Simple Transition Metal Oxides Research Articles

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Continued efforts towards the decarbonization of the power sector through an uptake of renewable energy generation, namely solar and wind, play a key role in the fight against climate change. However, due to their variable nature, the simultaneous implementation of energy storage solutions capable of ensuring a reliable delivery of energy at any time of day is of the utmost importance. Aqueous rechargeable zinc-ion batteries (RZIBs) are a promising technology for this end. Offering several advantages over lithium-ion batteries in terms of cost, environmental impact, and material abundance, the investment in RZIB research continues to grow. However, the realization of commercial RZIBs is currently hindered by the lack of cathode materials with adequate performance for long-term storage solutions. This is the case for manganese (e.g., MnO2, Mn2O3, Mn3O4) and vanadium (e.g., V2O5, VO2) based oxides, which exhibit considerable capacity fade during realistic charge and discharge times. While simple transition metal oxides (MyOx, M=transition metal) are one of the most studied classes of materials for RZIB cathodes, a literature survey shows that there are still many unexplored redox active elements and redox pairs which may be employed in next-generation RZIBs. Therefore, to accelerate the discovery of these novel cathode systems, we mapped the theoretical Zn intercalation potential for simple oxides from 12 different transition metals using Density Functional Theory (DFT) calculated thermodynamic properties. The screened elements were chosen upon considering their commercial availability, toxicity, price, and existence of previously reported structures containing zinc. During the present analysis, the feasibility of Zn intercalation for each system was accounted for by analyzing the atomic arrangement in the charged and discharged phases. Experimentally obtained Pourbaix Diagrams were also used to probe the electrochemical stability of the cathodes in aqueous solution, with the possibility of electrolyte degradation (oxygen or hydrogen evolution reaction) and competing reactions (metal dissolution or solid phase change) also considered. Experimental validation of the computationally predicted potentials was also done for select materials. The result for the 35+ redox pairs evaluated in this study provides a clear roadmap for the future development of RZIBs cathodes.

Conversion Reactions and Redox Changes on the Surface of Lithium-Ion Battery Cathode Materials during Chemical Vapor Treatment for ALD

Atomic layer deposition (ALD) has emerged as a promising technology for applying ultrathin protective coatings on lithium-ion battery (LIB) cathode surfaces to improve their cycling stability. While there have been numerous reports evaluating the electrochemical performance of these surface-modified cathode materials, the chemical changes induced on the surface of the cathode materials by the ALD coatings and the individual ALD precursors are not fully studied. We performed a systematic investigation to understand the interfacial changes of 12 different cathode materials upon coating with aluminum oxide (Al2O3) using trimethyl aluminum (TMA) and H2O, and aluminum fluoride (AlF3) using TMA and hydrogen fluoride pyridine (HFPy). We also explored the effects of the individual TMA and HFPy precursors on the cathode surfaces. The surface composition and microstructure of these cathode materials, which range from simple transition metal oxides (e.g., NiO and MnO) to complex multi-element cathode materials (e.g., LiNixMn1-x-yCoyO2, NMC), were studied via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The XPS measurements reveal that the transition metals in the cathode materials undergo selective oxidation/reduction depending upon the nature of the precursor, the coating, and the cathode material. Furthermore, XPS and STEM measurements show the conversion of surface carbonate species to the corresponding metal fluorides upon HF exposure. This conversion reaction is self-limiting but extends hundreds of nanometers below the surface in the case of Li2CO3. ALD and chemical vapor treatment provide new avenues to systematically control the interface of the cathode materials in LIBs that are not possible by conventional coating methods.

Multiple Factors on Catalytic Activity for Oxygen Evolution Reaction in Magnetoplumbite Fe–Co Oxide BaFe12–xCoxO19

Complex metal oxides consisting of multiple transition-metal elements exhibit a higher electrocatalytic performance than simple transition-metal oxides. In this study, we demonstrate the physical and electrochemical properties of BaFe12–xCoxO19 (x = 0–12), a solid solution of magnetoplumbite-structured BaFe12O19 and BaCo12O19. Single-phase samples in the whole composition range are successfully obtained by using high-pressure and high-temperature conditions of 6.5 GPa and 1373 K. Co- and Fe-doping into BaFe12O19 and BaCo12O19, respectively, efficiently increases the catalytic activity for the oxygen evolution reaction (OER). The OER activity of BaFe12–xCoxO19 is maximized at two compositions of x = 5 and 10, whereas the nonsystematic change in the OER activity for the intermediate compositions between x = 5 and 10 indicates a competition of positive and negative factors on the OER activity such as the dopant as an active site, electrical conductivity, spin polarization, and charge-transfer resistance. We eventually found a characteristic relationship between specific activity and charge-transfer resistance reflecting the mechanistic difference for BaFe12–xCoxO19.

