Spinel Cobalt Oxide Research Articles

Short-Range Ordered Iridium Single Atoms Integrated into Cobalt Oxide Spinel Structure for Highly Efficient Electrocatalytic Water Oxidation.

Noble metals manifest themselves with unique electronic structures and irreplaceable activity toward a wide range of catalytic applications but are unfortunately restricted by limited choice of geometric structures spanning single atoms, clusters, nanoparticles, and bulk crystals. Herein, we propose how to overcome this limitation by integrating noble metal atoms into the lattice of transition metal oxides to create a new type of hybrid structure. This study shows that iridium single atoms can be accommodated into the cationic sites of cobalt spinel oxide with short-range order and an identical spatial correlation as the host lattice. The resultant Ir0.06Co2.94O4 catalyst exhibits much higher electrocatalytic activity than the parent oxide by 2 orders of magnitude toward the challenging oxygen evolution reaction under acidic conditions. Because of the strong interaction between iridium and cobalt oxide support, the Ir0.06Co2.94O4 catalyst shows significantly improved corrosion resistance under acidic conditions and oxidative potentials. This work eliminates the "close-packing" limitation of noble metals and offers promising opportunity to create analogues with desired topologies for various catalytic applications.

Insight into the effect of manganese substitution on mesoporous hollow spinel cobalt oxides for catalytic oxidation of toluene

The cobalt oxides and manganese oxides have high-activity potential for catalytic oxidation of volatile organic compounds (VOCs), while the mesoporous hollow morphology is crucial to the mass transfer of reactant and product. Therefore, it is worth investigating the effect of manganese substitution in mesoporous hollow cobalt oxides on catalytic oxidation. Herein, a partially disordered spinel structure is formed by the Mn substitution in Co3O4 and the mesoporous hollow microsphere is improved in morphology homogeneity with the decrease of Co/Mn ratio in the range of 1.8–28.8. The 5Co1Mn (Mn-substituted Co3O4 with Co/Mn at 5.4) exhibits outstanding catalytic activity for toluene oxidation with 50% CO2 generation at 237 °C, which is 21 °C lower than Co3O4. Moreover, the 5Co1Mn displays satisfactory stability in reusability, lifetime, and water resistance. The small defective crystallite, mesoporous hollow morphology, and high specific surface area endow Mn-substituted Co3O4 with more surface chemical adsorbed oxygen, enhancing the catalytic oxidation of toluene. Theoretical calculation on (311) plane of Co3O4 reveals that Mn2+ or Mn3+ substitution increases the formation energy of oxygen vacancy and makes it difficult to adsorb gaseous oxygen on the defective surface. The interaction between Co and Mn impedes the improvement of toluene oxidation because the mobility of lattice oxygen, the surface distribution of Co3+, and the ratio of surface adsorbed oxygen to surface lattice oxygen are hindered by Mn substitution. The chemical adsorbed oxygen is more active than lattice oxygen in the oxidation of adsorbed intermediates (phenolate, benzoate species, etc.). The Langmuir-Hinshelwood mechanism dominates in the catalytic oxidation at 200–250 °C, while the catalytic oxidation follows both the Langmuir-Hinshelwood mechanism and Mars-van Krevelen mechanism above 250 °C. This work provides some enlightenment for exploring the role of surface oxygen species in VOCs oxidation and uncovering the interaction in binary spinel oxides.

Manipulating morphology and surface engineering of spinel cobalt oxides to attain high catalytic performance for propane oxidation

The selective synthesis of nanomaterials with different morphologies and crystal facets is of great significance for catalytic properties and practical applications. We report a strategy for controllable fabrication of hierarchical Co3O4 materials with various morphologies (ellipsoidal, flowerlike, book-shaped, spindlelike) and study their catalytic properties in propane oxidation. Co3O4-B (book-shaped) is found to exhibit the highest propane oxidation rate (0.86 × 10-8 mol m−2 s−1) and the highest turnover frequency (TOF = 11.49 × 10−3 s−1) at 220 °C. This confirms that Co3O4-B provides a higher specific surface area, a highly exposed {110} facet, and abundant Co3+ cations, which make it exhibit favorable low-temperature reducibility and oxygen mobility and thus improve its catalytic activity. In situ diffuse reflectance infrared Fourier transform spectroscopic analysis reveals that the intermediates, such as carboxylate and carbonate species, are involved in propane oxidation. Furthermore, Co3O4-B shows high water-resistance performance, and no significant deactivation is observed after long-term stability and reusability tests.

