Ternary Transition Metal Oxides Research Articles

NiCo2O4@TiN Core-shell Electrodes through Conformal Atomic Layer Deposition for All-solid-state Supercapacitors

Ternary transition metal oxides such as NiCo2O4 show great potential as supercapacitor electrode materials. However, the unsatisfactory rate performance of NiCo2O4 may prove to be a major hurdle to its commercial usage. Herein, we report the development of NiCo2O4@TiN core–shell nanostructures for all-solid-state supercapacitors with significantly enhanced rate capability. We demonstrate that a thin layer of TiN conformally grown by atomic layer deposition (ALD) on NiCo2O4 nanofiber arrays plays a key role in improving their electrical conductivity, mechanical stability, and rate performance. Fabricated using the hybrid NiCo2O4@TiN electrodes, the symmetric all-solid-state supercapacitor exhibited an impressive stack power density of 58.205mWcm−3at a stack energy density of 0.061 mWh cm−3. To the best of our knowledge, these values are the highest of any NiCo2O4-based all-solid-state supercapacitor reported. Additionally, the resulting NiCo2O4@TiN all-solid-state device displayed outstanding cycling stability by retaining 70% of its original capacitance after 20,000 cycles at a high current density of 10mAcm−2. These results illustrate the promise of ALD-assisted hybrid NiCo2O4@TiN electrodes within sustainable and integrated energy storage applications.

Thermal stability of mullite RMn2O5 (R = Bi, Y, Pr, Sm or Gd): combined density functional theory and experimental study

Understanding and effectively predicting the thermal stability of ternary transition metal oxides with heavy elements using first principle simulations are vital for understanding performance of advanced materials. In this work, we have investigated the thermal stability of mullite RMn2O5 (R = Bi, Pr, Sm, or Gd) structures by constructing temperature phase diagrams using an efficient mixed generalized gradient approximation (GGA) and the GGA + U method. Simulation predicted stability regions without corrections on heavy elements show a 4–200 K underestimation compared to our experimental results. We have found the number of d/f electrons in the heavy elements shows a linear relationship with the prediction deviation. Further correction on the strongly correlated electrons in heavy elements could significantly reduce the prediction deviations. Our corrected simulation results demonstrate that further correction of R-site elements in RMn2O5 could effectively reduce the underestimation of the density functional theory-predicted decomposition temperature to within 30 K. Therefore, it could produce an accurate thermal stability prediction for complex ternary transition metal oxide compounds with heavy elements.

Modulation of stoichiometry, morphology and composition of transition metal oxide nanostructures through hot wire chemical vapor deposition

Abstract

Thermochemistry of Multiferroic Organic-Inorganic Hybrid Perovskites [(CH3)2NH2][M(HCOO)3] (M = Mn, Co, Ni, and Zn).

Organic-inorganic hybrid materials have enormous potential for applications in catalysis, gas storage, sensors, drug delivery, and energy generation, among others. A class of hybrid materials adopts the ABX3 perovskite topology. We report here the synthesis and characterization of an isostructural series of dense hybrid perovskites, [(CH3)2NH2][M(HCOO)3], with M = Mn, Co, Ni, and Zn. These compounds have shown promising multiferroic behavior. Understanding their stability is crucial for their practical application. We report their formation enthalpies based on direct measurement by room-temperature acid solution calorimetry. The enthalpy of formation of this dimethylammonium metal formate series becomes less exothermic in the order Mn, Zn, Co, Ni. The stability of the hybrid perovskite decreases as the tolerance factor increases, unlike trends seen in inorganic perovskites. However, the trends are similar to those seen in a number of ternary transition metal oxides, suggesting that specific bonding interactions rather than geometric factors dominate the energetics.

In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation.

The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochemical tuning of catalysts via lithium insertion and extraction has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochemical oxidation tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidation. The electrochemically tuned cobalt–nickel–iron oxides grown directly on the three-dimensional carbon fiber electrodes exhibit a low overpotential of 232 mV at current density of 10 mA cm–2, small Tafel slope of 37.6 mV dec–1, and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alkaline medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution associated with the electrochemical oxidation tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size reduction and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications.

Ternary Transition Metal Oxide Nanoparticles with Spinel Structure for the Oxygen Reduction Reaction

AbstractIt is crucial to develop electrocatalysts for the oxygen reduction reaction (ORR) for renewable energy applications. Mixed‐valence transition‐metal oxides with a spinel structure have been explored for this purpose. In this work, we study the influence of the composition of the catalysts (XY2O4, X=Ni, Zn and Y=Co, Mn) on the ORR. The four different types of spinel oxide nanocrystals (NiCo2O4, NiMn2O4, ZnCo2O4, and ZnMn2O4) were synthesized by a simple and scalable method. This allowed for a systematic investigation of the transition‐metal influence on the performance of the ORR. Given the general spinel structure of XY2O4, we systematically changed X (Ni, Zn) and Y (Co, Mn). The effects of the presence of different metals in the spinel oxide on the morphology and electrocatalytic properties of the materials toward the ORR were investigated and compared by using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron microscopy, and voltammetry. In general, cobalt‐based spinel oxides displayed a significant electrocatalytic activity towards the ORR, with Ni‐substituted spinel oxides outperforming their respective Zn‐substituted congeners. These findings may have great impact in the research field of renewable energy.

