Complex Metal Oxides Research Articles

Nickel-Copper Bimetallic Oxide Nanoparticles Prepared by Simple Coprecipitation Method as High Performance Electrode Materials for Asymmetric Supercapacitors.

Supercapacitors with transition bimetallic oxides as pseudocapacitive materials have been of wide concern for their excellent energy storage performance. In this work, a simple coprecipitation method was used to synthesize the precursor, followed by calcination to prepare Ni-Cu bimetallic oxide materials. The structure, morphology and properties of the materials prepared by different precipitating agents and different calcination temperatures of NCO-H2C2O4 precursor were investigated. The optimum precipitant was determined to be H2C2O4, and Ni-Cu nanoparticles with regular lamellar microstructure were obtained at the calcination temperature of 400 °C. The nanostructure and morphology provide a large active channel for the rapid diffusion of electrolyte ions, and the specific capacitance of NCO-H2C2O4-400 electrode material can reach 740.31 F/g Cs at 1 A/g. The investigation of charge storage mechanism shows that the contribution rate of capacitance and diffusion control is about 37.9% and 67.2%, respectively. The electrochemical test results of the asymmetric supercapacitors (ASC) constructed with NCO-H2C2O4-400 and activated carbon show that the specific capacitance, energy density, and power density of the capacitor are 52.66 F/g, 16.45 Wh/kg, and 759.51 W/kg, respectively. Even after 5000 charge/discharge cycles at 5 A/g, it can still keep 90.57% of its initial capacity. This work not only provides competitive electrode materials for energy storage devices but also provides a feasible strategy for producing complex transition metal oxide materials with high capacitance performance.

Structural Characterization of Mixed Metal Cathodes via in Operando X-Ray Diffraction

Complex metal oxides used in lithium-based energy storage technologies undergo distinct crystallographic changes based on chemical composition, specific voltage and current states, degree of lithiation, and more. Crystallographic studies via X-ray diffraction (XRD) are a critical part of understanding structure-property relationships and engineering devices to meet specific performance requirements. For the raw electrode materials, XRD provides information about exact crystal structure (e.g. symmetry, unit cell parameters, atomic site mixing) as well as the presence of impurity phases that might arise from a poor sintering process or non-stoichiometric starting reagents. For formed devices such as button- or pouch-cells, XRD can be used in operando to measure changes in phase composition, phase quantification, and crystal lattice expansion/contraction as a function of charge state. This can provide useful information such as the level of reversibility of a device or the onset of impurity phases during aging and long cycling.In this presentation, we will review diffraction data for case studies based on NMC electrodes and highlight key insights into reversible structural changes during device cycling. The figure attached to this abstract shows diffraction data as a function of charge state during a single charge/discharge cycle. The observed peaks show modifications to the crystalline lattice (expansion in one direction, contraction in another orthogonal direction). Figure 1

Standardization of Chemically Selective Atomic Force Microscopy for Metal Oxide Surfaces.

The structures of metal oxide surfaces and inherent defects are vital for a variety of applications in materials science and chemistry. While scanning probe microscopy can reveal atomic-scale details, elemental discrimination usually requires indirect assumptions and extensive theoretical modeling. Here, atomic force microscopy with O-terminated copper tips on a variety of sample systems demonstrates not only a clear and universal chemical contrast but also immediate access to the atomic configuration of defects. The chemically selective contrast is explained by purely electrostatic interactions between the negatively charged tip-apex and the strongly varying electrostatic potential of metal and oxygen sites. These results offer a standardized methodology for the direct characterization of even the most complex metal oxide surfaces, providing fundamental insight into atomic-scale processes in these material systems.

