Amorphous Bimetallic Co₃Sn₂ Nanoalloys Are Better Than Crystalline Counterparts for Sodium Storage

Sodium-ion batteries are considered as a promising alternative to replace the existing lithium-ion batteries for energy storage due to the benefits of low cost and safety. However, it is still challenging to develop suitable electrode materials for reversible storage of sodium. Metal anodes have high capacity for sodium storage but suffer the issue of poor cyclability due to pulverization caused by large volume variation and electrode disintegration. To address this issue, amorphous bimetallic active–inactive nanoalloy Co–Sn with Sn acting as a high capacity active compound and Co acting as a conductive inactive matrix has been explored here. We demonstrated that amorphous nanoalloys exhibited superior electrochemical performances as compared to the low-crystalline and crystalline counterpart nanoalloys as negative electrode materials for sodium-ion batteries. The degree of crystallinity has negative effects on electrochemical performances. The improved performance of amorphous nanoalloys could be attributed to the easy accessibility for sodium ions, strain accommodation, and defect sites to host sodium ions

Facile Synthesis of Fe₃O₄@g‑C Nanorods for Reversible Adsorption of Molecules and Absorption of Ions

It is an interesting but challenging task to design a facile and scalable procedure for the making of multifunctional materials for energy and environmental applications. Here, we developed a one-pot facile procedure for the preparation of disordered carbon (a-C) coated Fe₂O₃ nanorods. By heating Fe₂O₃@a-C nanorods under argon, they were easily converted to graphite carbon (g-C) coated magnetic Fe₃O₄, or Fe₃O₄@g-C, nanorods. We demonstrated that the as-prepared magnetic Fe₃O₄@g-C nanorods could reversibly store molecules, using dye as a model. This suggested that one of the possible applications would be as recyclable and reusable adsorbents for water remediation. At the same time, the magnetic Fe₃O₄@g-C nanorods are proposed as vehicles for the controlled release of drugs in an aqueous environment and, in particular, for the targeted treatment of infected regions through guided external magnetic forces. The Fe₃O₄@g-C nanorods were also investigated for their performances in the reversible storage of sodium ions, which is closely relevant to future sodium-ion batteries. We discovered that thin graphite carbon sheaths, which encapsulate the high-capacity Fe₃O₄ cores, could actually prevent the cores from having full access to sodium ions. We suggested that carbon coating, commonly used in electrode materials for lithium-ion batteries, may not be generally suitable for electrode materials used in future sodium-ion batteries. This discovery is helpful in guiding future studies on the use and selection of carbon coating, a common strategy to overcome electrode pulverization in lithium-ion batteries, for electrodes in future sodium-ion batteries

Ammonia-Assisted Wet-Chemical Synthesis of ZnO Microrod Arrays on Substrates for Microdroplet Transfer

It is still a challenging task to facilely grow microscale arrays on arbitrary substrates at low temperature conditions in solutions. Here, we have successfully formed ZnO microrod arrays on various substrates, including glass, gold coated glass, silicon wafer, and Teflon, by a single-step wet-chemical synthesis approach. We employ ammonia as the multifunctional reactant to modify the surface properties of the substrates and to regulate the pH of the reaction environment. Compared to other methods, no preloaded additives or seeds are required. The surface wettability of the ZnO microrod coated substrates can be tuned, achieving both hydrophilic and hydrophobic properties in air. We have studied both static wettability and dynamic behaviors of droplet impact or rebound on the modified substrates. We demonstrate that it is possible to achieve micromass transfer by using the hydrophobic substrate to repel water microdroplet while using the hydrophilic substrate to capture the water microdroplets utilizing their different dynamic wettability-induced responses to water droplets. We believe that the ZnO microrod array coated substrates with different static/dynamic wettability may find many potential applications, such as antiwetting, self-cleaning, inject printing, micromass transfer and capture, biomedical diagnosis, microanalysis, and so forth

