Electronic and structural properties of single-crystal Jahn-Teller active Co1+x Mn2-x O4 thin films

Recent investigations on spinel CoMn2O4 have shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline Co1+x Mn2-x O4 thin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry. Our results indicate that excess Co ions occupy tetrahedral interstitial sites at lower excess Co stoichiometries, and become substitutional for octahedrally-coordinated Mn at higher Co levels. We compare these results with density functional theory models of stoichiometric CoMn2O4 to understand how the Jahn-Teller distortion and hybridization in Mn-O bonds impact the ability to hole dope the material with excess Co. The findings provide important insights into CoMn2O4 and related spinel oxides that are promising candidates for inexpensive oxygen reduction reaction catalysts.

Yolk-Shell Nanostructures: Syntheses and Applications for Lithium-Ion Battery Anodes

Yolk-shell nanostructures have attracted tremendous research interest due to their physicochemical properties and unique morphological features stemming from a movable core within a hollow shell. The structural potential for tuning inner space is the focal point of the yolk-shell nanostructures in a way that they can solve the long-lasted problem such as volume expansion and deterioration of lithium-ion battery electrodes. This review gives a comprehensive overview of the design, synthesis, and battery anode applications of yolk-shell nanostructures. The synthetic strategies for yolk-shell nanostructures consist of two categories: templating and self-templating methods. While the templating approach is straightforward in a way that the inner void is formed by removing the sacrificial layer, the self-templating methods cover various different strategies including galvanic replacement, Kirkendall effect, Ostwald ripening, partial removal of core, core injection, core contraction, and surface-protected etching. The battery anode applications of yolk-shell nanostructures are discussed by dividing into alloying and conversion types with details on the synthetic strategies. A successful design of yolk-shell nanostructures battery anodes achieved the improved reversible capacity compared to their bare morphologies (e.g., no capacity retention in 300 cycles for Si@C yolk-shell vs. capacity fading in 10 cycles for Si@C core-shell). This review ends with a summary and concluding remark yolk-shell nanostructures.

Advances in the synthesis and design of nanostructured materials by aerosol spray processes for efficient energy storage

The increasing demand for energy storage has motivated the search for highly efficient electrode materials for use in rechargeable batteries with enhanced energy density and longer cycle life. One of the most promising strategies for achieving improved battery performance is altering the architecture of nanostructured materials employed as electrode materials in the energy storage field. Among numerous synthetic methods suggested for the fabrication of nanostructured materials, aerosol spray techniques such as spray pyrolysis, spray drying, and flame spray pyrolysis are reliable, as they are facile, cost-effective, and continuous processes that enable the synthesis of nanostructured electrode materials with desired morphologies and compositions with controlled stoichiometry. The post-treatment of spray-processed powders enables the fabrication of oxide, sulfide, and selenide nanostructures hybridized with carbonaceous materials including amorphous carbon, reduced graphene oxide, carbon nanotubes, etc. In this article, recent progress in the synthesis of nanostructured electrode materials by spray processes and their general formation mechanisms are discussed in detail. A brief introduction to the working principles of each spray process is given first, and synthetic strategies for the design of electrode materials for lithium-ion, sodium-ion, lithium-sulfur, lithium-selenium, and lithium-oxygen batteries are discussed along with some examples. This analysis sheds light on the synthesis of nanostructured materials by spray processes and paves the way toward the design of other novel and advanced nanostructured materials for high performance electrodes in rechargeable batteries of the future.

Design of Hollow Nanostructures for Energy Storage, Conversion and Production

Hollow nanostructures have shown great promise for energy storage, conversion, and production technologies. Significant efforts have been devoted to the design and synthesis of hollow nanostructures with diverse compositional and geometric characteristics in the past decade. However, the correlation between their structure and energy-related performance has not been reviewed thoroughly in the literature. Here, some representative examples of designing hollow nanostructure to effectively solve the problems of energy-related technologies are highlighted, such as lithium-ion batteries, lithium-metal anodes, lithium-sulfur batteries, supercapacitors, dye-sensitized solar cells, electrocatalysis, and photoelectrochemical cells. The great effect of structure engineering on the performance is discussed in depth, which will benefit the better design of hollow nanostructures to fulfill the requirements of specific applications and simultaneously enrich the diversity of the hollow nanostructure family. Finally, future directions of hollow nanostructure design to solve emerging challenges and further improve the performance of energy-related technologies are also provided.

