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"Transition metal"
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Electrochemical Sensors Based on Transition Metal Materials for Phenolic Compound Detection
Electrochemical sensors have been recognized as crucial tools for monitoring comprehensive chemical information, especially in the detection of a significant class of molecules known as phenolic compounds. These compounds can be present in water as hazardous analytes and trace contaminants, as well as in living organisms where they regulate their metabolism. The sensitive detection of phenolic compounds requires highly efficient and cost-effective electrocatalysts to enable the development of high-performance sensors. Therefore, this review focuses on the development of advanced materials with excellent catalytic activity as alternative electrocatalysts to conventional ones, with a specific emphasis on transition metal-based electrocatalysts for the detection of phenolic compounds. This research is particularly relevant in diverse sectors such as water quality, food safety, and healthcare.
Journal Article
Solar hydrogen generation : transition metal oxides in water photoelectrolysis
\"Expert techniques for extracting hydrogen from water using transition metal oxides as catalysts Solar Hydrogen Generation details the complex process of separating hydrogen from oxygen--photoelectrolysis. This book comprehensively covers the chemical characteristics of transition metal oxides, explaining how to covert solar energy to electron energy through transition metal oxides. Past experimentations and future directions are discussed. Solar Hydrogen Generation Comprehensively reviews physical characteristics of transition metal oxides both in electrochemical and photocatalytic applications Includes history and future prospects for water photoelectrolysis Reviews state-of-the-art achievements in the fields of condensed matter physics, nanostructured material science, electrochemistry, and photocatalysis Addresses potential problems and solutions In-depth coverage: Hydrogen Production; Electrochemistry and Photoelectrolysis; Transition Metal Oxides; Molecular Structure, Crystal Structure, and Electronic Structure; Optical Properties and Light Absorption; Bandgap, Band Edge, and Engineering; Impurity, Dopants, and Defects; Photocatalytic Reactions, Oxidation and Reduction; Organic and Inorganic Systems; Surface and Interface Chemistry; Nanostructured and Morphology; Synchrotron Radiation and Soft X-Ray Spectroscopy\"--Provided by publisher.
Book
Green Synthesis of Transition-Metal Nanoparticles and Their Oxides: A Review
In recent years, many researchers have begun to shift their focus onto the synthesis of nanomaterials as this field possesses an immense potential that may provide incredible technological advances in the near future. The downside of conventional synthesis techniques, such as co-precipitation, sol-gel and hydrothermal methods, is that they necessitate toxic chemicals, produce harmful by-products and require a considerable amount of energy; therefore, more sustainable fabrication routes are sought-after. Biological molecules have been previously utilized as precursors for nanoparticle synthesis, thus eliminating the negative factors involved in traditional methods. In addition, transition-metal nanoparticles possess a broad scope of applications due to their multiple oxidation states and large surface areas, thereby allowing for a higher reactivity when compared to their bulk counterpart and rendering them an interesting research topic. However, this field is still relatively unknown and unpredictable as the biosynthesis of these nanostructures from fungi, bacteria and plants yield undesired diameters and morphologies, rendering them redundant compared to their chemically synthesized counterparts. Therefore, this review aims to obtain a better understanding on the plant-mediated synthesis process of the major transition-metal and transition-metal oxide nanoparticles, and how process parameters—concentration, temperature, contact time, pH level, and calcination temperature affect their unique properties such as particle size, morphologies, and crystallinity.
Journal Article
Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry
In lithium-ion batteries (LIBs), many promising electrodes that are based on transition metal oxides exhibit anomalously high storage capacities beyond their theoretical values. Although this phenomenon has been widely reported, the underlying physicochemical mechanism in such materials remains elusive and is still a matter of debate. In this work, we use in situ magnetometry to demonstrate the existence of strong surface capacitance on metal nanoparticles, and to show that a large number of spin-polarized electrons can be stored in the already-reduced metallic nanoparticles (that are formed during discharge at low potentials in transition metal oxide LIBs), which is consistent with a space charge mechanism. Through quantification of the surface capacitance by the variation in magnetism, we further show that this charge capacity of the surface is the dominant source of the extra capacity in the Fe
3
O
4
/Li model system, and that it also exists in CoO, NiO, FeF
2
and Fe
2
N systems. The space charge mechanism revealed by in situ magnetometry can therefore be generalized to a broad range of transition metal compounds for which a large electron density of states is accessible, and provides pivotal guidance for creating advanced energy storage systems.
