Cobalt Oxalate Precursor Research Articles

Excellent hydrogen generation from ultrathin nanosheets of cobalt cyclotetraphosphate

The production of hydrogen from electrolysis of water is an emerging field for the generation of clean energy sources. The platinum based electrocatalyst are the state of art material for hydrogen generation but their scarcity limit their wide implementation. Therefore, non-noble electrocatalyst gains immerse attention to meet the demand of H2 generation. Herein ultrathin cobalt cyclotetraphosphate (thickness ~1–2 nm) has been synthesized by phosphorization of cobalt oxalate at 350 °C and utilized as cathode material. Cobalt oxalate precursor has been synthesized via micellar route at room temperature. The as-prepared Co2P4O12 has been deposited on graphite sheet and used as a working electrode for HER. In comparison with Pt/C (ɳ20 = 54 mV), nanosheets of Co2P4O12 requires 118 mV overpotential to achieve 20 mA/cm2 current density in 0.5 M H2SO4 and almost same current was retained even at 24 h stability study at −0.4 V vs Ag/AgCl.

Inception of Co3O4 as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co0.85Se/Co9Se8 Network.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s-1) compared to Co0.85Se/Co9Se8 (0.0102 s-1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the Cdl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender Cdl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

Facile synthesis of Co3O4 nanochains and their improved TEA sensing performance by decorating with Au nanoparticles

A novel chain-like nanostructure of Co3O4 was successfully prepared via a facile and reliable oxalate sacrificial template route, in which coralloid cobalt oxalate (CoC2O4·2H2O) precursor was first obtained through a room-temperature precipitation method and then used as sacrificial template to prepare Co3O4 by annealing at 500 °C. Au nanoparticles-decorated Co3O4 nanochains were also prepared by soaking the CoC2O4 precursor in Au+ solution before the annealing process. The prepared samples were characterized by XRD, FESEM, TEM, and N2 adsorption-desorption. Results indicated that the pure and Au-decorated Co3O4 nanochains were constructed by several end-to-end connected nanoparticles, and their specific surface areas were 28.42 m2/g and 37.39 m2/g, respectively. The gas sensing properties of the prepared samples were tested and compared. It was found that after being functionalized with Au nanoparticles, the Co3O4 nanochains showed an improved TEA sensing performance, such as lower optimal working temperature, higher response, and faster response and recover speed. In addition, the Au/Co3O4 sensor can also give a good linearity in the TEA concentration range from 10 to 200 ppm and considerable stability within 7 weeks, suggesting its potential application for quantitative detection of TEA. The improved gas sensing mechanism of the Au/Co3O4 nanochain was discussed.

Synthesis of hierarchical flower-like Co3O4 superstructure and its excellent catalytic property for ammonium perchlorate decomposition

Hierarchical flower-like cobalt tetroxide (Co3O4) was successfully synthesized via a facile precipitation method in combination with heat treatment of the cobalt oxalate precursor. The samples were systematically characterized by thermo gravimetric analysis and derivative thermo gravimetric analysis (TGA-DTG), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N2 adsorption-desorption measurements. The results indicate that the as-fabricated Co3O4 exhibits uniform flower-like morphologies with diameters of 8–12 μm, which are constructed by one-dimensional nanowires. Furthermore, catalytic effect of this hierarchical porous Co3O4 on ammonium perchlorate (AP) pyrolysis was investigated using differential scanning calorimetry (DSC) techniques. It is found that the pyrolysis temperature of AP shifts 142 °C downward with a 2 wt% addition content of Co3O4. Meanwhile, the addition of Co3O4 results in a dramatic reduction of the apparent activation energy of AP pyrolysis from 216 kJ mol−1 to 152 kJ mol−1, determined by the Kissinger correlation. The results endorse this material as a potential catalyst in AP decomposition.

High‐Performance LiCoO2 Sub‐Micrometer Materials from Scalable Microparticle Template Processing

AbstractOne attribute that has limited performance for some lithium‐ion battery active material systems is large particle size. While many methods have been reported in the literature for producing high‐performance sub‐micrometer sized battery particles, often these procedures are difficult to adapt to large battery electrode powder production and/or the processing is relatively expensive compared to traditional methods. We report a highly scalable process to produce high performance sub‐micrometer battery active material using an initial demonstration cathode chemistry, LiCoO2 (LCO). We adopted a template‐based process which took advantage of a cobalt oxalate precursor material with a rod morphology. Lithiation of the precursor via calcination produced loosely connected sub‐micrometer sized LCO particles which were easily dispersed into individual particles through a low energy mechanical method. The sub‐micrometer sized LCO particulates exhibited excellent electrochemical performance as lithium‐ion battery cathode active materials, including high discharge capacity, rate capability, and coulombic efficiency.

Synthesis of Cubic Phase-Co Microspheres by Mechanical Solid-State Reaction-Thermal Decomposition and Research on Its Growth Kinetics

Cubic phase cobalt (Co), which can be used as a key component for composite materials given its excellent ductility and internal structure, is not easy to obtain at room temperature. In this study, oxalic acid and cobalt nitrate are used as raw materials to synthesize the cobalt oxalate precursor, which has a stable structure with a five-membered chelate ring. Cobalt oxalate microspheres, having a high internal energy content, were prepared by using mechanical solid-state reaction in the presence of a surfactant, which can produce spherical micelles. The thermal decomposition of the precursor was carried out by maintaining it in a nitrogen atmosphere at 450°C for 3 h. At the end of the procedure, 100 nm cubic phase-Co microspheres, stable at room temperature, were obtained. Isothermal and nonisothermal kinetic mechanisms of cobalt grain growth were investigated. The cubic-Co grain growth activation energy, Q, was calculated in this study to be 71.47 kJ/mol. The required reaction temperature was low, making the production process simple and suitable for industrial applications.

Effect of microwave power on the thermal genesis of Co3O4 nanoparticles from cobalt oxalate micro-rods

This study focuses on investigating the influence of microwave power (MWP) change on the morphology and size of Co3O4 nanoparticles (NPs), which was obtained from the thermal decomposition of cobalt oxalate precursor. The oxalate precursor was prepared via the microwave-assisted route in the presence of cetyltrimethylammonium bromide (CTAB) employing an MWP of 280 and 700W. Physicochemical properties of the prepared solids were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry-differential thermal analyses (TGA-DTA). The results obtained indicated that the applied MWP has a crucial effect in controlling the morphology and the size of CoC2O4·2H2O as well as Co3O4 NPs. Acicular- and rod-like morphologies of both phases were obtained employing an MWP of 280 and 700W during the preparation, respectively. Further, both the prepared Co3O4 nanoneedles and nanorods are composed of net-like structure of interconnected nanocapsules. Moreover, although all the routes led to the same phase, additional difference existed in terms of surface Co2+ and hydroxyl-carbonate concentrations. Lower MWP favors high Co2+ and low cobalt hydroxyl-carbonate surface concentrations.

Effects of pulsed electromagnetic field on morphology and size of cobalt oxalate particles

It is of much significance to control the morphology and size of cobalt oxalate precursor for the preparation of cobalt powders. The cobalt oxalate powders were prepared by conventional precipitation at different initial cobalt chloride concentrations in the presence of pulsed electromagnetic field. Scanning electron microscopy images and size analysis indicate that spherical and fine cobalt oxalate particles with uniform size are obtained. Conductivity analysis demonstrates that pulsed electromagnetic field plays an important role in the preparation of monodisperse cobalt oxalate particles owing to the inhibition of the secondary nucleation. X-ray powder diffraction results show the formation of β-CoC2O4·2H2O with a micro-size change of cobalt oxalate grain when the extra pulsed electromagnetic field is present. Fourier transform infrared spectroscopy results indicate that the transition of bond way in CoC2O4·2H2O favours to develop stable crystal nucleus. Besides, a possible mechanism for the interaction between pulsed electromagnetic field and cobalt oxalate reaction system was preliminarily discussed.

High-Performance Oxygen Redox Catalysis with Multifunctional Cobalt Oxide Nanochains: Morphology-Dependent Activity

Future advances in renewable and sustainable energy require advanced materials based on earth-abundant elements with multifunctional properties. The design and the development of cost-effective, robust, and high-performance catalysts that can convert oxygen to water, and vice versa, is a major challenge in energy conversion and storage technology. Here we report cobalt oxide nanochains as multifunctional catalysts for the electrochemical oxygen evolution reaction (OER) at both alkaline and neutral pH, oxidant-driven, photochemical water oxidation in various pH, and the electrochemical oxygen reduction reaction (ORR) in alkaline medium. The cobalt oxide nanochains are easily accessible on a multigram scale by low-temperature degradation of a cobalt oxalate precursor. What sets this study apart from earlier ones is its synoptical perspective of reversible oxygen redox catalysis in different chemical and electrochemical environments.

