Healing the structural defects of spinel MnFe_(2)O_(4) to enhance the electrocatalytic activity for oxygen reduction reaction

Spinel metal oxides containing Mn,Co,or Fe(AB_(2)O_(4),A/B=Mn/Fe/Co)are one of the most promising nonPt electrocatalysts for oxygen reduction reaction(ORR)in alkaline conditions.However,the low conductivity of metal oxides and the poor intrinsic activities of transition metal sites lead to unsatisfactory ORR performance.In this study,eutectic molten salt(EMS)treatment is employed to reconstruct the atomic arrangement of MnFe_(2)O_(4)electrocatalyst as a prototype for enhancing ORR performance.Comprehensive analyses by using XAFS,soft XAS,XPS,and electrochemical methods reveal that the EMS treatment reduces the oxygen vacancies and spinel inverse in MnFe_(2)O_(4)effectively,which improves the electric conductivity and increases the population of more catalytically active Mn^(2+)sites with tetrahedral coordination.Moreover,the enhanced Mn-O interaction after EMS treatment is conducive to the adsorption and activation of O_(2),which promotes the first electron transfer step(generally considered as the ratedetermining step)of the ORR process.As a result,the EMS treated MnFe_(2)O_(4)catalyst delivers a positive shift of 40 mV in the ORR half-wave potential and a two-fold enhanced mass/specific activity.This work provides a convenient approach to manipulate the atomic architecture and local electronic structure of spinel oxides as ORR electrocatalysts and a comprehensive understanding of the structureperformance relationship from the molecular/atomic scale.

Microwave-assisted exploration of the electron configuration-dependent electrocatalytic urea oxidation activity of 2D porous NiCo_(2)O_(4) spinel

Urea holds promise as an alternative water-oxidation substrate in electrolytic cells.High-valence nickelbased spinel,especially after heteroatom doping,excels in urea oxidation reactions(UOR).However,traditional spinel synthesis methods with prolonged high-temperature reactions lack kinetic precision,hindering the balance between controlled doping and highly active two-dimensional(2D)porous structures design.This significantly impedes the identification of electron configuration-dependent active sites in doped 2D nickel-based spinels.Herein,we present a microwave shock method for the preparation of 2D porous NiCo_(2)O_(4)spinel.Utilizing the transient on-off property of microwave pulses for precise heteroatom doping and 2D porous structural design,non-metal doping(boron,phosphorus,and sulfur)with distinct extranuclear electron disparities serves as straightforward examples for investigation.Precise tuning of lattice parameter reveals the impact of covalent bond strength on NiCo_(2)O_(4)structural stability.The introduced defect levels induce unpaired d-electrons in transition metals,enhancing the adsorption of electron-donating amino groups in urea molecules.Simultaneously,Bode plots confirm the impact mechanism of rapid electron migration caused by reduced band gaps on UOR activity.The prepared phosphorus-doped 2D porous NiCo_(2)O_(4),with optimal electron configuration control,outperforms most reported spinels.This controlled modification strategy advances understanding theoretical structure-activity mechanisms of high-performance 2D spinels in UOR.

Effects of iron oxide on crystallization behavior and spatial distribution of spinel in stainless steel slag

Chromium plays a vital role in stainless steel due to its ability to improve the corrosion resistance of the latter.However,the re-lease of chromium from stainless steel slag(SSS)during SSS stockpiling causes detrimental environmental issues.To prevent chromium pollution,the effects of iron oxide on crystallization behavior and spatial distribution of spinel were investigated in this work.The results revealed that FeO was more conducive to the growth of spinels compared with Fe2O3 and Fe3O4.Spinels were found to be mainly distrib-uted at the top and bottom of slag.The amount of spinel phase at the bottom decreased with the increasing FeO content,while that at the top increased.The average particle size of spinel in the slag with 18wt%FeO content was 12.8μm.Meanwhile,no notable structural changes were observed with a further increase in FeO content.In other words,the spatial distribution of spinel changed when the content of iron oxide varied in the range of 8wt%to 18wt%.Finally,less spinel was found at the bottom of slag with a FeO content of 23wt%.

