O4 Spinel Research Articles

Investigation on the microstructure and magnetic properties of Mg(Ga2−xFex)O4 spinel ferrites

Investigation on the microstructure and magnetic properties of Mg(Ga2−xFex)O4 spinel ferrites

Synthesis and Characterization of Rare Earth Doped Ferrite / Polyethylene Oxide Nanocomposites

Nano-sized Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 spinel ferrite nanoparticles were synthesized employing the micro-emulsion synthesis method. Polyethylene oxide was prepared through in-situ polymerization route. The ferrite-polymer nanocomposites have been synthesized by combining Li0.5Ni0.48Tb0.02Dy0.1Fe1.9O4 ferrite with polyethylene oxide polymer. Spectral, structural, morphological, and dielectric properties of the prepared nano-ferrite powders as well as nanocomposites were investigated by “X-ray diffraction analysis” (XRD), “scanning electron microscopy” (SEM), “Fourier transform infrared spectroscopy” (FTIR) and dielectric measurements. XRD analysis confirmed the synthesis of single-phase spinel structure only. The dielectric parameter was augmented with an increase of ferrite amount. FTIR spectra confirmed the existence of interactions between polyethylene oxide and ferrite particles. SEM study revealed that the nanocomposites comprised core/shell structure and inhomogeneous distribution of grain size. The dielectric parameters such as “real part of dielectric constant” (?), “imaginary part of dielectric constant” (?"), “tan loss”, “AC conductivity” and “quality factor” were investigated in the required range of frequency; that is, 1 MHz – 3 GHz. The peaking behavior has been observed for real (??) and “imaginary (???) parts of dielectric constant” and “dielectric loss” (tan?). “The peaking behavior” was detected beyond 1.5 GHz. A decrease in “the dielectric constants” and “dielectric loss” was found to with the increasing frequency. Dielectric parameters have been well elucidated by explaining “Debye-type relaxation model” in agreement with two layer “Koop's phenomenological theory”. The present investigated samples might have potential applications in high frequency.

Hexaamminecobalt(III)] Dichloride Permanganate—Structural Features and Heat-Induced Transformations into (CoII,MnII)(CoIII,MnIII)2O4 Spinels

We synthesized and characterized (IR, Raman, UV, SXRD) hexaamminecobalt(III) dichloride permanganate, [Co(NH3)6]Cl2(MnO4) (compound 1) as the precursor of Co–Mn–spinel composites with atomic ratios of Co:Mn = 1:1 and 1:3. The 3D−hydrogen bond network includes N–HO–Mn and N–HCl interactions responsible for solid-phase redox reactions between the permanganate anions and ammonia ligands. The temperature-limited thermal decomposition of compound 1 under the temperature of boiling toluene (110 ∘C) resulted in the formation of (NH4)4Co2Mn6O12. which contains a todorokite-like manganese oxide network (MnII4MnIII2O1210−). The heat treatment products of compounds 1 and [Co(NH3)5Cl](MnO4)2 (2) synthesized previously at 500 ∘C were a cubic and a tetragonal spinel with Co1.5Mn1.5O4 and CoMn2O4 composition, respectively. The heating of the decomposition product of compounds 1 and 2 that formed under refluxing toluene (a mixture with an atomic ratio of Co:Mn = 1:1 and 1:2) and after aqueous leaching ((NH4)4Co2Mn6O12, 1:3 Co:Mn atomic ratio in both cases) at 500 ∘C resulted in tetragonal Co0.75Mn2.25O4 spinels. The Co1.5Mn1.5O4 prepared from compound 1 at 500 ∘C during the solid-phase decomposition catalyzes the degradation of Congo red with UV light. The decomposition rate of the dye was found to be nine times faster than in the presence of the tetragonal CoMn2O4 spinel prepared in the solid-phase decomposition of compound 2. The todorokite-like intermediate prepared from compound 1 under N2 at 115 ∘C resulted in a 54 times faster degradation of Congo red, which is a great deal faster than the same todorokite-like phase that formed from compound 2 under N2.

