Electronic Structure Of Metal Oxides Research Articles

Chemical bonding and electronic properties along Group 13 metal oxides

ContextThe present work provides a systematic theoretical analysis of the nature of the chemical bond in Al2O3, Ga2O3, and In2O3 group 13 cubic crystal structure metal oxides. The influence of the functional in the resulting band gap is assessed. The topological analysis of the electron density provides unambiguous information about the degree of ionicity along the group which is linearly correlated with the band gap values and with the cost of forming a single oxygen vacancy. Overall, this study offers a comprehensive insight into the electronic structure of metal oxides and their interrelations. This will help researchers to harness information effectively, boosting the development of novel metal oxide catalysts or innovative methodologies for their preparation.MethodsPeriodic density functional theory was used to predict the atomic structure of the materials of interest. Structure optimization was carried out using the PBE functional, using a plane wave basis set and the PAW representation of the atomic cores, using the VASP code. Next, the electronic properties were computed by carrying out single point calculations employing PBE, PBE + U functionals using VASP and also with PBE and the hybrid HSE06 functionals using the FHI-AIMS software. For the hybrid HSE06, the impact of the screening parameter, ω, and mixing parameter, α, on the calculated band gap has also been assessed.

Enhanced Catalytic Performance of Carbon Nitride-Functionalized Titanium Dioxide through Efficient Oxygen Vacancy Defect Engineering for Electrochemical Recognition of Epinephrine

Oxygen defect engineering is a reliable and efficient approach to modulate the electronic structure of metal oxides for the improvement of catalytic efficiency. In this work, carbon nitride supported titanium dioxide nanoparticle, with the space group of I41/amd, was prepared using a high temperature synthesis route. Transmission electron microscope study revealed that titanium dioxide particle were dispersed uniformly on the carbon nitride network. The X-ray photoelectron spectroscopy analysis predicted the formation of oxygen defects in the matrix of titanium oxide, and it also indicated the presence of titanium ions with mixed valence states. The synthesized hybrid system was evaluated as an electrocatalyst for the electrochemical detection of epinephrine using cyclic voltammetric and square wave voltammetric techniques. A custom-made device was also fabricated using synthesized hybrid material for the purpose of evaluating the electrochemical sensing of epinephrine in a pharmaceutical sample.

Frontispiece: Cation‐Tuning Engineering on Metal Oxides for Oxygen Electrocatalysis

Cation-tuning engineering has recently been regarded as an efficient strategy to modify the electronic structure of metal oxides, thus improving the electrochemical performance towards oxygen-related reactions. In this Concept Article, L. Cao, B.-W. Zhang, and S. Zhao highlight the advantages of cation-tuning engineering, summarize the current state of this field, and propose future opportunities and challenges for its practical application (DOI: 10.1002/chem.202202000).

Intrinsic catalytic Sites-Rich Co-doped SnO2 nanoparticles enabling enhanced conversion and capture of polysulfides

The serious shuttle effect and sluggish reaction kinetics hinder the commercialization implementation of lithium-sulfur battery, despite its ultra-high theoretical energy density and low cost outrivaling the lithium-ion battery. Regulating the electronic structure of metal oxides at the atomic level could be an effective strategy to improve the intrinsic catalytic activity for polysulfides conversion. Herein, we proposed cobalt-doped stannic oxide which was uniformly grown on carbon nanotubes (Co-SnO2@CNT) as a multifunctional sulfur host. Evidenced by experimental characterizations and theoretical simulations, it is found that due to the appropriate doping amount, this host is endowed with abundant polar sites that exhibit robust polysulfides adsorption and confinement, fast Li-ion, and electron transfer, and rapid conversion reaction kinetics of sulfur species. As a result, the Co-SnO2@CNT host exhibits high sulfur loading (∼79.3 wt%), excellent rate capability (808 mAh g−1 at 2C), and superior long-term cycle stability (0.042% per cycle degeneration for 600 cycles at 1C). Excellent performances are also obtained at practical lean electrolyte conditions (E/S ratio ∼ 5 uL mg−1). This work verifies the feasibility of cobalt-doped SnO2 as catalyst and adsorbent for polysulfide species and reveals the internal mechanism of transition metal doped metal oxides at an atomic scale. In addition, a strategy was proposed that could overcome the intrinsic drawbacks of metal oxides and open up more feasible ways for high-performance lithium-sulfur batteries.