Enhanced urea oxidization electrocatalysis on spinel cobalt oxide nanowires via on-site electrochemical defect engineering

A reversed-potential tuning strategy is proposed to introduce defects on the surface of cobalt oxide nanowires, enabling significantly improved electrocatalytic performance for urea oxidization under alkaline conditions.

Correction to “Spontaneous Delithiation under Operando Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Correction to “Spontaneous Delithiation under Operando Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Synthesis of Mesoporous NiCo2O4 By Spray Pyrolysis Method for Air Electrode of Zinc-Air Rechargeable Batteries

Recently, rechargeable zinc-air batteries have been attracted attention as promising energy storage devices because of their theoretical large capacity, low cost, and safety. However zinc-air battery still has limits in cycle file and energy efficiency. In particular, increase in air electrode performance is strongly required. Therefore, variety of materials, mainly perovskite oxide, have been studied for air electrode, however, activity and stability are still not high enough. In this study, nickel cobalt spinel oxide was synthesized by spray pyrolysis method in order to increase in surface area and formation of mesoporous structure. In our previous study, it was found that introduction of mesoporous structure in LaCoO3 electrode with hard template method is effective for increasing cycle performance and decrease in overpotential of air electrode for zinc-air battery. NiCo2O4 based spinel oxide is active to oxygen reduction (ORR) and oxygen evolution reaction (OER), however, surface area is still insufficient by the preparation of conventional hydrothermal method. Therefore, it is expected that introduction of mesoporous structure into NiCo2O4 spinel oxide will increase ORR/OER activity and stability.On spray pyrolysis method, precursor solvent turned into nano-sized droplet by ultrasonic wave vaporizer, and the droplets are transferred to the tubular electric furnaces by air as carrier gas. The solvent evaporates from the droplets resulting in the formation of mesopore and after calcination, the fine powder is gathered in filters. Nitrate solution was used as precursor, and air at 3 L/min was used as oxidant and carrier gas in this work. Air electrode performance was measured by using gas diffusion layer and PTFE and graphitic carbon was mixed with NiCo2O4 spinel for electrode. 8M KOH aqueous solution at 313K was used for electrode and constant current of 20 mA/cm2 was applied by battery charge discharge equipment.Single phase of NiCo2O4 spinel phase was obtained from XRD measurement and the SEM image of the sample was spherical with many meso size pore. The estimated BET surface area was 76m2/g and average pore diameter was 2.12 nm. Therefore, it is considered that NiCo2O4 oxide with mesoporous structure was successfully prepared. ORR/OER activity of mesoporous NiCo2O4 was measured. It was found that NiCo2O4 shows reasonable activity to ORR and OER reaction. On the other hand, partial substitution of Ni with Fe is effective for increasing ORR/OER activity. Two different compositions of iron added NiCo2O4 (Ni0.8Fe0.2Co2O4, Ni0.65Fe0.35Co2O4) are successfully prepared. At beginning of charge/discharge cycle, spray pyrolysis synthesized NiCo2O4 shows slightly larger overpotential for ORR and OER comparing with that of NiCo2O4 prepared with hydrothermal method. However, after some cycles, ORR potentials are increased and OER potentials are decreased, so mesoporous NiCo2O4 shows superior electrochemical performance which is almost the same with that of hydrothermal NiCo2O4. Moreover, cycle stability is much higher than that of hydrothermal NiCo2O4 and ORR/OER more than 500 cycles was stably sustained and so introduction of mesoporous structure is effective for increasing cycle stability of air electrode. Effects of calcination temperature during splay pyrolysis were also studied and it was found that calcination of NiCo2O4 based spinel oxide at 673 K is the most active and stable to ORR/OER. Therefore, this study reveals that Fe doped NiCo2O4 with mesoporous structure is highly active and stable air electrode catalyst for Zn-air battery.