Multi-scale designed CoxMn3–xO4 spinels: Smart pre-catalysts towards high-efficiency pyrolysis-catalysis recycling of waste plastics

In this work, multiscale designed 3-dimensional (3D) rose-like CoxMn3–xO4 spinel smart pre-catalysts that can self-convert into the targeted active site-rich Co/MnO catalysts were developed for the high-efficiency conversion of waste plastics. At a pre-catalyst to plastic weight ratio of 1:14, the carbon nanotube composites (CNCs) and H2 yield can reach 41 wt% and 36 mmol·g˗1pla., while the specific CNCs and H2 yield can be as high as 7.48 g˗1cat. and 634 mmol·g˗1pla.·g˗1cat. The latter is more than one order of magnitude higher than reported in the literature. Density functional theory calculations indicate that the Co/MnO catalyst exhibits excellent activity in the dissociation of alkanes (e.g., CH4). The resulting CNCs demonstrated excellent discharge capability and extended cycling performance when used as a lithium-ion battery anode. This work revealed an innovative recipe and novel insight for developing advanced catalyst materials as the next generation catalysts for the conversion of waste plastics.

Microwave assisted preparation of LiFePO4/C coated LiMn1.6Ni0.4O4 for Li-ion batteries with superior electrochemical properties

LiMn1.6Ni0.4O4 (LMNO) spinel is a promising cobalt-free electrode for high potential applications. However, its chemical stability against electrolytes is relatively poor. Inorganic coatings have widely used to achieve superior chemical and electrochemical properties. A promising example is LiFePO4/C (LFP/C) olivine coated LMNO spinel particles, in which olivine provides a high chemical stability. Chemical incompatibility between them during atmospheric synthesis conditions makes the process extremely challenging. Herein, we propose a simple and practical route to prepare LFP/C-coated LMNO using microwave irradiation. This process significantly improves the crystallographic order of the spinel structure and provides sufficient physical interaction between both materials while avoiding side reactions. Li-ion battery using LFP/C-coated LMNO electrode exhibits a higher discharge capacity at 25°C and 60°C than those of uncoated spinel. Moreover, cyclability (up to 500 cycles) at 25°C and C-rate capability performances at 60°C are superior in LFP/C-coated LMNO particles and not possible using uncoated spinel.

Microwave synthesis of nanostructured high entropy spinel

A single-phase high entropy (CoCrFeMnNi)3O4 spinel presenting a cubic structure (Fd-3m) was microwave synthesized by a polymer-based synthesis. The complete synthesis route lasted no longer than 2 h. The high entropy spinels (HES) were characterized by X-ray diffractometry, transmission electron microscopy and diffuse reflectance spectroscopy. The as-synthesized powders yielded nanostructures and the calcination temperature of single-phase formation was observed to be at least 800 °C. The band gap energy of the microwave-irradiated HES was 2.2 eV and 2.45 eV of the conventionally calcined one. These band gap energy values indicate possibilities as a promising catalyst with tunable properties for application in the field of catalytic conversion.

To study the structural, electrical, and magnetic properties of M (M = Mg2+, Mn2+, and Cd2+) doped Cu-Ni-Co-La spinel ferrites

Tertiary Cu0.25Ni0.15M0.25Co0.35La0.15Fe1.85O4 (M = Mg2+, Mn2+, and Cd2+) spinel ferrites powders were prepared using the cost-effective sol-gel auto combustion route. The lattice parameters, absorption and vibrational bands, energy band gap, AC conductivity, and dielectric loss of the as-prepared ferrites were all measured. The Cd2+ doped ferrite has a minimum crystallite size (D) of 50.9 nm, which is smaller compared to Mg2+ and Mn2+ doped ferrites. Furthermore, the X-ray diffraction (XRD), as well as Fourier transform infrared radiation (FTIR) and Raman analysis confirmed the doping of Mg2+, Mn2+, and Cd2+ ions on their respective lattice sites. The resistivity of the divalent ions (Mg2+, Mn2+, and Cd2+) doped ferrites decreased in the para region and increased in the ferro region as the temperature increased. Moreover, the resistivity of the Cd2+ doped ferrite was smaller when compared to the ferrites doped with Mg2+ and Mn2+ ions. From Arrhenius plots, the minimum activation energy (ΔE) 0.8671 eV was observed for Cd2+ doped ferrites. The Cd2+ substituted ferrite also has the smallest AC conductivity and dielectric loss compared to Mg2+ and Mn2+ substituted ferrites. The coercivity and saturation magnetization were 136.41 Oe and 92.29 emu/g for the Cd2+ doped ferrite, respectively. These results suggest that the Cd2+ doped ferrite material could be used in high-frequency and high-power applications.