Interfacial Reaction-Induced Defect Engineering: Enhanced Visible and Near-Infrared Absorption of Wide Band Gap Metal Oxides with Abundant Oxygen Vacancies.

Modified metal oxides with narrow band gaps have attracted great interest in photothermal applications because of their wide optical absorption range. To tune wide band gap metal oxides into visible and near-infrared responsive materials, we deploy a unique interfacial reaction-induced defect engineering approach, which enables us to effectively modify the electronic structure of metal oxides by introducing oxygen vacancy defects. This approach reduced the band gap of zirconia from 5.47 to 1.38 eV, accompanied by a color change to black. More importantly, it is not limited by the size of the metal oxides, and bulk black zirconia was successfully obtained for the first time. It has been demonstrated that the prepared black zirconia can be applied as an effective photothermal therapy agent in vitro. Additionally, the interfacial reaction-induced defect engineering approach has been successfully extended to enhance the optical absorption of other metal oxides.

Probing Active Sites and Reaction Intermediates of Electrocatalysis Through Confocal Near-Infrared Photoluminescence Spectroscopy: A Perspective.

Electrocatalytic reactions such as oxygen evolution (OER) and oxygen reduction reactions (ORR) are one of the most complex heterogeneous charge transfer processes because of the involvement of multiple proton-coupled-electron transfer steps over a narrow potential range and the formation/breaking of oxygen-oxygen bonds. Obtaining a clear mechanistic picture of these reactions on some highly active strongly-correlated oxides such as MnOx, NiOx, and IrOx has been challenging due to the inherent limitations of the common spectroscopic tools used for probing the reactive intermediates and active sites. This perspective article briefly summarizes some of the key challenges encountered in such probes and describes some of unique advantages of confocal near-infrared photoluminescence (NIR-PL) technique for probing surface and bulk metal cation states under in-situ and ex-situ electrochemical polarization studies. Use of this technique opens up a new avenue for studying changes in the electronic structure of metal oxides occurring as a result of perturbation of defect equilibria, which is crucial in a broad range of heterogeneous systems such as catalysis, photocatalysis, mineral redox chemistry, and batteries.

Unraveling the promoted nitrogen dioxide detection performance of N-doped SnO2 microspheres at low temperature

Abstract Nitrogen doping has been proven an efficient strategy to modulate the electronic structure of metal oxides to tune their properties. Herein, we report the synthesis of N-doped SnO2 microspheres through calcining the pristine SnO2 in NH3 atmosphere. Texture characterizations show that N–SnO2 microspheres exhibit 3D-porous architectures with a diameter of ca. 300–500 nm. After NH3 treatment, the SnO2 exhibits the formation of the N-doping and oxygen vacancies on the surface of the material, rich free-electrons and the narrow energy band. It is found that the as-prepared N-doped SnO2 microspheres at 200 °C (N–SnO2-200), show superior selectivity and high response (S = 155 to 5 ppm NO2) compared with its counterparts. DFT calculations and experimental results illustrate that N impurities and oxygen vacancies as N-induced active sites favor the adsorption of NO2 molecules; rich free-electrons increase the amount of adsorbed NO2 molecules; and the narrow energy band promotes the effectively electron transfer during the sensing reaction. Therefore, in this work we unravel the improved NO2 gas-sensing performances of the N-doped SnO2 and provide new guidance for the development of highly efficient metal oxide sensing materials for NO2 detection.