Unveiling the geometric site dependent activity of spinel Co_(3)O_(4)for electrocatalytic chlorine evolution reaction

Spinel cobalt oxide(Co_(3)O_(4)),consisting of tetrahedral Co^(2+)(CoTd)and octahedral Co^(3+)(CoOh),is considered as promising earth-abundant electrocatalyst for chlorine evolution reaction(CER).Identifying the catalytic contribution of geometric Co site in the electrocatalytic CER plays a pivotal role to precisely modulate electronic configuration of active Co sites to boost CER.Herein,combining density functional theory calculations and experiment results assisted with operando analysis,we found that the Co_(Oh) site acts as the main active site for CER in spinel Co_(3)O_(4),which shows better Cl^(-)adsorption and more moderate intermediate adsorption toward CER than CoTd site,and does not undergo redox transition under CER condition at applied potentials.Guided by above findings,the oxygen vacancies were further introduced into the Co_(3)O_(4) to precisely manipulate the electronic configuration of Co_(Oh) to boost Cl^(-)adsorption and optimize the reaction path of CER and thus to enhance the intrinsic CER activity significantly.Our work figures out the importance of geometric configuration dependent CER activity,shedding light on the rational design of advanced electrocatalysts from geometric configuration optimization at the atomic level.

Striking Stabilization Effect of Spinel Cobalt Oxide Oxygen Evolution Electrocatalysts in Neutral pH by Dual-Sites Iron Incorporation

Developing stable and efficient nonprecious-metal-based oxygen evolution catalysts in the neutral electrolyte is a challenging but essential goal for various electrochemical systems.Particularly,cobalt-based spinels have drawn a considerable amount of attention but most of them operate in alkali solutions.However,the frequently studied Co-Fe spinel system never exhibits appreciable stability in nonbasic conditions,not to mention attract further investigation on its key structural motif and transition states for activity loss.Herein,we report exceptional stable Co-Fe spinel oxygen evolution catalysts(~30%Fe is optimal)in a neutral electrolyte,owing to its unique metal ion arrangements in the crystal lattice.The introduced iron content enters both the octahedral and tetrahedral sites of the spinel as Fe^(2+)and Fe^(3+)(with Co ions having mixed distribution as well).Combining density functional theory calculations,we find that the introduction of Fe to Co_(3)O_(4)lowers the covalency of metal-oxygen bonds and can help suppress the oxidation of Co^(2+/3+)and 0^(2-).It implies that the Co-Fe spinel will have minor surface reconstruction and less lattice oxygen loss during the oxygen evolution reaction process in comparison with Co_(3)O_(4)and hence show much better stability.These findings suggest that there is still much chance for the spinel structures,especially using reasonable sublattices engineering via multimetal doping to develop advanced oxygen evolution catalysts.

The Spectral Characterization of Blue Spinel and Other Blue Gemstones with the Alexandrite Effect

In gemmology,the term“Alexandrite effect”is used to describe colour change phenomenon when a gemstone is observed under different light sources,usually between daylight and incandescent light.The definition of the Alexandrite effect is constantly being broadened with new discovery of gem resource.The traditional definition of the Alexandrite effect attributing the colour change phenomenon to the presence of two maximum transmission regions and a maximum absorption region in the absorption spectra.In this study,7 blue spinels and 5 blue gemstones(including tanzanite,kyanite,fluorite,and 2 sapphires)showing the Alexandrite effect were investigated.The goal is to explain the cause of blue-to-violet Alexandrite effect and the spectral features causing such colour change.In the UV-Vis spectra,all samples showed a maximum absorption peak in the range of 534-610 nm,within the green region to orange region.The traditional explanation of green to red Alexandrite effect required a transmission window in the red region;however,some of our samples did not show this transmission window and the blue-to-violet Alexandrite effect was still visible.Therefore,it is incomplete to explain the mechanism of the Alexandrite effect according to their characteristic absorption spectra,a systematic study based on modern colour science and colour perception in human vision is required to elucidate the blue-to-violet Alexandrite effect.

Effect of Sc_2O_3 addition on densification and microstructure of different spinelized magnesium aluminate spinels

The densification and microstructure of different spinelized magnesium aluminate spinels（MAS） were studied adding Sc_2O_3 as additive. Sintered products were then characterized in terms of densification, phase analysis, quantitative elemental analysis and microstructure. The results show that Sc_2O_3 is found to be beneficial for the densification of MAS. Sc_2O_3 has a more significant effect on the densification of partially spinelized MAS batch than that of fully spinelized MAS batch. At the sintering temperature of 1650 °C, the bulk density of sintered products of partially spinelized powders increases by 0.243 g/cm3 as the Sc_2O_3 content increases from 0 to 4%（mass fraction） and that of fully spinelized powder increases by 0.14 g/cm3. Compared with the sintered samples prepared from the fully spinelized powder, the sintered samples using the partially spinelized powders as raw materials have more compact microstructures.