A new precursor strategy to prepare ZnCo2O4 nanorods and their excellent catalytic activity for thermal decomposition of ammonium perchlorate

We present a new preparation of zinc cobaltite (ZnCo2O4) nanorods via a hydrothermal-annealing method. Zinc cobalt oxalate (ZnCo2(C2O4)3·6H2O) nanorods as the precursor have been firstly synthesized by solvothermal method at 120°C using the mixed solvents as the reaction medium without the assistance of soft/hard template. It is found that the mixed solvent plays an important role for zinc cobalt oxalate precursor nanorods and 1D growth of zinc cobalt oxalate precursor is gradually improved with the increasing ethylene glycol (EG) in the mixed solvent. The as-prepared zinc cobalt oxalate precursor (ZnCo2(C2O4)3·6H2O) nanorods can convert to 1D zinc cobaltite (ZnCo2O4) nanostructures while maintaining original frame structure. The obtained samples are characterized by means of XRD, SEM, TEM and HRTEM. Furthermore, the effect of zinc cobaltite (ZnCo2O4) nanostructures on the thermal decomposition of ammonium perchlorate (AP) is investigated by differential thermal analysis (DTA). The results show that the addition of zinc cobaltite (ZnCo2O4) nanorods to AP remarkably decreases the decomposition temperature. The as-prepared zinc cobaltite (ZnCo2O4) nanorods are promising as a high-performing ballistic modifier in AP-based composite solid rocket propellants.

Controlled synthesis of highly active mesoporous Co3O4 polycrystals for low temperature CO oxidation

Polycrystalline mesoporous Co3O4 has been successfully fabricated using a simple but efficient controlled thermal decomposition approach and their catalytic activities for low temperature CO oxidation were evaluated. In such a synthesis, micrometer-sized polyhedral cobalt oxalate crystals were first prepared and used as precursor. Mesoporosity was then generated via the pyrolysis of the cobalt oxalate precursor and the resultant nano-sized Co3O4 crystallites connected together to form mesoporous structure within the original micrometer-sized particles. The as-prepared material by calcination at 300°C at a heating rate of 0.5°C/min possessed high surface area and showed extraordinarily high catalytic activity for low temperature CO oxidation, the full CO conversion can be achieved at as low as −70°C.

A Facile Preparation of the Co3O4 Villiform Nanostructure

A Co3O4 villiform nanostructure was prepared by the aid of the cobalt oxalate precursor and characterized with x-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and UV-vis spectrum. It is found that the villiform structure obtained consists of Co3O4 nanorods with diameters of 50–80 nm. Moreover, the UV-vis absorptions of the villiform Co3O4 show the apparent blue shifts by comparison with the bulk Co3O4, indicating a quantum size effect similar to the free Co3O4 nanoparticles.

Study of cobalt-doped lithium–nickel oxides as cathodes for MCFC

Cobalt substituted lithium–nickel oxides were synthesized by a solid-state reaction procedure using lithium nitrate, nickel hydroxide and cobalt oxalate precursor and were characterized as cathodes for molten carbonate fuel cell (MCFC). LiNi 0.8Co 0.2O 2 cathodes were prepared using non-aqueous tape casting technique followed by sintering in air. The X-ray diffraction (XRD) analysis of sintered LiNi 1− x Co x O 2 indicated that lithium evaporation occurs during heating. The lithium loss decreases with an increase of the cobalt content in the mixed oxides. The stability studies showed that dissolution of nickel into the molten carbonate melt is smaller in the case of LiNi 1− x Co x O 2 cathodes compared to the dissolution values reported in the literature for state-of-the-art NiO. Pore volume analysis of the sintered electrode indicated a mean pore size of 3 μm and a porosity of 40%. A current density of 160 mA/cm 2 was observed when LiNi 0.8Co 0.2O 2 cathodes were polarized at 140 mV. The electrochemical impedance spectroscopy (EIS) studies done on LiNi 0.8Co 0.2O 2 cathodes under different gas conditions indicated that the rate of the cathodic discharge reaction depends on the O 2 and CO 2 partial pressures.

Characterization and activity of cobalt oxide catalysts for total oxidation of hydrocarbons

In view of the importance of catalytic combustion in the field of air pollution control, a study on the total oxidation of lean mixtures of hexane (approximately 0.5 mol%) in air was undertaken. Silica-supported cobalt oxide catalysts prepared by the impregnation of silica hydrogel by ammoniacal cobalt oxalate precursor effectively catalysed the total oxidation at 553 K. The dependence of the catalyst activity on the temperature and environment during decomposition was investigated. A low decomposition temperature and an inert environment yielded better activity of the catalysts. This has been explained with the help of the decomposition mechanism of cobalt oxalate and has been supported by estimating the particle size distribution by X-ray diffraction analysis.