An effective strategy of constructing multi-metallic oxides of ZnO/ CoNiO_(2)/CoO/C microflowers for improved supercapacitive performance

In this work,a new ZnO/CoNiO_(2)/CoO/C metal oxides composite is prepared by cost-effective hydrothermal method coupled with annealing process under N_(2) atmosphere.Notably,the oxidation-defect annealing environment is conducive to both morphology and component of the composite,which flower-like ZnO/CoNiO_(2)/CoO/C is obtained.Benefited from good chemical stability of ZnO,high energy capacity of CoNiO_(2) and CoO and good conductivity of C,the as-prepared sample shows promising electrochemical behavior,including the specific capacity of 1435 C·g^(-1) at 1 A·g^(-1),capacity retention of 87.3%at 20 A·g^(-1),and cycling stability of 90.5%for 3000 cycles at 5 A·g^(-1),respectively.Furthermore,the prepared ZnO/CoNiO_(2)/CoO/C/NF//AC aqueous hybrid supercapacitors device delivers the best specific energy of 55.9 W·h·kg^(-1) at 850 W·kg^(-1).The results reflect that the as-prepared ZnO/CoNiO_(2)/CoO/C microflowers are considered as high performance electrode materials for supercapacitor,and the strategy mentioned in this paper is benefit to prepare mixed metal oxides composite for energy conversion and storage.

Activation of Transition Metal(Fe,Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO_(2) Reduction Reaction

The electrochemical carbon dioxide reduction reaction(CO_(2)RR),which can produce value-added chemical feedstocks,is a proton-coupled-electron process with sluggish kinetics.Thus,highly efficient,cheap catalysts are urgently required.Transition metal oxides such as CoO_(x),FeO_(x),and NiO_(x)are low-cost,low toxicity,and abundant materials for a wide range of electrochemical reactions,but are almost inert for CO_(2)RR.Here,we report for the first time that nitrogen doped carbon nanotubes(N-CNT)have a surprising activation effect on the activity and selectivity of transition metal-oxide(MO_(x)where M=Fe,Ni,and Co)nanoclusters for CO_(2)RR.MO_(x)supported on N-CNT,MO_(x)/N-CNT,achieves a CO yield of 2.6–2.8 mmol cm−2 min−1 at an overpotential of−0.55 V,which is two orders of magnitude higher than MO_(x)supported on acid treated CNTs(MO_(x)/O-CNT)and four times higher than pristine N-CNT.The faraday efficiency for electrochemical CO_(2)-to-CO conversion is as high as 90.3%at overpotential of 0.44 V.Both in-situ XAS measurements and DFT calculations disclose that MO_(x)nanoclusters can be hydrated in CO_(2)saturated KHCO_(3),and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions,which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

Catalysis of Active Carbon Supporting Transition Metal Oxides for Pyrotechnical Reagent with Potassium Perchlorate

In order to improve the pyrotechnical reagent with potassium perchlorate,composite catalyst of active carbon supporting transition metal oxides （TMO）,Fe2O3 and CuO,were prepared and added into pyrotechnical reagent with potassium perchlorate.Accelerating rate calorimeter （ARC） was used to study the catalysis of pyrotechnical reagent which is consisted of potassium perchlorate and composite catalyst.Composite catalyst of both Fe2O3 and CuO supported by active carbon can catalyze pyrotechnical reagent with potassium perchlorate.Furthermore,it can lower the apparent activation energy and accelerate the reaction with a smaller quantity than that with Fe2O3 and CuO.The maximal reaction rate of pyrotechnical reagent with potassium perchlorate mixed with Fe2O3/active carbon and CuO/active carbon is 8.31 min-1 and 9.13 min-1,which is 1.74 times and 1.91 times of pyrotechnical reagent mixed with no catalyst;time to maximal rate was 18.99 min and 1.96 min respectively,which is lower than pyrotechnical reagent mixed with no catalyst by 86.46% and 98.67% ;the apparent activation energy is 368.10 kJ·mol-1 and 325.29 kJ·mol-1,which is lower than pyrotechnical reagent mixed with no catalyst by 31.89% and 39.81% respectively.