Interplay of Capacitive and Diffusion Contributions in Redox Active Complex Metal Oxide Rods Channelled into MXene for Improved Charge Transfer Dynamics

Interplay of Capacitive and Diffusion Contributions in Redox Active Complex Metal Oxide Rods Channelled into MXene for Improved Charge Transfer Dynamics

Antifungal Activity of Submicrometer Particles of Complex Metal Oxides with Photocatalytic Activity

Antifungal Activity of Submicrometer Particles of Complex Metal Oxides with Photocatalytic Activity

Role of oxygen vacancy in controlling the resistive switching mechanism for the development of conducting filaments in response of homo and hetero electrodes: Using DFT approach

In the realm of progression of internet of things, artificial intelligence and cloud services, nonvolatile memory devices such as, resistive random access memory (RRAM) emulated the vision of building internet of everything. In this study, robustness of homo- (Ag–Ag, and Pt–Pt), and hetero- (Ag–Pt) top, and bottom electrodes material without and with incorporated oxygen vacancies (Vos) in Sr4Ti4O12 RS layer were investigated. Presence of conductivity in the absence of external electric field proves the presence of nonvolatile memory behavior. Observed RS behavior (in the range of a few Angstroms) may be used to resolve the scalability issue of the proposed RRAM device system. At the same time, oxygen vacancies (Vos) introduced additional functionalities like: additional reduction sites, and reduction of leakage current by quantizing the conduction within RS material. Diffusion barrier elucidated the diffusion mechanism of oxygen vacancies in the considered heterostructure to understand the energy state and the type of RS conduction mechanism. Potential energy line ups, formation energy and electronic properties identified the Vos as principal sites for reduction of Ag atoms by forming metal oxide (Ag-Vos) complex. It is predicted that ReSET, and hence high resistance state (HRS) is harder to achieve with homo-electrodes. The findings of this study provides the effective solution to scalability, stability, and low power consumption in the realm of Pt–Sr4Ti4O12–Ag (with 2Vos mediated in RS layer) based RRAM devices.

Effect of Preparation Methods on the Interface of LiBH4/SiO2 Nanocomposite Solid Electrolytes.

Nanocomposites of complex metal hydrides and oxides are promising solid state electrolytes. The interaction of the metal hydride with the oxide results in a highly conducting interface layer. Up until now it has been assumed that the interface chemistry is independent of the nanoconfinement method. Using 29Si solid state NMR and LiBH4/SiO2 as a model system, we show that the silica surface chemistry differs for nanocomposites prepared via melt infiltration or ball milling. After melt infiltration, a Si···H···BH3 complex is present on the interface, together with silanol and siloxane groups. However, after ball milling, the silica surface consists of Si- H sites, and silanol and siloxane groups. We propose that this change is related to a redistribution of silanol groups on the silica surface during ball milling, where free silanol groups are converted to mutually hydrogen-bonded silanol groups. The results presented here help to explain the difference in ionic conductivity between nanocomposites prepared via ball milling and melt infiltration.

Exploring microstructures of metal-doped oxides via simulated Raman spectrum

Solid solution of metal-doped oxide has been widely used in material industry and catalysis process. Its performance is highly correlated with the distribution of doped ions. Due to the complex distribution of doped ions in solid solution and its variation with temperatures, to obtain the microstructures of metal-doped ions in solid solution remains a substantial challenge. Taken Ce1-xZrxO2 as a model, the global structure searching, structures proportion with temperature determined by Boltzmann distribution, and the weighted simulation Raman spectra were integrated to explore the microstructures of metal-doped solid solution oxides. It was further verified by application into rutile and anatase TiO2 mixture, indicating that the present method is feasible to deduce the microstructure of metal composite oxides. We anticipate that it provides a powerful solution to explore microstructures of solid solution and complex metal oxides.