Room-temperature multiferroicity and magnetoelectric couplings in (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 spinel films

The electric field manipulation of a magnetic order is a key feature of advanced information technologies and the development of room-temperature multiferroic magnetoelectrics remains an important task. In this work, we report novel single-phase magnetoelectric (ME) films consisting of a (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 spinel ferrite. The (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 thin films display a switchable polarization and magnetization with a remnant polarization of about 2.1 µC cm–2 and a remnant magnetization of about 82.0 emu cm–3 at 300 K. Electric field control of magnetism is detected, the magnetization modulation reaches 8.5 % at room temperature with an electric field of 500 kV cm−1, revealing the existence of magnetoelectric coupling. We believe that the substitutions of Al3+ and Mg2+ cations at the spinel sublattices might induce local distortions and local electric field and modulate the superexchange interactions between magnetic ions, which give rise to the ferroelectricity and ME effect in the (Co0.75Al0.25)2(Fe0.75Mg0.25)O4 thin films. The electric field-induced charge modulation may also contribute to the observed magnetoelectric effect, which likely results from the migration and redistribution of oxygen vacancies in the prepared nanofilms. The findings of this work can stimulate research studies on the development of room temperature multiferroics and magnetoelectrics based on the spinel ferrite compounds.

Stabilizing High-Voltage Cathodes via Ball-Mill Coating with Flame-Made Nanopowder Electrolytes.

LiMn1.5Ni0.5O4 (LMNO) spinel has recently been the subject of intense research as a cathode material because it is cheap, cobalt-free, and has a high discharge voltage (4.7 V). However, the decomposition of conventional liquid electrolytes on the cathode surface at this high oxidation state and the dissolution of Mn2+ have hindered its practical utility. We report here that simply ball-mill coating LMNO using flame-made nanopowder (NPs, 5-20 wt %, e.g., LiAlO2, LATSP, LLZO) electrolytes generates coated composites that mitigate these well-recognized issues. As-synthesized composite cathodes maintain a single P4332 cubic spinel phase. Transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) show island-type NP coatings on LMNO surfaces. Different NPs show various effects on LMNO composite cathode performance compared to pristine LMNO (120 mAh g-1, 93% capacity retention after 50 cycles at C/3, ∼67 mAh g-1 at 8C, and ∼540 Wh kg-1 energy density). For example, the LMNO + 20 wt % LiAlO2 composite cathodes exhibit Li+ diffusivities improved by two orders of magnitude over pristine LMNO and discharge capacities up to ∼136 mAh g-1 after 100 cycles at C/3 (98% retention), while 10 wt % LiAlO2 shows ∼110 mAh g-1 at 10C and an average discharge energy density of ∼640 Wh kg-1. Detailed postmortem analyses on cycled composite electrodes demonstrate that NP coatings form protective layers. In addition, preliminary studies suggest potential utility in all-solid-state batteries (ASSBs).

High efficient vanadium extraction from vanadium slag using an enhanced acid leaching-coprecipitation process

Vanadium slag (VS) is a by-product of vanadium titanium magnetite BOF steelmaking process and becomes an important material for vanadium products preparation. Sodium roasting-water leaching is a mainstream process for industrial production, but the water leaching residue (WLR) usually remains 1.0 wt% to 3.0 wt% V2O5, which still has value for recycling extraction of vanadium. In this research, a two-stage leaching process was proposed for high efficient vanadium extraction. The first stage leaching was sodium roasting-water leaching for vS and the second stage leaching was sulfuric acid leaching for WLR. As a result, the total leaching efficiency of vanadium can reach as high as 98.52%, which was 7.72% higher than that of conventional water leaching efficiency of vanadium (90.80%). The mechanism analysis indicates that the CaNaFe2Si4O12 and NaFeSi2O6 water-insoluble phases formed and covered on (Mn,Fe)(V,Cr)2O4 spinel surface during roasting, hindering vanadium oxidation and dissolution. The structures of wrapping phases and spinel can be effectively destroyed by acid leaching, releasing vanadium in WLR. By using hydrolytic precipitation of iron ions in acid leachate, 99.78% of vanadium can be recovered as V-Fe precipitation slag, which contains 6.83 wt% V2O5 and can be cycled back to sodium roasting process. The V-Fe slag belongs to amorphous precipitation, illustrating that residual vanadium in WLR can be changed to unstable compound by acid leaching and hydrolysis precipitation, which makes vanadium easier to extract during sodium roasting-water leaching process. This research has the advantages of enhanced reuse of V resource in the WLR, achieving a high V recovery. The short process has a strong adaptability and can provide technical support for efficient V extraction from vS.

