Cobaltite Spinel Research Articles

Electrochemical Characteristics of Nanosized Cu, Ni, and Zn Cobaltite Spinel Materials

For a long time, transition metal oxide systems have been considered well explored materials in heterogeneous catalysis. Amongst, the spinel-type oxides, materials such as cobaltites (Co3O4) received significant attention, owing to their use in many industrial applications. In the present study, nanosized Cu, Ni, and Zn cobaltite spinel oxides were synthesized by a simple hydrothermal method. Physicochemical characterization of the synthesized materials was performed utilizing XRD, HRTEM, CO2-TPD, and XPS techniques. The textural characteristics (BET-surface area, pore size, etc.) of samples were determined from N2 physisorption measurements at −196 °C. The CO2-electrocatalytic reduction was selected as a model reaction to evaluate the electrochemical performance of the synthesized spinel cobaltites. For Ni, Cu, and Zn spinel materials, hydrogen was produced as the main product at the whole potential, along with other products, such as CO and HCOOH. Despite the advantages, the catalytic electrochemical CO2 reduction performance of spinel cobaltite catalysts is still far from adequate, which is principally ascribed to the low number of active sites combined with poor electrical conductivity.

Progress in Spinel‐Structured Cobaltite‐Based Positive Electrode Materials for Supercapacitors

AbstractIn recent days, the family of spinel cobaltites with multiple oxidation states has received much attention as an electrode material for supercapacitors. Profiting from its superior electrochemical performance, these cobaltites play a significant role in energy storage and conversion devices. In this review, we provided an in‐depth description of spinel cobaltites. Further, we review several cobaltites and their composites, corresponding synthesis methods, and the application of these materials for supercapacitors. As a result of several extraordinary outputs, spinel cobaltites are likely to be widely studied in the future.

Study of Thermal, Microstructural, Optical, Dielectric, and Magnetic Characterizations of Ni–Fe Spinel Cobaltite for Various Applications

Study of Thermal, Microstructural, Optical, Dielectric, and Magnetic Characterizations of Ni–Fe Spinel Cobaltite for Various Applications

Covalency Competition Induced Active Octahedral Sites in Spinel Cobaltites for Enhanced Pseudocapacitive Charge Storage

AbstractSpinel cobaltites are widely presented as promising pseudocapacitive materials, however, a fundamental understanding of their structure–property relationship at an atomic level remains vague. Herein, their geometrical‐site‐dependent charge storage capability is investigated by substituting Co with inactive Zn and redox‐active Mn. Experimental and theoretical analyses reveal that redox‐active cations in octahedral sites contribute to enhanced capacitance, intrinsically determined by the covalency competition between tetrahedral and octahedral sites. The Zn2+ incorporation leads to increased occupancy of Co in octahedral sites and 2.9× increased capacitance at 1 A g−1 current density, whereas the substituted Mn cations mainly sit in octahedral sites which can react with OH− upon cycling and separate on the spinel surface to reconstruct into δ‐MnO2 nanosheets, leading to 4× increased capacitance at 1 A g−1 current density with a detected K+ ion intercalation. Thus, the exposure of redox‐active cations in octahedral sites and their intrinsic properties are influential in determining spinel oxides’ pseudocapacitive properties. This work provides a general principle to optimize the pseudocapacitive properties of spinel cobaltites by deliberately selecting cations for substitution and controlling their distribution in octahedral/tetrahedral sites. It also offers a fundamental understanding of geometrical‐site‐dependent activity, and can effectively guide the development of spinel oxides for enhanced pseudocapacitance.

Nanoarchitecturing bimetallic manganese cobaltite spinels for sonocatalytic degradation of oxytetracycline

Degradation of contaminants of emerging concern in aqueous media using bimetallic oxides is a promising novel strategy that requires engineering new catalytic routes in bimetallic oxides to perform advanced oxidation; however, several challenges to synthesizing and developing such materials with enhanced, sustainable catalytic features are still being investigated. This study presents the effective use of a manganese cobaltite bimetallic spinel compound for sonocatalysis. We prepared three morphologies of manganese cobaltite for using in the sonocatalytic degradation of oxytetracycline (OTC). The morphology of manganese cobaltite was tuned by changing the amounts of the Mn and Co precursors in the early stage of synthesis. Several manganese cobaltite spinels with different structures—porous layered-like cubes (MCO-PLC), layered-like ellipsoids (MCO-LE), and rough spheroids (MCO-RS) were obtained and characterized using various techniques. A promising catalytic degradation capability of MCO-PLC for OTC (10.0 mg L−1) was obtained at a natural pH within 120 min. We also investigated the reusability of MCO-PLC sonocatalyst and metal (Mn and Co) leaching in water media. The sonocatalytic mechanisms and fragments produced from OTC during degradation were determined via electron paramagnetic resonance and gas chromatography-mass spectroscopy analyses.

Oxidative Thermal Conversion of Hydrothermal Derived Precursors toward the Mixed-Metal Cobaltite Spinel Oxides (ZnCo2O4 and NiCo2O4): In-Situ Investigation by Synchrotron-Radiation XRD and XAS Techniques

In-situ investigations of structural transitions during the thermal-oxidative event of mixed-metal spinel oxide precursors, the so-called nickel- (NCO) and zinc-containing (ZCO) cobaltite spinel precursors, were investigated to understand the formations of the derived NiCo2O4 and ZnCo2O4 spinel oxides, respectively. In-situ XRD investigation revealed that emerged temperatures for spinel oxide phase were between 325 and 400 °C, depending on the cationic substituent. It indicated that the emerged temperature correlated with the absolute octahedral site preference energy (OSPE) of those cations that participated in the development of the spinel framework. Moreover, the incorporated nickel and zinc in the precursors was beneficial for inhibiting the occurrence of the undesired CoO phase. Time-resolved X-ray absorption spectroscopic (TRXAS) data suggested the local structure rearrangement of nickel and zinc throughout the calcination process, which differed from the behavior of single-metal cobalt system. The essential information reported herein provides a benefit to control the cationic distribution within spinel materials, leading to the tunable physical and chemical properties.

Synthesis, Characterization and Applications of Spinel Cobaltite Nanomaterials.

Recently, spinel structures (AB2O4) Nanoparticles (NPs) having binary and ternary mixtures of metal oxides have been established as promising redox catalysts. Due to the presence of two mixed valence metal cations, transport of electrons takes place easily between multiple transition-metal cations with relatively low energy of activation. Among these, spinel cobaltite (MCo2O4) is very attractive due to its low cost, non-toxicity, higher stability, higher electronic conductivity and electrochemical property. To date, MCo2O4 has been used in the fabrication of supercapacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. A variety of MMCo2O4materials have been synthesized, characterized, and utilized in the fabrication of super capacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. The progress in the field of the spinel MCo2O4 materials opens the door to novel and efficient applications in the nanoscience and nanotechnology, and elctrochemistry.

Synthesis and magnetism of MoCo2O4 spinel thin films

Spinel MoCo2O4 was synthesized through epitaxial stabilization. X-ray photoemission spectroscopy revealed that the Mo and Co ions mainly exist as Mo4+ and high-spin (HS) Co2+ in the MoCo2O4 film, respectively. These valence states were consistent with the prediction based on the relation between lattice constants and ionic radii of cations in various spinel cobaltites. The magnetization of the film was composed of paramagnetic and ferrimagnetic components. Density function theory based calculations suggested that the paramagnetic component mainly corresponds to HS Mo4+ 4d2 ions at the octahedral site, while the ferrimagnetic component is derived from the antiferromagnetic interaction between HS Co2+ 3d7 ions at the tetrahedral and octahedral sites in inverse spinel Co[CoMo]O4.

High electrical conductivity at room temperature of MnCo2O4 cobaltite spinel prepared by sol–gel method

The cobaltite spinel MnCo2O4 nanopowder was prepared by the sol–gel method. X-ray diffraction shows the pure compound that crystallized in the cubic structure with the Fd $$\stackrel{-}{3}$$ m space group. The infrared spectrum (IR) revealed two absorption peaks that can be attributed to Mn–O and Co–O vibrations in the octahedral and tetrahedral sites, respectively. The electrical and dielectric studies were characterized by impedance spectroscopy (IS) at different frequencies (40–106Hz) and temperatures (200–440K). As a matter of fact, the DC conductivity exhibits a semiconductor behavior. It is worth mentioning that the conductivity of our investigated cobaltite spinel was found to be σ = 6.10−3 Sm−1 at room temperature. These results allowed this material to be a good candidate for potential application as an anode material (fuel cell). The AC conductivity obeys the Jonscher's law at low temperatures T 340K. Moreover, the dielectric result shows the permittivity (e '≈ 103) which is due to the contribution of the Maxwell–Wagner polarization.

P-type cobaltite oxide spinels enable efficient electrocatalytic oxygen evolution reaction.

Currently, energy-efficient electrocatalytic oxygen evolution from water involves the use of noble metal oxides. Here, we show that highly p-conducting zinc cobaltite spinel Zn1.2Co1.8O3.5 offers an enhanced electrocatalytic activity for oxygen evolution. We refer to previous studies on sputtered Zn–Co spinels with optimized conductivity for implementation as (p-type) transparent conducting oxides. Based on that, we manufacture off-stoichiometric conducting p-spinel catalytic anodes on tetragonal Ti, Au–Ti and hexagonal Al-doped ZnO carriers and report the evolution of O2 at Tafel slopes between 40.5 and 48 mV dec−1 and at overpotentials between 0.35 and 0.43 V (at 10 mA cm−2). The anodic stability, i.e., 50 h of continuous O2 electrolysis in 1 M KOH, suggests that increasing the conductivity is advantageous for electrolysis, particularly for reducing the ohmic losses and ensuring activity across the entire surface. We conclude by pointing out the merits of improving p-doping in Zn–Co spinels by optimized growth on a tetragonal Ti-carrier and their application as dimension-stable 3d-metal anodes.

Isostructural metal hydrazones of 2-(methoxycarbonyl-hydrazono)-pentanedioic acid, H2L: Synthesis, cytotoxic activity of nano spinel ZnCo2O4 derived from single source precursor, [Zn1/3Co2/3(HL)2]·3H2O

Metal Schiff base [2-(methoxycarbonyl-hydrazono)-pentanedioic acid, H2L] complexes of type [M(HL)2]·3H2O, where M = Co (1), Zn (2) & Co-Zn (3), have been synthesized by condensation of α-ketoglutaric acid and methyl carbazate in the presence of divalent metal ions. A stoichiometric reaction of the Schiff base ligand with metal ions resulted in a solid solution precursor of [Zn1/3Co2/3(HL)2]. The crystal structures of metal and mixed metal (Zn-Co) complexes were isostructural and crystallized in monoclinic systems. The synthesized solid solution was employed as a precursor for preparing zinc cobaltite spinel (ZnCo2O4) nanoparticles. As-synthesized nanospinel cobaltite was characterized using Fourier-Transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and transmission electron microscopy (TEM) techniques. PXRD indicated that the product had a spinel type structure with high purity and a crystalline nature. The TEM images show that the spinels were constructed via self-assembled agglomeration of nanoparticles with irregular shapes. The elemental compositions and oxidation states of as-prepared ZnCo2O4 were further analyzed by X-ray photoelectron spectroscopy (XPS). Further, the cytotoxicity was determined against human breast adenocarcinoma (MCF-7) cancer cell lines at different concentrations using a thiazolyl blue tetrazolium bromide (MTT) assay. The spinel oxides prepared from the precursors showed promising results, demonstrating their clinical importance.

Unraveling mechanistic aspects of the total oxidation of methane over Mn, Ni and Cu spinel cobaltites via in situ electrical conductivity measurements

Mn, Ni and Cu cobaltite spinels were synthesized by coprecipitation, characterized and evaluated in the total oxidation of methane. To gain a deeper insight into their catalytic behavior, their electrical conductivity was studied as a function of temperature and oxygen partial pressure, and was followed with time during sequential exposures to different gases in conditions close to those used for the catalytic tests. The Ni cobaltite is in a metallic conductivity state and cannot be reduced in the reaction conditions, suggesting that it functions via a suprafacial mechanism. The Cu cobaltite behaves as a p-type semiconductor, but it is not reduced under the reaction mixture at the reaction temperature of 350 °C, suggesting that, at least in these conditions, the suprafacial mechanism is operating. The Mn cobaltite has an n-type semiconducting character and is reduced in the reaction conditions, suggesting that a heterogeneous redox mechanism is involved.