Ultra-high performance concrete with metal mine tailings and its properties: a review

Abstract Metal mine tailings (MMT) are a kind of industrial solid waste, with an increasing accumulation year by year, which has seriously damaged the ecological environment. Incorporating MMT in ultra-high performance concrete (UHPC) is an effective means to achieve green sustainable development, which can not only make wastes be resources and prevent pollution but also save raw material costs and reduce energy consumption. However, metal mine tailings contain complex and diverse metal oxides and other chemical substance and even contain certain radioactive elements and heavy metal ions. These factors can affect the corrosion resistance of UHPC, accelerate its aging and damage, and in addition may have serious impacts on the environment and human health. This paper summarizes the material properties of MMT and its application in UHPC; analyzes the effects of MMT as powder or fine aggregate on the workability, mechanical properties, durability, and leaching toxicity of UHPC; and elaborates the hydration products, interfacial transition zone, and pore structure of UHPC incorporating MMT (MMT-UHPC). Based on previous research results, the relationship between flowability, flexural strength, porosity, and compressive strength of MMT-UHPC is established.

Enhanced Energy Storage Performance through Controlled Composition and Synthesis of 3D Mixed Metal-Oxide Microspheres.

Binary transition metal oxide complexes (BTMOCs) in three-dimensional (3D) layered structures show great promise as electrodes for supercapacitors (SCs) due to their diverse oxidation states, which contribute to high specific capacitance. However, the synthesis of BTMOCs with 3D structures remains challenging yet crucial for their application. In this study, we present a novel approach utilizing a single-step hydrothermal technique to fabricate flower-shaped microspheres composed of a NiCo-based complex. Each microsphere consists of nanosheets with a mesoporous structure, enhancing the specific surface area to 23.66 m2 g-1 and facilitating efficient redox reactions. When employed as the working electrode for supercapacitors, the composite exhibits remarkable specific capacitance, achieving 888.8 F g-1 at 1 A g-1. Furthermore, it demonstrates notable electrochemical stability, retaining 52.08% capacitance after 10,000 cycles, and offers a high-power density of 225 W·kg-1, along with an energy density of 25 Wh·kg-1, showcasing its potential for energy storage applications. Additionally, an aqueous asymmetric supercapacitor (ASC) was assembled using NiCo microspheres-based complex and activated carbon (AC). Remarkably, the NiCo microspheres complex/AC configuration delivers a high specific capacitance of 250 F g-1 at 1 A g-1, with a high energy density of 88 Wh kg-1, for a power density of 800 W kg-1. The ASC also exhibits excellent long-term cyclability with 69% retention over 10,000 charge-discharge cycles. Furthermore, a series of two ASC devices demonstrated the capability to power commercial blue LEDs for a duration of at least 40 s. The simplicity of the synthesis process and the exceptional performance exhibited by the developed electrode materials hold considerable promise for applications in energy storage.

Electrochemical charge storage performance of (Mn, Ni, Mo, Co, Fe)3O4 high entropy oxide nanoparticles produced via thermal plasma route

Highly complex high entropy metal oxides (HEOs) have several unique characteristics, such as more active sites and material stability that improve the electrochemical charge storage capacity. In this study, HEOs (Mn, Ni, Mo, Co, Fe)3O4 nanoparticles were synthesized using a thermal plasma route and its electrochemical energy storage performance was studied with two distinct electrolytes such as 1 M KOH and NaOH. The X-ray diffraction analysis revealed the phase pure spinel structured HEOs with crystalline size ranging from 13 to 29 nm. Scanning electron microscopy and electron dispersive X-ray spectroscopy results revealed the quasi-spherical morphology and uniform distribution of constitutional cations in the as-synthesized HEOs. The X-ray photoelectron spectroscopy results identified the oxidation states of cations in spinel HEOs. The charge/discharge studies of as-synthesized HEOs showed a specific capacitance of 215 F g-1 /26.9 mAh g-1 at a current density of 2 A g-1 in 1 M KOH electrolyte which is 156 % greater than 1 M NaOH electrolyte. Furthermore, a high capacitance retention of 91 % was achieved after completing 3000 cycles at 10 A g-1 current density which indicates that the HEOs have excellent charge/discharge reversibility. Electrochemical impedance spectroscopy revealed that the solution and charge transfer resistances of HEOs electrodes were 1.04 and 3.2 Ω, respectively. This novel synthesis strategy attempts to overcome the difficulties experienced by established methods for bulk manufacture of phase pure HEOs since thermal plasma method is a rapid and a single-step approach for the bulk production of nanomaterial.