Quantitative Evaluation of the Activity of Nickel Ion Site of LiNi0.5Mn1.5O4 Spinel for Oxygen Evolution Reaction

Suntivich et al. found a volcano relationship between the eg occupancy in perovskite oxide and OER activity. eg filling of ~ 1.2 is the optimum value1. Nevertheless, some materials do not follow this trend. A typical example is oxides containing a high valence Ni(4+) state. To elucidate the effect of high-valence Ni on OER activity, it is necessary to evaluate the OER activity of materials with stable Ni in a high oxidation state (4+). However, in case of the perovskite family, the formation of Ni4+ requires calcination under high oxygen partial pressures (60-200 bar). In contrast, LiNi0.5Mn1.5O4 (LNMO) with a spinel structure is known that lithium ions are desorbed by oxidation to produce tetravalent nickel ions quantitatively. Therefore, by using this material as an oxygen-evolving electrode, it is possible to quantitatively evaluate the activity of tetravalent nickel ions. Herein, we report the OER activity of nickel-manganese spinel, in which Ni4+ was stable up to the bulk. LiNi0.5Mn1.5O4 powder was synthesized as follows. Stoichiometric amounts of LiNO3, Ni(NO3)2.6H2O, and Mn(NO3)2.6H2O were dissolved in ultrapure water. A four-to-five-fold molar excess of citric acid was added while stirring. This solution was heated at 400 °C to obtain the precursor. The obtained powder was calcined at 800 °C for 12 h and at 700 °C for 48 h under pure O2.Various levels of chemical delithiation were achieved by reacting LiNi0.5Mn1.5O4 with nitronium tetrafluoroborate in acetonitrile solution for 48 h at 25 ºC. The degree of delithiation was controlled by changing the ratio of LiNi0.5Mn1.5O4 to NO2BF4. The suspension of LiNi0.5Mn1.5O4 and NO2BF4 was stirred for 48 h to obtain a uniform particle composition. Subsequently, the suspension was filtered, thoroughly washed with acetonitrile at least three times, and dried overnight in a vacuum oven. Then, chemical composition was determined using inductively coupled plasma optical emission spectrometry, X-ray diffraction (XRD) patterns were collected in BL02B2 at SPring-8, Japan. XAS was conducted for Mn and Ni K-edges, XAS for Mn, Ni L-edges, and O K-edge was also conducted. This study focused on the electrocatalytic activity of LixNi0.5Mn1.5O4 spinels with different lithium contents. The lithium (x) content in LixNi0.49Mn1.51O4 was controlled by topochemical delithiation using NO2BF4 in an acetonitrile solution. Upon applying this approach, nickel changed from the divalent to tetravalent state, while the tetravalent state of manganese was maintained. The OER activity was found to increase with decreasing x. x = 0.00 showed the highest OER activity. The Tafel slopes indicated that the RDS changed from OH− adsorption to proton transfer from OH*; thus, the OER kinetics was enhanced. The XAS spectra of Ni and O indicated that the presence of Ni4+ caused a downshift in the unoccupied Ni 3d state and decreased the energy barrier of charge transfer from the oxygen intermediate species to the metal active site; hence, the OER activity was enhanced. This study revealed the mechanism underpinning the high OER activity of high-valence Ni(4+) and also provided a approach for the development of highly active catalyst materials, namely, topochemical delithiation. Acknowledgement This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y., Science 2011, 334, 1383-1385. Ren Y. et al., ACS Appl. Energy Mater. 2021 4 (10), 10731-10738

(Invited) Non-Conventional, Multimodal Strategies to Create Synergistic Effects on Electrode-Electrolyte Interphase Stabilities in Lithium-Ion Batteries

