Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4-δ Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution.

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese (Mn) doping method to decrease the concentration of oxygen vacancy (VO) and form the Mn-O structure adjacent octahedral sites in spinel NiCo2O4-δ (NiMn1.5Co3O4-δ), which highly enhanced the activity and stability of spinel NiCo2O4-δ with a low overpotential (η) of 280 mV at j=10 mA cm-2 and long-term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4-δ is more stable due to strong Mn-O bond and shows synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4-δ after Mn doping. More importantly, the highly hydrogen bonding between Mn-O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

Recent Advances on Spinel Zinc Manganate Cathode Materials for Zinc-Ion Batteries.

Zinc metal is abundant in nature, non-toxic, harmless, and cheap. Zinc-ion batteries (ZIBs) have also emerged as the times require, which has attracted scholars' research interest. In the zinc-ion batteries, the cathode material is indispensable. Manganese oxides are widely used in electrode materials because of their various valence states (+2, +3, +4, +7). ZnMn2 O4 (ZMO) is a mixed metal oxide with a spinel structure similar to LiMn2 O4 . Due to the synergistic effect of Zn and Mn, it has the advantages of high theoretical capacity. In recent years, researchers have gradually applied ZnMn2 O4 to zinc ion batteries. In order to obtain high-energy-density zinc ion batteries, it is also very important to match electrolytes with a wide operating voltage window and develop a highly reversible anode. In the first instance, we investigate the research progress of spinel ZnMn2 O4 as a reliable candidate material for zinc ion batteries. Later on, we review the optimization and modification measures of anode and electrolyte to improve the electrochemical properties of spinel ZnMn2 O4 . On this basis, we propose the reasonable research direction and development prospects for this material. It is hoped that there will be a help to researchers in this field.

Effect of praseodymium in cation distribution, and temperature-dependent magnetic response of cobalt spinel ferrite nanoparticles.

This work reports cation distribution, magnetic, structural, and morphological studies of rare-earth Pr doped cobalt ferrite nanoparticles CoFe2-xPrxO4(x= 0, 0.02, 0.04, 0.06 at%) fabricated by sol-gel auto-combustion method. X-ray diffraction analysis, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier-transform infrared (FTIR) microscopy were utilized to study the structural and morphological characteristics of the prepared samples. Rietveld refinement by the Material Analyses Using Diffraction (MAUD) software showed the formation of mono-phase cubic spinel structure with Fd-3m space group; however, there was a trace of impure PrFeO3phase for the sample CoFe1.96Pr0.04O4(x= 0.06). Cation distribution was inferred from the XRD patterns using MAUD program. FESEM analysis revealed the spherical-shaped particles with dimensions close to the data extracted from XRD analysis and HRTEM images confirmed it. FTIR measurements revealed the presence of two prominent stretching vibrational modes confirming the successful formation of ferrite spinel structure. Magnetic properties of the nanoparticles were measured at two different temperatures 300 K and 10 K. For the low temperature of 10 K a high sensitive measurement method as Superconducting Quantum Interference Device (SQUID) magnetometry was used and Vibrating Sample Magnetometer (VSM) recorded the magnetic data at 300 K. Comparison of the magnetic results exhibited a significant enhancement with temperature drop due to the reduction in thermal fluctuations. Paramagnetic nature of rare-earth ions may be the main reason forMSdecrement from 76 emu g-1(x= 0.0) to 60 emu g-1(x= 0.02) at 300 K. At 10 K, the estimated cation distribution played a vital role in justification of obtained magnetic results. All the obtained data showed that the synthesized magnetic nanoparticles can be implemented in permanent magnet industry and information storage fields, especially when it comes to lower temperatures.

UV light assisted photocatalytic degradation of textile waste water by Mg0.8-xZnxFe2O4 synthesized by combustion method and in-vitro antimicrobial activities.