固体废弃物铝灰和粉煤灰原位合成Spinel-Sialon复相材料的研究

本文利用铝灰和粉煤灰为原料,经原位铝热还原氮化法合成了Spinel-Sialon复相材料。通过XRD、SEM、EDS等分析手段,研究了合成温度和还原剂铝的添加量对合成产物物相及微观形貌的影响。结果表明:合成Spinel-Sialon的优化工艺参数为铝的添加量为过量100%、合成温度为1550℃,保温时间3 h,合成得到发育良好的柱状β-Sialon及八面体形的镁铝尖晶石。合成温度、还原剂铝的添加量均是影响氮化产物的重要因素。随着温度的升高或还原剂铝的添加量增多,Al2O3越来越少,β-Sialon和镁铝尖晶石均增多,且β-Sialon的Z值增大,MgAl2O4转变成富铝尖晶石。

活性CP-Spinel复合生物材料的研究

采用Ｘ射线衍射、扫描电镜和差热分析等手段，研究了钙磷化合物－镁铝尖晶石（ＣＰ－Ｓｐｉｎｅｌ）复合生物材料的微观结构、力学性能和生物学特性。结果表明，Ｓｐｉｎｅｌ的加入显著地提高ＣＰ材料的力学性能，在高温下它还阻止磷酸钙发生相转变，从而保证了该材料的生物活性及适合于人体骨需求的力学性能．ＣＰ－Ｓｐｉｎｅｌ材料具有很好的生物相容性，无毒无刺激性，溶血指数小于２％。

Spinel增强HAP·TCP复合生物材料研究

采用化学共沉淀法制得羟基磷灰石(HAP)粉和铝镁尖晶石(Spinel)粉,并以HAP粉体和Spinel粉体为原料采用粉末冶金方法制得HAP·TCF-Spinel复合生物材料。采用红外光谱分析、X射线衍射、透射电镜、扫描电镜、金相、力学性能测试和蛋白质吸附实验等对上述合成的材料进行了表征。微观结构表明HAP·TCP与Spinel两相分布均匀,且界面结合良好。该复合材料具有良好的抗弯强度(σ抗弯)和抗压强度(σ抗压)。当HAP的含量为62.5wt％时其抗弯强度和抗压强度分别达到σ抗弯=212MPa,σ抗压=352MPa。蛋白质吸附实验表明,HAP·TCP-S-Spinel复合生物材料对白蛋白和血清蛋白具有较强的吸附能力。

Fabrication and characterization of electrodeposited nanocrystalline Ni-Fe alloys for NiFe_2O_4 spinel coatings

Nanocrystalline Ni-Fe FCC alloy coatings with Fe content of 1.3%-39%（mass fraction） were fabricated on the nickel substrates using a DC electrodeposition technique. The crystal structure, lattice strain, grain size and lattice constant of the Ni-Fe alloy coatings were studied by X-ray diffraction technique. The chemical composition and surface morphology of the FCC Ni-Fe alloy coatings were investigated with the energy dispersive X-ray spectroscopy（EDS） and atomic force microscopy（AFM）. The results show that the Fe content of the Ni-Fe alloy coatings has a great influence on the preferred orientation, grain size, lattice constant and lattice strain. FCC Ni-Fe alloy coatings exhibit preferred orientations of（200） or（200）（111）. With an increase of Fe content, the preferred growth orientation of（200） plane is weakened gradually, while the preferred growth orientation of（111） increases. An increase of the Fe content in the range of 1.3%-25%（mass fraction） results in a significant grain refinement of the coatings. Increasing the Fe content beyond 25% does not decrease the grain size of FCC Ni-Fe alloys further. The lattice strain increases with increasing the Fe content in the FCC Ni-Fe alloys. Since the alloys with Fe content not less than 25% has similar grain size（~11 nm）, the increase in the lattice strain with the increase of Fe content cannot be attributed to the change in the grain size.