MICROSTRUCTURE AND INFRARED EMISSIVITY AT NORMAL TEMPERATURE IN TRANSITIONAL METAL OXIDES SYSTEM CERAMICS

The fabrication of Fe2O3-MnO2-Co2O3-CuO system ceramics, and the composite system ceramics of transitional metal oxides-cordierite and transitional metal oxides-kaolinit are presented in this work. The research was carried out with the main attention to the infrared emissivity in the band of 8 similar to 14 mu m at room temperature, the microstructure of the ceramics and the relation between them. High infrared emissivities exceeding 0.9 in the band of 8 similar to 14 mu m at room temperature were gained in the transitional metal oxide ceramics and the composite system ceramics. It is suggested that the formation of inverse spinels and partially inverse spinels, such as Fe3O4, CoFe2O4, CuFe2O4 and CuMn2O4, is beneficial to the enhancement of the infrared emissivity of the transitional metal oxide ceramics. The transitional metal oxides play an important role in determining the infrared emissivity of the composite system ceramics.

Role of transition metal oxides in g-C_(3)N_(4)-based heterojunctions for photocatalysis and supercapacitors

g-C_(3)N_(4) emerges as a star 2D photocatalyst due to its unique layered structure,suitable band structure and low cost.However,its photocatalytic application is limited by the fast charge recombination and low photoabsorption.Rationally designing g-C_(3)N_(4)-based heterojunction is promising for improving photocatalytic activity.Besides,g-C_(3)N_(4) exhibits great potentials in electrochemical energy storage.In view of the excellent performance of typical transition metal oxides(TMOs)in photocatalysis and energy storage,this review summarized the advances of TMOs/g-C_(3)N_(4) heterojunctions in the above two areas.Firstly,we introduce several typical TMOs based on their crystal structures and band structures.Then,we summarize different kinds of TMOs/g-C_(3)N_(4) heterojunctions,including type Ⅰ/Ⅱ heterojunction,Z-scheme,p-n junction and Schottky junction,with diverse photocatalytic applications(pollutant degradation,water splitting,CO_(2) reduction and N_(2) fixation)and supercapacitive energy storage.Finally,some promising strategies for improving the performance of TMOs/g-C_(3)N_(4) were proposed.Particularly,the exploration of photocatalysis-assisted supercapacitors was discussed.

Recent progress on transition metal oxides and carbon-supported transition metal oxides as catalysts for thermal decomposition of ammonium perchlorate

As a main oxidizer in solid composite propellants,ammonium perchlorate(AP)plays an important role because its thermal decomposition behavior has a direct influence on the characteristic of solid composite propellants.To improve the performance of solid composite propellant,it is necessary to take measures to modify the thermal decomposition behavior of AP.In recent years,transition metal oxides and carbon-supported transition metal oxides have drawn considerable attention due to their extraordinary catalytic activity.In this review,we highlight strategies to enhance the thermal decomposition of AP by tuning morphology,varying the types of metal ion,and coupling with carbon analogue.The enhanced catalytic performance can be ascribed to synergistic effect,increased surface area,more exposed active sites,and accelerated electron transportation and so on.The mechanism of AP decomposition mixed with catalyst has also been briefly summarized.Finally,a conclusive outlook and possible research directions are suggested to address challenges such as lacking practical application in actual formulation of solid composite propellant and batch manufacturing.

Effect of Crystallinity on Electrochemical Insertion/Extraction of Li in Transition Metal Oxides Part I: LiMn_2O_4 and LiCo_(0.5)Ni_(0.5)O_2

Electrochemical insertion/extraction of Li on cathode materials of spinel type LiMn2O4 and ordered rock-salt type LiCo0.5 Ni0.5O2 was measured on samples of which structures were well characterized. On the basis of experimental results on structure, morphology and charge-discharge characteristics, the effect of crystallinity of the cathode materiaIs on electrochemical Li insertion/extraction performance was discussed. These two transition metal oxides belong to onegroup that the crystallinity of these oxides affects to the performance.

