Electrochemical characteristics of LiNi0.9Co0.1O2 synthesized at 800 °C from the different combinations of carbonates and oxides

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 800 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄ as the sources of Li, Ni, and Co, respectively. The electrochemical properties of the synthesized samples were then investigated. The structure of the synthesized LiNi_0.9Co_0.1O₂ was analyzed, and the microstructures of the samples were observed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiCO₃, and Co₃O₄ had the largest first discharge capacity (152 mAh/g), with a discharge capacity deterioration rate of 1.4 mAh/g/cycle.     

Comparison of lithium nickel cobalt oxides synthesized from NiO,Co3O4, and LiOH·H2O or Li2CO3 by solid-state reaction method

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) cathode materials were synthesized by the solid-state reaction method at different temperatures from LiOH·H₂O, NiO and Co₃O₄ and from Li₂CO₃, NiO and Co₃O₄ as the starting materials. The physical and electrochemical properties of the synthesized samples were then compared. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized for 40 h from LiOH·H₂O, NiO and Co₃O₄, and from Li₂CO₃, NiO and Co₃O₄, LiNi_0.5Co_0.5O₂ synthesized from Li₂CO₃, NiO and Co₃O₄ at 800 °C has relatively large first discharge capacity and relatively good cycling performance. This sample is considered the best one with relatively good electrochemical properties.     

Enhancement of Ca3Co4O9+δ thermoelectric properties by dispersing SiC nanoparticles

Misfit-layered oxides Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) samples were synthesized using solid-state sintering method and the effects of SiC nanoparticles diapersion on the thermoelectric properties were investigated. Thermoelectric properties of Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) were investigated up to 923 K. Compared with pure sample, the electrical resistivity of SiC-added samples reduces, for Ca₃Co₄O_9+δ + z wt% SiC (z = 0.00, 0.025, 0.05, 0.1, 0.2) ceramic samples with x ≤ 0.05, the electrical resistivity decreases with increasing SiC nanoparticles adding amounts. And, the electrical resistivity exists transition from semiconductor to metal conduction mechanism. While, the thermal conductivity also decreases due to the addition of SiC nanoparticles. As a result, the Ca₃Co₄O_9+δ + 0.2 wt% SiC sample had the lowest thermal conductivity of 1.47 W/Km at 923 K, which was 18.4% lower than that of the Ca₃Co₄O_9+δ sample. The ZT value of Ca₃Co₄O_9+δ + 0.05 wt% SiC can reach 0.218, which is 40.9% higher than the pure Ca₃Co₄O_9+δ sample.     

Charge–discharge curves and discharge capacities of LiNi1−yCoyO2 synthesized from lithium carbonate and nickel and cobalt oxides

LiNi_1?yCo_yO₂ (y=0.1, 0.3, and 0.5) were synthesized by a solid-state reaction method at 800 °C and 850 °C using Li₂CO₃, NiO, and Co₃O₄ as the starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were then investigated. For samples with the same composition, the particles synthesized at 850 °C were larger than those synthesized at 800 °C. The particles of all the samples synthesized at 850 °C were larger than those synthesized at 800 °C. LiNi_0.5Co_0.5O₂ synthesized at 850 °C had the largest first discharge capacity (159 mA h/g), followed in order by LiNi_0.7Co_0.3O₂ synthesized at 800 °C (158 mA h/g) and LiNi_0.9Co_0.1O₂ synthesized at 850 °C (151 mA h/g). LiNi_0.9Co_0.1O₂ synthesized at 850 °C had the best cycling performance with discharge capacities of 151 mA h/g at n=1 and 156 mA h/g at n=5.     

