Synergetic ternary metal oxide nanodots-graphene cathode for high performance zinc energy storage

Zinc-based electrochemistry energy storage with high safety and high theoretical capacity is considered to be a competitive candidate to replace lithium-ion batteries. In electrochemical energy storage, multi-metal oxide cathode materials can generally provide a wider electrochemical stability window and a higher capacity compared with single metal oxides cathode. Here, a new type of cathode material, MnFe₂Co₃O₈ nanodots/functional graphene sheets, is designed and used for aqueous hybrid Zn-based energy storage. Coupling with a hybrid electrolyte based on zinc sulfate and potassium hydroxide, the as-fabricated battery was able to work with a wide electrochemical window of 0.1∼1.8 V, showed a high specific capacity of 660 mAh/g, delivered an ultrahigh energy density of 1135 Wh/kg and a scalable power density of 5754 W/kg (calculated based on the cathode), and displayed a long cycling life of 1000 cycles. These are mainly attributed to the valence charge density distribution in MnFe₂Co₃O₈ nanodots, the good structural strengthening as well as high conductivity of the cathode, and the right electrolyte. Such cathode material also exhibited high electrocatalytic activity for oxygen evolution reaction and thus could be used for constructing a Zn-air battery with an ultrahigh reversible capacity of 9556 mAh/g.     

Effect of the preparation method on the catalytic performance of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> for methane oxidation

The layered structure oxide Ca₃Co₄O₉ particle was synthesized by two routes of citrate sol–gel method. The structure, morphology and surface property of Ca₃Co₄O₉ was characterized by XRD, SEM and XPS, respectively. The catalytic activity of Ca₃Co₄O₉ for methane combustion was tested in a fixed bed quartz tubular microreactor. The catalysis results reveal that the catalytic activity is sensitive to the texture of Ca₃Co₄O₉ by different route. TG measures confirm that the small particle size of Ca₃Co₄O₉ favors the oxygen transformation on the surface, which can be ascribed the random distribution of the crystal axes in irregular Ca₃Co₄O₉ particle.     

Molecular Engineering of a 3D Self‐Supported Electrode for Oxygen Electrocatalysis in Neutral Media

Electrodes for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are required in energy conversion and storage technologies. An assembly strategy involves covalently grafting Co corrole 1 onto Fe₃O₄ nanoarrays grown on Ti mesh. The resulted electrode shows significantly improved activity and durability for OER and ORR in neutral media as compared to Fe₃O₄ alone and with directly adsorbed 1 . It also displays higher atom efficiency (at least two magnitudes larger turnover frequency) than reported electrodes. Using this electrode in a neutral Zn‐air battery, a small charge–discharge voltage gap of 1.19 V, large peak power density of 90.4 mW cm^?2, and high rechargeable stability for >100 h are achieved, opening a promising avenue of molecular electrocatalysis in a metal–air battery. This work shows a molecule‐engineered electrode for electrocatalysis and demonstrates their potential applications in energy conversion and storage.     

Core–Shell‐Structured CNT@RuO2 Composite as a High‐Performance Cathode Catalyst for Rechargeable Li–O2 Batteries

A RuO₂ shell was uniformly coated on the surface of core CNTs by a simple sol–gel method, and the resulting composite was used as a catalyst in a rechargeable Li–O₂ battery. This core–shell structure can effectively prevent direct contact between the CNT and the discharge product Li₂O₂, thus avoiding or reducing the formation of Li₂CO₃, which can induce large polarization and lead to charge failure. The battery showed a high round‐trip efficiency (ca. 79 %), with discharge and charge overpotentials of 0.21 and 0.51 V, respectively, at a current of 100 mA g_total^?1. The battery also exhibited excellent rate and cycling performance.     