Asymmetry in band widening and quasiparticle lifetimes inSrVO3: Competition between screened exchange and local correlations from combinedGWand dynamical mean-field theoryGW + DMFT

The very first dynamical implementation of the combined GW and dynamical mean field scheme "GW+DMFT" for a real material was achieved recently [J.M. Tomczak et al., Europhys. Lett. 100 67001 (2012)], and applied to the ternary transition metal oxide SrVO3. Here, we review and extend that work, giving not only a detailed account of full GW+DMFT calculations, but also discussing and testing simplified approximate schemes. We give insights into the nature of exchange and correlation effects: Dynamical renormalizations in the Fermi liquid regime of SrVO3 are essentially local, and nonlocal correlations mainly act to screen the Fock exchange term. The latter substantially widens the quasi-particle band structure, while the band narrowing induced by the former is accompanied by a spectral weight transfer to higher energies. Most interestingly, the exchange broadening is much more pronounced in the unoccupied part of spectrum. As a result, the GW+DMFT electronic structure of SrVO3 resembles the conventional density functional based dynamical mean field (DFT+DMFT) description for occupied states, but is profoundly modified in the empty part. Our work leads to a reinterpretation of inverse photoemission spectroscopy (IPES) data. Indeed, we assign a prominent peak at about 2.7 eV dominantly to eg states, rather than to an upper Hubbard band of t2g character. Similar surprises can be expected for other transition metal oxides, calling for more detailed investigations of the conduction band states.

Composition profiles across MIMs for resistive switching studied by EDS and EELS

Resistive switching in MIM (metal-insulator-metal) stacks is an effect that enables a promising data storage technology which is able to overcome the size limitations of conventional non-volatile memories. The resistive switching effect was already demonstrated for several binary as well as ternary transition metal oxides (TiO2, NiO, SrTiO3, Nb2O5) [1,2]. The current models of the switching mechanisms suggest the important role of defects like oxygen vacancies [3]. Here, we report on the local structural and electronic properties of transition metal oxides embedded in MIM stacks that were obtained by using transmission electron microscopy and electron spectroscopy. We focus on the development of the stoichiometry across the MIM stack for amorphous and partial crystalline niobium oxides. Therefore, electron energy loss spectra (EELS) as well as the energy dispersive X-ray spectra (EDS) were collected on the atomic scale utilizing a nanometer probe in the scanning transmission electron microscope (STEM). The differences in the oxygen content among the electrodes and the concentration profiles at the metal/oxide interfaces in particular were investigated in dependence on the preparation method and on the electrode material. Besides, focusing on the electron loss near edge structure (ELNES) of the oxygen K edge we employed simulations using FEFF9 to describe the modifications of the electronic structure with variations in the oxygen content.

Stoichiometry determined exchange interactions in amorphous ternary transition metal oxides: Theory and experiment

Amorphous transition metal oxides exhibit exotic transport and magnetic properties, while the absence of periodic structure has long been a major obstacle for the understanding of their electronic structure and exchange interaction. In this paper, we have formulated a theoretical approach, which combines the melt-quench approach and the spin dynamic Monte-Carlo simulations, and based on it, we explored amorphous Co0.5Zn0.5O1−y ternary transition metal oxides. Our theoretical results reveal that the microstructure, the magnetic properties, and the exchange interactions of Co0.5Zn0.5O1−y are strongly determined by the oxygen stoichiometry. In the oxygen-deficient sample (y > 0), we have observed the long-range ferromagnetic spin ordering which is associated with the non-stoichiometric cobalt-rich region rather than metallic clusters. On the other hand, the microstructure of stoichiometric sample takes the form of continuous random networks, and no long-range ferromagnetism has been observed in it. Magnetization characterization of experimental synthesized Co0.61Zn0.39O1−y films verifies the relation between the spin ordering and the oxygen stoichiometry. Furthermore, the temperature dependence of electrical transport shows a typical feature of semiconductors, in agreement with our theoretical results.

锂离子电池三元正极材料的研究进展

As the most promising commercial lithium-ion battery, the ternary transition metal oxides Li(Ni,Co,Mn)O2 have been widespread concerned by researchers and companies in recent years. They are expected to become a series of major cathode active material for EV batteries. The latest research progress on Li(Ni,Co,Mn)O2 is reviewed in terms of synthetic methods, property modifications and suitable electrolyte functional additives. Finally, its commercial application prospects are discussed and evaluated.