Electrochemical characteristics of LiNi0.5Co0.5O2 synthesized at 800 °C from the different combinations of carbonates,oxides, and hydroxides

LiNi_0.5Co_0.5O₂ cathode materials were synthesized by a solid-state reaction method at 800 °C using Li₂CO₃, LiOH·H₂O; NiO, NiCO₃; CoCO₃, or Co₃O₄ as the sources of Li, Ni, and Co, respectively. The electrochemical properties of the synthesized samples were then investigated. The structure of the synthesized LiNi_0.5Co_0.5O₂ was analyzed, and the microstructures of the samples were observed. The curves of voltage vs. x in Li_xNi_0.5Co_0.5O₂ for first charge–discharge and intercalated and deintercalated Li quantity Δx were studied. Destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.5Co_0.5O₂. The LiNi_0.5Co_0.5O₂ sample synthesized from Li₂CO₃, NiCO₃ and Co₃O₄ has the largest first discharge capacity (142 mAh/g). The LiNi_0.5Co_0.5O₂ sample synthesized from Li₂CO₃, NiO and Co₃O₄ has a relatively large first discharge capacity (141 mAh/g) and the smallest capacity deterioration rate (4.6 mAh/g/cycle).     

Bi-functional green-synthesis of Co3O4 NPs for photocatalytic and electrochemical applications

Wastewater of industries, which is polluted with different dyes is becoming a severe issue, which should be tackled on priority bases such as to provide an eco-friendly environment. In addition to this, in search of an efficient green synthesized capacitive electrode material, we have synthesized cobalt oxide (Co₃O₄) nano-materials by employing green chili and sunflower seeds extracts. The as synthesized samples are labeled as Co-P, Co-GC and Co-SF. The successful fabrication of these samples was tested by X-ray diffraction (XRD), scanning electron microscope (SEM), Xray photoelectron spectroscope (XPS). These tests have explored successful fabrication of Co₃O₄-based samples comprised on nanoparticles (NPs) in the range of 35–45 nm. Optical properties were studied by UV–vis spectroscope and Co-SF sample has exhibited lowest energy band gap i.e 2.41 eV. Photoluminescence (PL) analysis has explored that Co₃O₄ NPs prepared by sunflower extracts have offered lowest recombination rate. Among of Co-P, Co-GC and Co-SF photocatalysts, Co-SF has shown excellent photodegradation activity, which is 90% against a water pollutant name as methylene blue (MB) under UV–Vis light. This sample also has shown a good catalytic stability i.e 80.7%. Moreover, for electrochemical performance analysis, cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopic (EIS) tests were also performed. Among of Co-P, Co-GC and Co-SF samples, Co-SF sample has offered 1080.32 F/g specific capacitance and 86.70% capacitance retention at higher scan rate i.e 10 A/g. Additionally, this optimized sample has also maintained 83.51% capacitance even after 5000 GCD cycles performed at 1 A/g, and good conductive nature. These extraordinary results have provided new platform for water purification and energy storage appliances.     

Electrochemical performance of cobalt-substituted lithium nickel oxides synthesized from lithium and nickel carbonates and cobalt oxide

LiNi_1?yCo_yO₂ (y=0.1, 0.3 and 0.5) cathode materials were synthesized by a solid-state reaction method at different temperatures using Li₂CO₃ as a Li source, NiCO₃ as a Ni source, and Co₃O₄ as a Co source. The electrochemical properties of the synthesized samples were then investigated. Structures of the synthesized LiNi_1?yCo_yO₂ (y=0.1, 0.3 and 0.5) samples were analyzed, and microstructures of the samples were observed. Voltage vs. x in Li_xNi_1?yCo_yO₂ curves for the first and second charge–discharge cycles and intercalated and deintercalated Li quantity Δx were studied. LiNi_0.9Co_0.1O₂ synthesized at 800 °C had the largest first discharge capacity (152 mAh/g) and quite good cycling performance, with a discharge capacity of 146 mAh/g at n=5. It had a discharge capacity fading rate of 1.4 mAh/g/cycle.     