In this paper, Magnesium Zinc Ferrite (MZF) nanoparticles (Mg0.8-xZnxFe2O4, where x = 0.2, 0.4 and 0.6) are successfully fabricated by combustion process. The prepared nanoparticles are characterized through XRD, FTIR, UV, SEM, EDS and TEM. It has been confirmed that the samples produced cubic spinel structure with crystal size in the range of 13-15 nm. From the ultraviolet spectrum, the optical band gap is calculated which ranges from 5.6 to 4.6 eV. TEM micrographs confirm the nanocrystalline nature of combustion derived ferrite nanoparticles with average particle diameter of 7-28 nm. Antibacterial studies confirmed that the nanoparticles are toxic to Pseudomonas aeruginosa consists of greatest zone of inhibition of 25 mm. The antibacterial and photocatalytic studies exhibited improved activity which is strongly influenced by the zinc doping. Photocatalytic degradation study reveal that the prepared nanoparticles function as perfect catalyst for degradation of Methylene Blue (MB) dye and Textile Dyeing Waste Water (TDWW) under UV light, thus revealing their potential usage on organic pollutants.

Annealing Temperature Effects on Humidity Sensor Properties for Mg0.5W0.5Fe2O4 Spinel Ferrite.

The effects of annealing temperature on the structural, physical and humidity sensing properties of stoichiometric Mg0.5W0.5Fe2O4 spinel ferrite are investigated. In order to highlight the influence of sintering temperature on the structural, magnetic and electrical properties, ferrite samples were sintered for 2 h at 850 °C, 900 °C, 950 °C, 1000 °C and 1050 °C and the physical properties and humidity influence on magnesium-tungsten ferrite materials were analyzed. X-ray diffraction investigations confirmed the formation of magnesium-tungsten ferrite in the analyzed samples. SEM micrographs revealed the influence of annealing temperature on the microstructures of the samples and provided information related to their porosity and crystallite shape and size. This material, treated at different temperatures, is used as an active element in the construction of capacitive and resistive humidity sensors, whose characteristics were also investigated in order to determine the most suitable sintering temperature.

A Simple Gas-Solid Treatment for Surface Modification of Li-Rich Oxides Cathodes.

Li-rich layered oxides with high capacity are expected to be the next generation of cathode materials. However, the irreversible and sluggish anionic redox reaction leads to the O2 loss in the surface as well as the capacity and voltage fading. In the present study, a simple gas-solid treatment with ferrous oxalate has been proposed to uniformly coat a thin spinel phase layer with oxygen vacancy and simultaneously realize Fe-ion substitution in the surface. The integration of oxygen vacancy and spinel phase suppresses irreversible O2 release, prevents electrolyte corrosion, and promotes Li-ion diffusion. In addition, the surface doping of Fe-ion can further stabilize the structure. Accordingly, the treated Feox-2 % cathode exhibits superior capacity retention of 86.4 % and 85.5 % at 1 C and 2 C to that (75.3 % and 75.0 %) of the pristine sample after 300 cycles, respectively. Then, the voltage fading is significantly suppressed to 0.0011 V per cycle at 2 C especially. The encouraging results may play a significant role in paving the practical application of Li-rich layered oxides cathode.

Spinel-Type Materials Used for Gas Sensing: A Review.

Demands for the detection of harmful gas in daily life have arisen for a period and a gas nano-sensor acting as a kind of instrument that can directly detect gas has been of wide concern. The spinel-type nanomaterial is suitable for the research of gas sensors because of its unique structure. However, the existing instability, higher detection limit, and operating temperature of the spinel materials limit the extension of the spinel material sensor. This paper reviews the research progress of spinel materials in gas sensor technology in recent years and lists the common morphological structures and material sensitization methods in combination with previous works.

An Ultra-Sensitive Electrochemical Sensor for the Detection of Carcinogen Oxidative Stress 4-Nitroquinoline N-Oxide in Biologic Matrices Based on Hierarchical Spinel Structured NiCo2O4 and NiCo2S4; A Comparative Study.

Various factors leads to cancer; among them oxidative damage is believed to play an important role. Moreover, it is important to identify a method to detect the oxidative damage. Recently, electrochemical sensors have been considered as the one of the most important techniques to detect DNA damage, owing to its rapid detection. However, electrode materials play an important role in the properties of electrochemical sensor. Currently, researchers have aimed to develop novel electrode materials for low-level detection of biomarkers. Herein, we report the facile hydrothermal synthesis of NiCo2O4 micro flowers (MFs) and NiCo2S4 micro spheres (Ms) and evaluate their electrochemical properties for the detection of carcinogen-causing biomarker 4-nitroquinoline n-oxide (4-NQO) in human blood serum and saliva samples. Moreover, as-prepared composites were fabricated on a glass carbon electrode (GCE), and its electrochemical activities for the determination of 4-NQO were investigated by using various electrochemical techniques. Fascinatingly, the NiCo2S4-Ms showed a very low detection limit of 2.29 nM and a wider range of 0.005 to 596.64 µM for detecting 4-NQO. Finally, the practical applicability of NiCo2S4-Ms in the 4-NQO spiked human blood serum and saliva samples were also investigated.

Mn2NiO4 spinel catalyst for high-efficiency selective catalytic reduction of nitrogen oxides with good resistance to H2O and SO2 at low temperature.

Mn-Ni oxides with different compositions were prepared using standard co-precipitation (CP) and urea hydrolysis-precipitation (UH) methods and optimized for the selective catalytic reduction of nitrogen oxides (NOx) by NH3 at low temperature. Mn(2)Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH (with Mn:Ni molar ratio of 2:1) catalysts showed almost identical selective catalytic reduction (SCR) catalytic activity, with about 96% NOx conversion at 75°C and ~99% in the temperature range from 100 to 250°C. X-ray diffraction (XRD) results showed that Mn(2)Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH catalysts crystallized in the form of Mn2NiO4 and MnO2-Mn2NiO4 spinel, respectively. The latter gave relatively good selectivity to N2, which might be due to the presence of the MnO2 phase and high metal-O binding energy, resulting in low dehydrogenation ability. According to the results of various characterization methods, it was found that a high density of surface chemisorbed oxygen species and efficient electron transfer between Mn and Ni in the crystal structure of Mn2NiO4 spinel played important roles in the high-efficiency SCR activity of these catalysts. Mn(2)Ni(1)Ox catalysts presented good resistance to H2O or/and SO2 with stable activity, which benefited from the Mn2NiO4 spinel structure and Eley-Rideal mechanism, with only slight effects from SO2.

Manipulating Layered P2@P3 Integrated Spinel Structure Evolution for High-Performance Sodium-Ion Batteries.

Structural evolution of the cathode during cycling plays a vital role in the electrochemical performance of sodium-ion batteries. A strategy based on engineering the crystal structure coupled with chemical substitution led to the design of the layered P2@P3 integrated spinel oxide cathode Na0.5 Ni0.1 Co0.15 Mn0.65 Mg0.1 O2 , which shows excellent sodium-ion half/full battery performance. Combined analyses involving scanning transmission electron microscopy with atomic resolution as well as in situ synchrotron-based X-ray absorption spectra and in situ synchrotron-based X-ray diffraction patterns led to visualization of the inherent layered P2@P3 integrated spinel structure, charge compensation mechanism, structural evolution, and phase transition. This study provides an in-depth understanding of the structure-performance relationship in this structure and opens up a novel field based on manipulating structural evolution for the design of high-performance battery cathodes.

Microstructure Characteristics of Cathode Materials for Rechargeable Magnesium Batteries.

Rechargeable magnesium batteries (RMBs) that use pure Mg or Mg alloy as anode and materials allowing Mg ions to insert/extract as cathode have many advantages such as high energy density, environmental friendliness, low cost, and safety of handling. RMBs are regarded as a promising candidate for portable power sources and heavy load energy devices. However, there are still some technological issues impeding their commercial application. The most important issue is the absence of applicable cathode materials because of the high charge density, strong polarization effect, and very slow insertion/extraction speed of Mg2+ ions. In recent years, the research reports on the cathode materials of RMBs have increased significantly. Here, an extensive number of research papers are reviewed in terms of the microstructure characteristics of cathode materials for RMBs. The status and issues of cathode materials are analyzed and discussed in detail. The future development directions and perspectives are prospected for providing an understanding of the related research activities on RMBs.

A density functional theory investigation of the electronic structure and spin moments of magnetite.

We present the results of density functional theory (DFT) calculations on magnetite, Fe3O4, which has been recently considered as electrode in the emerging field of organic spintronics. Given the nature of the potential applications, we evaluated the magnetite room-temperature cubic [Formula: see text] phase in terms of structural, electronic, and magnetic properties. We considered GGA (PBE), GGA + U (PBE + U), and range-separated hybrid (HSE06 and HSE(15%)) functionals. Calculations using HSE06 and HSE(15%) functionals underline the impact that inclusion of exact exchange has on the electronic structure. While the modulation of the band gap with exact exchange has been seen in numerous situations, the dramatic change in the valence band nature and states near the Fermi level has major implications for even a qualitative interpretation of the DFT results. We find that HSE06 leads to highly localized states below the Fermi level while HSE(15%) and PBE + U result in delocalized states around the Fermi level. The significant differences in local magnetic moments and atomic charges indicate that describing room-temperature bulk materials, surfaces and interfaces may require different functionals than their low-temperature counterparts.

Chemical Stability of High-Entropy Spinel in a High-Pressure Pure Hydrogen Atmosphere.

This paper focuses on high-entropy spinels, which represent a rapidly growing group of materials with physicochemical properties that make them suitable for hydrogen energy applications. The influence of high-pressure pure hydrogen on the chemical stability of three high-entropy oxide (HEO) sinter samples with a spinel structure was investigated. Multicomponent HEO samples were obtained via mechanochemical synthesis (MS) combined with high-temperature thermal treatment. Performing the free sintering procedure on powders after MS at 1000 °C for 3 h in air enabled achieving single-phase (Cr0.2Fe0.2Mg0.2Mn0.2Ni0.2)3O4 and (Cu0.2Fe0.2Mg0.2Ni0.2Ti0.2)3O4 powders with a spinel structure, and in the case of (Cu0.2Fe0.2Mg0.2Ti0.2Zn0.2)3O4, a spinel phase in the amount of 95 wt.% was achieved. A decrease in spinel phase crystallite size and an increase in lattice strains were established in the synthesized spinel powders. The hydrogenation of the synthesized samples in a high-pressure hydrogen atmosphere was investigated using Sievert's technique. The results of XRD, SEM, and EDS investigations clearly showed that pure hydrogen at temperatures of up to 250 °C and a pressure of up to 40 bar did not significantly impact the structure and microstructure of the (Cr0.2Fe0.2Mg0.2Mn0.2Ni0.2)3O4 ceramic, which demonstrates its potential for application in hydrogen technologies.

Fabrication of Li4Ti5O12 (LTO) as Anode Material for Li-Ion Batteries.

The most popular anode material in commercial Li-ion batteries is still graphite. However, its low intercalation potential is close to that of lithium, which results in the dendritic growth of lithium at its surface, and the formation of a passivation film that limits the rate capability and may result in safety hazards. High-performance anodes are thus needed. In this context, lithium titanite oxide (LTO) has attracted attention as this anode material has important advantages. Due to its higher lithium intercalation potential (1.55 V vs. Li+/Li), the dendritic deposition of lithium is avoided, and the safety is increased. In addition, LTO is a zero-strain material, as the volume change upon lithiation-delithiation is negligible, which increases the cycle life of the battery. Finally, the diffusion coefficient of Li+ in LTO (2 × 10-8 cm2 s-1) is larger than in graphite, which, added to the fact that the dendritic effect is avoided, increases importantly the rate capability. The LTO anode has two drawbacks. The energy density of the cells equipped with LTO anode is lower compared with the same cells with graphite anode, because the capacity of LTO is limited to 175 mAh g-1, and because of the higher redox potential. The main drawback, however, is the low electrical conductivity (10-13 S cm-1) and ionic conductivity (10-13-10-9 cm2 s-1). Different strategies have been used to address this drawback: nano-structuration of LTO to reduce the path of Li+ ions and electrons inside LTO, ion doping, and incorporation of conductive nanomaterials. The synthesis of LTO with the appropriate structure and the optimized doping and the synthesis of composites incorporating conductive materials is thus the key to achieving high-rate capability. That is why a variety of synthesis recipes have been published on the LTO-based anodes. The progress in the synthesis of LTO-based anodes in recent years is such that LTO is now considered a substitute for graphite in lithium-ion batteries for many applications, including electric cars and energy storage to solve intermittence problems of wind mills and photovoltaic plants. In this review, we examine the different techniques performed to fabricate LTO nanostructures. Details of the synthesis recipes and their relation to electrochemical performance are reported, allowing the extraction of the most powerful synthesis processes in relation to the recent experimental results.

