Copper-Nanoparticle-Induced Porous Si/Cu Composite Films as an Anode for Lithium Ion Batteries

“Welcome-mat”-like porous Si/Cu composite amorphous films are fabricated by applying the predeposited Cu-nanoparticle-assembled film as the growth direction template for the subsequent deposition of a Si active layer with the cluster beam deposition technique. When used as the binder-free anodes for lithium ion batteries, the acquired single-layer porous Si/Cu composite film exhibits a large reversible capacity of 3124 mA h g^–1 after 1000 cycles at 1 A g^–1. Even when cycled at 20 A g^–1 for 450 cycles, the porous Si/Cu composite film still delivers a decent reversible capacity of 2086 mA h g^–1. Also, multilayer porous Si/Cu composite films are synthesized through layer-by-layer sputtering and exhibit outstanding cyclability and relatively high specific capacity and initial Coulombic efficiency irrespective of increasing the layer number from two to four layers. The reasons for the excellent electrochemical properties of single-layer and multilayer porous Si/Cu composite films are discussed in detail

Electrostatic Assembly of Sandwich-like Ag-C@ZnO-C@Ag‑C Hybrid Hollow Microspheres with Excellent High-Rate Lithium Storage Properties

Herein, we introduce a facile electrostatic attraction approach to produce zinc–silver citrate hollow microspheres, followed by thermal heating treatment in argon to ingeniously synthesize sandwich-like Ag-C@ZnO-C@Ag-C hybrid hollow microspheres. The 3D carbon conductive framework in the hybrids derives from the <i>in situ</i> carbonation of carboxylate acid groups in zinc–silver citrate hollow microspheres during heating treatment, and the continuous and homogeneous Ag nanoparticles on the outer and inner surfaces of hybrid hollow microspheres endow the shells with the sandwiched configuration (Ag-C@ZnO-C@Ag-C). When applied as the anode materials for lithium ion batteries, the fabricated hybrid hollow microspheres with sandwich-like shells reveal a very large reversible capacity of 1670 mAh g^–1 after 200 cycles at a current density of 0.2 A g^–1. Even at the very large current densities of 1.6 and 10.0 A g^–1, the high specific capacities of about 1063 and 526 mAh g^–1 can be retained, respectively. The greatly enhanced electrochemical properties of Ag-C@ZnO-C@Ag-C hybrid microspheres are attributed to their special structural features such as the hollow structures, the sandwich-like shells, and the nanometer-sized building blocks

Template-Free Synthesis of Amorphous Double-Shelled Zinc–Cobalt Citrate Hollow Microspheres and Their Transformation to Crystalline ZnCo₂O₄ Microspheres

A novel and facile approach was developed for the fabrication of amorphous double-shelled zinc–cobalt citrate hollow microspheres and crystalline double-shelled ZnCo₂O₄ hollow microspheres. In this approach, amorphous double-shelled zinc–cobalt citrate hollow microspheres were prepared through a simple route and with an aging process at 70 °C. The combining inward and outward Ostwald ripening processes are adopted to account for the formation of these double-shelled architectures. The double-shelled ZnCo₂O₄ hollow microspheres can be prepared via the perfect morphology inheritance of the double-shelled zinc–cobalt citrate hollow microspheres, by calcination at 500 °C for 2 h. The resultant double-shelled ZnCo₂O₄ hollow microspheres manifest a large reversible capacity, superior cycling stability, and good rate capability

Shape-Selective Formation of Monodisperse Copper Nanospheres and Nanocubes via Disproportionation Reaction Route and Their Optical Properties

Synthesis of stable and monodisperse Cu nanocrystals of controlled morphology has been a long-standing challenge. In this Article, we report a facile disproportionation reaction approach for the synthesis of such nanocrystals in organic solvents. Either spherical or cubic shapes can be produced, depending on conditions. The typical Cu nanospheres are single crystals with a size of 23.4 ± 1.5 nm, and can self-assemble into three-dimensional (3D) nanocrystal superlattices with a large scale. By manipulating the chemical additives, monodisperse Cu nanocubes with tailorable sizes have also been obtained. The probable formation mechanism of these Cu nanocrystals is discussed. The narrow size distribution results in strong surface plasmon resonance (SPR) peaks even though the resonance is located in the interband transition region. Double SPR peaks are observed in the extinction spectra for the Cu nanocubes with relative large sizes. Theoretical simulation of the extinction spectra indicates that the SPR band located at longer wavelengths is caused by assembly of Cu nanocubes into more complex structures. The synthesis procedure that we report here is expected to foster systematic investigations on the physical properties and self-assembly of Cu nanocrystals with shape and size singularity for their potential applications in photonic and nanoelectronic devices

Enhanced Microwave Absorption Properties by Tuning Cation Deficiency of Perovskite Oxides of Two-Dimensional LaFeO₃/C Composite in X‑Band

Development of microwave absorption materials with tunable thickness and bandwidth is particularly urgent for practical applications but remains a great challenge. Here, two-dimensional nanocomposites consisting of perovskite oxides (LaFeO₃) and amorphous carbon were successfully obtained through a one pot with heating treatment using sodium chloride as a hard template. The tunable absorption properties were realized by introducing A-site cation deficiency in LaFeO₃ perovskite. Among the A-site cation-deficient perovskites, La_0.62FeO₃/C (L_0.62FOC) has the best microwave absorption properties in which the maximum absorption is −26.6 dB at 9.8 GHz with a thickness of 2.94 mm and the bandwidth range almost covers all X-band. The main reason affecting the microwave absorption performance was derived from the A-site cation deficiency which induced more dipoles polarization loss. This work proposes a promising method to tune the microwave absorption performance via introducing deficiency in a crystal lattice

Facile Preparation of Well-Dispersed CeO₂–ZnO Composite Hollow Microspheres with Enhanced Catalytic Activity for CO Oxidation

In this article, well-dispersed CeO₂–ZnO composite hollow microspheres have been fabricated through a simple chemical reaction followed by annealing treatment. Amorphous zinc–cerium citrate hollow microspheres were first synthesized by dispersing zinc citrate hollow microspheres into cerium nitrate solution and then aging at room temperature for 1 h. By calcining the as-produced zinc–cerium citrate hollow microspheres at 500 °C for 2 h, CeO₂–ZnO composite hollow microspheres with homogeneous composition distribution could be harvested for the first time. The resulting CeO₂–ZnO composite hollow microspheres exhibit enhanced activity for CO oxidation compared with CeO₂ and ZnO, which is due to well-dispersed small CeO₂ particles on the surface of ZnO hollow microspheres and strong interaction between CeO₂ and ZnO. Moreover, when Au nanoparticles are deposited on the surface of the CeO₂–ZnO composite hollow microspheres, the full CO conversion temperature of the as-produced 1.0 wt % Au–CeO₂–ZnO composites reduces from 300 to 60 °C in comparison with CeO₂–ZnO composites. The significantly improved catalytic activity may be ascribed to the strong synergistic interplay between Au nanoparticles and CeO₂–ZnO composites

High-Performance Na–O₂ Batteries Enabled by Oriented NaO₂ Nanowires as Discharge Products

Na–O₂ batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO₂ nanowires inside Na–O₂ batteries that significantly boosts the performance of Na–O₂ batteries. For this purpose, a high-spin Co₃O₄ electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO₂ nanowires are 10–20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na–O₂ batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g^–1, an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na–O₂ batteries but also opens up the opportunity to explore growing nanowires in novel conditions