Evolution of physicochemical and electrocatalytic properties of NiCo2O4 (AB2O4) spinel oxide with the effect of Fe substitution at the A site leading to efficient anodic O2 evolution in an alkaline environment

Within the framework of this work, spinel-type ternary transition metal oxides of nickel, cobalt and iron with the composition FexNi1−xCo2O4 (0 ≤ x ≤ 1) were prepared and tested as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline water electrolysis. The hydroxide precipitation method was used for the synthesis. The morphology, structure and specific surface area of the prepared electrocatalysts were determined by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, the Brunauer Emmet Teller method and X-ray photo electron spectroscopy. The electrochemical properties were tested by thin-film technique on a rotating disk electrode and in a single-cell laboratory water electrolyzer coupled with electrochemical impedance spectroscopy. The OER studies indicate that substitution of Ni by Fe increases the electrocatalytic activity of the resulting material significantly. The highest activity was achieved for x = 0.1. Whereas the current density obtained using a pure nickel anode in the water electrolysis test was 54 mA cm−2 at a cell voltage of 1.85 V, in the case of the anode modified with NiCo2O4 catalyst the value was 87 mA cm−2. Using ternary transition metal oxides in the water electrolysis test and under identical conditions, the catalyst with the highest activity displayed a current density of 115 mA cm−2.

Prediction of Quaternary Spinel Oxides as Li-Battery Cathodes: Cation Site Preference, Metal Mixing, Voltage and Phase Stability

Using first-principles calculations, we explore the quaternary spinel oxides of the 3d transition metal series (Ti, V, Cr, Mn, Fe, Co, Ni) having pairs of transition metals in equal concentrations. We examine several properties of these materials relevant to Li-ion battery cathode applications. By examining cation site preference, delithiation voltage and thermodynamic stability, we predict five new quaternary spinel compounds which show promise as novel cathode materials: LiTiFeO4, LiCrFeO4, LiMnFeO4 and LiFeCoO4 and LiCoNiO4. The predicted compounds have tetrahedral Li/vacancy sublattice for efficient Li-transport, average voltage greater than 4.4 V, and are predicted to be stable ground states on a T = 0 K computed phase diagram. These predictions should be tested experimentally by synthesis and electrochemical measurements of these five compounds. For the lithiated oxides, we find predominant preference for the normal spinel structure (with Li in tetrahedrally coordinated sites), and for most of the delithiated oxides, transition metal cations spontaneously relax to non-spinel octahedral sites. We also find that metal mixing in these spinels is a strong function of charge state: most of the pairs of ternary transition metal oxide spinels tend to mix when lithiated and phase separate when delithiated.

Synthesis of porous CoFe2O4 octahedral structures and studies on electrochemical Li storage behavior

Ternary transition metal oxides are the important alternatives to commercial graphite for future lithium-ion batteries (LIBs). In this work, porous Co2FeO4 octahedral structures were synthesized by annealing the precursor from hydrothermal process, and the electrochemical properties of the samples as anode for LIBs were studied. Electrochemical measurements demonstrate that porous Co2FeO4 structures with octahedral shape display remarkably high discharge capacity, which is even slightly higher than the theoretical value of Co2FeO4. The specific capacity retention of Co2FeO4 porous structure annealed at 700°C reaches ca. 96.4% of that in the first cycle after 50 cycles. It is expected that the as-synthesized porous Co2FeO4 octahedrons can be a promising anode material for LIBs.

Ag2V4O11 nanostructures for highly ethanol sensitive performance

Ag2V4O11 brush-like nanostructures with a large specific surface area have been synthesized by a unique electrochemistry assisted laser ablation in liquids without any template or surfactant in an ambient environment. Considering the large surface-to-volume ratio of the as-synthesized nanostructures, an Ag2V4O11 brush-like nanostructured gas sensor was fabricated and exhibited an excellent performance in sensor response to ethanol concentrations in the range of 10 to 600 ppm under low working temperature. This high response was attributed to the highly crystalline and brush-like surface, which leads to the effective adsorption and desorption, and provides more active sites for gas molecules reacting. These findings show our desire to encourage the synthesis of new nanomaterials, e.g. ternary transition metal oxides, as gas sensors prepared by novel means.