Hydrophobic POM Electrocatalyst Achieves Low Voltage “Charge” in Zn-Air Battery Coupled with Bisphenol A Degradation

Zn-air batteriesare a perspective power source for grid-storage. But, after they are discharged at1.1 to 1.2 V, large overpotential is required for their charging (usually 2.5 V). This is due to a sluggish oxygen evolution reaction (OER). Incorporating organic pollutants into the cathode electrolyte is a feasible strategy for lowering the required charging potential. In the discharge process, the related oxygen reduction reaction, hydrophobic electrocatalysts are more popular than hydrophilic ones. Here, a hydrophobic bifunctional polyoxometalate electrocatalyst is synthesized by precise structural design. It shows excellent activities in both bisphenol A degradation and oxygen reduction reactions. In bisphenol A containing electrolyte, to achieve 100 mA ⋅ cm⁻², its potential is only 1.32 V, which is 0.34 V lower than oxygen evolution reaction. In the oxygen reduction reaction, this electrocatalyst follows the four-electron mechanism. In both bisphenol A degradation and oxygen reduction reactions, it shows excellent stability. With this electrocatalyst as cathode material and bisphenol A containing KOH as electrolyte, a Zn-air battery was assembled. When “charged” at 85 mA ⋅ cm⁻², it only requires 1.98 V. Peak power density of this Zn-air battery reaches 120.5 mW ⋅ cm⁻². More importantly, in the “charge” process, bisphenol A is degraded, which achieves energy saving and pollutant removal simultaneously in one Zn-air battery.     

氮掺杂碳纳米管负载Co3O4氧还原电催化剂的制备与性能

以碳纳米管(CNT)为原料,通过负载维生素B₁₂,简单热解得到了一种氮掺杂碳纳米管(N/CNT)负载低含量Co₃O₄纳米颗粒的氧还原电催化剂(Co₃O₄@N/CNT)。得益于均匀分散的Co₃O₄纳米颗粒以及氮掺杂,Co₃O₄@N/CNT表现出了优异的氧还原催化性能,其半波电位达到了0.844 V(vs RHE),超越了商业Pt/C(0.820 V(vs RHE))。与Pt/C相比,基于Co₃O₄@N/CNT组装的锌-空气电池表现出了更优的放电性能和循环稳定性。     

氮掺杂碳纳米管负载Co3O4氧还原电催化剂的制备与性能

以碳纳米管(CNT)为原料,通过负载维生素B₁₂,简单热解得到了一种氮掺杂碳纳米管(N/CNT)负载低含量Co₃O₄纳米颗粒的氧还原电催化剂(Co₃O₄@N/CNT)。得益于均匀分散的Co₃O₄纳米颗粒以及氮掺杂,Co₃O₄@N/CNT表现出了优异的氧还原催化性能,其半波电位达到了0.844 V(vs RHE),超越了商业Pt/C(0.820 V(vs RHE))。与Pt/C相比,基于Co₃O₄@N/CNT组装的锌-空气电池表现出了更优的放电性能和循环稳定性。     

Studies of Nano－sized Co304 as Anode Materials for Lithium－ion Batteries

The structural evolution of the Co₃O₄ fine powders prepared by rheological phase reaction and pyrolysis method upon different temperature has been investigated using X‐ray diffraction (XRD) topography. The electrochemical performance of Co₃O₄ electrode materials for Li‐ion batteries is studied in the form of Li/Co₃O₄ cells. The reversible capacity as high as 930 mAh/g for the Co₃O₄ sample heat‐treated at 600 °C is achieved and sustained over 30 times charge‐discharge cycles at room temperature. The detailed information concerning the reaction mechanism of Co₃O₄ active material together with lithium ion is obtained through ex‐situ XRD topography, X‐ray photoelectron spectroscopy (XPS) analysis and cyclic voltammetry (CV) technique. And it is revealed that a “two‐step” reaction is involved in the charge and discharge of the Li/Co₃O₄ cells, in which Co₃O₄ active material is reversibly reduced into xCoO(3 ‐ x)CoO and then into metallic Co.     

Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide Nanostructures as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction

The relationship between controllable morphology and electrocatalytic activity of Co₃O₄ and CoSe₂ for the oxygen evolution reaction (OER) was explored in alkaline medium. Based on the time‐dependent growth process of cobalt precursors, 1D Co₃O₄ nanorods and 2D Co₃O₄ nanosheets were successfully synthesized through a facile hydrothermal process at 180 °C under different reaction times, followed by calcination at 300 °C for 2 h. Subsequently, 1D and 2D CoSe₂ nanostructures were derived by selenization of Co₃O₄, which achieved the controllable synthesis of CoSe₂ without templating agents. By comparing the electrocatalytic behavior of these cobalt‐based catalysts in 1 m KOH electrolyte toward the OER, both 2D Co₃O₄ and 2D CoSe₂ nanocrystals have lower overpotentials and better electrocatalytic stability than that of 1D nanostructures. The 2D CoSe₂ nanosheets require overpotentials of 372 mV to reach a current density of 50 mA cm⁻² with a small Tafel slope of 74 mV dec⁻¹. A systematic contrast of the electrocatalytic performances for the OER increase in the order: 1D Co₃O₄<2D Co₃O₄<1D CoSe₂<2D CoSe₂. This work provides fundamental insights into the morphology–performance relationships of both Co₃O₄ and CoSe₂, which were synthesized through the same approach, providing a solid guide for designing OER catalysts.     

La<Subscript>0.1</Subscript>Ca<Subscript>0.9</Subscript>MnO<Subscript>3</Subscript>/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> for oxygen reduction and evolution reactions (ORER) in alkaline electrolyte

Non-precious metal bifunctional catalysts are of great interest for metal–air batteries, electrolysis, and regenerative fuel cell systems due to their performance and cost benefits compared to the Pt group metals (PGM). In this work, metal oxides of La_0.1Ca_0.9MnO₃ and nano Co₃O₄₇ catalyst as bifunctional catalysts were used in oxygen reduction and evolution reactions (ORER). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption isotherms. The electrocatalytic activity of the perovskite-type La_0.1Ca_0.9MnO₃ and Co₃O₄ catalysts both as single and mixtures of both were assessed in alkaline solutions at room temperature. Electrocatalyst activity, stability, and electrode kinetics were studied using cyclic voltammetry (CV) and rotating disk electrode (RDE). This study shows that the bifunctional performance of the mixed La_0.1Ca_0.9MnO₃ and nano Co₃O₄ was superior in comparison to either La_0.1Ca_0.9MnO₃ or nano Co₃O₄ alone for ORER_. The improved activity is due to the synergistic effect between the La_0.1Ca_0.9MnO₃ and nano Co₃O₄ structural and surface properties. This work illustrates that hybridization between these two metal oxides results in the excellent bifunctional oxygen redox activity, stability, and cyclability, leading to a cost-effective application in energy conversion and storage, albeit to the cost of higher catalyst loadings.     

Photo‐energy Conversion and Storage in an Aprotic Li‐O2 Battery

A photo‐involved Li‐O₂ battery with carbon nitride (C₃N₄) is presented as a bifunctional photocatalyst to accelerate both oxygen reduction and evolution reactions. With illumination in a discharge process, photoelectrons generated in the conduction band (CB) of C₃N₄ are donated to O₂ for O₂^?, which undergoes a second electron reduction to O₂^2? and gives the final product of Li₂O₂; in a reverse process, holes left behind in the valence band (VB) of C₃N₄ plus an applied lower voltage than the equilibrium drive the Li₂O₂ oxidation. The discharge voltage is significantly increased to 3.22 V, surpassing the thermodynamic limit of 2.96 V, and the charge voltage is reduced to 3.38 V. This leads to a record‐high round‐trip efficiency of 95.3 % and energy density increase of 23.0 % compared to that in the dark.     

Preparation of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> by polyacrylamide gel processing and its thermoelectric properties

Ca₃Co₄O₉ powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10⁻⁴ W m⁻¹ K⁻² at 700 °C, which is larger than that of Ca₃Co₄O₉ ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily scaled up chemical route to improve the thermoelectric properties of Ca₃Co₄O₉ ceramics by preparing the homogeneous and pure Ca₃Co₄O₉ phase.     

