Cobalt-based Metal Oxides Research Articles

Spinel cobalt-based binary metal oxides as emerging materials for energy harvesting devices: synthesis, characterization and synchrotron radiation-enabled investigation.

The synthesis and characterization of spinel cobalt-based metal oxides (MCo2O4) with varying 3d-transition metal ions (Ni, Fe, Cu, and Zn) were explored using a hydrothermal process (140 °C for two hours) to be used as alternative counter electrodes for Pt-free dye-sensitized solar cells (DSSCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed distinct morphologies for each metal oxide, such as NiCo2O4 nanosheets, Cu Co2O4 nanoleaves, Fe Co2O4 diamond-like, and Zn Co2O4 hexagonal-like structures. The X-ray diffraction analysis confirmed the cubic spinel structure for the prepared MCo2O4 films. The functional groups of MCo2O4 materials were recognized in metal oxides throughout Fourier transform infrared (FTIR) analysis. The local structure analysis using X-ray absorption fine structure (XAFS) at Fe and Co K-edge identified octahedral (Oh) Co3+ and tetrahedral (Td) Co2+ coordination, with Zn2+ and Cu2+ favoring Td sites, while Ni3+ and Fe3+ preferred Oh active sites. Further investigations utilizing the Fourier transformation (FT) analysis showed comparable coordination numbers and interatomic distances ranked as Co-Cu > Co-Fe > Zn-Co > Co-Ni. Furthermore, the utilization of MCo2O4 thin films as counter electrodes in DSSC fabrication showed promising results. Notably, solar cells based on CuCo2O4 and ZnCo2O4 counter electrodes showed 1.9% and 1.13% power conversion efficiency, respectively. These findings indicate the potential of employing these binary metal oxides for efficient and cost-effective photovoltaic device production.

A Review of Cobalt-Based Metal Hydroxide Electrode for Applications in Supercapacitors

Supercapacitors are the cutting-edge, high performing, and emerging energy storage devices in the future of energy storage technology. It delivers high energy and produces higher specific capacitances. This research study provides insights into supercapacitor materials and their potential applications by examining different battery technologies compared with supercapacitors’ advantages and disadvantages. Transition metal hydroxides (cobalt hydroxides) have been studied to develop electrodes for supercapacitors and their use in various fields of energy and conversion devices. Cobalt-based metal oxides and hydroxides provide high-capacitance electrodes for supercapacitors. Metal hydroxides combine high electrical conductivity and excellent stability over time. The metal oxides used to prepare the electrodes for supercapacitors are cobalt-based metal oxides and hydroxides. It is stronger than most of the other oxides and has tremendous electrical conductivity. Cobalt hydroxides are also used in supercapacitors instead of other metal hydroxides, such as aluminum hydroxide, copper hydroxide, and nickel hydroxide. This study gives a complete overview of the preparation, synthesis, analysis, and characterization of cobalt hydroxide thin film electrodes by using the electrochemical deposition technique, parameters measurements, important characteristics, material properties, various applications, and future enhancement in supercapacitors.

Co-MOFs as Emerging Pulse Modulators for Femtosecond Ultrafast Fiber Laser.

The metal organic framework (MOF) has attracted more and more attention due to its unique morphology, functional linkers, and orderly network structure. Zeolitio imidazolata frameworks (ZIFs), which are formed by bivalent transition metals (Zn, Co, etc.) and nitrogen-containing heterocyclic imidazole or purine organic ligands, are a very attractive subclass of MOFs. ZIF-67, obtained by the nucleation growth of dimethylimidazole and Co 2p, has been developed as a precursor for porous nanostructured cobalt-based metal oxides. During material preparation we add rGO because it can be used as a basic element to construct macroscopic three-dimensional carbon structural materials, which self-assemble into a 3D network structure with ZIF-67 through simple van der Waals forces or hydrogen bonds, and some samples contain specific functional groups that are added to the precursor. In this paper, we employ liquid-phase synthesis to generate rGO-ZIF-67 and calcine it at the temperature of 350 °C to obtain rGO-Co3O4. Then we fabricate rGO-Co3O4 and rGO-ZIF-67 modulators based on microfibers and test their nonlinear optical absorption in 1.5 μm range. The modulation depths of rGO-Co3O4 and rGO-ZIF-67 are measured as 10.41% and 6.61%, respectively. By using microfiber-based rGO-Co3O4 modulator, we have obtained a conventional soliton and a soliton molecule in Er3+-doped fiber lasers. The conventional soliton has a pulse width of 793.4 fs and a spectral width of 3.3 at 1558.9 nm, respectively. The obtained soliton molecule has a spectral modulation period of 1.65 nm and temporal separation of 4.94 ps at 1563.2 nm. By employing a microfiber-based rGO-ZIF-67 modulator, we obtain conventional solitons with a spectral width of 1.9 nm at the central wavelength of 1529.8 nm. Our research may expand the MOF-based materials for ultrafast photonics, blazing a new path for fiber laser, optical communications, and optoelectronics, etc.