Harnessing Interlayer Magnetic Coupling for Efficient, Field‐Free Current‐Induced Magnetization Switching in a Magnetic Insulator

Owing to the unique features of low Gilbert damping, long spin‐diffusion lengths, and zero Ohmic losses, magnetic insulators are promising candidate materials for next‐generation spintronic applications. However, due to the localized magnetic moments and the complex metal–oxide interface between magnetic insulators and heavy metals, spin‐functional Dzyaloshinskii–Moriya interactions or spin Hall and Edelstein effects are weak, which diminishes the performance of these typical building blocks for spintronic devices. Herein, the exchange coupling between metallic and insulating magnets is exploited for efficient electrical manipulation of heavy metal/magnetic insulator heterostructures. By inserting a thin Co layer, the spin‐orbit torque efficiency is enhanced by more than 20 times, which significantly reduces the switching current density. Moreover, field‐free current‐induced magnetization switching caused by a symmetry‐breaking non‐collinear magnetic texture is demonstrated. This work launches magnetic insulators as an alternative platform for low‐power spintronic devices.

Structure and phase transitions in niobium and tantalum derived nanoscale transition metal perovskites, Ba(Ti,MV)O3, M=Nb,Ta.

The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared single phase nanocrystals of Ba(Ti, M)O3. Compositional and elemental analysis puts the empirical formulas close to BaTi0.5Nb0.5O3-δ and BaTi0.5Ta0.5O3-δ. For both materials, a reversible temperature dependent phase transition (non-centrosymmetric to symmetric) is observed in the Raman spectrum in the region 533-583K (260-310°C); for Ba(Ti, Nb)O3, the onset is at 543K (270°C); and for Ba(Ti, Ta)O3, the onset is at 533K (260°C), which are comparable with 390-393K (117-120°C) for bulk BaTiO3. The crystal structure was resolved by examination of the powder x-ray diffraction and atomic pair distribution function (PDF) analysis of synchrotron total scattering data. It was postulated whether the structure adopted at the nanoscale was single or double perovskite. Double perovskites (A2B'B″O6) are characterized by the type and extent of cation ordering, which gives rise to higher symmetry crystal structures. PDF analysis was used to examine all likely candidate structures and to look for evidence of higher symmetry. The feasible phase space that evolves includes the ordered double perovskite structure Ba2(Ti, MV)O6 (M = Nb, Ta) Fm-3m, a disordered cubic structure, as a suitable high temperature analog, Ba(Ti, MV)O3Pm-3m, and an orthorhombic Ba(Ti, MV)O3Amm2, a room temperature structure that presents an unusually high level of lattice displacement, possibly due to octahedral tilting, and indication of a highly polarized crystal.

Ultrasound-assisted synthesis of Dy2Mo3O12-Dy2O3 nanostructures for enhanced electrochemical hydrogen storage

Among the major challenges facing the hydrogen economy is the issue of hydrogen storage. In terms of "future energy needs", electrochemical hydrogen storage in solid-state materials is an accepted perspective that could mitigate the discontinuation of primary energy sources. In this study, we demonstrate the electrochemical properties of a complex metal oxide that contains the molybdate group, Dy2Mo3O12. Wet-chemical synthesis of nanostructured Dy2Mo3O12 is primarily carried out using ultrasound-assisted wet-chemical methods in the presence of a variety of surfactants. The structural and morphological observations of the samples confirm a pure and highly crystalline structure obtained in the presence of CTAB surfactant at 900 °C and 30 min of sonication, with an average crystalline size of 29 nm. Based on the FTIR spectrum of this sample, it can be concluded that there are significant absorptions indicating the formation of oxygen-metal bonds. The specific surface area and pore volume of the selected sample are 4.543 m2/g and 0.0284 cm3/g, respectively, demonstrating its porous structure. Electrochemical studies of this sample at various temperatures have revealed an enhanced discharge capacity (5100 mAh/g at 65 °C) with a capacity retention rate of 97%. Based on these findings, mixed metal oxides containing at least one active charge transfer species (Red./Ox.) are suitable for use in solid-state hydrogen storage devices.