Effect of Crystallinity on Electrochemical Insertion/Extraction of Li in Transition Metal Oxides Part Ⅱ: TiO_2, V_2O_5 and MoO_3

Electrochemical insertion/extraction of Li on cathode materials of anatase type TiO_2, quasilayered structure V_2O_5 and layered structure MoO_3 was measured on samples of which structures were well characterized and showed a wide range of crystallinity. On the basis of experimental results on structure, morphology and charge-discharge characteristics, the effect of crystallinity of the cathode materials on electrochemical Li insertion/extraction pedermance was discussed. These three transition metal oxides were classified as one group on the basis of whether the crystallinity of these oxides affects to the performance or not; LiMn_2O_4 and LiCo_(0.5)O_2 belongs to the former group and TiO_2, V_2O_5 and MoO_3 to the latter.

Protonated and layered transition metal oxides as solid acids for dehydration of biomass-based fructose into 5-hydroxymethylfurfural

A serial of protonated and layered transition metal oxides, including layered HTaWO6, HNbMoO6 as well as HNbWO6, were synthesized by solid-state reaction and ion-exchange. The layered HTaWO6 has been systematically studied as a solid acid to realize the dehydration of fructose to 5-hydroxymethylfurfural (HMF). The transition metal oxide samples were characterized with ICP-OES, EDS, XRD, XPS, SEM, TGA, FT-IR, N-2 adsorption-desorption and NH3-TPD. The influential factors such as reaction temperature, reaction time, solvent, catalyst amount and substrate concentration were deeply investigated. The optimized fructose conversion rate of 99% with HMF yield of 67% were achieved after 30 min at 140 degrees C in dimethylsulfoxide. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Electron Donating Property and Catalytic Activity ofPerovskite-type Mixed Oxides (ABO_3) Consisting of Rare Earth and 3d Transition Metals

The catalytic activity of Perovskite-type mixed oxides (LaCoO3, PrCoO3 and SmCoO3) for the reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-PonndorfVerley reduction) has been studied. The data have been correlated with the surface electron donor properties of these mixed oxides

Interior and Exterior Decoration of Transition Metal Oxide Through Cu^(0)/Cu^(+) Co-Doping Strategy for High-Performance Supercapacitor

Although CoO is a promising electrode material for supercapacitors due to its high theoretical capacitance,the practical applications still suffering from inferior electrochemical activity owing to its low electrical conductivity,poor structural stability and inefficient nanostructure.Herein,we report a novel Cu0/Cu+co-doped CoO composite with adjustable metallic Cu0 and ion Cu+via a facile strategy.Through interior(Cu+)and exterior(Cu0)decoration of CoO,the electrochemical performance of CoO electrode has been significantly improved due to both the beneficial flower-like nanostructure and the synergetic effect of Cu0/Cu+co-doping,which results in a significantly enhanced specific capacitance(695 F g^(-1) at 1 A g^(-1))and high cyclic stability(93.4%retention over 10,000 cycles)than pristine CoO.Furthermore,this co-doping strategy is also applicable to other transition metal oxide(NiO)with enhanced electrochemical performance.In addition,an asymmetric hybrid supercapacitor was assembled using the Cu0/Cu+co-doped CoO electrode and active carbon,which delivers a remarkable maximal energy density(35 Wh kg^(-1)),exceptional power density(16 kW kg^(-1))and ultralong cycle life(91.5%retention over 10,000 cycles).Theoretical calculations further verify that the co-doping of Cu^(0)/Cu^(+)can tune the electronic structure of CoO and improve the conductivity and electron transport.This study demonstrates a facile and favorable strategy to enhance the electrochemical performance of transition metal oxide electrode materials.