The Effects of Grain Size, Oxidizers and Catalysts on Band Gap Energy of Gelam-Wood Carbon

The research of the effects of grain size, oxidizers, and catalysts on band gap energy of gelam-wood carbon has been conducted in which the carbons were produced from gelam-wood pyrolysis in high temperatures. The instrumentations used in this study were UV-Vis, FTIR spectrophotometer, and SEM. SEM and FTIR were used to characterize the morphology and the functionality of the carbon surface. UV-Vis spectrograms showed that the electronic property of carbon such as band gap was affected when grain size and surface area were changed. The increase of the functional groups in carbon occurred as the surface area of the carbon was increased. Band gap energy of crystalline carbon became much lower along with the increase in grain size due to the effects of bands-broadening. FTIR spectrograms showed that the carbon contained of hydroxyl and carboxylic groups. The hydroxyls were derived from steam-oxidized carbon that was provided narrower in the interlayer distance and lower-set band gap energy. Carboxylic groups were derived from acid nitric oxidation causing flat layer to become curved. The layers were wider and the band energy was higher. The main factor that affects the electronic structure of metal oxide in carbon/metal oxide composites was atomic alignments. The band gap energy increased along with the increase of the asymmetry alignments in metal oxide.

Fast triethylamine gas sensing response properties of Ho-doped SnO2 nanoparticles

Doping is benefical to the formation of defects on the surface and modification of the electronic structure of metal oxides. In this work, SnO2 nanoparticles (NPs) with different holmium ions concentrations of 0 at.%, 0.11 at.%, 0.45 at.%, and 0.53 at.% have been synthesized by a gas-liquid phase chemical deposition method with following annealing process. The SnO2:Ho3+ NPs exhibit superior triethylamine (TEA) gas sensing properties. The TEA sensing performance of the 0.45 at.% Ho-doped SnO2 NPs based sensor markedly improve compared with other different Ho doped based sensors. The response time for detecting 50 ppm TEA is only 2 s, and the response value is about 12. The as fabricated sensor shows fast response, excellent selectivity and reproducibility to TEA gas at a relatively low working temperature of 175 °C. Gas sensing testing shows that a suitable concentration of Ho doping leads to the enhancement of the sensor response. The enhanced sensing mechanism is attributed to the formation of oxygen vacancies and change of carrier concentration.

Exceptional anodic performance of Sb-doped SnO2 nanoparticles on electrochemically exfoliated graphene for lithium-ion batteries

Metal oxides such as SnO2 are widely studied as anode materials for next-generation lithium-ion batteries because of their high theoretical capacities. However, the lithium storage capability of SnO2 is suppressed by its poor electrical conductivity and serious volume change during the charge and discharge processes. In this work, SnO2 nanoparticles are directly grown on the surface of electrochemically exfoliated graphene, followed by doping Sb into SnO2 nanoparticles. As a high quality of graphene, electrochemically exfoliated graphene possesses high electrical conductivity and strong mechanical strength, which is beneficial to the charge transfer from graphene to SnO2 nanoparticles. Moreover, the doping of Sb into SnO2 nanoparticles inhibits the agglomeration and growth of SnO2 nanoparticles, and further improves the electron conductivity of SnO2 by changing the electronic structure of SnO2. As a result, electrochemically exfoliated graphene-based SnO2 with Sb doping exhibits superior electrochemical performance including high reversible capacity, excellent cycling stability and remarkable rate capability. Modifying the electronic structure of metal oxides by doping with appropriate metals may provide an avenue to realize the demand of high-performance electrodes for secondary batteries.

Noninvasively Modifying Band Structures of Wide-Bandgap Metal Oxides to Boost Photocatalytic Activity.