Hydrothermal synthesis of cobalt substitute zinc-ferrite (Co1-xZnxFe2O4) nanodot, functionalised by polyaniline with enhanced photocatalytic activity under visible light irradiation.

Fabrication and development of effective visible-light-responsive photocatalysts are required to tackle critical environmental issues. The aim of this study was to develop a nanocomposite material with improved photocatalytic activity for the degradation of industrial dyes such as Reactive Orange-16 (RO-16), Reactive Blue (RB-222), Reactive Yellow-145 (RY-145), and Disperse Red-1 (DR-1) without the need for a post-separation process after use. Here we report the hydrothermal synthesis of nanodots of Co1-xZnxFe2O4 (x = 0.3, 0.5 and 0.7), coated with polyaniline, by in situ polymerization. The Co1-xZnxFe2O4 nanodots, coated with polyaniline (PANI) nanograins, facilitated optical properties by easily capturing visible light. X-ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) images have confirmed the single-phase spinel structure of Co1-xZnxFe2O4 nanodot and nano-pore size of the Co1-xZnxFe2O4/PANI nanophotocatalyst. The specific surface area of the Brunauer-Emmett-Teller (BET) of the Co1-xZnxFe2O4/PANI photocatalyst was determined to be 24.50 m2/g by multipoint analysis. The final Co1-xZnxFe2O4/PANI (x = 0.5) nanophotocatalyst showed high efficiency in the catalytic degradation of toxic dyes (∼98% within 5 min), with good mechanical stability and recyclability under visible light irradiation. The nanophotocatalyst was re-used and its efficiency was largely maintained, even after seven cycles (∼82%) of degradation. The effects of various parameters, such as initial dye concentration, nanophotocatalyst concentration, initial pH of dye solution, and reaction kinetics were studied. According to the Pseudo-first-order kinetic model, photodegradation data followed the first-order reaction rate (R2 > 0.95) of degradation of dyes. In conclusion, a simple and low-cost synthesis process, speedy degradation and excellent stability of polyaniline-coated Co1-xZnxFe2O4 nanophotocatalyst could be used as a promising photocatalyst for dye-wastewater treatment.

Fabrication of Co3O4/Co3S4/CNTs for photocatalytic treatment of wastewater under xenon lamp.

The current study is about the synthesis of nanoparticles (NPs) of cobalt oxide (CO) and cobalt sulfide (CS) followed by their nanocomposites as CO/CS and CO/CS/CNT by ultrasonication approach. The addition of carbon-based materials in the oxides and sulfides enhances their performance by developing physico-chemical interactions. Prepared NPs were utilized for the photodegradation of organic contaminants. The characteristics, as well as the efficiency of the prepared samples, have been systematically examined by X-ray diffraction (XRD) technique, Fourier transform infrared spectroscopy (FTIR), and UV-vis spectroscopy. Photocatalytic activities of bare samples and synthesized nanocomposites were tested for the degradation of methyl orange (MO) using a xenon lamp. The percentage degradation of dye was 24.14%, 57.94%, 71.66%, and 85.04% in the presence of CO, CS, CO/CS, and CO/CS/CNT, respectively. Crystal violet (CV), Rhodamine B (rho-B), and industrial wastewater were also degraded by the ternary composite. The comparative studies showed the best performance of CO/CS/CNT, which enhanced the generation of electron-hole pairs by absorption of photons of incoming radiations, increased charge separation, and maximum surface area for adsorption.

