Cobalt‐Doped Perovskite‐Type Oxide LaMnO3 as Bifunctional Oxygen Catalysts for Hybrid Lithium–Oxygen Batteries

Perovskite‐type oxides based on rare‐earth metals containing lanthanum manganate are promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte. Perovskite‐type LaMnO₃ shows excellent ORR performance, but poor OER activity. To improve the OER performance of LaMnO₃, the element cobalt is doped into perovskite‐type LaMnO₃ through a sol–gel method followed by a calcination process. To assess electrocatalytic activities for the ORR and OER, a series of LaMn_1?xCo_xO₃ (x=0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) perovskite oxides were synthesized. The results indicate that the amount of doped cobalt has a significant effect on the catalytic performance of LaMn_1?xCo_xO₃. If x=0.3, LaMn_0.7Co_0.3O₃ not only shows a tolerable electrocatalytic activity for the ORR, but also exhibits a great improvement (>200 mV) on the catalytic activity for the OER; this indicates that the doping of cobalt is an effective approach to improve the OER performance of LaMnO₃. Furthermore, the results demonstrate that LaMn_0.7Co_0.3O₃ is a promising cost‐effective bifunctional catalyst with high performance in the ORR and OER for application in hybrid Li?O₂ batteries.     

Synthesis and Electrochemical Characterization of Gradient Composite LiNi1-yCoyO2 Used as Cathode Materials in Lithium-ion Battery

Gradient composites, LiNi1-yCoyO2, are synthesized from coated spherical Ni(OH)2 precursor. These composites could be applied as new cathode materials in lithium-ion batteries because they have low cobalt content (y≤0.2)and exhibit excellent properties during high-rate charge/discharge cycles. The initial discharge capacity of coated composite of LiNio.95Co0.05O2 is 186 mAh/g, and the decreasing rate of the capacity is 3.2% in 50 cycles at 1C rate. It has been verified by TEM and EDX experiments that a core-shell structure of the composite particles develops because of the cobalt enrichment near the surfaces, and the formation of the cobalt enrichment layer is sensitive to sintering temperature. High cobalt surface concentration may reduce the undesired reactions and stabilize the structure of the particles.     

Cobalt‐Doped FeS2 Nanospheres with Complete Solid Solubility as a High‐Performance Anode Material for Sodium‐Ion Batteries

Considering that the high capacity, long‐term cycle life, and high‐rate capability of anode materials for sodium‐ion batteries (SIBs) is a bottleneck currently, a series of Co‐doped FeS₂ solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na‐storage properties were investigated. The optimized Co_0.5Fe_0.5S₂ (Fe0.5) has discharge capacities of 0.220 Ah g^?1 after 5000 cycles at 2 A g^?1 and 0.172 Ah g^?1 even at 20 A g^?1 with compatible ether‐based electrolyte in a voltage window of 0.8–2.9 V. The Fe0.5 sample transforms to layered Na_xCo_0.5Fe_0.5S₂ by initial activation, and the layered structure is maintained during following cycles. The redox reactions of Na_xCo_0.5Fe_0.5S₂ are dominated by pseudocapacitive behavior, leading to fast Na⁺ insertion/extraction and durable cycle life. A Na₃V₂(PO₄)₃/Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g^?1.     

Structure and Electrochemical Behavior of Lithium-Manganese Spinels Doped with Chromium and Nickel

A series of compounds with the general formula LiMn_{2 - x - y} Cr _x Ni _y O₄, where x + y = 0.05, 0.5, or 1.0, is synthesized. It is shown that all these compounds are pure-phase spinels with parameter aequal to 0.8193-0.8236 nm. Doping a stoichiometric lithium-manganese spinel simultaneously with chromium and nickel makes the spinel structure stable. The initial specific capacity of a spinel depends on its doping degree. Doping LiMn₂O₄ with chromium and nickel simultaneously at an Mn : Cr : Ni ratio of 195 : 3 : 2 raises the spinel's specific capacity and reduces the cycling degradation. The change in the discharge capacity of LiMn_1.95Cr_0.03Ni_0.02O₄ electrodes cycled at 20, 0, and -14°C is determined.     

Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

Thermodynamic Stability of Transition‐Metal‐Substituted LiMn2−xMxO4 (M=Cr,Fe, Co,and Ni) Spinels

The formation enthalpies from binary oxides of LiMn₂O₄, LiMn_2?xCr_xO₄ (x=0.25, 0.5, 0.75 and 1), LiMn_2?xFe_xO₄ (x=0.25 and 0.5), LiMn_2?xCo_xO₄ (x=0.25, 0.5, and 0.75) and LiMn_1.75Ni_0.25O₄ at 25 °C were measured by high temperature oxide melt solution calorimetry and were found to be strongly exothermic. Increasing the Cr, Co, and Ni content leads to more thermodynamically stable spinels, but increasing the Fe content does not significantly affect the stability. The formation enthalpies from oxides of the fully substituted spinels, LiMnMO₄ (M=Cr, Fe and Co), become more exothermic (implying increasing stability) with decreasing ionic radius of the metal and lattice parameters of the spinel. The trend in enthalpy versus metal content is roughly linear, suggesting a close‐to‐zero heat of mixing in LiMn₂O₄—LiMnMO₄ solid solutions. These data confirm that transition‐metal doping is beneficial for stabilizing these potential cathode materials for lithium‐ion batteries.     

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.     

Catalytic Properties of Nanoscale Iron‐Doped Zirconia Solid‐Solution Aerogels

Nanoscale iron‐doped zirconia solid‐solution aerogels are prepared via a simple ethanol thermal route using zirconyl nitrate and iron nitrate as starting materials, followed by a supercritical fluid drying process. Structural characteristics are investigated by means of powder X‐ray diffraction (XRD), thermal analyses (TG/DTA), N₂ adsorption measurements and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the resulting iron‐doped solid solutions are metastable tetragonal zirconia which exhibit excellent dispersibility and high solubility of iron oxide. Further, when the Fe:(Fe+Zr) ratio x is lower than 0.10, all of the Fe³⁺ ions can be incorporated into ZrO₂ by substituting Zr⁴⁺ to form Zr_1?xFe_xO_y solid solutions. Moreover, for the first time, an additional hydroxyl group band that is not present in pure ZrO₂ is observed by DRIFTS for the Zr(Fe)O₂ solid solution. This is direct evidence of Fe³⁺ ions incorporated into ZrO₂. These Zr_1?xFe_xO_y solid solutions are excellent catalysts for the solvent‐free aerobic oxidation of n‐hexadecane using air as the oxidant under ambient conditions. The Zr_0.8Fe_0.2O_y solid‐solution catalyst demonstrates the best catalytic properties, with the conversion of n‐hexadecane reaching 36.2 % with 48 % selectivity for ketones and 24 % selectivity for alcohols and it can be recycled five times without significant loss of activity.     

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co_4?xZn_xO₄ (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.     

A Titanium‐Doped SiOx Passivation Layer for Greatly Enhanced Performance of a Hematite‐Based Photoelectrochemical System

This study introduces an in situ fabrication of nanoporous hematite with a Ti‐doped SiO_x passivation layer for a high‐performance water‐splitting system. The nanoporous hematite with a Ti‐doped SiO_x layer (Ti‐(SiO_x/np‐Fe₂O₃)) has a photocurrent density of 2.44 mA cm^?2 at 1.23 V_RHE and 3.70 mA cm^?2 at 1.50 V_RHE. When a cobalt phosphate co‐catalyst was applied to Ti‐(SiO_x/np‐Fe₂O₃), the photocurrent density reached 3.19 mA cm^?2 at 1.23 V_RHE with stability, which shows great potential of the use of the Ti‐doped SiO_x layer with a synergistic effect of decreased charge recombination, the increased number of active sites, and the reduced hole‐diffusion pathway from the hematite to the electrolyte.     

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.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

Electrochemical performance of LiMn2O4 microcubes prepared by a self-templating route

LiMn₂O₄ microcubes with a size of 10–15 μm have been synthesized by a facile self-templating route starting from cubic MnCO₃. The LiMn₂O₄ microcubes exhibit a hierarchical structure, where the cubes are stacked from parallel plates with a thickness of 200 nm, where each plate is composed of interconnected nanoparticles with a size of around 200 nm. The cubic LiMn₂O₄ shows excellent rate capability and high-rate cycling stability. At 10 C, it can yield a discharge capacity of 108 mAh g^?1. A discharge capacity of 88 mAh g^?1 can be retained after 100 cycles at 10 C. The excellent electrochemical performance makes it a promising cathode for high-power Li-ion batteries.     