Although doping with appropriate heteroatoms is a powerful way of increasing visible light absorption of wide-bandgap metal oxide photocatalysts, the incorporation of heteroatoms into the photocatalysts usually leads to the increase of deleterious recombination centers of photogenerated charge carriers. Here, a conceptual strategy of increasing visible light absorption without causing additional recombination centers by constructing an ultrathin insulating heterolayer of amorphous boron oxynitride on wide-bandgap photocatalysts is shown. The nature of this strategy is that the active composition nitrogen in the heterolayer can noninvasively modify the electronic structure of metal oxides for visible light absorption through the interface contact between the heterolayer and metal oxides. The photocatalysts developed show significant improvements in photocatalytic activity under both UV-vis and visible light irradiation compared to the doped counterparts by conventional doping process. These results may provide opportunities for flexibly tailoring the electronic structure of metal oxides.

Ultrahigh capacitive performance of three-dimensional electrode nanomaterials based on α-MnO2 nanocrystallines induced by doping Au through Å-scale channels

Poor electrical conductivity of metal oxides is the primary challenge that limits their energy storage capacity. Intercalating metal atoms into the crystal lattices of metal oxides are expected to change the electronic structure of metal oxides, and thus improve the conductivity as well as electrochemical performance of the metal oxides. Herein, we demonstrate the doping of α-MnO2 nanocrystallines by Au through Å-scale channels via cyclic voltammetry at different scan rates on the basis of first-principle calculation. Experiments elucidate that the doped Au atoms in α-MnO2 lattice and distributed Au nanoparticles in α-MnO2 nanothin layers can greatly enhance the conductivity and electrochemical performance of MnO2. Hence, the designed carbon cloth electrodes modified with ZnO-nanorods/Au-doped-α-MnO2 (ZNs/ADM) nanocomposites exhibit excellent electrochemical performances. Moreover, an asymmetric supercapacitor based on ZNs/ADM (positive) and reduced-graphene-oxide-CNTs (negative) hybrid materials demonstrates cycled reversibly in a wide potential window and exhibits high energy density (101Wh/kg), power density (33.6kW/kg), and reasonable cycling performance. This work opens the possibility to develop new types of metal-doped metal-oxides that can meet the needs of specific applications, ranging from energy-storage devices to biosensors.

Linking diffusion kinetics to defect electronic structure in metal oxides: Charge-dependent vacancy diffusion in alumina

We study the diffusion of charged vacancies in α-Al2O3 crystal using the first-principles calculation method. We predict that the migration energy for vacancy diffusion strongly depends on the charge state of the vacancy involved. Importantly, we reveal that this charge-dependent vacancy diffusion is directly related to the electron occupancy and energy level change of the defect states of the charged vacancy in alumina. Hence, our study establishes a direct link between the diffusion kinetics and electronic structure of metal oxides.

Structurally and Electronically Designed TiO2Nx Nanofibers for Lithium Rechargeable Batteries

The morphology and electronic structure of metal oxides, including TiO(2) on the nanoscale, definitely determine their electronic or electrochemical properties, especially those relevant to application in energy devices. For this purpose, a concept for controlling the morphology and electrical conductivity in TiO(2), based on tuning by electrospinning, is proposed. We found that the 1D TiO(2) nanofibers surprisingly gave higher cyclic retention than 0D nanopowder, and nitrogen doping in the form of TiO(2)N(x) also caused further improvement. This is due to higher conductivity and faster Li(+) diffusion, as confirmed by electrochemical impedance spectra. Our findings provide an effective and scalable solution for energy storage efficiency.

Synthesis and Characterization of Nitrogen-doped SnO2 and Comparison to Nitrogen-doped CeO2 Nanoparticles for Visible-light Applications

Nitrogen-doped SnO2 with varying amounts of nitrogen have been synthesized via a wet-chemical method and compared to CeO2 nanoparticles synthesized under similar conditions. Morphologies, N-doping level, and optical properties were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (DRS). The N-doped nanoparticles showed enhanced visible-light absorption and photocatalytic activity compared to commercially available TiO2 nanoparticles (Degussa P25). This N-doping process can efficiently modify the physical and chemical properties of metal oxides, which in turn can provide scientists in the field with a promising approach to modify the electronic structure of metal oxides, and thus potentially extend the scope of applications.