Trash to Treasure: Waste Eggshells as Chemical Reactors for the Synthesis of Amorphous Co(OH)₂ Nanorod Arrays on Various Substrates for Applications in Rechargeable Alkaline Batteries and Electrocatalysis

Bioinspired synthesis has been attracting much attention. Here, we demonstrate a novel approach to directly use waste eggshells as a reactor system for controlled synthesis of nanostructures formed on different substrates. This approach can recycle and transform the “trash” of waste eggshells into “treasure” of unique reactor systems for nanofabrication. The eggshell reactor system can provide unique conditions for the formation of nanostructures on various substrates. Using Co­(OH)₂ as a model, amorphous Co­(OH)₂ nanorod arrays, which cannot be synthesized conventionally by direct mixing of precursors, have been successfully formed on various substrates, including Ni foam, metal foil, and glass. To illustrate their potential applications, we use the as-fabricated amorphous Co­(OH)₂ nanorod arrays on Ni foam as (1) binder-free electrodes for rechargeable alkaline batteries, demonstrating impressively good electrochemical performances, and (2) electrocatalyst for oxygen evolution reaction, demonstrating improved electrocatalytic performances as compared to their crystalline counterpart. We believe the idea outlined here, using eggshell reactor system, can be further expanded to synthesize many different functional materials and precursors which can find additional applications, including self-cleaning, catalysis, sensor, electrochromic devices, etc

Core–Shell Ti@Si Coaxial Nanorod Arrays Formed Directly on Current Collectors for Lithium-Ion Batteries

Silicon is a promising candidate to replace the dominantly used carbon as the anode material for lithium ion batteries (LIBs). Si has the highest theoretical capacity (4200 mA·h/g) and is one of the most abundant elements. Unfortunately, Si has the issues of huge volume variation upon dis/charge cycling and low conductivity, leading to poor cycling and rate performances. Designing special nanostructures and improving conductivity and integration of Si electrodes could dramatically enhance their performance. Here, we introduce a novel strategy to integrate the core–shell nanorod arrays of Ti@Si on Ti foil with good conductivity as an additive-free electrode. The Ti core functions as a stable metallic support for the Si shell and dramatically reduces the diffusion length. The as-prepared core–shell nanorod arrays of Ti@Si on Ti foil, without any postsynthesis treatment, as electrodes demonstrated reversible capacity of 1125 mA·h/g over at least 30 cycles with highly improved Coulombic efficiency

Meso-oblate Spheroids of Thermal-Stabile Linker-Free Aggregates with Size-Tunable Subunits for Reversible Lithium Storage

The organization of nanoscale materials as building units into extended structures with specific geometry and functional properties is a challenging endeavor. Hereby, an environmentally benign, simple, and scalable method for preparation of stable, linker-free, self-supported, high-order 3D meso-oblate spheroids of CuO nanoparticle aggregates with size-tunable building nanounits for reversible lithium-ion storage is reported. In contrast to traditional spherical nanoparticle aggregation, a unique oblate spheroid morphology is achieved. The formation mechanism of the unusual oblate spheroid of aggregated nanoparticles is proposed. When tested for reversible lithium ion storage, the unique 3D meso-oblate spheroids of CuO nanoparticle aggregate demonstrated highly improved electrochemical performance (around ∼600 mAh/g over 20 cycles), which could be ascribed to the nanoporous aggregated mesostructure with abundant crystalline imperfection. Furthermore, the size of building units can be controlled (12 and 21 nm were tested) to further improve their electrochemical performance

Hollow Cocoon-Like Hematite Mesoparticles of Nanoparticle Aggregates: Structural Evolution and Superior Performances in Lithium Ion Batteries

We report the facile, fast, and template-free preparation of hollow α-Fe₂O₃ with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe₂O₃ nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge–discharge cycles. The unusual structural stability of the hollow α-Fe₂O₃ nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage

Trash to Treasure: Transforming Waste Polystyrene Cups into Negative Electrode Materials for Sodium Ion Batteries

Modern society generates a huge amount of plastic wastes that are posing potential disasters to our environment and society. For example, waste polystyrene (PS), such as used PS cups and packing materials, is mainly disposed into landfills. It is very challenging to recycle PS economically. PS cannot be carbonized under conventional conditions, because PS is completely decomposed into toxic gases at moderate temperature instead of carbonization. Here, we demonstrated a facile procedure to transform waste PS cups collected from a local coffee shop into disordered carbon in a sealed reactor at moderate temperature but under high pressure. The as-obtained disordered carbon demonstrated interesting electrochemical characteristics for reversible storage of sodium ions. A highly reversible capacity of 116 mAh g^–1 could be achieved for at least 80 cycles. Our preliminary results demonstrated that the trash of waste PS cups could be facilely transformed into treasure of promising negative electrode materials for sodium ion batteries, offering an alternative and sustainable approach to manage the waste PS issue

Micro Single Crystals of Hematite with Nearly 100% Exposed {104} Facets: Preferred Etching and Lithium Storage

The controlled synthesis of inorganic single crystals with a large percentage of exposed high-index facets has attracted much attention. However, high-index facets usually disappear during the early stage of crystal growth due to the minimization of surface energy and typically facet-controlling agents are employed. Here a facile fast hydrothermal method for the preparation of microsize α-Fe₂O₃ rhombohedra with nearly 100% exposed {104} facets was developed in a simple formulated solvent without any additives. The hydrothermal reaction time could be as short as 75 min, in contrast to typical hydrothermal reactions over days. The preferred etching edges along the diagonal axis of microsize rhombohedra by the self-generated ions was observed, which could be potentially extended to synthesize and tailor other transition metal oxides. The formation mechanism was revealed by ex situ FESEM observations of the samples prepared at different reaction times. Improved electrochemical performances in terms of cyclability, specific capacity, and high rate were achieved. The specific capacity was maintained at 550 mAh/g after 120 cycles at a rate of 200 mA/g. Experimental evidence clearly shows that the as-designed solid microsize α-Fe₂O₃ can effectively and reversibly store lithium ions with performance comparable to nanosize α-Fe₂O₃, suggesting electrode materials with particle size at the microscale will be worth further exploration

A Family of Mesocubes

It is challenging to develop a general universal procedure to fabricate mesoscale cubic structures on a large scale with different nanoscale building units. It is always desirable to tune the chemical compositions within confined arrangements without damaging the mesostructures to provide the desired physiochemical properties required by various devices/applications. Herein, we report the successful design and facile preparation of a family of mesocubes with different compositions, including (a) ZnSn­(OH)₆, (b) evenly distributed Zn₂SnO₄ and SnO₂ nanoparticles, (c) hollow cubes of SnO₂ nanoparticles, (d) high-ordered nanoparticles of Zn₂SnO₄&Sn@C; (e) SnO₂@C core–shell subunits, (f) SnO₂@C nanoparticle aggregates enclosed with oxidized carbon sheath, and (g) C nanobubbles, as building units, all, except ZnSn­(OH)₆, with the same confined arrangements of nanoparticles as building units inside the same framework of cubic mesostructures. This family of mesocubes will provide a rich pool of materials with different functional properties to meet demands in different applications and offer opportunities to evaluate fundamentals of structure–property–performance relationships. On the basis of the best of our knowledge, this family of facilely prepared mesocubes with unique combination of microsize cubes and compositions was reported for the first time, especially the carbon mesocubes formed by aggregation of carbon nanobubbles as the building subunits. Additionally, we demonstrated, for the first time, that two family members of mesocubes of Zn₂SnO₄&SnO₂ and Zn₂SnO₄&Sn@C can be used as anode materials in lithium ion batteries with impressive high packing densities and superior rate performance