Air Electrode Property of Doped NiCo2O4 Based Oxide for Rechargeable Zn-Air Battery

There is a strong demand for rechargeable battery with large energy density and capacity because of increase in performance of mobile equipment such as mobile phone, laptop personal computer (PC) and also electric vehicle. At present, Li ion battery (LIB) have been widely used for such purpose. However, there are several issues such as the insufficient capacity and safety required to solve. Zinc-air batteries have been used commercially as a non rechargeable battery at present, however, recently, there is strong interest for development of rechargeable Zn-air battery because of its theoretical large capacity, low cost, and safety. However zinc-air rechargeable battery still has limits in cycle file and energy efficiency. In particular, increase in air electrode performance is strongly required. In this study, nickel cobalt spinel oxide, NiCo2O4, was studied as reversible air electrode for Zn-air battery. In addition, effects of dopant on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were studied. NiCo2O4 based spinel oxide is active to ORR and OER, however, surface area is still insufficient by the preparation of conventional hydrothermal method. Therefore, application of splay pyrolysis method for preparation of NiCo2O4 oxide is also studied for increasing ORR/OER activity and stability.NiCo2O4 based oxide was prepared by hydrothermal synthesis method and partial substitution was performed by using Mn, Fe, and Cu. On spray pyrolysis method, precursor solvent turned into nano-sized droplet by ultrasonic wave vaporizer, and the droplets are transferred to the tubular electric furnaces by air as carrier gas. The solvent evaporates from the droplets resulting in the formation of mesopore and after calcination, the fine powder is gathered in filters. Air electrode performance was measured by using gas diffusion layer, and PTFE and graphitic carbon were mixed with NiCo2O4 spinel for electrode. 8MKOH aqueous solution at 313K was used for electrolyte and a constant current of 20 mA/cm2 was applied by battery charge discharge equipment.Various spinel oxides were successfully prepared by hydrothermal synthesis method from XRD measurement. It was found that ORR and OER activity of MnCo2O4 and NiCo2O4 was reasonably high among the spinel oxides prepared. ORR activity is slightly higher on MnCo2O4, however, NiCo2O4 shows much longer cycle stability of ORR/OER. In addition, elution of Mn was observed in case of MnCo2O4, in contrast, almost no change in composition was observed for NiCo2O4 after cycle measurement. Therefore, NiCo2O4 shows reasonable activity to ORR and OER and high chemical stability. Effects of dopant on NiCo2O4 on ORR and OER activity and doping Cu and Fe is effective for increasing ORR potential and decreasing OER potential. Although the most superior performance of air electrode was observed on Cu doped one, elution of Cu is obviously observed. Therefore, from chemical stability, Fe doped NiCo2O4 is the most active to air electrode catalyst. The optimization of Fe amount in Ni site was also studied and it was found that Ni0.65Fe0.35Co2O4 is the most active and stable air electrode catalyst. On this electrode, overpotential for ORR reaction is around 0.25V at 20mA/cm2, 313 K and almost 500 cycles of ORR/OER which is 1 h ORR and OER each. In addition, introduction of mesoporous structure was achieved by splay pyrolysis method and increase in surface area is also effective for increasing stability to ORR/OER activity.This work is based on results obtained from a project, "Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING2)", JPNP16001, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Synthesis, structural, magnetic, textural, optical investigation and photocatalytic performance of undoped and doped cobaltite nanoparticles