Controllable synthesis of 3D hierarchical cactus-like ZnCo2O4 films on nickel foam for high-performance asymmetric supercapacitors

High-performance ternary cobalt-based metal oxides, especially ZnCo2O4, have attracted increasing attention as promising electrode materials for supercapacitors. However, there are still great challenges for the as-reported ZnCo2O4 materials, such as self-aggregation during repeated discharging-charging process and low packing density. To tackle the above issues, it is envisaged as an efficient strategy to combine the advantages of both hierarchical porous micro/nanostructures and self-supporting electrode to fabricate a free-standing hierarchical micro/nanostructured ZnCo2O4 electrode. Herein we propose an efficient and simple synthetic strategy for the controllable synthesis of self-supporting hierarchical porous cactus-like ZnCo2O4 material directly grown on Ni-foam using a facile hydrothermal method with post-calcination treatment. Furthermore, a growth mechanism is also proposed. The as-prepared cactus-like ZnCo2O4 material possesses unique structural merits, such as hierarchical porous structures, large specific surface area, robust structural stability, and strong connections between the substrate and the ZnCo2O4 active material. The unique cactus-like ZnCo2O4 film electrode displayed excellent electrochemical performance, including a high specific capacity of 1115.7 F g−1 at 1 A g−1 and remarkable long cycle stability with 80.8% capacity retention after 30,000 cycles. A practical asymmetric supercapacitor (ASC) device was assembled using cactus-like ZnCo2O4 and active carbon, which showed an excellent energy density of 35.4 Wh kg−1 at high power density of 160.1 W kg−1 and superior cycle stability (62.5% capacity retention after 30,000 cycles at 1 A g−1). All these results show that such hierarchical porous ZnCo2O4 micro/nanostructured films are a promising candidate for high-performance supercapacitors for energy storage application.

Cobalt-based metal oxide coated with ultrathin ALD-MoS2 as an electrode material for supercapacitors

A novel approach of preparing a composite supercapacitor electrode consisting of ternary metal oxide nanostructure decorated with transition metal sulfide is presented. High-surface area NiCo2O4 nano-sheets grown on Ni-foam are coated with an ultrathin layer of MoS2 by atomic layer deposition (ALD) and the hybrid structure reveals superior electrochemical performance. The composite is thoroughly studied with several characterizations like XRD, Raman, XPS, SEM and TEM. A comparative study with MoS2 coated Co3O4 electrodes not only ensures the advantage of the more conducting sulfide layer in enhancing the supercapacitor performance significantly but also establishes the superiority of the ternary oxide (NiCo2O4) for this application. The thinner and well-connected nano-sheets of NiCo2O4 provides the more interface between the electrode and the electrolyte whereas an optimal thickness of MoS2 helps to maximize the performance of the device. The high areal capacitance (2445 mF cm−2), enhanced rate capability of the optimized NiCo2O4-MoS2 composite is therefore ascribed to the synergistic effect of high-surface area of the oxide nano-sheets and better electronic conductivity of the sulfide. The current study thus opens a route to combine the conventional hydrothermal synthesis of ternary oxide nanostructures with ALD grown layered transition metal dichalcogenides to achieve a superior electrode for next-generation supercapacitor.

Recovery of cathode materials from spent lithium-ion batteries and their application in preparing multi-metal oxides for the removal of oxygenated VOCs: Effect of synthetic methods

Due to the sustainable use of wastes, cathode materials of spent lithium-ion batteries are recovered and used as transition metal precursors to prepare metal oxides catalysts for the oxidation of VOCs. In this work, a series of manganese-based and cobalt-based metal oxides are synthesized via different preparation methods. Catalytic activities of the catalysts prepared are investigated through complete oxidation of oxygenated VOCs and the physicochemical properties of optimum samples are characterized. Evaluation results indicate that MnOx (SY) (HT) sample prepared via hydrothermal method and CoOx (GS) (CP) synthesized via co-precipitation method had better performance, because they have higher specific surface area, higher concentration of active oxygen species and high-valence metal ion, as well as better low-temperature reducibility compared to the other multi-metal oxides used in the study. In addition, TD/GC-MS results imply that further oxidation of by-products requires high reaction temperature during VOCs oxidation.

Nanorose-like ZnCo2O4 coatings synthesized via sol–gel route: morphology, grain growth and DFT simulations

Ternary cobalt-based metal oxide (ZnCo2O4) has been successfully coated onto aluminum substrate via sol–gel method. The coatings were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and UV–Vis–NIR spectrophotometry. Thermal degradation of the coatings was probed by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Model of crystal growth kinetics and density functional theory (DFT) calculations further probed the crystalline structure evolution. The predicted ZnCo2O4 crystalline structures were confirmed by XRD and EDX. The grain growth kinetic model for ZnCo2O4, derived from Lifshitz–Slyozov–Wagner (LSW) theory, determined that the growth of crystalline phases is unaffected by the annealing temperature; however, the crystallites’ sizes decreased with the increase in precursor concentration. DFT analysis indicated that structural energy stability between the bulk state and slabs of ZnCo2O4 was at two oxygen layers (O-layers) with an optimum grain width of 17.21 A. Interestingly, the morphology of ZnCo2O4 represented a rose-like template structure formed by inter-connecting layers of nanosheets. This unique surface morphology enhanced the optical absorptance properties up to α = 70.7%.