Ni- or Mn-rich cathode materials have attracted great interest for electric vehicle (EV) applications due to their high gravimetric and volumetric energy densities and low- or cobalt-free compositions. For example, Ni-rich LiNi1-xCox/2Mnx/2O2 (NMC) layered cathodes can deliver > 200 mAh/g when they operate at above 4.3 Vvs.Li. Cobalt-free LiNi0.5Mn1.5O4 (LNMO) spinel operates at around 4.75 Vvs.Li and delivers an excellent rate capability due to three-dimensional Li-diffusion pathways in its lattice. However, due to lack of high-voltage stabilities of conventional, carbonate-based electrolytes, such high-voltage operation (> 4.3 Vvs.Li) led to unwanted electrolyte oxidation and simultaneous parasitic reactions occurring at CEI. Different types of cathodes have their own failure mechanisms which are often associated with side reactions occurring at solid-electrolyte interphase (SEI) on graphite anodes. This was possible because the reaction by-products from CEI could migrate and attack SEI layers on anodes.To address the high-voltage related issues, various approaches have been proposed such as tuning chemical compositions of cathode active materials, surface modification of cathodes or anodes, and stabilizing the CEI or SEI using electrolyte additives. In literature, however, there was no single solution that can resolve all the complex issues occurring in the high-voltage battery cells. For example, coated layers on active materials are prone to fail during long-term cycling due to mechanical failure (e.g., crack and pulverization) of active materials. In addition, not only active materials but carbon conductors (e.g., acetylene black) inside a cathode leads to the electrolyte oxidation, prompted by its high electronic conductivity and large surface area. Considering that such parasitic reactions originate from CEI and propagate to anode SEI, there is a dire need of multimodal strategies that can create synergistic effect on stabilizing the electrode-electrolyte interphases in cell level.In this presentation, I will introduce non-conventional strategies that can effectively enhance electrode-electrolyte interphase stabilities and improve full-cell (i.e., using graphite anodes) performances. First, formation of self-healing CEI on cathode active materials will be demonstrated. The interface of LNMO spinel oxide will be passivated by Ti-enriched shell via sacrificial transition metal dissolutions and suppress the side reactions occurring at CEI. Second, a strategy for passivating both cathode active materials and carbon black conductor by using functional binders will be demonstrated. Since the binder coating will be performed in-situ during a slurry preparation, no extra process will be required while implementing this approach to a cell manufacturing. Finally, solid-electrolyte implemented NMC or LNMO cathodes will be demonstrated as an effective approach to stabilize the high-voltage performance by offering good Li-ion conduction pathways at CEI layer.Improvement mechanism of each approach will be also presented based on physical and electrochemical characterization data. Electrochemical impedance spectroscopy (EIS) revealed a suppression of CEI interfacial resistance during cycling, suggesting the enhanced stability of the multifunctional CEI. Various microscopy and spectroscopy data acquired from cycle-aged CEI and graphite SEI will be corelated to the cell performance data and identify the CEI property-performance relationship. These unique multifunction CEI strategies will be applicable to various cathode materials for the next-generation Li-ion batteries. Figure 1

Conformal LiF Stabilized Interfaces via Electrochemical Fluorination on High Voltage Spinel Cathodes (≈4.9 V) for Lithium‐Ion Batteries

AbstractThe high voltage LiNi0.5Mn1.5O4 (LNMO) spinel is one of the promising cathodes for the lithium‐ion batteries due to its high energy densities, good rate performance. However, its high operating potential (≈4.75 V) causes extensive oxidation of conventional carbonate electrolytes, resulting an unstable and thick cathode electrolyte interphase (CEI) layer with a large irreversible capacity and low coulombic efficiency. Herein, this work reports the formation of thin LiF stabilized interfaces on LNMO via electrochemical fluorination that significantly improves the cycling stability and enhanced the capacity. An electrochemically induced conformal LiF layer acts as a part of a robust CEI by reducing the leakage of electrons and allowing the conduction of Li ions through it. Because of the robust LiF stabilized CEI, LNMO delivers a discharge capacity of ≈148.5 and ≈117.1 mAh g−1 at 0.1 and 1 C rate, respectively. It exhibits excellent cyclability with 80% capacity retention (CR) after 600 cycles in lithium‐half cell and ≈90% CR after 200 cycles in full cell with only 0.03% and 0.05% capacity decay per cycle in conventional carbonate electrolytes without additives. Such an excellent electrochemical performance could lead to the potential development of high energy density batteries with high voltage cathodes for grid‐based applications.