The present work deals with the synthesis and characterization of pure and transition metal (Ni, Cu and Fe) doped spinel Co3O4 nanoparticles (NPs), which are well known for their physical and chemical features. These transition metal doped Co3O4 NPs were tailored through thermal decomposition of precursors synthesized by simple co-precipitation, the simple and cost-effective strategy of fabricating mesoporous spinel cobalt oxide. This study investigates the photocatalytic degradation of industrial dyes Rhodamine B (RhB) and Methyl Orange (MO) under sunlight by using NPs as catalysts. Among the different nanocatalysts, Ni doped Co3O4 NP exhibited the highest efficiency in degrading the environmentally harmful dyes, proving the positive correlation between surface area and photodegradation efficiency. The structures and optical properties were investigated by Powder X-Ray Diffraction (PXRD), X-ray Photoelectron Spectroscopy (XPS), High-Resolution Transmission Electron Microscopy (HR-TEM), Ultraviolet-Diffuse Reflectance Spectroscopy (UV-DRS) and Photoluminescence (PL) under dopant control. The morphology and polycrystallinity of the samples were studied using SEM-EDS and SAED patterns, respectively. The doped ferromagnetic samples showed unsaturation in hysteresis loops which specified the oxygen vacancy.

A simplified electrochemical model for modelling Li-ion batteries comprising blend and bidispersed electrodes for high power applications

A fast computing electrochemical model has been developed in order to account for the electrothermal behavior of Li-ion batteries with multiple and/or multidispersed active materials in each electrode. In this study, the cell studied is a high power cell with lithium manganese spinel and lithium cobalt oxide at the positive and Lithium titanate at the negative with 2 particle populations. The model has been calibrated on the said cell and validated on realistic duty profile. It has been then compared against a state-of-the-art Newmann model that showed similar results for both global and inner behavior. However, due to the simplifications adopted for our modelling approach, calculation times of the newly developed model are significantly lower allowing to specific use where fast computing modelling approaches are required. Finally, this model has been used in order to understand the inner behavior of each electrode during constant current charge and discharges as well as hybrid electric vehicle duty cycles and further calculations have been performed to understand the impact of active material repartition in each electrode.

Morphologically controlled cobalt oxide nanoparticles for efficient oxygen evolution reaction

Electrochemical water oxidation is one of the thrust areas of research today in solving energy and environmental issues. The morphological control in the synthesis of nanomaterials plays a crucial role in designing efficient electrocatalyst. In general, various synthetic parameters can direct the morphology of nanomaterials and often this is the main driving force for the electrocatalyst in tuning the rate of the oxygen evolution reaction (OER) for the electrochemical water-splitting. Here, a facile and cost-effective synthesis of spinel cobalt oxides (Co3O4) via a one-pot hydrothermal pathway with tunable morphology has been demonstrated. Different kinds of morphologies have been obtained by systematically varying the reaction time i.e. nanospheres, hexagon and nanocubes. Their catalytic activity has been explored towards OER in 1.0 M alkaline KOH solution. The catalyst Co3O4-24 h nanoparticles synthesized in 24 h reaction time shows the lowest overpotential (η) value of 296 mV at 10 mA cm−2 current density, in comparison to that of other as-prepared catalysts i.e. Co3O4-pH9 (311 mV), Co3O4-12 h (337 mV), and Co3O4-6 h (342 mV) with reference to commercially available IrO2 (415 mV). Moreover, Co3O4-24 h sample shows the outstanding electrochemical stability up to 25 h time.

The Effect of Heteroatom Doping on Nickel Cobalt Oxide Electrocatalysts for Oxygen Evolution and Reduction Reactions.

The synthesis of nickel cobalt oxide materials and their electrocatalytic performance toward the oxygen reduction and evolution reactions are reported. Nickel cobalt oxides were synthesized in a sol-gel process with different precursors, namely nitrate, sulfate, and chloride. Structural analyses show that the structures have mesoporous morphologies and indicate the formation of nickel cobalt oxide spinel structures with a size ranging from 35 to 65 nm. Furthermore, the physicochemical properties differ depending on the nature of the selected precursors, including the materials' morphology and the chemical composition. Electrocatalytic investigations demonstrate that the catalytic activity toward the oxygen reduction reaction (ORR) could be modulated between two- and four-electron pathways, depending on the precursors used. The Cl-NiCoO sample displays a selective two-electron reduction of O2 , with H2 O2 production higher than 90 %. The sample prepared using sulfate displays the highest performance toward the oxygen evolution reaction (OER), with a low overpotential value (0.34 V) to drive a current density of 10 mA.cm-1 . Overall, these results confirm that the chemical composition of the precursor used during the nanomaterials synthesis can be used to tune the electrocatalytic performances toward ORR and OER.