Electrical properties of Co-doped CaCu3Ti4O12

Co-doped CaCu₃Ti₄O₁₂ samples were synthesized by solid-phase reaction. Electrical properties were studied by impedance spectroscopy in wide temperature (25–450 °C) and frequency (10 Hz–10 MHz) intervals. It was shown that the presence of the copper oxide interlayer significantly reduces the value of the dielectric constant. The amount of impurity copper in the CaCu₃Ti_4-хCo_хO_12-δ samples (x = 0.06; 0.12; 0.24) rise with an increase in the cobalt content. The samples are characterized by a granular microstructure, with an average grain size ranging from 2 to 10 μm. The impedance of the samples was simulated at a temperature of 25 °C and in the range of 100–450 °C. It was found that the samples are characterized by low- and high-frequency polarization. The conductivity activation energy varied from 0.94 to 0.87 eV depending on the cobalt content. The CaCu₃Ti_3.94Co_0.06O_12-δ sample are characterized by the best values of the dielectric permittivity and the dielectric loss tangent, ε = 400 and tanδ = 0.2 (at 1 MHz and room temperature), respectively.     

Synthesis and characterization of Ca3-xLaxCo4-yCuyO9+δ cathodes for intermediate temperature solid oxide fuel cells

The calcium cobaltite Ca_3-xLa_xCo_4-yCu_yO_9+δ with x and y = 0 and 0.1 were synthesized and the electrical, thermal, and catalytic behaviors for the oxygen reduction reaction (ORR) for use as air electrodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) were evaluated. X?ray diffraction confirms the Ca_3-xLa_xCo_4-yCu_yO_9+δ samples were crystallized in a monoclinic structure and scanning electron microscopic image shows lamella-like grain formation. Introduction of dopants decreases slightly the loss of lattice oxygen and thermal expansion co-efficient. The Ca_3-xLa_xCo_4-yCu_yO_9+δ samples exhibit good phase stability for long-term operation, thermal expansion, and chemical compatibility with the Ce_0.8Gd_0.2O_2-δ electrolyte. Among the studied samples, Ca_2.9La_0.1Co₄O_9+δ shows a maximum conductivity of 176 Scm^?1 at 800 °C. Although the doped samples exhibit a higher total electrical conductivity, an improved symmetrical cell performance is displayed by the undoped sample. Comparing the sintering temperatures, the composite cathode Ca₃Co₄O_9+δ + Ce_0.8Gd_0.2O_2-δ sintered at 800 °C exhibit the lowest area specific resistance of 0.154 Ω cm² at 800 °C in air. In the Ca_3-xLa_xCo_4-yCu_yO_9+δ + GDC composite cathodes, the charge-transfer process at high frequencies presents a major rate limiting step for the oxygen reduction reaction.     

Synthesis of lithium LiNi1−yCoyO2 from lithium carbonate,nickel oxide and cobalt carbonate and their electrochemical properties

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from Li₂CO₃, NiO and CoCO₃ as starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized at 850 °C, LiNi_0.7Co_0.3O₂ has the largest intercalated and deintercalated Li quantity Δx at the first charge–discharge cycle, followed in order by LiNi_0.9Co_0.1O₂ and LiNi_0.5Co_0.5O₂. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (142 mAh/g), followed in order by LiNi_0.9Co_0.1O₂ synthesized at 850 °C (113 mAh/g), and LiNi_0.5Co_0.5O₂ synthesized at 800 °C (109 mAh/g).     