Density Functional Theory Studies on the Mechanism of Activation Formic Acid Catalyzed by Transition Metal Oxide MoO

This paper systematically studies the reaction mechanisms of formic acid catalyzed by transition metal oxide MoO. Three different reaction pathways of Routes I, Ⅱ and Ⅲ were found through studying the reaction mechanism of transition metal oxide MoO catalyzing the formic acid. The transition metal oxide MoO interacts with the C=O double bond to form chiral chain compounds（Routes I and Ⅱ） and metallic compound MoOH2（Route Ⅲ）. In this paper, we have studied the mechanisms of two addition reaction pathways and hydrogen abstraction reaction pathway. Routes I and Ⅱ are both addition reactions, and their products are two different chiral compounds MoO3CH2, which are enantiomeric to each other. In Route Ⅲ, metal compounds MoOH2 and CO2 are obtained from the hydrogen abstraction reaction. Among them, the hydrogen abstraction reaction occurring in Route Ⅲ is more likely to occur than the others. By comparing the results of previous studies on the reaction of MxOy-＋ ROH（M= Mo,W; R = Me, Et）, we found that the hydrogen abstraction mechanism is completely different from the mechanism of oxygen-containing organic compound catalyzed by MxOy.

A new approach for the aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid without using transition metal catalysts

The organic compound 2,5-furandicarboxylic acid（FDCA） has been identified by the US Department of Energy（DOE） as a valuable platform chemical for a wide range of industrial applications. Currently, the most popular route for FDCA synthesis is reported to be the oxidation of 5-hydroxymethylfurfural（HMF）by O_2 over the catalysis of noble metals（e.g., Au, Pt, Ru, and Pd）. However, the high costs of noble metal catalysts remain a major barrier for producing FDCA at an industrial scale. Herein, we report a transition metal-free synthesis strategy for the oxidation of HMF to FDCA under O_2 or ambient air. A simple but unprecedented process for the aerobic oxidation of HMF was carried out in organic solvents using only bases as the promoters. According to the high performance liquid chromatography（HPLC） analysis, excellent product yield（91%） was obtained in the presence of NaOH in dimethylformamide（DMF） at room temperature（25 ℃）. A plausible mechanism for the NaOH-promoted aerobic oxidation of HMF in DMF is also outlined in this paper. After the reaction, the sodium salt of FDCA particles were dispersed in the reaction mixture, making it possible for product separation and solvent reuse. The new HMF oxidation approach is expected to be a practical alternative to current ones, which depend on the use of noble metal catalysts.

Magnetic Behavior of Some Rare-Earth Transition-Metal Perovskite Oxide Systems

Magnetic properties were investigated for the rare-earth 3d-transition metal oxides with the perovskite structure. Intriguing magnetic phenomena were reviewed for a few systems:magnetization peak effect in the titanates, magnetization reversal in the chromites and metallic ferromagnetism in the cobaltites. The results suggest an important role of the rare-earth ions for the magnetic properties of such complex oxides.

A review on transition metal oxides based photocatalysts for degradation of synthetic organic pollutants

This review provides insight into the current research trend in transition metal oxides(TMOs)-based photocatalysis in removing the organic colouring matters from water.For easy understanding,the research progress has been presented in four generations according to the catalyst composition and mode of application,viz:single component TMOs(the firstgeneration),doped TMOs/binary TMOs/doped binary TMOs(the second-generation),inactive/active support-immobilized TMOs(the third-generation),and ternary/quaternary compositions(the fourth-generation).The first two generations represent suspended catalysts,the third generation is supported catalysts,and the fourth generation can be suspended or supported.The review provides an elaborated comparison between suspended and supported catalysts,their general/specific requirements,key factors controlling degradation,and the methodologies for performance evaluation.All the plausible fundamental and advanced dye degradation mechanisms involved in each generation of catalysts were demonstrated.The existing challenges in TMOs-based photocatalysis and how the researchers approach the hitch to resolve it effectively are discussed.Future research trends are also presented.

Screening of transition metal oxides for electrocatalytic nitrate reduction to ammonia at large currents

Electrochemical nitrate reduction reaction(NO_(3)RR)towards ammonia,as an emerging and appealing technology alternative to the energy-intensive Haber-Bosch process and inefficient nitrogen reduction reaction,has recently aroused wide concern and research.However,the current research of the NO_(3)RR towards ammonia lacks the overall performance comparison of various electrocatalysts.Given this,we here make a comparison of 12 common transition metal oxide catalysts for the NO_(3)RR under a high cathodic current density of 0.25 A·cm^(-2),wherein Co_(3)O_(4) catalyst displays the highest ammonia Faradaic efficiency(85.15%)and moderate activity(ca.-0.25 V vs.reversible hydrogen electrode).Other external factors,such as nitrate concentrations in the electrolyte and applied potential ranges,have also been specifically investigated for the NO_(3)RR.

Advances in catalytic elimination of atmospheric pollutants by two-dimensional transition metal oxides

Atmospheric pollutants can deteriorate air quality and put human health at risk.There is a growing need for green,economical,and efficient technologies,among which catalytic elimination technology is the most promising,to remove atmospheric pollutants.Two-dimensional transition metal oxides(2D TMOs)have recently become attractive catalysts due to their highly exposed active sites,excellent reactant transport properties,and extraordinary catalytic performance.This review systematically summarizes the topdown and bottom-up preparation methods of 2D TMOs and focuses on the specific applications of 2D TMOs in the catalytic elimination of atmospheric inorganic pollutants and volatile organic pollutants.The development of 2D TMOs in the catalytic elimination of atmospheric pollutants is prospected.This review is expected to provide design insights into efficient 2D TMOs to remove atmospheric pollutants.

Molecular Simulation Study on Interaction of Thiophene Sulfides with Transition Metals

The computer molecular simulation technique was applied to study the chemisorption of thiophene and tetramethylthiophene as the model sulfides on the simple oxides and complex oxides of some transition metals as the catalytic materials. The study disclosed that the thiophene sulfides could enter into chemisorption with metal oxides such as VO, ZnO, NiO and Zn-Al-spinel. This interaction could lead to thiophene molecular structure deformation to be in an activated adsorption state, which could help to promote the conversion of thiophene sulfides in the course of catalytic cracking. The VO with a valence of 2 could provide relatively strong selective adsorption sites for the conversion of thiophene sulfides to apparently transform the molecular structures and electron cloud states of such heterocyclic sulfur compounds such as thiophene and tetramethylthiophene into an activated adsorption state. The effect of this interaction was more pronounced with respect to tetramethylthiophene.

Layered Potassium Titanium Niobate/Reduced Graphene Oxide Nanocomposite as a Potassium‑Ion Battery Anode

With graphite currently leading as the most viable anode for potassium-ion batteries(KIBs),other materials have been left relatively underexamined.Transition metal oxides are among these,with many positive attributes such as synthetic maturity,longterm cycling stability and fast redox kinetics.Therefore,to address this research deficiency we report herein a layered potassium titanium niobate KTiNbO5(KTNO)and its rGO nanocomposite(KTNO/rGO)synthesised via solvothermal methods as a high-performance anode for KIBs.Through effective distribution across the electrically conductive rGO,the electrochemical performance of the KTNO nanoparticles was enhanced.The potassium storage performance of the KTNO/rGO was demonstrated by its first charge capacity of 128.1 mAh g^(−1) and reversible capacity of 97.5 mAh g^(−1) after 500 cycles at 20 mA g^(−1),retaining 76.1%of the initial capacity,with an exceptional rate performance of 54.2 mAh g^(−1)at 1 A g^(−1).Furthermore,to investigate the attributes of KTNO in-situ XRD was performed,indicating a low-strain material.Ex-situ X-ray photoelectron spectra further investigated the mechanism of charge storage,with the titanium showing greater redox reversibility than the niobium.This work suggests this lowstrain nature is a highly advantageous property and well worth regarding KTNO as a promising anode for future high-performance KIBs.