Incorporation of Cu and Mn ions into hydroxyapatite channels and deposition of complex metal oxide

The Cu-and Mn-incorporated apatite-type phosphate, Ca10(PO4)6CuxMny(O,OH)2, was successfully synthesized by heating the hydroxyapatite under N2 at 900 °C after Cu- and Mn-nitrate aqueous solution loading with x = 0–0.2 and y = 0–0.2 onto it. In Ca10(PO4)6Cu0·2Mn0·2(O,OH)2, Cu occupies the apatite channel center site, and the Mn site shifts from the center. The deposition of Cu and Mn species was found to occur upon heating Cu0·2Mn0.2-Ca-HAp at 600–800 °C in air, accommodating the spinel-type complex metal oxide, (Cu, Mn)3O4 formation from the apatite channel. In addition, the CuO deposition from the Ca10(PO4)6Cu0·2(O,OH)2 apatite was observed for samples heated at 600–800 °C, whereas Mn3O4 was observed for the Ca10(PO4)6Mn0·2(O,OH)2 sample heated at 800 °C. These results suggest that the presence of Cu in the apatite channel facilitates the deposition of Mn species.

CATALYTIC ACTIVITY OF METAL-BASED IONIC LIQUIDS IN OXIDATIVE DESULFURIZATION

Effective desulfurization techniques are required due to the operational and environmental difficulties caused by sulfur compounds found in petroleum fuels. The use of Fenton catalysts in the oxidative desulfurization of petroleum fuels is examined in this work. Evaluating the viability and effectiveness of Fenton catalysts in lowering sulfur concentration while maintaining fuel quality is the main goal. Promising outcomes are found in laboratory tests using hydrogen peroxide (H2O₂) and ferrous iron (Fe³⁺) as catalysts. Fenton catalysts focus on sulfur compounds and transform them into forms that are soluble in water, making the process of separating them from the fuel easier. This procedure offers a more environmentally friendly and financially feasible desulfurization option because it works in milder circumstances than other techniques. The results provide a viable path for the development of sustainable fuel and have ramifications for greener energy sources and environmental legislation. There has been a growing interest in ionic liquids (ILs) as innovative materials for functional desulfurization. Based on their definition and fundamental structure, metal-based ionic liquids (MILs) are divided into three categories in this critical article: metal chloride MILs, metal oxide MILs, and metal complex MILs. To enhance the oxidative desulfurization (ODS) process, MILs have both the oxidation and absorption sites for intramolecular adsorption and oxidation. A noteworthy characteristic of MILs in ODS is biomimetic catalysis, which serves to enhance oxidation performance by triggering molecular oxygen. Hydrogen peroxide or oxygen combined with the available water, together with metal oxide and metal complex ions, create a Fenton-like reaction that transforms hydrophobic organic sulfur (SO2) or hydrophilic sulfoxide/sulfone (Seroxide), or sulfur acid, respectively. Promising approaches for developing environmentally friendly and highly effective desulfurization procedures for large-scale applications are also given. Keywords: supported ionic liquid catalyst (SILC), hydrogen peroxide, catalytic oxidative desulfurization, copper (I) chlorocomplexes.