Although some transition metal oxide-based electrodes exhibit high storage capacities beyond theoretical values, the underlying physicochemical mechanism remains elusive. Surface capacitance on metal nanoparticles involving spin-polarized electrons is now shown to be consistent with a space charge mechanism.
Journal Article
A library of atomically thin metal chalcogenides
Investigations of two-dimensional transition-metal chalcogenides (TMCs) have recently revealed interesting physical phenomena, including the quantum spin Hall effect
1
,
2
, valley polarization
3
,
4
and two-dimensional superconductivity
5
, suggesting potential applications for functional devices
6
–
10
. However, of the numerous compounds available, only a handful, such as Mo- and W-based TMCs, have been synthesized, typically via sulfurization
11
–
15
, selenization
16
,
17
and tellurization
18
of metals and metal compounds. Many TMCs are difficult to produce because of the high melting points of their metal and metal oxide precursors. Molten-salt-assisted methods have been used to produce ceramic powders at relatively low temperature
19
and this approach
20
was recently employed to facilitate the growth of monolayer WS
2
and WSe
2
. Here we demonstrate that molten-salt-assisted chemical vapour deposition can be broadly applied for the synthesis of a wide variety of two-dimensional (atomically thin) TMCs. We synthesized 47 compounds, including 32 binary compounds (based on the transition metals Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re, Pt, Pd and Fe), 13 alloys (including 11 ternary, one quaternary and one quinary), and two heterostructured compounds. We elaborate how the salt decreases the melting point of the reactants and facilitates the formation of intermediate products, increasing the overall reaction rate. Most of the synthesized materials in our library are useful, as supported by evidence of superconductivity in our monolayer NbSe
2
and MoTe
2
samples
21
,
22
and of high mobilities in MoS
2
and ReS
2
. Although the quality of some of the materials still requires development, our work opens up opportunities for studying the properties and potential application of a wide variety of two-dimensional TMCs.
Molten-salt-assisted chemical vapour deposition is used to synthesize a wide variety of two-dimensional transition-metal chalcogenides.
Journal Article
Self-assembly tungsten selenide hybrid ternary MOF derived magnetic alloys via multi-polarization to boost microwave absorption
Confronted with severe electromagnetic wave pollution, the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it. Notably, double transition metal alloys and transition metal dichalcogenides have attracted extensive attention in electromagnetic wave absorption, but few reports have studied the effects of these two materials on electromagnetic wave absorption at the same time. In this work, cobalt-based alloy with magnetic loss mechanism was selected for composition optimization. The ternary metal-organic framework was prepared by the one-step method, and then CoCu/C was prepared by high temperature annealing. Finally, in the hydrothermal process, ultra-thin tungsten selenide nanosheets were coated on the surface of magnetic component, and the final polyhedral WSe
2
/CoCu/C composites with multiple heterogeneous interfaces were obtained. The synergistic effect of dielectric and magnetic components optimizes impedance matching and allows more electromagnetic waves to enter the absorber. Subsequently, through the conduction loss of high conductivity graphitized carbon, interfacial polarization, and dipole polarization of heterogeneous interfaces between the components, the magnetic loss provided by CoCu alloy can work together to maximize the attenuation ability of electromagnetic waves. Exactly, the minimum reflection loss (RL
min
) value of the composite reaches −53.43 dB when the matched thickness is 2.1 mm, while the maximum effective absorption bandwidth (EAB
max
) reaches 6.0 GHz at a thin thickness of 1.8 mm. This work provides some support and reference for the design of novel electromagnetic wave absorbing materials via the dielectric/magnetic loss synergistic mechanism.