Two-step sintering of magnesium aluminate spinels and their corrosion in Na_3AlF_6-AlF_3-CaF_2-Al_2O_3 bath

New types of refractory materials need to be developed for designing the man-made ledge of the Hall-Heroult cell for aluminum electrolysis, which are currently constructed by frozen ledge.Magnesium aluminate spinel （MAS） as potential candidate materials was prepared by two-step sintering. The densification and grain growth of the MAS wereinvestigatedbytheArchimedes drainage method and scanning electron microscope （SEM）. All the specimens were corroded in aNa3AlF6-AlF3-CaF2-Al2O3bath to assess the corrosion resistance. The results show that a MAS material with a high relative density of 99.2% and ahomogeneous microstructure is achieved under two-step sintering conditions. The corrosion mechanisms of MAS inNa3AlF6-AlF3-CaF2-Al2O3 bathare mainly proposed by dissolution of MAS, formation of aluminum oxide, and diffusion of fluorides. The MAS prepared by two-step sintering exhibits good corrosion resistance to theNa3AlF6-AlF3-CaF2-Al2O3bath.

Spinel Castables for Steel Ladle Lining:In-Situ Versus Preformed

The paper discusses the difference in the formulation concepts of alumina - spinel （spinel containing ） and alumina - magnesia （ spin, el forming） castables and the influence on their physical properties. The individual property profile is discussed with respect to the requirements of refactory lining materials for the different zones of a steel ladle.

Ni/Al_2O_3 catalysts derived from spinel NiAl_2O_4 for low-temperature hydrogenation of maleic anhydride to succinic anhydride

Ni/Al2O3 catalysts were derived from spinel NiAl2O4 with different Ni content ((2.5, 5 and 7.5) wt%). The catalysts were obtained by H-2 reduction and were investigated for the low-temperature hydrogenation of maleic anhydride (MA) to produce succinic anhydride (SA). The characterization results showed that Ni-0 active sites were mainly derived during the H2 reduction from spinel NiAl2O4 Among the catalysts studied, employing the optimum preparation and reaction conditions with Ni(5%)/Al2O3 yielded the highest catalytic performance. A near-100% conversion of MA and similar to 90% selectivity to SA were achieved at 120 degrees C and 0.5 MPa of H-2 with a weighted hourly space velocity (MA) of 2 h(-1). (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Effect of Ultrafine Spinel Sources on Slag Resistance and Microstructure of Alumina-spinel Castables

In order to clarify the effect of ultrafine spinel sources on slag resistance and microstructure of alumina -spinel castables,using tabular alumina and spinel as coarse aggregates,tabular alumina powders,spinel powders,calcium aluminate cement,spinel containing cement,spinel micro-powder and reactive alumina ultrafines as matrix,alumina-spinel castables used for RH snorkels were prepared by changing the particle size and sources of preformed spinel.The effects of different ultrafine spinel sources (CMA72,spinel micro-powder) on the properties of alumina-spinel castables were investigated.Thermal shock resistance and slag resistance of specimens were compared by the residual strength rate (1 100 ℃,air cooling 1 cycle) and static crucible method.The microstructure and the slag corrosion resistance mechanism of the specimens were analyzed by SEM and EDS.The result shows that slag resistance of alumina-spinel castables can be improved by adding ultrafine preformed spinel,such as CMA72,and spinel micro-powder.The introduction of ultra-fine preformed spinel has little effect on HMOR of alumina-spinel castables,but has negative effect on TSR.ultra-fine and dispersive preformed spinel in the matrix and fine microstructure are the main reasons for the improvement of slag resistance of castables.

Feasibility of aluminum recovery and MgAl_2O_4 spinel synthesis from secondary aluminum dross

The feasibility of aluminum recovery from secondary aluminum dross by extraction with NaOH solution and the subsequent synthesis of MgAl_2O_4 spinel by sintering the extracted slag were studied. The extraction percentage of soluble aluminum from the dross reached 80% at a temperature of 353 K, liquid-to-solid ratio of 12 mL·g^(-1), stirring speed of 300 r·min^(-1), and an extraction time of 15 min; the hydrolysis percentage of AlN reached 40% with an extraction time of 30 min. The activation energies of the soluble aluminum and AlN extracted from the dross were 7.15 and 8.98 kJ·mol^(-1), respectively, indicating that their kinetics were controlled by outer diffusion without a product layer. The extracted slag was sintered in the temperature range 1373–1773 K; MgAl_2O_4 spinel with a compressive strength as high as 69.4 MPa was produced in the sample sintered at 1673 K for 3 h. This value exceeds the threshold(40 MPa) prescribed by the National Standard for the Magnesia and Magnesia-alumina Refractory Bricks of China(GB/T 2275-2007). These results establish the effectiveness of aluminum recovery from secondary aluminum dross and subsequent MgAl_2O_4 spinel synthesis.

