critically.

Recent developments on graphene and graphene oxide based solid state gas sensors

Because of the interesting and multifunctional properties, recently, ZnO nanostructures are considered as excellent material for fabrication of highly sensitive and selective gas sensors. Thus, ZnO nanomaterials are widely used to fabricate efficient gas sensors for the detection of various hazardous and toxic gases. The presented review article is focusing on the recent developments of NO2 gas sensors based on ZnO nanomaterials. The review presents the general introduction of some metal oxide nanomaterials for gas sensing application and finally focusing on the structure of ZnO and its gas sensing mechanisms. Basic gas sensing characteristics such as gas response, response time, recovery time, selectivity, detection limit, stability and recyclability, etc are also discussed in this article. Further, the utilization of various ZnO nanomaterials such as nanorods, nanowires, nano-micro flowers, quantum dots, thin films and nanosheets, etc for the fabrication of NO2 gas sensors are also presented. Moreover, various factors such as NO2 concentrations, annealing temperature, ZnO morphologies and particle sizes, relative humidity, operating temperatures which are affecting the NO2 gas sensing properties are discussed in this review. Finally, the review article is concluded and future directions are presented.

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Zinc Oxide Nanostructures for NO2 Gas–Sensor Applications: A Review

The properties and applications of molybdenum oxides are reviewed in depth. Molybdenum is found in various oxide stoichiometries, which have been employed for different high-value research and commercial applications. The great chemical and physical characteristics of molybdenum oxides make them versatile and highly tunable for incorporation in optical, electronic, catalytic, bio, and energy systems. Variations in the oxidation states allow manipulation of the crystal structure, morphology, oxygen vacancies, and dopants, to control and engineer electronic states. Despite this overwhelming functionality and potential, a definitive resource on molybdenum oxide is still unavailable. The aim here is to provide such a resource, while presenting an insightful outlook into future prospective applications for molybdenum oxides.

Molybdenum Oxides – From Fundamentals to Functionality

In this work, MoO 3 was thermally evaporated onto gold interdigital fingers on quartz substrates and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques The deposited MoO 3 consist of stratified long rectangles (average length of 50 μm width of 5 μm and thickness of 500 nm) which are predominantly orthorhombic (α-MoO 3 ) Each of these plates was composed of many nano-thick layers (average ∼30 nm) placed by Van der Waals forces on top of each other forming lamellar patterns The devices were used as sensors and exhibited considerable change in surface conductivity when exposed to NO 2 and H 2 gases at elevated temperature of 225 °C The structural and gas sensing properties of thermally evaporated MoO 3 thin films were investigated

/pdf/gas-sensing-properties-of-thermally-evaporated-lamellar-moo3-dfclscs4b4.pdf

Gas sensing properties of thermally evaporated lamellar MoO3

There has been significant interest in using electronically contacted nanorod or nanotube arrays as gas sensors, whereby an adsorbate modifies either the impedance or the Fermi level of the array, enabling detection. Typically, such arrays demonstrate the I-V curves of a Schottky diode that is formed using a metal-semiconductor junction with rectifying characteristics. We show in this work that nanostructured Schottky diodes have a functionally different response, characteristic of the large electric field induced by the size scale of the array. Specifically, they are characterized by a low reverse breakdown voltage. As a result, the reverse bias current becomes a strong function of the applied voltage. In this work, for the first time, we model this unique feature by describing the enhancement effect of high aspect ratio nanostructures on the I-V characteristics of a Schottky diode. A Pt/ZnO/SiC nanostructured Schottky diode is fabricated to verify the theoretical equations presented. The gas sensing properties of the Schottky diode in reversed bias is investigated and it is shown that the theoretical calculations are in excellent agreement with measurements.

https://iopscience.iop.org/article/10.1088/0957-4484/21/26/265502/pdf

Nanorod based Schottky contact gas sensors in reversed bias condition

In this paper, the effect of electric field enhancement on Pt/nanostructured ZnO Schottky diode based hydrogen sensors under reverse bias condition has been investigated. Current–voltage characteristics of these diodes have been studied at temperatures from 25 to 620 °C and their free carrier density concentration was estimated by exposing the sensors to hydrogen gas. The experimental results show a significantly lower breakdown voltage in reversed bias current–voltage characteristics than the conventional Schottky diodes and also greater lateral voltage shift in reverse bias operation than the forward bias. This can be ascribed to the increased localized electric fields emanating from the sharp edges and corners of the nanostructured morphologies. At 620 °C, voltage shifts of 114 and 325 mV for 0.06% and 1% hydrogen have been recorded from dynamic response under the reverse bias condition.

Reversed bias Pt/nanostructured ZnO Schottky diode with enhanced electric field for hydrogen sensing

Pt/nanostructured molybdenum oxide (MoO3)/SiC Schottky diode based gas sensors were fabricated for hydrogen (H2) gas sensing. Due to the enhanced performance, which is ascribed to the application of MoO3 nanostructures, these devices were used in reversed bias. MoO3 characterization by scanning electron microscopy showed morphology of randomly orientated nanoplatelets with thicknesses between 50 and 500 nm. An α-β mixed phase crystallographic structure of MoO3 was characterized by x-ray diffraction. At 180 °C, 1.343 V voltage shift in the reverse I-V curve and a Pt/MoO3 barrier height change of 20 meV were obtained after exposure to 1% H2 gas in synthetic air.

J. Yu

Papers

Gas sensing properties of thermally evaporated lamellar MoO3

Nanorod based Schottky contact gas sensors in reversed bias condition

Reversed bias Pt/nanostructured ZnO Schottky diode with enhanced electric field for hydrogen sensing

Reverse biased Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors

Facile synthesis of Nb2O5 nanorod array films and their electrochemical properties