Superconductivity in Uniquely Strained RuO_{2} Films.

We report on strain engineering of superconductivity in RuO_{2} single-crystal films, which are epitaxially grown on rutile TiO_{2} and MgF_{2} substrates with various crystal orientations. Systematic mappings between the superconducting transition temperature and the lattice parameters reveal that shortening of specific ruthenium-oxygen bonds is a common feature among the superconducting RuO_{2} films. Abinitio calculations of electronic and phononic structures for the strained RuO_{2} films suggest the importance of soft phonon modes for emergence of the superconductivity. The findings indicate that simple transition metal oxides such as those with a rutile structure may be suitable for further exploring superconductivity by controlling phonon modes through the epitaxial strain.

Wet chemical route synthesis of spinel oxide nano-catalysts for photocatalytic applications

Transition metal spinel type mixed oxides (FeCo2O4, MnCo2O4 and ZnCo2O4) nano-catalysts have been synthesized via co-precipitation route. The samples were characterized using XRD and FE-SEM techniques to determine structure and morphologies respectively. Furthermore, FTIR and BET analysis were carried out in order to confirm the structure and calculate surface areas of the samples. The photocatalytic potency of synthesized nano-catalysts have been examined for aqueous solution of methylene blue under visible light. It is found that photocatalytic activity of simple transition metal oxides was enhanced by making their binary/ternary metal oxides. FeCo2O4 exhibited highest photocatalytic efficiency among the prepared spinel structures while MnCo2O4 possess lowest efficiency. The photocatalytic behavior of mixed transition metal oxides can be accredited to its spinel structure, small particle size and large surface area. XRD and BET results revealed the small crystallite and particle size of spinel mixed oxides. The small crystallite size of spinel mixed oxides nano-structures contributes to increased photocatalytic activity by increasing the surface area of photocatalyst, decreasing the chance of reunion of charge carriers. It is observed that these binary oxide nano-structures have potential applications in heterogeneous photo decay of environmental contaminants and can act as propitious materials for resolving environmental issues and establishing green environment.

Electrochemical performances of iron-cobalt oxides nanoparticles loaded crumpled graphene for supercapacitor

Mixed transition metal oxides (MTMOs) have been explored as attractive electrode materials for supercapacitors owing to their higher electronic conductivity and larger specific capacitance compared with simple transition metal oxides. Among MTMOs, cobalt-based binary metal oxides such as Fe-Co oxides have emerged as alternative electrode materials for supercapacitors because they have the advantages of low cost, natural abundance, and environmental friendliness. Recently, graphene-based Fe-Co oxides composites have become of particular interest for their improved electrochemical performance of supercapacitors due to the synergetic effect of both materials. In this study, we present three-dimensional (3D) crumpled graphene (CGR) decorated with Fe-Co oxides nanoparticles to determine which molar ratio of Fe/Co can exhibit higher electrochemical performance. The Fe-Co oxides/CGR composites were synthesized in different molar ratios of Fe/Co via aerosol spray pyrolysis and post heat treatment. Sizes of Fe-Co oxides nanoparticles ranged from 5 to 10 nm when loaded onto 500 nm CGR. The electrochemical properties of the Fe-Co oxides/CGR composites with different molar ratios of Fe/Co were examined. The Fe-Co oxides/CGR electrodes fabricated at the Fe/Co ratio of 0.1 showed the highest performances in the capacitance and electrical conductivity among those electrodes with different molar ratios of Fe/Co.

Towards Novel High-Voltage Cathode Polyanionic Materials: Exploration of the Na2Ο–V2O3–P2O5 System

Polyanionic-type materials have a wider variety of crystal architectures compared to structurally simple transition metal oxides, thus leading to a huge diversity of possible structural features beneficial to some specific electrochemical properties of the batteries [1, 2]. In particular, the 4-, 5-, and 6-fold coordinations and various oxidation states (from +2 to +5) of vanadium in polyanionic compositions may result in the formation of various structural building units, each with its own structural role in the crystal structures. Electrochemically, vanadium also provides the opportunity of exchanging more than one electron per transition metal upon charge/discharge processes. At the same time, natural abundance of sodium and its low cost compared to lithium used in widespread electrode materials have recently attracted a significant attention of the research community to such Na-containing polyanion-based materials [3,4]. However, there are still only 5 reported compositions in the Na2O–V2O3–P2O5 system so far (Fig. 1). Among them, the only NASICON-type Na3V3+ 2(PO4)3 phase with a theoretical capacity of about 118 mAh/g at 3.4 V vs. Na/Na+ has been deeply investigated owing to its stable long-term cyclability and high mobility of sodium ions [5]. It was recently also demonstrated that the metal substitution in NASICON-type phases may lead to increasing of the theoretical gravimetric capacity and the average operating voltage due to the access to the V4+/V5+redox couple [6]. In order to continue further exploration of the Na2O–V2O3–P2O5 system, herein we present new compounds, which were structurally and electrochemically characterized. We also report the results of our investigation of the influence of a substitution of a part of vanadium by aluminum in the Na7V3+ 4(P2O7)4(PO4) and Na3V3+ 2(PO4)3 compositions on the electrochemical behavior of these materials. This work was carried out under the framework of the NAIADES project titled “Na-ion battery demonstration for electric storage” supported by the Regional Council of Picardie and the University of Picardie Jules Verne.

Theoretical Investigation of the Gas-Phase Reaction of CrO+ with Propane

Transition metal oxide cations (e.g., MO+) have been shown to oxidize small alkanes in the gas phase. The chromium oxide cation is of particular interest because it is more reactive than oxides of earlier transition metals but is more selective than oxides of later transition metals. The reaction of CrO+ with propane has been shown to produce a number of products: propanol, propene, ethene, and hydrogen. Few theoretical studies exist for reactions of simple transition metal oxide cations with larger alkanes. We have analyzed the potential energy surfaces associated with the reaction of CrO+ with propane using two DFT methods, B3LYP and M06-L. Energetically viable reaction paths leading to each experimentally observed product have been characterized. Each reaction path begins with formation of a reactive intermediate in which either an α- or β-hydrogen from propane is extracted by the oxygen atom of CrO+. While pathways leading to formation of hydrogen and ethene were found to occur on a single spin surface, energetically viable pathways to forming propanol and propene require a transition from the quartet spin surface to the sextet surface. The minimum-energy crossing points between the quartet and sextet surfaces were found to be well below the energy level of the reactants and structurally resemble the initial reactive intermediates.

ChemInform Abstract: Novel Features of Multiferroic and Magnetoelectric Ferrites and Chromites Exhibiting Magnetically Driven Ferroelectricity

AbstractReview: 86 refs.

Novel features of multiferroic and magnetoelectric ferrites and chromites exhibiting magnetically driven ferroelectricity

A few oxides such as YMnO3, TbMnO3, YMn2O5 and BiFeO3 constituted the small family of well-characterized multiferroics until recently, but this area of research has been enlarged significantly due to the advent of a novel class of oxides exhibiting interesting multiferroic and magnetoelectric properties arising from magnetically induced ferroelectricity. Interestingly, these materials are simple transition metal oxides, most of them possessing the perovskite structure. In this review article, we present the significant features of multiferroic and magnetoelectric ferrites and chromites which owe their ferroelectricity to magnetic interactions. Some of the important systems discussed are BiFeO3 whose properties are affected by magnetic and electric fields, rare-earth orthoferrites LnFeO3 (Ln = Dy, Gd and Sm) and rare-earth orthochromites LnCrO3, where exchange-striction plays a significant role. Perovskite oxides of the type Y(A1−xBx)O3 (A, B = Fe, Cr, Mn) exhibit multiferroic properties, although the existence of these properties in YFeO3 and YCrO3 is in doubt. Such oxides with a non-magnetic rare-earth cation at the A site and two transition metal ions in the B-site permit tuning the transition temperatures by varying the B site ions and their relative proportions or the Ln ion. Multiferroic properties of simple ferrites such as Al(Ga)FeO3 where cation disorder appears to play a role are also discussed. Problems and challenges in this area of research are indicated.

Selective epoxidation of styrene to styrene oxide by TBHP using simple transition metal oxides (NiO, CoO or MoO3) as highly active environmentally-friendly catalyst

Simple transition metal oxides, such as NiO, CoO or MoO3, etc. show high catalytic activity for the selective epoxidation of styrene to styrene oxide by TBHP. The order of choice for different transition metal oxides for epoxidation is NiO > CoO > MoO3 > Cr2O3 > Fe2O3 > ZnO ⩾ U3O8 >> TiO2 >> MnO2.

Oxidation kinetics of Ni metallic films: Formation of NiO-based resistive switching structures

Resistive switching controlled by external voltage has been reported in many Metal/Resistive oxide/Metal (MRM) structures in which the resistive oxide was simple transition metal oxide thin films such as NiO or TiO 2 deposited by reactive sputtering. In this paper, we have explored the possibility to form NiO-based MRM structures from the partial oxidation of a blanket Ni metallic film using a Rapid Thermal Annealing route, the remaining Ni layer being used as bottom electrode. X-ray diffraction was used to apprehend the Ni oxidation kinetics while transmission electron microscopy enabled investigating local microstructure and film interfaces. These analyses have especially emphasized the predominant role of the as-deposited Ni metallic film microstructure (size and orientation of crystallites) on (i) oxidation kinetics, (ii) NiO film microstructural characteristics (crystallite size, texture and interface roughness) and (iii) subsequent electrical behavior. On this latter point, the as-grown NiO films were initially in the low resistance ON state without the electro-forming step usually required for sputtered films. Above the threshold voltage varying from 2 to 5 V depending on oxidation conditions, the Pt/NiO/Ni MRM structures irreversibly switched into the high resistance OFF state. This irreversibility is thought to originate in the microstructure of the NiO films that would cause the difficulty to re-form conductive paths.

Defect CHEMISTRY and Charge TRANSPORT in SrBi2Nb2O9

Equilibrium dc conductivity and thermopower measurements at 650–800°C on undoped and 1% acceptor-doped SrBi2Nb2O9, SBN, indicate that the n-type conductivity is similar to that of a simple transition metal oxide that contains 1–2% donor excess. The donor content is attributed to the presence of Bi+3 on Sr+2 sites in the perovskite-like layers of the structure. These centers arise from cation place exchange between these ions in the alternating layers of the crystal. This exchange is apparently not completely self-compensating, and there is local charge compensation in each layer. While the equilibrium conductivity of SrBi2Ta2O9, SBT, is dominated by ionic conduction in the Bi layers, in SBN conduction by electrons in the perovskite-like layers prevails. The difference in behavior is attributed to the expected smaller band gap of the niobate. The electron mobility in SBN is extremely small, of the order of 10−5 cm2/v · sec at 750°C, and is highly activated with an activation energy of about 1.6 eV. The resulting low mobility at ambient temperatures is proposed as the basis for the observed resistance to ferroelectric fatigue. Reports of metallic Bi on the surface of SBT and SBN by XPS analysis are shown to result from the highly reducing atmosphere of the XPS apparatus.

Orbital moment determination of simple transition metal oxides using magnetic X-ray diffraction

Non-resonant magnetic X-ray scattering (NRXMS) is a unique tool allowing the separation of the spin and orbital moment density contributions to the total magnetization density. This method has been successfully applied to the simple transition metal oxides: MnO, CoO and CuO. It is common habit to consider the orbital moment of these oxides to be quenched by the cubic crystal electric field. We do, however, observe non-vanishing orbital moments in the case of CoO and CuO. The partial re-establishment of the orbital moment is related to spin-orbit coupling.

Mechano-catalytic overall water splitting on some mixed oxides

Simple transition metal oxides such as NiO, Co 3O 4, Fe 3O 4 and Cu 2O were found to catalytically decompose water into H 2 and O 2 by mechanical energy. The reaction is regarded as “mechano-catalytic” overall water splitting” and is a quite novel catalytic reaction. In this paper, some general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO 4 (A=Fe, Co, Ni and Cu, etc., B=W, Mo), are shown. AWO 4 (A=Fe, Co, Ni and Cu) decomposed water into H 2 and O 2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO 4 (A=Fe, Co, Ni) also decomposed water into H 2 and O 2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed.

Chemisorption and the electronic structure of transition metal oxides and transition metals bonded to oxide surfaces

Abstract Some simple transition metal oxides such as NiO have incomplete atomic subshells and yet are highly insulating. This implies a high degree of electronic localization and also indicates that the chemical bonds are saturated. In this respect these oxides are similar to alkaline earth oxides such as MgO. The analogy extends to their surface properties. MgO and NiO, for example, are both good catalysts although a pure, perfect surface of either seems inactive. It is argued that defects or impurities are required to activate the perfect surface and that catalytic properties relate weakly, at best, to the nature of the cation. These oxides are contrasted with the more studied industrial catalyst which consists of a group of transition metal ions bonded to an oxide surface. The electronic structure properties which determine the behaviour of such catalysts are explored in terms of the unrestricted Hartree-Fock model augmented with explicit inclusion of correlation. The results obtained produce a satisfactory band structure and describe surface prupcrties adequately.