Comparison of Structure and Reactivity of Hydrothermally Prepared Bi−Mo−Co−Fe−O Catalysts in Selective Propylene and Isobutene Oxidation

AbstractThe elucidation of structure‐activity correlations in selective oxidation of propylene and isobutene over mixed metal oxides (MMO) is attractive for knowledge‐based catalyst design and process optimisation. Particularly, 4‐component Bi−Mo−Co−Fe−O catalysts need to be studied since their complex metal oxide phase mixture leads to higher activity and selectivity than 2‐component Bi−Mo−O. Hence, three Bi−Mo−Co−Fe‐oxides with different metal ratios were prepared by hydrothermal synthesis and compared during selective oxidation tests with propylene and isobutene. The active phases after several days on stream were investigated by synchrotron X‐ray diffraction (XRD) and Raman spectroscopy, while the structural evolution under reaction conditions was followed by operando Raman spectroscopy, synchrotron XRD, and multi‐edge X‐ray absorption spectroscopy. Similar structural transformations were observed during selective oxidation of propylene and isobutene, with similar influence on catalytic performance. A phase mixture of β‐CoMoO4/β‐Co0.7Fe0.3MoO4, γ‐Bi2MoO6, Fe3O4 and Bi3FeMo2O12 was observed, whereby high amounts of β‐CoMoO4/β‐Co0.7Fe0.3MoO4 increased selectivity to acrolein/methacrolein. In contrast, high amounts of γ‐Bi2MoO6 and Fe3O4 favoured total oxidation to CO and CO2. The simultaneous presence of β‐CoMoO4/β‐Co0.7Fe0.3MoO4, Bi3FeMo2O12 and Fe2O3 increased selectivity to methacrolein in isobutene oxidation, whereas no comparative increase in acrolein selectivity was observed in propylene oxidation. This suggests different key active phases in both reactions.

Antimicrobial Effect of Submicron Complex Oxide Particles CsTeMoO6 under Visible Light

The antimicrobial activity of submicron particles of new photocatalytic active complex metal oxide CsTeMoO6 against bacteria Escherichia coli and Staphylococcus aureus and fungi Aspergillus niger and Penicillium chrysogenum (spores and vegetative mycelium) was studied. It has been established that CsTeMoO6 has the antimicrobial activity in both under dark and visible light conditions in relation to all test cultures of microorganisms. The most inhibitory effect of CsTeMoO6 was noted for E. coli. The light enhanced the antimicrobial effect of the test compound against all cultures of bacteria and fungi, which is associated with the presence of photocatalytic activity of CsTeMoO6. The antifungal activity of CsTeMoO6 increased against spores and vegetative mycelium of fungi under light condition, and this effect increased with an increasing duration of time exposure. The different degree of survival rate of the studied microorganisms in the presence of this compound (under both dark and light) may be associated with the physiological and biochemical characteristics of the used microorganisms, including different mechanisms of resistance against complex metal oxide and reactive oxygen species.

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells.

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

The SCAN+U method in the investigation of complex transition metal oxides: a case study on YSr2Cu2FeO7+δ (δ = 0, 1).

Assessment of DFT methods is essential to sustain reliability in the computational investigation of complex transition metal oxides. This work evaluates the performance of the strongly constrained and appropriately normed (SCAN) functional and its extended Hubbard-U methodology (SCAN+U) to model the YSr2Cu2FeO7+δ (0 < δ < 1) perovskite-based system. The influence of the individual UCu and UFe Hubbard parameters (0 < U < 4 eV) on the calculated electronic, magnetic and crystal structures of the end members δ = 1 (metallic) and δ = 0 (insulating) is analyzed. The introduction of the U-correction terms enhances the reproduction of the crystal structures, with a UCu value of 1 eV improving the band gap accuracy for the YSr2Cu2FeO7 phase, while maintaining the metallic characteristics of YSr2Cu2FeO8. At a fixed UCu value, the results are almost insensitive to the UFe value used in the calculations. The findings emphasize that for oxides containing several TM ions, the optimal UTM values may differ from those of the simple TM oxides.