The Synthesis of Cu–Mn–Al Mixed-Oxide Combustion Catalysts by Co-Precipitation in the Presence of Starch: A Comparison of NaOH with Organic Precipitants

Cu–Mn mixed oxides are well known as active combustion catalysts. The common method for their synthesis is based on co-precipitation, with NaOH as a precipitant, and is burdened with the possibility of introducing undesired Na contamination. This work describes the use of two organic bases, tetrabutylammonium hydroxide and choline hydroxide, as precipitating agents in a novel alkali-free route for Cu–Mn–Al catalyst synthesis. To obtain fine crystalline precursors, which are considered advantageous for the preparation of active catalysts, co-precipitation was carried out in the presence of starch gel. Reference materials prepared with NaOH in the absence of starch were also obtained. Mixed oxides were produced by calcination at 450 °C. The precursors contained MnCO3 doped with Cu and Al, and an admixture of amorphous phases. Those prepared in the presence of starch were less crystalline and retained biopolymer residues. The combustion of these residues during calcination enhanced the formation of larger amounts of the Cu1.5Mn1.5O4 spinel phase, with better crystallinity in comparison to catalysts prepared from conventionally synthesized precursors. Tests of toluene combustion demonstrated that the catalysts prepared with starch performed better than those obtained in starch-free syntheses, and that the mixed oxides obtained by the alkali-free route were more active than catalysts prepared with NaOH. Catalytic data are discussed in terms of property–performance relationships.

Mechanism of Iron Integration into LiMn1.5Ni0.5O4 for the Electrocatalytic Oxygen Evolution Reaction

Spinel-type LiMn1.5Ni0.5O4 has been paid temendrous consideration as an electrode material because of its low cost, high voltage, and stabilized electrochemical performance. Here, we demonstrate the mechanism of iron (Fe) integration into LiMn1.5Ni0.5O4 via solution methods followed by calcination at a high temparature, as an efficient electrocatalyst for water splitting. Various microscopic and structural characterizations of the crystal structure affirmed the integration of Fe into the LiMn1.5Ni0.5O4 lattice and the constitution of the cubic LiMn1.38Fe0.12Ni0.5O4 crystal. Local structure analysis around Fe by extended X-ray absorption fine structure (EXAFS) showed Fe3+ ions in a six-coordinated octahedral environment, demonstrating incorporation of Fe as a substitute at the Mn site in the LiMn1.5Ni0.5O4 host. EXAFS also confirmed that the perfectly ordered LiMn1.5Ni0.5O4 spinel structure becomes disturbed by the fractional cationic substitution and also stabilizes the LiMn1.5Ni0.5O4 structure with structural disorder of the Ni2+ and Mn4+ ions in the 16d octahedral sites by Fe2+ and Fe3+ ions. However, we have found that Mn3+ ion production from the redox reaction between Mn4+ and Fe2+ influences the electronic conductivity significantly, resulting in improved electrochemical oxygen evolution reaction (OER) activity for the LiMn1.38Fe0.12Ni0.5O4 structure. Surface-enhanced Fe in LiMn1.38Fe0.12Ni0.5O4 serves as the electrocatalytic active site for OER, which was verified by the density functional theory study.

Stabilizing High-Voltage LiNi0.5 Mn1.5 O4 Cathodes for High Energy Rechargeable Li Batteries by Coating With Organic Aromatic Acids and Their Li Salts.

Here, three types of surface coatings based on adsorption of organic aromatic acids or their Li salts are applied as functional coating substrates to engineer the surface properties of high voltage LiNi0.5 Mn1.5 O4 (LNMO) spinel cathodes. The materials used as coating include 1,3,5-benzene-tricarboxylic acid (trimesic acid [TMA]), its Li-salt, and 1,4-benzene-dicarboxylic acid (terephthalic acid). The surface coating involves simple ethanol liquid-phase mixing and low-temperature heat treatment under nitrogen flow. In typical comparative studies, TMA-coated (3-5%) LNMO cathodes deliver >90% capacity retention after 400 cycles with significantly improved rate performance in Li-coin cells at 30 °C compared to uncoated material with capacity retention of ≈40%. The cathode coating also prevents the rapid drop in the electrochemical activity of high voltage Li cells at 55 °C. Studies of high voltage full cells containing TMA coated cathodes versus graphite anodes also demonstrate improved electrochemical behavior, including improved cycling performance and capacity retention, increased rate capabilities, lower voltage hysteresis, and very minor direct current internal resistance evolution. In line with the highly positive effects on the electrochemical performance, it is found that these coatings reduce detrimental transition metal cations dissolution and ensure structural stability during prolonged cycling and thermal stability at elevated temperatures.