Effect of FeO on the formation of spinel phases and chromium distribution in the CaO-SiO_2-MgO-Al_2O_3-Cr_2O_3 system

Synthetic slag samples of the CaO-SiO2-MgO-A1203-Cr203 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction （XRD） and scanning electron microscopy （SEM） equipped with energy-dispersive spectroscopy （EDS）, as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250℃ with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.

Spinel lithium titanate (Li_4Ti_5O_(12)) as novel anode material for room-temperature sodium-ion battery

This is the first time that a novel anode material, spinel Li4Ti5O12 which is well known as a ＂zero-strain＂ anode material for lithium storage, has been introduced for sodium-ion battery. The Li4Ti5O12 shows an average Na storage voltage of about 1.0 V and a reversible capacity of about 145 mAh/g, thereby making it a promising anode for sodiumion battery. Ex-situ X-ray diffraction （XRD） is used to investigate the structure change in the Na insertion/deinsertion process. Based on this, a possible Na storage mechanism is proposed.

Synthesis and electrochemical properties of dual doped spinels LiNi_xAl_yMn_(2-x-y)O_4 via facile novel chelated sol–gel method as possible cathode material for lithium rechargeable batteries

LiMnOand LiNiAlyMnO（x= 0.50;y = 0.05-0.50） powders have been synthesized via facile solgel method using Behenic acid as active cheiating agent.The synthesized samples are subjected to physical characterizations such as thermo gravimetric analysis（TG/DTA）,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,field-emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM） and electrochemical studies viz.,galvanostatic cycling properties,electrochemical impedance spectroscopy（EIS） and differential capacity curves（dQ/dE）.Finger print XRD patterns of LiMnOand LiNiAlMnOfortify the high degree of crystallinity with better phase purity.FESEM images of the undoped pristine spinel illustrate uniform spherical grains surface morphology with an average particle size of 0.5 μm while Ni doped particles depict the spherical grains growth（50nm） with ice-cube surface morphology.TEM images of the spinel LiMnOshows the uniform spherical morphology with particle size of（100 nm） while low level of Al-doping spinel（LiNio.5Alo.05Mn1.45O4） displaying cloudy particles with agglomerated particles of（50nm）.The LiMnOsamples calcined at 850℃ deliver the discharge capacity of 130 mAh/g in the first cycle corresponds to 94%coiumbic efficiency with capacity fade of 1.5 mAh/g/cycle over the investigated 10 cycles.Among all four dopant compositions investigated,LiNiAlMnOdelivers the maximum discharge capacity of 126 mAh/g during the first cycle and shows the stable cycling performance with low capacity fade of 1 mAh/g/cycle（capacity retention of 92%） over the investigated 10 cycles.Electrochemical impedance studies of spinel LiMnOand LiNiAlMnOdepict the high and low real polarization of 1562 and 1100 Ω.

Studies on the Influence of Sintering Temperature on Crystalline Structures of Mg-Al Spinel Synthesized by Waste Aluminum Slag

Mg-Al spinel is synthesized by using industrial waste-residue and basic magnesium carbonate in the aluminum factory as the main raw materials. The influence of sintering temperature on crystalline structure and microstructure of Mg-Al spinel has been mainly discussed. The crystalline structure of sample is characterized by using XRD, SEM and relevant analytical software. The experimental results show that compared to the conventional synthetic method, the application of waste aluminum slag as the raw material can greatly decrease the synthetic tem-perature. The content of Mg-Al spinel first increases and then decreases with the rise of sintering temperature, and its purity can reach as high as 96wt% at 1550 ℃, which is therefore determined to be the optimum synthetic temperature. SEM observations demonstrate that as the rise of sintering temperature, the grain of Mg-Al spinel grows up obviously with typical octahedral characteristic appearance.