Highly Active Catalytic CO2 Hydrogenation to Lower Olefins via Spinel ZnGaOx Combined with SAPO-34.

A key primary method for creating a carbon cycle and carbon neutrality is the catalytic hydrogenation of CO2 into high value-added chemicals or fuels. In this work, ZnGaOx oxides were prepared by parallel co-precipitation and physically mixed with SAPO-34 molecular sieves prepared by hydrothermal synthesis to produce ZnGaOx /SAPO-34 bifunctional catalysts, which were evaluated for the catalytic synthesis of lower olefins (C2 = -C4 = ) from carbon dioxide hydrogenation. It was demonstrated that the reaction process requires oxygen defect activation, synergistic hydrogenation, and CO2 alkaline adsorption of ZnGaOx . The spinel structure of ZnGaOx has more abundant oxygen defects and alkaline adsorption sites than the ZnGaOx solid solution, which effectively enhances the catalytic performance. The CO2 conversion was 28.52%, the selectivity of C2 = -C4 = in hydrocarbons reached 70.01%, and the single-pass yield of C2 = -C4 = was 10.95% at 370 °C, 3.0 MPa, and 4800 mL/gcat /h.

Synthesis of high-voltage cathode material using the Taylor-Couette flow-based co-precipitation method.

LiNi0.5Mn1.5O4 (LNMO), a next-generation high-voltage battery material, is promising for high-energy-density and power-density lithium-ion secondary batteries. However, rapid capacity degradation occurs due to problems such as the elution of transition metals and the generation of structural distortion during cycling. Herein, a new LNMO material was synthesized using the Taylor-Couette flow-based co-precipitation method. The synthesized LNMO material consisted of secondary particles composed of primary particles with an octahedral structure and a high specific surface area. In addition, the LNMO cathode material showed less structural distortion and cation mixing as well as a high cyclability and rate performance compared with commercially available materials.

Sulfidation of CoCuOx Supported on Nickel Foam to Form a Heterostructure and Oxygen Vacancies for a High-Performance Anion-Exchange Membrane Water Electrolyzer.

Anion-exchange membrane water electrolyzer (AEMWE) is attracting attention for hydrogen production owing to its ability to employ nonprecious metal catalysts and high energy conversion efficiency. Spinel-structured transition metal oxides exhibit excellent potential in oxygen evolution reaction (OERs). Nevertheless, the research on highly active and durable spinel-structured electrodes for the anodic OER of AEMWE is deficient. Herein, a self-supported S-CoCu oxide/nickel foam (S-CoCuOx/NF) anode was synthesized through a two-step method (electrodeposition and sulfidation). The formation of abundant oxygen vacancies and heterostructure collaboratively enhances the electron and mass transfer, resulting in an overpotential of 313 mV at 100 mA cm-2 for OER. For the lab-scale AEMWE system with the S-CoCuOx/NF anode, a current density of 1 A cm-2 was obtained at 1.87 V (cell voltage) with high durability for 110 h (1 A cm-2) at 60 °C. The results will provide insights into developing the spinel structure-derived anode for high-performance AEMWE.

Synthesis, Structure, and Physicochemical Characteristics of Zn1-xRexCr2Se4 Single Crystals.

This study aimed to obtain and investigate ZnCr2Se4 single crystals doped with rhenium. The single crystals were obtained by applying chemical vapour transport. An X-ray study confirmed the cubic (Fd3¯m) structure of the tested crystals. Thermal, magnetic, electrical, and specific heat measurements accurately determined the physicochemical characteristics, which revealed that the obtained single crystals are p-type semiconductors with antiferromagnetic order below the Néel temperature TN = 21.7 K. The Debye temperature had a value of 295 K. The substitution of Re-paramagnetic ions, possessing a screened 5d-shell, in place of Zn-diamagnetic ions, caused an increase in the activation energy, Fermi energy, and Fermi temperature compared to the pure ZnCr2Se4. The boost of the dc magnetic field induced a shift of TN towards lower temperatures and a spin fluctuation peak visible at Hdc = 40 and 50 kOe. The obtained single crystals are thermally stable up to 1100 °C.