Journal Article
Toward high‐performance lithium‐oxygen batteries with cobalt‐based transition metal oxide catalysts: Advanced strategies and mechanical insights
Aprotic lithium‐oxygen (Li‐O2) batteries represent a promising next‐generation energy storage system due to their extremely high theoretical specific capacity compared with all known batteries. Their practical realization is impeded, however, by the sluggish kinetics for the most part, resulting in high overpotential and poor cycling performance. Due to the high catalytic activity and favorable stability of Co‐based transition metal oxides, they are regarded as the most likely candidate catalysts, facilitating researchers to solve the sluggish kinetics issue. Herein, this review first presents recent advanced design strategies for Co‐based transition metal oxides in Li‐O2 batteries. Then, the fundamental insights related to the catalytic processes of Co‐based transition metal oxides in traditional and novel Li‐O2 electrochemistry systems are summarized. Finally, we conclude with the current limitations and future development directions of Co‐based transition metal oxides, which will contribute to the rational design of catalysts and the practical applications of Li‐O2 batteries. Advanced design strategies, fundamental insights, and challenges for CoxOy‐catalyzed lithium‐oxygen batteries are critically analyzed, with possible development directions emphasized.
Journal Article
Freestanding crystalline oxide perovskites down to the monolayer limit
Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides reveal the electronic phases that emerge when a bulk crystal is reduced to a monolayer
1
–
4
. Transition-metal oxide perovskites host a variety of correlated electronic phases
5
–
12
, so similar behaviour in monolayer materials based on transition-metal oxide perovskites would open the door to a rich spectrum of exotic 2D correlated phases that have not yet been explored. Here we report the fabrication of freestanding perovskite films with high crystalline quality almost down to a single unit cell. Using a recently developed method based on water-soluble Sr
3
Al
2
O
6
as the sacrificial buffer layer
13
,
14
we synthesize freestanding SrTiO
3
and BiFeO
3
ultrathin films by reactive molecular beam epitaxy and transfer them to diverse substrates, in particular crystalline silicon wafers and holey carbon films. We find that freestanding BiFeO
3
films exhibit unexpected and giant tetragonality and polarization when approaching the 2D limit. Our results demonstrate the absence of a critical thickness for stabilizing the crystalline order in the freestanding ultrathin oxide films. The ability to synthesize and transfer crystalline freestanding perovskite films without any thickness limitation onto any desired substrate creates opportunities for research into 2D correlated phases and interfacial phenomena that have not previously been technically possible.
Ultrathin freestanding crystalline films of transition-metal oxide perovskites are fabricated and transferred to various substrates, proving their potential for exploring emergent 2D correlated phases.
Journal Article
Layered Transition Metal Sulfides for Supercapacitor Applications
Supercapacitor (SC) devices holds an important position between traditional capacitors and ion batteries in terms of energy density and power density values. In particular, SC′s greater power density values than Li‐ion batteries make them useful for some specific applications, such as storing energy in hybrid cars while the car slows down. Increasing energy density values is one of the key challenges for the SC community. Transition metal dichalcogenides (TMDCs), are one of the new developing important material systems to have this potential, compared to their counterparts’ transition metal oxides and conductive polymers. This review is about giving insight into the electrochemical performances of two‐dimensional (2D) layered transition metal sulfides (TMS) such as MoS2, WS2, TaS2, NbS2, VS2, TiS2 and ZrS2 materials. On the other hand, the methods mostly used in synthesizing these materials are presented. TMS materials have potentials to be a good candidate for supercapacitor devices because of their layered structures (more space for charges to accumulate), having metallic phases (good conductivity), multiple oxidation steps (large specific capacitance). The current review summarizes the six different synthesis methods, electrochemical performances and some future perspectives.
Journal Article