Influence of SiC dispersion and Ba(Sr) substitution on the thermoelectric properties of Ca3Co4O9+δ

Ca₃Co₄O_9+δ is a typical p-type thermoelectric oxide material with a low thermal conductivity. In this study, double-layered oxide samples Ca(Ba,Sr)₃Co₄O_9+δ dispersed with different SiC contents were obtained via the traditional solid phase reaction method. The effects of different elemental substitutions and SiC dispersion contents on the microstructure and thermoelectric properties of the samples were studied. The double optimisation of partial substitution of Ca-site atoms and SiC dispersion considerably improved the thermoelectric properties of Ca₃Co₄O_9+δ. Through the elemental substitution, the resistivity of the Ca₃Co₄O_9+δ material was reduced. Conversely, introducing an appropriate amount of SiC nanoparticles enhanced phonon scattering and was crucial in reducing its thermal conductivity. After double optimisations, the dimensionless thermoelectric figure of merit (ZT) values of both Ca_2.93Sr_0.07Co₄O_9+δ + 0.1 wt% SiC and Ca_2.9Ba_0.1Co₄O_9+δ + 0.1 wt% SiC achieved an optimum value of 0.25 at 923 K.     

Ceramic pigments from CoxNi3-xP2O8 (0 ≤ x ≤ 3) solid solutions

Co_xNi_3-xP₂O₈ (0 ≤ x ≤ 3) solid solutions were synthesized via the chemical co-precipitation method. Variation of unit cell parameters and interatomic distances indicated that these solid solutions with the Ni₃P₂O₈ structure are stable between 800 and 1200 °C in compositions with 0 ≤ x ≤ 1.5 and between 800 and 1000 °C when (0 ≤ x ≤ 3). When (2.5 ≤ x ≤ 3.0), the solid solutions lead to the Co₃P₂O₈ structure, being stable between 800 and 1000 °C.The yellow colour of the Ni₃P₂O₈ compound changes to pink or red when Co(II) ions are incorporated in the structure as Ni₃P₂O₈ solid solutions are formed. Bands corresponding to second and third electronic transitions of the Co(II) ions in octahedral coordination appear in the 450–600 nm in the UV-V spectra, and they are responsible of the observed changes in the colour. Absorbance in the visible spectra was also obtained from enamelled samples but a new band at 650 nm with considerable absorbance when x > 1.0 increased the blue amount, and colour of the enamelled samples was yellowish brown, brown, green and blue.     

Highly ordered crystalline mesoporous metal oxides for hydrogen peroxide decomposition

Highly ordered mesoporous metal oxides (meso-MO _x ) such as CeO₂, Co₃O₄, Cr₂O₃, Mn₂O₃, NiO, RuO₂, SnO₂ and TiO₂ were successfully synthesized using mesoporous silica KIT-6 as a hard template via the nano-replication method. The physicochemical properties of as-prepared meso-MO _x were characterized by scanning electron microscopy, X-ray diffraction, N₂ adsorption–desorption and temperature programmed techniques. Their catalytic behavior toward H₂O₂ decomposition was investigated and compared with the corresponding bulk metal oxides (bulk-MO _x ) synthesized by the conventional precipitation method. These meso-MO _x materials exhibited much higher catalytic activities than their bulk counterparts. In particular, meso-Mn₂O₃ and meso-RuO₂ showed high activities, while meso-SnO₂ resulted in no activity toward H₂O₂ decomposition. The overall conversion of H₂O₂ followed a general order: Mn₂O₃ > RuO₂ > Co₃O₄ > CeO₂ > NiO > Cr₂O₃ > TiO₂ > SnO₂.     

Selective Allylic oxidation of Cyclohexene by a Magnetically Recoverable Cobalt Oxide Catalyst

Abstract  

In this work, we prepared a new magnetically recoverable CoO catalyst through the deposition of the catalytic active metal nanoparticles of 2–3 nm on silica-coated magnetite nanoparticles to facilitate the solid separation from liquid media. The catalyst was fully characterized and presented interesting properties in the oxidation of cyclohexene, as for example, selectivity to the allylic oxidation product. It was also observed that CoO is the most active species when compared to Co²⁺, Co₃O₄ and Fe₃O₄ in the catalytic conditions studied.     

Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg,Ni, Zn,Cu)

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S_BET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co₃O₄ at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co₃O₄ and CoAl₂O₄ due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.     