溶胶-凝胶法合成Li_(1-x)Na_xMn_2O_4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na+离子掺杂的Li_(1-x)Na_xMn_2O_4(x=0,0.01,0.03,0.05)。X射线衍射图表明Na+取代Li+进入Li_(1-x)Na_xMn_2O_4晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_(0.97)Na_(0.03)Mn_2O_4在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn_2O_4从51.2%提升到84.1%。循环伏安测试表明Na+离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li0.97Na0.03Mn2O4仍有79.0 m Ah·g-1的放电容量,高于未掺杂样品的52.1 m Ah·g~(-1)。Na+离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn_2O_4的电化学性能,是一种可行的改性方法。     

溶胶-凝胶法合成Li1-xNaxMn2O4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na⁺离子掺杂的Li_1-xNa_xMn₂O₄(x=0,0.01,0.03,0.05)。X射线衍射图表明Na⁺取代Li⁺进入Li_1-xNa_x Mn₂O₄晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_0.97Na_0.03Mn₂O₄在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn₂O₄从51.2%提升到84.1%。循环伏安测试表明Na⁺离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li_0.97Na_0.03Mn₂O₄仍有79.0 mAh·g^-1的放电容量,高于未掺杂样品的52.1 mAh·g^-1。Na⁺离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn₂O₄的电化学性能,是一种可行的改性方法。     

A Flame‐Reaction Method for the Large‐Scale Synthesis of High‐Performance SmxCoy Nanomagnets

We report a flame‐reaction method to synthesize high‐performance Sm_xCo_y (x=1, y=5; x=2, y=17) particles on a multigram scale. This flame reaction allows the controlled decomposition of Sm(NO₃)₃ and Co(NO₃)₂ to 320 nm SmCo‐O (SmCoO₃ + Co₃O₄) particles. A 5.8 g sample of SmCo_3.8‐O particles was coated with CaO and then reduced at 900 °C by Ca to give 4.2 g of 260 nm SmCo₅ particles. The SmCo₅ particles are strongly ferromagnetic and the aligned particles in epoxy resin exhibit a large room‐temperature coercivity (H_c) of 41.8 kOe and giant (BH)_max (maximum magnetic energy product) of 19.6 MGOe, the highest value ever reported for SmCo₅ made by chemical methods. This synthesis can be extended to synthesize Sm₂Co₁₇ particles, providing a general approach to scaling up the synthesis of high‐performance Sm_xCo_y nanomagnets for permanent magnet applications.     

Application of Nanosized Cu0.5Co0.5Fe2O4 Spinel Ferrite as a Nanocatalyst in the Synthesis of 14‐Aryl‐14H‐dibenzo[a,j]xanthene Derivatives under Solvent‐free Conditions

Copper and cobalt substituted spinel ferrites Cu_1‐xCo_xFe₂O₄ (0≤X≤1) have been synthesized by using hydrothermal method. The resultant spinel ferrites were systematically characterized by different techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FT‐IR). It was indicated that all the resultant spinel ferrites obtained by the hydrothermal method had the single‐phase crystalline. The resultant spinel ferrites were employed in the synthesis of 14‐aryl‐14‐H‐dibenzo[a,j]xanthene derivatives. It was found that the nanocatalyst Cu_0.5Co_0.5Fe₂O₄ displays the best performance in the synthesis of 14‐aryl‐14H‐dibenzo[a,j]xanthenes. The catalyst was reused several times without significant loss of its activity for the preparation of desired product. In addition high yields of the products, solvent‐free conditions and reusability of the catalyst are other worthwhile advantages of the present study.     

尖晶石型LiMn2-xInxO4(x=0，0.01，0.02，0.05)的合成及电化学性能研究

以醋酸锰、氢氧化锂和三氧化二铟为原料,以柠檬酸为配位剂,采用溶胶-凝胶法制备了掺杂In的尖晶石LiMn2-xInxO4(x=0,0.01,0.02,0.05),采用XRD、SEM对目标材料进行了结构和形貌表征,采用恒流充放电、循环伏安(CV)以及交流阻抗(EIS)谱测试对材料进行了电化学性能表征,考察了不同In掺杂量对材料性能的影响。结果表明,当In掺杂量为1%时,LiMn1.99In0.01O4样品具有纯的尖晶石锰酸锂结构,在0.5C和3.4～4.35 V电压范围条件下,LiMn1.99In0.01O4的初始放电容量为119.9 mAh.g-1,经过1C 30次,2C 30次,再0.5C 5次循环后,其放电容量保持率为84.9%,显示了良好的电化学性能。掺杂1%的In的样品比未掺杂的样品具有更优的高温循环稳定性能。     

Synthesis and Electrochemical Performance of Spinel LiMn2O4—x（SO4）x Cathode Materials

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Electrochemical Preparation of N‐Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen‐Reduction Reaction

Nitrogen‐doped CoO (N‐CoO) nanoparticles with high electrocatalytic activity for the oxygen‐reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl₂ in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen‐doped Co nanoparticles were readily oxidized to N‐CoO nanoparticles in air. In contrast to their N‐free counterparts (CoO or Co₃O₄), N‐CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The Co?N_x active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen‐doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells.