Synthesis of Co3O4/Carbon composite nanowires and their electrochemical properties

Porous nanowires of Co₃O₄/Carbon composite have been synthesized by using a simple and inexpensive electrospinning technique. The as-prepared materials were investigated by X-ray diffraction and scanning electron microscopy. The electrochemical properties of the composite have been characterized using cyclic voltammetry and galvanostatic methods. The results show a remarkably improved electrochemical performance in term of reversible capacity, rate capability, and cycling performance.     

Electrochemical capacitance of Co3O4 nanowire arrays supported on nickel foam

Co₃O₄ nanowire arrays freely standing on nickel foam are prepared via template-free growth followed by thermal treatment at 300 °C in air. Their morphology is examined by scanning and transmission electron microscopy. The electrochemical capacitance behavior of the self-supported binderless nanowire array electrode is investigated by cyclic voltammetry, galvanostatic charge-discharge test and electrochemical impedance spectroscopy. The results show that nanowires are formed by nanoplatelets packed roughly layer by layer. They densely cover the nickel foam substrate and have diameters around 250 nm and the lengths up to around 15 μm. The Co₃O₄ nanowires display a specific capacitance of 746 F g⁻¹ at a current density of 5 mA cm⁻². The capacitance loss is less than 15% after 500 charge-discharge cycles. The columbic efficiency is higher than 93%.     

A hierarchical nanostructure consisting of amorphous MnO2, Mn3O4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors

In this communication, a porous hierarchical nanostructure consisting of amorphous MnO₂ (a-MnO₂), Mn₃O₄ nanocrystals, and single-crystalline MnOOH nanowires is designed for the supercapacitor application, which is prepared by a simple two-step electrochemical deposition process. Because of the gradual co-transformation of Mn₃O₄ nanocrystals and a-MnO₂ nanorods into an amorphous manganese oxide, the cycle stability of a-MnO₂ is obviously enhanced by adding Mn₃O₄. This unique ternary oxide nanocomposite with 100-cycle CV activation exhibits excellent capacitive performances, i.e., excellent reversibility, high specific capacitances (470 F g⁻¹ in CaCl₂), high power property, and outstanding cycle stability. The highly porous microstructures of this composite before and after the 10,000-cycle CV test are examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).     

Low-temperature synthesis of Na2Mn5O10 for supercapacitor applications

The romanechite-like sodium manganese oxide Na₂Mn₅O₁₀ is synthesized through alkaline hydrolysis of [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄] followed by thermal calcination. Amorphous Na₂Mn₅O₁₀ is obtained at relatively low temperature (200 °C). Increasing the calcination temperature leads to highly crystalline nano-rods. Electrochemical studies demonstrate that Na₂Mn₅O₁₀ is a good candidate as positive electrode materials for supercapacitor: specific capacitances of 178, 173 and 175 F g⁻¹ are obtained for Na₂Mn₅O₁₀ calcined at different temperatures (200, 400 and 600 °C), respectively, by charge-discharge tests at 0.1 A g⁻¹. Moreover, capacitance losses of all the products in 1000 cycles are less than 3%.     

Growth of polyaniline on rGO-Co3S4 nanocomposite for high-performance supercapacitor energy storage

Recently, since the supercapacitors have drawn considerable attention, a vast study have been triggered in order to develop efficient electrodes for responding to the increasing demand of supercapacitors. In this report, a possible approach have been used to prepare a ternary nanocomposite, polyaniline/reduced graphene oxide-cobalt sulfide (PANI/rGO-Co₃S₄). At first, a simple and inexpensive hydrothermal route has been used for the preparation of cobalt sulfide (Co₃S₄) on the surface of graphene oxide sheets (rGO-Co₃S₄). Then, the polyaniline nanorods have been flourished on the surface of rGO-Co₃S₄ sheets via in situ chemical polymerization of aniline which was synergistically adjoined to the graphene surface. Polyaniline has uniformly covered the surface of the rGO-Co₃S₄ due to the rational combination of two components. Combining of PANI with rGO-Co₃S₄ electrode material amplify its electrochemical efficiency in terms of a high specific capacitance of 767 F g^?1 at 1 A g^?1 and 81.7% of specific capacitance maintenance after 5000 cycles due to the creation of synergistic effect. Therefore, the ternary nanocomposite of PANI/rGO-Co₃S₄ provides a new promising pathway for the expanding of high-performance electrode materials for supercapacitors.     

Co3O4 nanosheet arrays treated by defect engineering for enhanced electrocatalytic water oxidation

Due to its poor electrical conductivity and finite exposed active sites, the development of high activity Co₃O₄ oxygen evolution reaction (OER) electrocatalysts remains a major challenge. Oxygen vacancies can enhance the electrical conductivity of electrocatalysts and reduce the adsorption energy of H₂O molecules on surfaces, thereby significantly enhancing their electrocatalytic activity. Taking inspiration from this, we demonstrate a green and facile reduction strategy to prepare reduced Co₃O₄ nanosheet arrays (R-Co₃O₄ NSA) with large electrochemical surface area and rich in surface oxygen vacancies. Compared to pristine Co₃O₄ nanosheet arrays (P-Co₃O₄ NSA), R-Co₃O₄ NSA exhibits better OER performance, with a lower overpotential of 330 mV at a current density of 20 mA cm^?2 and a smaller Tafel slope of 72 mV dec^?1. Impressively, the excellent properties of R-Co₃O₄ NSA can rival to the state-of-the-art noble metal oxide electrocatalyst (IrO₂). This strategy of defect-engineering offers a briefness and cost-effective means for the development of highly efficient OER systems.     

Hollow Co3O4 thin films as high performance anodes for lithium-ion batteries

Cobalt oxide thin films composed of hollow spherical Co₃O₄ particles have been prepared by a two-step method. The first step involves in the synthesis of hollow cobalt alkoxide particles in a stable suspension from mixed polyalcohol solutions of cobalt acetate in oil bath at 170 °C. The second step includes the thin film fabrication by electrostatic spray deposition (ESD) and subsequent heat treatment in nitrogen. The obtained Co₃O₄ films with the unique hollow particle microstructure exhibit high reversible capacity of above 1000 mAh g⁻¹ during up to 50 cycles and good rate capability. The films are promising negative electrodes for high energy lithium-ion batteries.     

Electrospinning synthesis of C/Fe3O4 composite nanofibers and their application for high performance lithium-ion batteries

Carbon-based nanofibers can be used as anode materials for lithium-ion batteries. Both pure carbon nanofiber and C/Fe₃O₄ composite nanofibers were prepared by electrospinning and subsequent carbonization processes. The composition and structures were characterized by Fourier transformation infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy. The electrochemical properties were evaluated in coin-type cells versus metallic lithium. It is found that after an annealing temperature of 500–700 °C, the carbon has disordered structure while Fe₃O₄ is nanocrystalline with a particle size from 8.5 to 52 nm. Compared with the pure carbon nanofiber, the 600 °C-carbonized C/Fe₃O₄ composite nanofiber exhibits much better electrochemical performance with a high reversible capacity of 1007 mAh g⁻¹ at the 80th cycle and excellent rate capability. A beneficial powderization phenomenon is discovered during the electrochemical cycling. This study suggests that the optimized C/Fe₃O₄ composite nanofiber is a promising anode material for high performance lithium-ion batteries.     

One step synthesis of rGO-Ni3S2 nano-cubes composite for high-performance supercapacitor electrodes

In the last decade, supercapacitors possessing high power density and cyclic stability have attracted great interests in various applications. Graphene-based composite electrodes are known as a promising candidate for supercapacitors due to synergistic effects. For the first time, in this work, we develop a simple one-step hydrothermal synthesis of graphene wrapped Ni₃S₂ nanocubes (rGO-Ni₃S₂) composite for high-performance and low-cost supercapacitor electrodes. The rGO-Ni₃S₂ electrode exhibits an ultrahigh specific capacity of 616 C g^?1 at the current density of 1 A g^?1 with excellent cycling durability of 92.7% after 5000 cycles, which is much better when compared with the counterpart without graphene (pure Ni₃S₂). We attribute the remarkable performance of the rGO-Ni₃S₂ electrode to the synergistic effects of the graphene as the conductive support and Ni₃S₂ cubics as the pseudocapacitive material. This work constitutes a step forward towards the development of low-cost and high-performance supercapacitors for the next generation of portable electronics.     

Catalytic behavior of Co3O4 in electroreduction of H2O2

Spinel structure Co₃O₄ nanoparticles with an average diameter of around 17 nm were prepared and evaluated as electrocatalysts for H₂O₂ reduction. Results revealed that Co₃O₄ exhibits considerable activity and good stability for electrocatalytic reduction of H₂O₂ in 3 M NaOH solution. The reduction occurs mainly via the direct pathway when H₂O₂ concentration is lower than 0.5 M. An Al-H₂O₂ semi fuel cell using Co₃O₄ as cathode catalyst was constructed and tested at room temperature. The fuel cell displayed an open circuit voltage of 1.45 V and a peak power density of 190 mW cm⁻² at a current density of 255 mA cm⁻² operating with a catholyte containing 1.5 M H₂O₂. This study demonstrated that Co₃O₄ nanoparticles are promising cathode catalysts, in place of precious metals, for fuel cells using H₂O₂ as oxidant.     

Fe3O4 submicron spheroids as anode materials for lithium-ion batteries with stable and high electrochemical performance

A magnetite (Fe₃O₄) powder composed of uniform sub-micrometer spherical particles has been successfully synthesized by a hydrothermal method at low temperature. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and galvanostatic cell cycling are employed to characterize the structure and electrochemical performance of the as-prepared Fe₃O₄ spheroids. The magnetite shows a stable and reversible capacity of over 900 mAh g⁻¹ during up to 60 cycles and good rate capability. The experimental results suggest that the Fe₃O₄ synthesized by this method is a promising anode material for high energy-density lithium-ion batteries.     

Characterization of MnFe2O4/LiMn2O4 aqueous asymmetric supercapacitor

A new type of asymmetric supercapacitor containing a MnFe₂O₄ negative electrode and a LiMn₂O₄ positive electrode in aqueous LiNO₃ electrolyte has been synthesized and characterized. The nanocrystalline MnFe₂O₄ anode material has a specific capacitance of 99 F g⁻¹ and the LiMn₂O₄ cathode a specific capacity of 130-100 mAh g⁻¹ under 10-100 C rate. The cell has a maximum operating voltage window of ca. 1.3 V, limited by irreversible reaction of MnFe₂O₄ toward reducing potential. The specific power and specific energy of the full-cell increase with increasing anode-to-cathode mass ratio (A/C) and saturate at A/C ∼4.0, which gives specific cell energies, based on total mass of the two electrodes, of 10 and 5.5 Wh kg⁻¹ at 0.3 and 1.8 kW kg⁻¹, respectively. The cell shows good cycling stability and exhibits significantly slower self-discharge rate than either the MnFe₂O₄ symmetric cell or the other asymmetric cells having the same cathode but different anode materials, including activated carbon fiber and MnO₂.     

Synthesis,characterization and photocatalytic performances of Cu2MoS4

A novel visible-light-driven Cu₂MoS₄ photocatalyst was prepared by a facile hydrothermal method using Ammonium Tetrathiomolybdate reacting with cuprous chloride in aqua ammonia. The synthetic catalysts were characterized by XRD, UV–vis spectra, XRF and SEM techniques. The influence of the reaction temperature and time on the activities of the catalysts and the morphology of particles was investigated. The results showed that the catalysts exhibited strong absorption in visible light region. It was found that the photocatalyst prepared under hydrothermal condition at 140 °C for about 24 h showed good crystallinity with regular shape, and the highest activity for hydrogen production under visible light irradiation in an aqueous Na₂S–Na₂SO₃ solution. The reason for its better performance has been discussed in detail.     

Interlayer-free electrodes for IT-SOFCs by applying Co3O4 as sintering aid

The influence of Co₃O₄ as a sintering aid for a series of cobalt-containing perovskite oxides on the microstructure and electrical properties have been investigated. X-ray diffraction and scanning electron microscopic results showed that well connected electrode particles with firm adhesion to the 8 mol% yttria-stabilized zirconia (YSZ) electrolyte surface were realized at a temperature free from interfacial phase reaction. Both ohmic and polarization resistances of symmetric cells by adopting YSZ electrolyte, measured by electrochemical impedance spectroscopy, were much lower than that without adding Co₃O₄. The peak power density of 1176 mW cm⁻² at 750 °C was achieved when La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ + Co₃O₄ was selected as a representative cobaltite cathode, which is much higher than a similar fuel cell with the cathode fabricated by a conventional way. Fabrication of interlayer-free electrodes by applying Co₃O₄ as a sintering aid is very simple and general, applicable for a wide range of cobalt-containing electrode materials.     

Hydrogen generation from sodium borohydride with Ni and Co based catalysts supported on Co3O4

Hydrogen is an alternative and clean energy carrier, but there are still some production related problems. In this aspect, it is crucial to efficiently generate hydrogen from hydrogen rich materials such as sodium borohydride. In this study, Co₃O₄ supported Ni and Co catalysts are synthesized via microwave irradiation technique for hydrogen generation from sodium borohydride. In this context, firstly, Co₃O₄ support material is synthesized by chemical method. Then, Ni and Co catalysts are decorated onto Co₃O₄ support material by microwave irradiation-polyol method. Prepared catalysts and support material are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-mass spectrometer (ICP/MS). A new system is designed by our group in order to determine the activity of the prepared catalysts for hydrogen generation. The effects of different initial NaOH concentrations on hydrogen generation rate are investigated. It is observed that the rate of hydrogen generation increased with an increase in initial NaOH concentration. Co-Co₃O₄ catalyst at 10% NaOH initial concentration shows the highest hydrogen generation rate as 2823 ml/g_cat.min. In summary, Co-based catalysts are exhibited more activity than Ni-based catalysts in terms of hydrogen generation.     

Hierarchical Co3O4 decorated PPy nanocasting core-shell nanospheres as a high performance electrocatalysts for methanol oxidation

In recent times, much attention has been paid to explore economic and highly active precious metal free electrocatalysts for energy conversion and storage systems due to the expensiveness of Pt-based catalysts. Here we developed a mesoporous core-shell like nanospheres composed of a metallic cobalt oxide core wrapped with a polypyrrole nanoshell (PPy/Co₃O₄) for methanol electrooxidation. The performance of the core-shell PPy/Co₃O₄ nanospheres as anodic catalyst material was measured in 1 M KOH electrolyte and the results obtained demonstrated that the hybrid possesses high catalytic activity in terms of current density and onset voltage. The core-shell PPy/Co₃O₄ delivers an oxidation current density of ～111 mA/cm² at 0.5 V with superior stability long run stability. The observed electrocatalytic performance of the porous PPy/Co₃O₄ nanospheres is attributed to the integrative effects of both Co-species and layered carbon shell and presence of exceptionally numerous mesopores. Results show evidence that the earth abundant PPy/Co₃O₄ provide a potential electrode material for methanol electrooxidation with a satisfactory reaction activity.     

Characterization of electrolytic Co3O4 thin films as anodes for lithium-ion batteries

The electrolytic deposition of Co₃O₄ thin films on stainless steel was conducted in Co(NO₃)₂ aqueous solution for anodes in lithium-ion thin film batteries. Three major electrochemical reactions during the deposition were discussed. The coated specimens and the coating films carried out at −1.0 V (saturated KCl Ag/AgCl) were subjected to annealing treatments and further characterized by XRD, TGA/DTA, FE-SEM, Raman spectroscopy, cyclic voltammetry (CV) and discharge/charge cyclic tests. The as-coated film was β-Co(OH)₂, condensed into CoO and subsequently oxidized into nano-sized Co₃O₄ particles. The nano-sized Co₃O₄, CoO, Li₂O and Co particles revealed their own characteristics different from micro-sized ones, such as more interfacial effects on chemical bonding and crystallinity. The initial maximum capacity of Co₃O₄ coated specimen was 1930 mAh g⁻¹ which much more than its theoretical value 890 mAh g⁻¹, since the nano-sized particles offered more interfacial bondings for extra sites of Li⁺ insertion. However, a large ratio of them was trapped, resulting in a great part of irreversible capacity during the first charging. Still, it revealed a capacity 500 mAh g⁻¹ after 50 discharged-charged cycles.     

Modeling of oxygen evolution at Teflon-bonded Ti/Co3O4 electrodes

The oxygen evolution reaction (OER) at Teflon-bonded Ti/Co₃O₄ electrodes was investigated and the process was simulated using an equivalent circuit fitting method and a mathematical model based on the Faradaic impedance of the reacting system. The correlation between the auxiliary electrochemical parameters and the elements of the equivalent circuit was derived and the lumped kinetic parameters of the different steps involved during oxygen evolution were evaluated. The method was validated by comparing experimental and model predicted data.     

Oxygen evolution reaction on Ni-substituted Co3O4 nanowire array electrodes

Nanowire arrays of mixed oxides of Co and Ni freely standing on Ni foam are prepared by a template-free growth method. The effects of Ni content on the morphology, structure and catalyst performance for oxygen evolution reaction are investigated by scanning electron microscopy, X-ray diffraction spectroscopy and electrochemical techniques including cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. A transformation from nanowire arrays to nanoplate arrays is found with the increase of the atomic ratio of Ni to Co in the preparation solution. The Ni_xCo_3−xO₄ electrode obtained at 1:1 of Ni:Co in the preparation solution exhibits nanowire array structure and has better catalytic performance for oxygen evolution reaction than other Ni_xCo_3−xO₄ and Co₃O₄ electrodes. The catalytic activities of the Ni_xCo_3−xO₄ and Co₃O₄ electrodes are correlated with their surface roughness. Superior stability of the Ni_xCo_3−xO₄ nanowire array electrode is demonstrated by a chronopotentiometric test. The reaction orders with respect to OH⁻ on the Ni_xCo_3−xO₄ electrode are close to 2 and 1 at low and high overpotentials, respectively.