Combined GW and dynamical mean-field theory: Dynamical screening effects in transition metal oxides

We present the first dynamical implementation of the combined GW and dynamical mean-field scheme (“GW + DMFT”) for first-principles calculations of the electronic properties of correlated materials. The application to the ternary transition metal oxide SrVO3 demonstrates that this scheme inherits the virtues of its two parent theories: a good description of the local low-energy correlation physics encoded in a renormalized quasi-particle band structure, spectral weight transfer to Hubbard bands, and the physics of screening driven by long-range Coulomb interactions. Our data is in good agreement with available photoemission and inverse photoemission spectra; our analysis leads to a reinterpretation of the commonly accepted “three-peak structure” as originating from orbital effects rather than from the electron addition peak within the t2g manifold.

Mesoporous VN prepared by solid–solid phase separation

We recently reported a simple route to prepare mesoporous, conducting nitrides from Zn containing ternary transition metal oxides. Those materials result from the condensation of atomic scale voids created by the loss of Zn by evaporation, the replacement of 3 oxygen anions by 2 nitrogen anions, and in most cases the loss of oxygen to form water on the reduction of the transition metal. In this report, we present a different route to prepare mesoporous VN from K containing vanadium oxides. In this case, ammonolysis results in a multiphase solid product that contains VN, and other water soluble compounds such as KOH or KNH2. On removing the K containing products by washing with degassed water, only mesoporous VN remains. VN materials with different pore sizes (10nm–20nm) were synthesized at 600°C by varying the reaction time, while larger pores are obtained at higher temperatures (50nm at 800°C).

Synthesis and characterization of nanostructured CuFe2O4 anode material for lithium ion battery

A nanostructured binary transition metal oxide, copper ferrite (CuFe2O4) is synthesized via polymer-pyrolysis method. The effects of the processing temperature on the particle size and electrochemical performance of the nanostructured CuFe2O4 are investigated. The electrochemical results show that the sample synthesized at 700°C shows the best cycling performance, retaining a specific capacity of 551.9mAh g−1 beyond 100 cycles for lithium ion batteries. The electrode has a good rate capacity within the range of 0.2C–4C. At the highest rate of 4C, the reversible capacity of CuFe2O4 is about 200mAh g−1. It is believed that the ternary transition metal oxide CuFe2O4 is quite acceptable compared with other high performance nanostructured anode materials.

High capacity ZnFe 2O 4 anode material for lithium ion batteries

A nanostructured ternary transition metal oxide, ZnFe 2O 4, is synthesized via the simple polymer pyrolysis method. The characteristics of the material are examined by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical test results show that this method of ZnFe 2O 4 synthesis produces high specific capacities and good cycling performance, with an initial specific capacity as high as 1419.6 mAh g −1 at first discharge that is maintained at over 800 mAh g −1 even after 50 charge–discharge cycles. The electrode also presents a good rate capability, with a high rate of 4 C (1 C = 928 mA g −1), a reversible specific capacity that can be as high as 400 mAh g −1. ZnFe 2O 4 is a potential alternative to high-performance nanostructured anode material in lithium ion batteries.

Ab initio modeling of complex amorphous transition-metal-based ceramics

Binary and ternary amorphous transition metal (TM) nitrides and oxides are of greatinterest because of their suitability for diverse applications ranging from high-temperaturemachining to the production of optical filters or electrochromic devices. However,understanding of bonding in, and electronic structure of, these materials represents achallenge mainly due to the d electrons in their valence band. In the presentwork, we report ab initio calculations of the structure and electronic structure ofZrSiN materials. We focus on the methodology needed for the interpretation andautomatic analysis of the bonding structure, on the effect of the length of thecalculation on the convergence of individual quantities of interest and on the electronicstructure of materials. We show that the traditional form of the Wannier functioncenter-based algorithm fails due to the presence of d electrons in the valenceband. We propose a modified algorithm, which allows one to analyze bondingstructure in TM-based systems. We observe an appearance of valence p states ofTM atoms in the electronic spectra of such systems (not only ZrSiN but alsoNbOx and WAuO), and examine the importance of the p states for the character of the bondingas well as for facilitating the bonding analysis. The results show both the physicalphenomena and the computational methodology valid for a wide range of TM-basedceramics.

High capacity and high rate capability of nanostructured CuFeO 2 anode materials for lithium-ion batteries

Non-toxic, cheap, nanostructured ternary transition metal oxide CuFeO 2 was synthesised using a simple sol–gel method at different temperatures. The effects of the processing temperature on the particle size and electrochemical performance of the nanostructured CuFeO 2 were investigated. The electrochemical results show that the sample synthesised at 650 °C shows the best cycling performance, retaining a specific capacity of 475 mAh g −1 beyond 100 cycles, with a capacity fading of less than 0.33% per cycle. The electrode also exhibits good rate capability in the range of 0.5 C–4 C. At the high rate of 4 C, the reversible capacity of CuFeO 2 is around 170 mAh g −1. It is believed that the ternary transition metal oxide CuFeO 2 is quite acceptable compared with other high performance nanostructured anode materials.