MnxOy/NC and CoxOy/NC Nanoparticles Embedded in a Nitrogen‐Doped Carbon Matrix for High‐Performance Bifunctional Oxygen Electrodes

Reversible interconversion of water into H₂ and O₂, and the recombination of H₂ and O₂ to H₂O thereby harnessing the energy of the reaction provides a completely green cycle for sustainable energy conversion and storage. The realization of this goal is however hampered by the lack of efficient catalysts for water splitting and oxygen reduction. We report exceptionally active bifunctional catalysts for oxygen electrodes comprising Mn₃O₄ and Co₃O₄ nanoparticles embedded in nitrogen‐doped carbon, obtained by selective pyrolysis and subsequent mild calcination of manganese and cobalt N₄ macrocyclic complexes. Intimate interaction was observed between the metals and nitrogen suggesting residual M–N_x coordination in the catalysts. The catalysts afford remarkably lower reversible overpotentials in KOH (0.1 M ) than those for RuO₂, IrO₂, Pt, NiO, Mn₃O₄, and Co₃O₄, thus placing them among the best non‐precious‐metal catalysts for reversible oxygen electrodes reported to date.     

New Reaction Pathway of Superoxide Disproportionation Induced by a Soluble Catalyst in Li-O2 Batteries

Aprotic Li-O₂ battery has attracted considerable interest for high theoretical energy density, however the disproportionation of the intermediate of superoxide (O₂⁻) during discharge and charge leads to slow reaction kinetics and large voltage hysteresis. Herein, the chemically stable ruthenium tris(bipyridine) (RB) cations are employed as a soluble catalyst to alternate the pathway of O₂⁻ disproportionation and its kinetics in both the discharge and charge processes. RB captures O₂⁻ dimer and promotes their intramolecular charge transfer, and it decreases the energy barrier of the disproportionation reaction from 7.70 to 0.70 kcal mol⁻¹. This facilitates the discharge and charge processes and simultaneously mitigates O₂⁻ and singlet oxygen related side reactions. These endow the Li-O₂ battery with reduced discharge/charge voltage gap of 0.72 V and prolonged lifespan for over 230 cycles when coupled with RuO₂ catalyst. This work highlights the vital role of superoxide disproportionation for Li-O₂ battery.     

Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

The development of technologically viable electrodes for the electrochemical oxygen evolution reaction (OER) is a major bottleneck in chemical energy conversion. This article describes a facile one‐step hydrothermal route to deposit microcrystals of a robust Dexter–Silverton polyoxometalate oxygen evolution catalyst, [Co_6.8Ni_1.2W₁₂O₄₂(OH)₄(H₂O)₈], on a commercial nickel foam electrode. The electrode shows efficient and sustained electrochemical oxygen evolution at low overpotentials (360 mV at 10 mA cm⁻² against RHE, Tafel slope 126 mV dec⁻¹, faradaic efficiency (96±5) %) in alkaline aqueous solution (pH 13). Post‐catalytic analyses show no mechanical or chemical degradation and no physical detachment of the microcrystals. The results provide a blueprint for the stable “wiring” of POM catalysts to commercial metal foam substrates, thus giving access to technologically relevant composite OER electrodes.     

Recent advances in charge mechanism of noble metal-based cathodes for Li-O2 batteries

Lithium-oxygen(Li-O₂ ) batteries are considered as the next generation for energy storages systems due to the higher theoretical energy density than that of Li-ion batteries. However, the high charge overpotential caused by the insulated Li₂O₂ results in low energy efficiency, side reaction from electrolyte and cathode, and therefore poor battery performance. Designing noble metal-based catalysts can be an effective strategy to develop high-performance Li-O_2...     

Cobalt oxide–graphene nanocomposite as anode materials for lithium-ion batteries

Composites of Co₃O₄/graphene nanosheets are prepared and characterized by X-ray diffraction and scanning electron microscopy. Their electrochemical behavior as anode materials of lithium-ion rechargeable batteries is investigated by galvanostatic discharge/charge measurements and cyclic voltammetry. The composite is composed of Co₃O₄ nanorods (around 20??0?nm in diameter) and nanoparticles (around 10?nm in diameter) distributed within the graphene matrix. The specific capacity of the composite is higher than both Co₃O₄ and graphene nanosheets. The cycling stability of Co₃O₄ is obviously enhanced by compositing with graphene. After 100 cycles, the discharge and charge capacity of the composite is 1,005 and 975?mAh g^??, respectively, and the irreversible capacity loss is less than 3%.     

Large-area Free-standing Metalloporphyrin-based Covalent Organic Framework Films by Liquid-air Interfacial Polymerization for Oxygen Electrocatalysis

Synthesizing large-area free-standing covalent organic framework (COF) films is of vital importance for their applications but is still a big challenge. Herein, we reported the synthesis of large metalloporphyrin-based COF films and their applications for oxygen electrocatalysis. The reaction of meso-benzohydrazide-substituted metal porphyrins with tris-aldehyde linkers afforded free-standing COF films at the liquid-air interface. These films can be scaled up to 3000 cm² area and display great mechanical stability and structural integrity. Importantly, the Co-porphyrin-based films are efficient for electrocatalytic O₂ reduction and evolution reactions. A flexible, all-solid-state Zn-air battery was assembled using the films and showed high performance with a charge–discharge voltage gap of 0.88 V at 1 mA cm⁻² and high stability under bent conditions (0° to 180°). This work thus presents a strategy to synthesize functionalized COF films with high quality for uses in flexible electronics.     

高效析氧电催化剂Co3O4@NiMn-LDH异质结构阵列的制备

我们合理设计和制备了一种新型的高性能析氧电催化剂——泡沫镍负载Co_3O_4@NiMn-LDH(层状双金属氢氧化物)三维异质结构阵列(Co_3O_4@NiMn-LDH/NF)。这种基于泡沫镍基底的三维异质结构催化剂经简单的两步水热反应即可制得。对比Co_3O_4、NiMn-LDH及传统RuO2催化剂,所制备的Co_3O_4@NiMn-LDH/NF催化剂展示出更优异的电催化析氧性能。在1 mol·L~(-1)KOH溶液中,电流密度为50 mA·cm~(-2)时的过电势仅为282 mV,塔菲尔斜率为64 mV·dec~(-1)。通过有效的界面工程设计,使异质结构陈列Co_3O_4@NiMn-LDH发挥出Co_3O_4和NiMn-LDH各自优异的电催化性能。其中,基于泡沫镍基底生长的活性组分Co_3O_4纳米线阵列作为中间核支撑结构,保持了良好的空隙率,不仅有利于暴露更多的活性位点,而且有利于电解液的扩散和气体产物的释放;而依附于Co_3O_4纳米线阵列上的NiMn-LDH异质结构纳米片层则富有更多的亲水性基团,使得活性位点更易与水结合,从而促进氧析出反应的进行。     

Cobalt oxide–graphene nanocomposite as anode materials for lithium-ion batteries

Composites of Co₃O₄/graphene nanosheets are prepared and characterized by X-ray diffraction and scanning electron microscopy. Their electrochemical behavior as anode materials of lithium-ion rechargeable batteries is investigated by galvanostatic discharge/charge measurements and cyclic voltammetry. The composite is composed of Co₃O₄ nanorods (around 20–40 nm in diameter) and nanoparticles (around 10 nm in diameter) distributed within the graphene matrix. The specific capacity of the composite is higher than both Co₃O₄ and graphene nanosheets. The cycling stability of Co₃O₄ is obviously enhanced by compositing with graphene. After 100 cycles, the discharge and charge capacity of the composite is 1,005 and 975 mAh g⁻¹, respectively, and the irreversible capacity loss is less than 3%.