Inhibited Cr(VI) formation in Cr2O3-containing refractory castable using reactive MgO as hydraulic binder

Reactive MgO was used in the first time as alternative hydraulic binder of calcium aluminate cement (CAC) to prepare Cr2O3-bearing refractory castable. The formation of Cr(VI), and physical and mechanical properties of MgO-bonded refractory castables after heat-treating were investigated. Microstructural characterization and phase composition analyses on the heat-treated MgO-bonded refractory castable matrices resulted in a comprehensive understanding of the mechanism for the inhibition of Cr(VI), and of the strength development during firing. The results indicate that compared with CAC, Cr(VI) levels were 6.7–28.1 times lower using reactive MgO after firing at 700–1300 °C. The in situ Mg(Cr,Al)2O4 spinel formed from the preferential interactions among MgO and Cr2O3 and Al2O3 would be the main reason leading to the inhibited Cr(VI) formation and strength development during firing.

Tetrahedrally modified MnMe0.1Co1.9O4 (Me = Zn, Mg, Li) spinels for non-enzymatic glucose sensing

• Tetrahedrally modified MnMe 0.1 Co 1.9 O 4 (Me = Zn, Mg, Li) spinels were prepared via the sol–gel synthesis. • The influence of partial substitution of cobalt in MnCo 2 O 4 spinel on physicochemical properties is shown. • MnLi 0.1 Co 1.9 O 4 exhibits the highest glucose-sensing ability among studied samples. In this work, tetrahedrally modified MnMe 0.1 Co 1.9 O 4 (Me = Zn, Mg, Li) spinels were prepared via the sol–gel synthesis method with subsequent ball-milling fragmentation. The prepared samples were evaluated as glucose–sensing catalyst. The reference MnCo 2 O 4 spinel exhibited a sensitivity of 49 µA mM −1 cm −2 and a nonlinearity error of 5.2% in the response range from 0.02 to 1 mM. The partial substitution of cobalt in the reference spinel enhanced the glucose–sensing abilities, and the sample with Li was found to be the most active catalyst, exhibiting a sensitivity of 73.1 µA mM −1 cm −2 . Finally, the proposed material was tested for selectivity in the presence of interfering sucrose.

A new CoFe1.9Li0.1O4 spinel oxide cathode for proton-conducting solid oxide fuel cells

A new spinel oxide CoFe1.9Li0.1O4 (CFLO) has been synthesized as a cathode material for proton-conducting solid oxide fuel cells. CFLO has good structure stability up to 900 °C. In addition, the material can survive in both CO2 and steam-containing atmospheres. Compared with the Li-free sample, the Li-doping strategy significantly regulates the material's electronic structure. The low valence of Li leads to the increased amount of Fe and Co cations with higher valences. Furthermore, doping Li creates more oxygen vacancies at the material surface, which benefits the oxygen reduction reaction (ORR). The improved cathode performance for CFLO has been demonstrated that a cell using CFLO cathode reaches a peak power density of 1052 mW cm−2 at 700 °C. The cell performance is 60% larger than the Li-free cell, and similar results can be detected at other testing temperatures. In addition, the CFLO cell shows good long-term stability in the working condition. This study proposes the Li-doping strategy to modify spinel oxides and also provides a new spinel oxide as a high-performing cathode for H–SOFCs.

Microstructural examination of interactions between chromia‐based refractory and nuclear glass in a melter

AbstractThis study shows the effects of nuclear waste glass production on Monofrax K‐3 refractory corrosion. A continuously fed research‐scale melter containing an Fe‐ and Ni‐rich simulated nuclear waste feed with borosilicate glass‐forming chemicals was cyclically melted at 1150°C and idled at 1050°C for a total of 11 weeks. Chemical maps using scanning electron microscopy show the interactions between the quenched melt and the refractory. Nanoscale X‐ray‐computed tomography was used for a three‐dimensional visualization of certain parts of the interface. Unreacted K‐3 consists of primarily corundum (Al,Cr)2O3 and spinel (Fe2+,Mg)(Al,Cr)2O4 interlocking crystalline phases. Some of the Cr from the refractory interacts with the Ni and Fe from the melt to form a reaction layer comprising (Ni,Fe2+)(Cr,Fe3+)2O4 spinel crystals. Simultaneously, melt components (Na,Si) infiltrate into the refractory. This interaction proceeds at the expense of the integrity of the refractory structure. Intact refractory grains (e.g., (Al,Cr)2O3) as well as the reaction layer itself can lose mechanical integrity and spall off into the melt, especially near the top of the melter. As the reaction layer can be a protective boundary for the refractory against further melt infiltration, a reduction in the reaction layer thickness allows an increase in refractory corrosion.