A systematic variation in cationic distribution and its influence on the magnetization of mixed-metal (nickel and zinc) cobaltite spinels

Cobaltite oxide spinel (CoCo2O4) is one promising material that has been extensively studied for decades due to its versatile applications. Revealing the correlation among chemical compositions, cationic distributions, and physical properties are crucial for exploring its novel application. Here, a series of nickel/zinc co-substituted cobaltite spinels, Zn1−XNiXCo2O4 (ZNCO-X; where X = 0.00, 0.25, …, 1.00), was synthesized by calcining the hydrothermal-derived precursors and their magnetic properties have been investigated. Multiple x-ray based characterization techniques (XRD, XRF, XPS, and XAS) were applied to determine the crystalline structure and appropriated compositions of cation species (Zn2+, Ni2+, Ni3+, Co2+, and Co3+). In conjunction with Neel’s theory of antiferromagnetism, the theoretical magnetization of the spinel series was calculated based on the assumption that Zn2+ ion was located in tetrahedral (A site) while nickel cations (Ni2+ and Ni3+) occupying the octahedral (B site). The theoretical magnetization profile exhibited a good correlation. Superparamagnetic effect and cationic site exchange can be used to explain the discrepancies between the measured and calculated magnetizations. This work reported a systematic controlling of materials structure and cationic distribution, which are crucial for fine-tuning the magnetic property of the Zn1−XNiXCo2O4 cobaltite system.

Highly efficient mixed-metal spinel cobaltite electrocatalysts for the oxygen evolution reaction

Cation substitution in spinel cobaltites (e.g., ACo2O4, in which A = Mn, Fe, Co, Ni, Cu, or Zn) is a promising strategy to precisely modulate their electronic structure/properties and thus improve the corresponding electrochemical performance for water splitting. However, the fundamental principles and mechanisms are not fully understood. This research aims to systematically investigate the effects of cation substitution in spinel cobaltites derived from mixed-metal-organic frameworks on the oxygen evolution reaction (OER). Among the obtained ACo2O4 catalysts, FeCo2O4 showed excellent OER performance with a current density of 10 mA·cm−2 at an overpotential of 164 mV in alkaline media. Both theoretical calculations and experimental results demonstrate that the Fe substitution in the crystal lattice of ACo2O4 can significantly accelerate charge transfer, thereby achieving enhanced electrochemical properties. The crystal field of spinel ACo2O4, which determines the valence states of cations A, is identified as the key factor to dictate the OER performance of these spinel cobaltites.

The Photoactive Cation-Substituted Spinel Cobaltite XCo2O4 (X = Fe, Co, Ni, and Mn) Using As Air Cathodes in Zinc-Air Batteries

The development of catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are attracted enormous interest for improving the performance of Zn-air batteries (ZABs). However, the use of cation-substituted spinel cobaltite XCo2O4 (X = Fe, Co, Ni, and Mn) as photo-electrocatalysts for OER/ORR in ZABs has not yet been reported. The XCo2O4 materials were synthesized by using an electrospinning method followed by a calcination process at 700oC. Among these XCo2O4 catalysts, the NiCo2O4 exhibits the superior performance for both OER (η = 300 mV at 10 mA/cm2) and ORR (η = 460 mV at E1 / 2). It mainly attributes to the narrowest band gap energy at 1.50 eV which corresponds to the ratios of X2 +/X3 + and Co2 +/Co3 + that investigates by the UV-vis spectroscopy, Mott-Schottky plots, and XPS analysis. Under the exposure of light, the NiCo2O4 provides the lower in overpotential of OER and ORR around 10% - 30% due to the occurring of electron(e-) – hole (NiCo2O4 +) separation from absorbing the photon energy. Both of e- and NiCo2O4 + can accelerate the ORR and OER, which is confirmed by in - situ XAS under the light and dark conditions. Finally, the as-fabricated artificial ZAB cell by using NiCo2O4 as a photo-electrocatalyst presents the superb ZAB performance. Figure 1

Ambient pressure CO2 hydrogenation over a cobalt/manganese-oxide nanostructured interface: A combined in situ and ex situ study

We report on a cobalt/manganese-oxide interface catalyst with outstanding activity and selectivity towards methane even at high temperatures and ambient pressure in CO2 hydrogenation. The catalyst was formed from a MnCo2O4-based spinel structure during the oxidative-reductive pretreatment process just before the catalytic tests. Several Mn-, Fe- and Ni-containing cobaltite spinel and reverse spinel structures were tested to find the best overall performer. The reusable MnCo2O4-based structure featured a CO2 consumption rate of ~8500 nmol*g−1*s−1. Even though methane is not the thermodynamically favoured product, it was produced with ~80% and ~50% selectivity at ambient pressure at 673 K and 823 K, respectively. This unexpected finding is linked to the presence of a unique nanostructured Co/Mn(II)O catalyst with a surface composition of Mn3.3Co2.0O4.7 formed after the pretreatment activation step. Over this phase, the reduction of CO2 progresses through bridge bonded formate located at the Co/Mn2+ interface and this is mostly responsible for high temperature methane formation. This hypothesis is proven here by the reported combination of ex-situ XRD, TPR, HRTEM-ED, HAADF-EDX and in-situ NAP-XPS and DRIFTS techniques.