Rapid,Microwave-Assisted Synthesis of a Composite of Mesoporous MnCo2O4 and Reduced Graphene Oxide(RGO) As a High Perfomance Anode for Li- Ion Batteries

Over the last two decades Li-ion batteries (LIBs) have been investigated to improve their electrochemical properties. LIBs have ushered wireless technology and are now employed in large scale applications such as electric vehicles, solar and wind electricity generation systems. The performances of LIBs depend on properties of electrode materials. Since the first commercialization of LIBs by Sony in 1991, graphitic carbons have been used as anode materials. However graphite suffers from challenges like limited capacity, lithium plating at high current densities and formation solid electrolyte interface (SEI). This has motivated researchers to develop alternate anode materials which could deliver high energy and power densities. Cobalt oxide, iron oxide, manganese oxide and tin oxide are some among them. But most of these materials show rapid capacity fade due to low electronic conductivity. Binary metal oxides such as ZnFe2O4, CuCo2O4, ZnCo2O4, ZnMn2O4, NiCo2O4 and MnCo2O4 have shown good capacity upon cycling because of their better electronic conductivity. MnCo2O4, belongs to cubic spinel structure have attracted much attention due to its characteristics inherited from manganese and cobalt based metal oxides. One of the challenging issues in conversion reaction of a bulk electrode material is to maintain structural integrity during electrochemical cycling with associated issues such as volume changes, pulverization, etc., which affect the performance porous materials have been studied widely because of the easy percolation of electrolyte into core of particles which result in high rate capability and also by allowing volume expansion/contraction arising from intercalation/deintercalation of Li+ ions. Using templates become a general approach to synthesize these porous structures. However in most of the cases, the synthesis requires long duration and involves specially designed autoclaves. Here in we report a single step and rapid, microwave-assisted synthesis route to synthesize mesoporous microspheres of MnCo2O4 dispersed with low concentration (≤ 5 wt%) of reduced graphene oxide (RGO). In a typical synthesis, 0.02 g of graphite oxide (GtO) was added to 20 ml of ethylene glycol and sonicated for 20 minutes at room temperature to form graphene oxide (GO) dispersion. 0.5 mmol of Manganese (II)nitrate. tetra hydrate, 1.0 mmol of cobaltous(III)nitrate.hexahydrate and 15 mmol of ammonium bicarbonate were dissolved in 20 ml of ethylene glycol and stirred for 30 minutes to obtain a homogeneous solution. Then this solution was added drop wise to already prepared solution of graphite oxide under sonication. After sonication, solution was taken into 80 ml glass vessel, heated to 200 oC by microwave irradiation in a single mode microwave reactor (2.45 GHz, Discover, CEM, USA) equipped with a pressure sensor, and an optical fibre temperature sensor, and held at the same temperature for 30 minutes. The system was then cooled down to room temperature naturally. The dark grey coloured product was collected by centrifugation and washed several times with distilled water and ethanol, followed by drying at 60 oC overnight. As prepared dark grey powder was heated to 600 oC at an average heating rate 5 oC per minute in a tube furnace under the flow of nitrogen and held at the same temperature for 5 h to convert it into MnCo2O4 and RGO composite. The phase purity and morphology of the final product were studied by XRD, SEM and TEM analysis. The microscopic image (figure.1) shows that mesoporous MnCo2O4 microspheres were attached on to RGO sheets. The charge-discharge profile is shown in Fig. 2. The specific discharge capacities of 841, 801, 832 and 765 mAh g-1 were obtained for 1st, 2nd, 5th and 30th cycles, respectively, at a current density of 100 mA g-1 in the potential range of 0.01 and 3.0 V vs Li/Li+. These values are comparable with the values that were reported previously. Results pertaining to the aforementioned studies including both physical and electrochemical investigations would be presented. Figure 1

Optical and mechanical characterization of novel cobalt-based metal oxide thin films synthesized using sol–gel dip-coating method

New cobalt-based metal oxide thin films (MxCoyOz with M=Mn, Cu, Ni) have been deposited on commercial aluminum and glass substrates using sol–gel dip-coating method. The as-deposited films were characterized by a wide range of complementary techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), spectrophotometry and nanoindentation techniques. A light absorption study for coatings on glass substrates within a wavelength range of 300–1100nm was also conducted. Topographical and morphological investigations showed the presence of nano-sized, grain-like particles in the copper–cobalt oxide coatings, which consequently had the roughest surface among the three coatings. All coatings on glass substrate exhibited higher absorption of ultraviolet (UV) light compared to visible light, while coatings on aluminum substrate generally had low reflectance (<50%) of UV light, moderate reflectance (<80%) of visible light and high reflectance (up to 100%) of infrared light. Implications of optical properties as a function of film thickness controlled by dip-heating cycles were discussed. The elastic modulus (E) and hardness (H) of thin film samples compared with stand‐alone commercial aluminum substrate were also measured.