Promising high temperature thermoelectric properties of dense Ba2Co9O14 ceramics

Layered cobalt oxides have shown high thermoelectric properties. The n = 1 member of the Ba_n+1Co_nO_3n+3(Co₈O₈) family, Ba₂Co₉O₁₄, a new layered cobalt oxides family with Co(II) and Co(III) in the CdI₂ layers, has been synthesized by solid state reaction and sintered as dense ceramics (relative density ∼ 93%) by Spark Plasma Sintering. It presents promising p-type thermoelectric properties at high temperature. The dimensionless figure of merit ZT is 0.032 at 660 K and 0.04 at 1000 K, which is about one quarter to one third of the ZT value of Ca₃Co₄O₉ ceramics.     

Hydroformylation of olefins by Au/Co3O4 catalysts

The hydroformylation of olefins over supported gold catalysts in an autoclave reactor under mild conditions (100–140 °C, 3–5 MPa) has been studied. Over Au/AC (activated carbon), Au/PVP (polyvinylpyrrolidone), Au/Al₂O₃, Au/TiO₂, Au/Fe₂O₃, Au/ZnO, Au/CeO₂ and Co₃O₄, 1-olefin mainly remained unchanged and the major products were isomerized olefins or hydrogenated paraffin. In contrast, Au nanoparticles deposited on Co₃O₄ led to remarkably high catalytic activities in hydroformylation reaction with selectivities above 85% to desired aldehydes. The hydroformylation of olefins proceeds preferentially at temperatures below 140 °C, above which the reactions of olefins gradually shifted to isomerization and then to hydrogenation. It appeared that the activity and selectivity of hydroformylation reaction strongly depend on the molecular structure of olefins, which could be ascribed to steric constraints as internal olefins are relatively inappropriate to form alkyl group and subsequent acyl group by insertion of CO. The Au/Co₃O₄ catalyst can be recycled by simple decantation with slight decrease in catalytic activity along with an increase in recycle times, which is a great advantage over homogeneous catalysts. The role of gold nanoparticles can be assumed to dissociate hydrogen molecule into atomic species which reduce Co₃O₄ to Co metal under mild reaction conditions.     

Synthesis of sponge like Gd3+ doped vanadium oxide/2D MXene composites for improved degradation of industrial effluents and pathogens

Current report is based on the synthesis of Gd⁺³ doped V₂O₅ nanostructures (GVO) along with fabrication of GVO/MXene binary nanocomposite. As synthesized GVO and GVO/MXene were characterized by XRD (X-ray diffraction), FESEM (Field emission scanning electron microscopy), EDX (Energy dispersive X-ray), BET (Brunauer Emmett Teller technique) and UV–Visible spectroscopy. Diffraction and elemental analysis confirmed the substitution of Gd⁺³ ions in VO layers. Orthorhombic phase of VO was observed in both GVO and GVO/MXene samples with crystallite size range of 17.02–17.51 nm. FESEM analysis indicated asymmetrical VO particles and sheets distributed on MXene layers, giving out a sponge like appearance. Surface area of GVO and GVO/MXene was enhanced to 20.46 and 23.69 nm, respectively. Effect of Gd⁺³ contents was significant on optical properties, which reduced the band gap energy of VO to 2.33 eV. The photocatalytic performance of prepared samples was analysed by the degradation of Methylene blue (MB) under direct sunlight. Gd⁺³ ion doping was found useful to enhance degradation of MB up to ～71%. Among all samples, GVO/MXene showed maximum degradation (～92%) within 120 min. Meanwhile, GVO/MXene showed good recyclability for successive five cycles. In addition, GVO and GVO/MXene were effective antibacterial agents against Gram positive (S. aureus) and Gram negative (P. vulgaris) strains of bacteria. The results suggested that the GVO and GVO/MXene could serve as potential candidates for large scale treatment of organic pollutants and pathogens.     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).