Facile synthesis of spinel MgCo2O4 nanosheets for high-performance asymmetric supercapacitors

Two dimensional (2D) spinel cobaltite has great potential in electrochemical energy storage due to its unique structure and remarkable performance. Herein, we reported for a successful synthesis of MgCo2O4 nanosheets through direct hydrothermal decomposition of a mixed aqueous solution of MgCl2 and CoCl2 and formic acid (HCOOH, FA) at 200 °C for 6 h. The MgCo2O4 nanosheets yield a specific capacitance of 1431.2 F·g−1 at 1.0 A·g−1 in a three-electrode system and a high energy density of 32 Wh·kg−1 at a power density of 800 W·kg−1 in an aqueous asymmetric supercapacitor (MgCo2O4 thin sheets (+)//active carbon (AC) (−)). The MgCo2O4 nanosheets display potential applications in electrochemical energy storage.

Engineering RuO2 on CuCo2O4/CuO nanoneedles as multifunctional electrodes for the hybrid supercapacitors and water oxidation catalysis

Abstract Currently, designing and constructing multifunctional electrodes is highly desirable for energy conversion and storage devices. Spinel cobaltites have attracted considerable attention owing to the relative high conductivity and rich redox chemistry, but the limited electroactive sites and poor surface chemical reactivity are the highly concerned issues. Taking Co–Cu oxides as the model material, here we demonstrate that a surface restructuring strategy by constructing core-shell arrays can achieve simultaneous modulation of electroactive sites and surface chemical reactivity. Strating from the hydrothermal and annealing process, CuCo2O4/CuO nanoneedles are synthesized directly on the conductive Ni foam, and followed by electrodeposited RuO2 nanoparticles (denoted as CuCo2O4/CuO@RuO2). Core-shell CuCo2O4/CuO@RuO2 arrays show a high areal capacity up to 862.5 mAh cm−2 and a high capacity retention of about 90.1% after 8000 cycles. Moreover, the hybrid supercapacitor by CuCo2O4/CuO@RuO2 and activated carbon can achieve 0.84 mWh cm−2 energy density at 8 mW cm−2 power density, as well as good long-term stability. In addtion, working as water oxidation catalysis, CuCo2O4/CuO@RuO2 shows the low overpotential of 279 mV at 10 mA cm−2, as well as a low Tafel slope and stable long-term performance. This work provides a novel strategy to engineer surface nanostructure for energy conversion and storage devices.

Synthesis and Characterization of Spinel Cobaltite (Co3O4) Thin Films for Function as Hole Transport Materials in Organometallic Halide Perovskite Solar Cells

Conventional inorganic p-type conductive oxides, for example, NiO, CuOX, and CuCrOX, can serve as low-cost and efficient hole transport materials for wide-bandgap organolead halide perovskites [for...

Effect of cation substitution on the water splitting performance of spinel cobaltite MCo2S4 (M = Ni, Cu and Co)

The introduction of different ions is an effective method for regulating electron distribution and increasing the electrocatalytic activity of spinel cobalt sulfide (Co3S4). However, the effect of doping different ions on water splitting performance has not been systematically clarified. Therefore, a detailed research is done to illuminate the doping of different ions on the water splitting performance of spinel cobalt sulfide MCo2S4 (M = Ni, Cu and Co) nanorods grown on Ni foam. To drive the electrocatalytic current of 50 mA/cm2 and 10 mA/cm2, the CuCo2S4/NF material only requires an overpotential of 240 mV for oxygen evolution reaction (OER) and an overpotential of 142 mV for hydrogen evolution reaction (HER). The results of density functional theory and experiment demonstrate that the strong water adsorption energy and the large electrochemical activity area make CuCo2S4/NF show good catalytic activity. The CuCo2S4/NF nanorods material presents superior electrochemistry performance with a small voltage 1.53 V. The water oxidation activity increases linearly before nonlinearly improving with the increasing of pH, indicating that the substrate changes from water to hydroxyl. It is noteworthy that CuCo2S4/NF will be transformed into amorphous oxide active species, which will act as a stable catalyst during the reaction.