NiCo2O4 films fabricated by reactive molecular beam epitaxy and annealing in various oxygen atmospheres

Nickel cobalt spinel oxide, NiCo2O4, is an important material for spintronics because it exhibits both ferrimagnetic characteristics and electrical conductivity. Because high oxygen pressure during deposition is necessary to obtain useful properties, pulsed laser deposition has been used to fabricate NiCo2O4 films. In this study, we investigated the physical properties of NiCo2O4 films synthesized by reactive molecular beam epitaxy and annealing in a high-pressure oxygen atmosphere. The characteristics of the films strongly depended on the oxygen pressure, and a larger pressure tended to give larger magnetization and higher conductivity. Crystal structure analysis by x-ray diffraction and transmission electron microscopy revealed that the films consisted of a rock salt (Ni,Co)O phase and a spinel NiCo2O4 phase. This phase separation caused the small magnetization and large electric resistance because the rock salt phase was an antiferromagnetic insulator.

MnxCo3-xO4 spinel oxides as efficient oxygen evolution reaction catalysts in alkaline media

The design of efficient electrocatalysts for oxygen evolution reaction (OER) is an essential task in developing sustainable water splitting technology for the production of hydrogen. In this work, manganese cobalt spinel oxides with a general formula of MnxCo3-xO4 (x = 0, 0.5, 1, 1.5, 2) were synthesised via a soft chemistry method. Non-equilibrium mixed powder compositions were produced, resulting in high electrocatalytic activity. The oxygen evolution reaction was evaluated in an alkaline medium (1 M KOH). It was shown that the addition of Mn (up to x ≤ 1) to the cubic Co3O4 phase results in an increase of the electrocatalytic performance. The lowest overpotential was obtained for the composition designated as MnCo2O4, which exhibited a dual-phase structure (∼30% Co3O4 + 70% Mn1.4Co1.6O4): the benchmark current density of 10 mA cm−2 was achieved at the relatively low overpotential of 327 mV. The corresponding Tafel slope was determined to be ∼79 mV dec−1. Stabilities of the electrodes were tested for 25 h, showing degradation of the MnCo2O4 powder, but no degradation, or even a slight activation for other spinels.

Synthesis and evaluation of nickel doped Co3O4 produced through hydrothermal technique

The synthesis of undoped cobalt oxide and cobalt oxide with 4%nickel doping is studied in samples obtained through hydrothermal technique. After the final heat treatment at 300°C, X-ray diffraction analysis indicated the formation of cobalt spinel oxide with a complete replacement of nickel in the lattice. An average crystallite size of ~42 nm and ~31nm was found, as well as a particle size of ~ 20 nm and ~30 nm for Co3O4 and Co3-xNixO4, respectively. Structural parameters were established through Rietveld refinement with a good correspondence between the simulated and the experimental pattern with values of x2 = 1.25 and GOF = 0.90 for Co3O4. The energy band gap was found through UV-Vis spectroscopy in two different regions: Eg1 and Eg2 values vary between 1.54 and 2.04eV for samples doped with nickel. The SEM results indicated the formation of nanostructures with semi-cubic shape and irregular rods. Parameters such as crystal size, particle size, surface area, as well as morphology of the final product depend on doping.

Metal Oxide (Co3O4 and Mn3O4) Impregnation into S, N-doped Graphene for Oxygen Reduction Reaction (ORR).

To address aggravating environmental and energy problems, active, efficient, low-cost, and robust electrocatalysts (ECs) are actively pursued as substitutes for the current noble metal ECs. Therefore, in this study, we report the preparation of graphene flakes (GF) doped with S and N using 2-5-dimercapto-1,3,4-thiadiazole (S3N2) as precursor followed by the immobilization of cobalt spinel oxide (Co3O4) or manganese spinel oxide (Mn3O4) nanoparticles through a one-step co-precipitation procedure (Co/S3N2–GF and Mn/S3N2–GF). Characterization by different physicochemical techniques (Fourier Transform Infrared (FTIR), Raman spectroscopy, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD)) of both composites shows the preservation of the metal oxide spinel structure and further confirms the successful preparation of the envisaged electrocatalysts. Co/S3N2–GF composite exhibits the best ORR performance with an onset potential of 0.91 V vs. RHE, a diffusion-limiting current density of −4.50 mA cm−2 and selectivity for the direct four-electron pathway, matching the results obtained for commercial Pt/C. Moreover, both Co/S3N2–GF and Mn/S3N2–GF showed excellent tolerance to methanol poisoning and good stability.

Coulometric Titration of Active Sites at Mesostructured Cobalt Oxide Spinel by Surface Interrogation Mode of Scanning Electrochemical Microscopy

Cobalt-based transition-metal oxides are promising candidates for the oxygen evolution reaction (OER). However, a complex interplay between the catalyst crystal structures and material morphologies...

Enhancement of SO2 Gas Sensing Performance of Co3O4 Spinel by Cu Substitution

Single-phase spinel cobalt oxide (Co3O4) and copper-substituted cobalt oxide (Co2.8Cu0.2O4) nanomaterials were synthesized via a co-precipitation route. To explore the potential applicability of the Co3O4 and Co2.8Cu0.2O4 materials for gas sensor fabrication, their SO2 gas sensing characteristics were studied at three different temperatures using the gas concentration of 3 ppm. Unsubstituted Co3O4 sample exhibits poor response towards SO2 gas whereas the Cu-substituted sample showed superior gas sensing characteristics such as gas response, response time and recovery time at all three temperatures. Among the three studied temperatures, the maximum gas response of 7.5% was found at 200 °C with recovery and response times of 26 sec, indicating an optimal temperature. Our results demonstrate that the nanostructured Co2.8Cu0.2O4 material could be a potential candidate to design SO2 gas sensor for detection of low concentration gas.

Optical properties of Glass/ITO/Co3O4 heterojunction

In this work, at first simple spinel cobalt oxide nono powder was synthesized by a simple hydrothermal route combined with a heat treatment, in the next step the commercially available with Electrophoretic deposition of Co3O4 film on indium tin oxide is presented. Co3O4 is p type semiconductor and ITO, n type and Co3O4 on ITO creates a pn junction. The material was characterized by X-ray diffraction, UV–visible spectroscopy for energy band gap estimation and scanning electron microscopy to morphology investigation as well as size distribution and The BET specific surface area of the prepared sample. The optical transitions for single layer and device is investigated. Co3O4 on ITO nanostructured thin films shows the outstanding photocatalytic behavior that enhanced photo-catalytic oxidizing so that After 120 min of UV irradiation, degradation efficiency reaches to 91%.

Expression of Concern for “Spontaneous Delithiation under Operando Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Expression of Concern for “Spontaneous Delithiation under <i>Operando</i> Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Ab initio study of the magnetic, optical and electronic properties of spinel Co3O4 within DFT and GW approaches

The spinel cobalt oxide Co3O4 is an antiferromagnetic semiconductor containing two non-equivalent Co2+ and Co3+ cobalt ions with different local environments and different magnetic moments. We have performed ab initio study and comparison of the electronic, magnetic and optical properties of Co3O4 within GGA, GGA + U, and G0W0 approximations. GGA correctly predicts Co3O4 to be a semiconductor, but severely underestimates the bandgap. G0W0 approximations increase the bandgap indicating a better description of the cobalt localized d-states. The spectral weights of the bands near Fermi energy are about 0.5. Ab initio calculations confirm that the low-spin state of Co3+ ion arises due to the local environment and the crystal effect field. The investigation of the pressure dependencies of magnetic properties revealed the appearance of Co3+ ion abrupt transition from low-spin state to high-spin state under tensile pressure. This allows manipulating the spin state of Co3+ ions through the pressure or strain.