Sequential Templating Approach: A Groundbreaking Strategy to Create Hollow Multishelled Structures

Thanks to their distinguished properties such as optimized specific surface area, low density, high loading capacity, and sequential matter transfer and storage, hollow multishelled structures (HoMSs) have attracted great interest from scientists in broad fields, including catalysis, drug delivery, solar cells, supercapacitors, lithium-ion batteries, electromagnetic wave absorption, and sensors. However, traditional synthesis methods such as soft-templating and hierarchical self-assembly methods can hardly realize the controllable synthesis of HoMSs, thus limiting their development and application. Here, the development process of HoMSs is first succinctly reviewed and the shortcomings of the traditional synthesis method are concluded. Subsequently, the sequential templating approach, which shows great generality for the synthesis of HoMSs with controllable composition and geometry configuration and exhibits remarkable effect on the scientific research field, is introduced. The basic material science and chemical reaction mechanism involved in the synthesis and manipulation of HoMSs using the sequential templating approach are then explained in detail. In addition, the effect of the geometric characteristics of HoMSs on their application properties is highlighted. Finally, the current challenges and future research directions of HoMSs are also suggested.

Metal-Oleate Complex-Derived Bimetallic Oxides Nanoparticles Encapsulated in 3D Graphene Networks as Anodes for Efficient Lithium Storage with Pseudocapacitance

In this manuscript, we have demonstrated the delicate design and synthesis of bimetallic oxides nanoparticles derived from metal-oleate complex embedded in 3D graphene networks (MnO/CoMn₂O₄ ⊂ GN), as an anode material for lithium ion batteries. The novel synthesis of the MnO/CoMn₂O₄ ⊂ GN consists of thermal decomposition of metal-oleate complex containing cobalt and manganese metals and oleate ligand, forming bimetallic oxides nanoparticles, followed by a self-assembly route with reduced graphene oxides. The MnO/CoMn₂O₄ ⊂ GN composite, with a unique architecture of bimetallic oxides nanoparticles encapsulated in 3D graphene networks, rationally integrates several benefits including shortening the diffusion path of Li⁺ ions, improving electrical conductivity and mitigating volume variation during cycling. Studies show that the electrochemical reaction processes of MnO/CoMn₂O₄ ⊂ GN electrodes are dominated by the pseudocapacitive behavior, leading to fast Li⁺ charge/discharge reactions. As a result, the MnO/CoMn₂O₄ ⊂ GN manifests high initial specific capacity, stable cycling performance, and excellent rate capability.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.

Hollow multi-shelled structures for energy conversion and storage applications

Materials with hollow multi-shelled structures composed of various compositions are promising candidates for energy conversion and storage applications.

Intricate Hollow Structures: Controlled Synthesis and Applications in Energy Storage and Conversion

Intricate hollow structures garner tremendous interest due to their aesthetic beauty, unique structural features, fascinating physicochemical properties, and widespread applications. Here, the recent advances in the controlled synthesis are discussed, as well as applications of intricate hollow structures with regard to energy storage and conversion. The synthetic strategies toward complex multishelled hollow structures are classified into six categories, including well-established hard- and soft-templating methods, as well as newly emerging approaches based on selective etching of "soft@hard" particles, Ostwald ripening, ion exchange, and thermally induced mass relocation. Strategies for constructing structures beyond multishelled hollow structures, such as bubble-within-bubble, tube-in-tube, and wire-in-tube structures, are also covered. Niche applications of intricate hollow structures in lithium-ion batteries, Li-S batteries, supercapacitors, Li-O₂ batteries, dye-sensitized solar cells, photocatalysis, and fuel cells are discussed in detail. Some perspectives on the future research and development of intricate hollow structures are also provided.

Fabrication of TiO2 coated porous CoMn2O4 submicrospheres for advanced lithium-ion anodes

Uniform CoMn₂O₄@TiO₂ porous nanospheres have been developed with excellent electrochemical performance when evaluated as anode materials for lithium ion batteries.

Synthesis of porous MnCo2O4 microspheres with yolk–shell structure induced by concentration gradient and the effect on their performance in electrochemical energy storage

In this study, novel spherical yolk–shell MnCo₂O₄ powders with concentration gradient have been synthesized.

Controlled synthesis of CoxMn3−xO4 nanoparticles with a tunable composition and size for high performance lithium-ion batteries

Preparation of Co_xMn_3−xO₄ nanoparticles using bimetallic coordination-polymer precursors, and a case study of MnCo₂O₄ for LIBs, suggesting an optimal size for improved capacity retention.

Enhanced catalytic ozonation over reduced spinel CoMn2O4 for NOx removal: active site and mechanism analysis

In this paper, CO atmosphere reduced cobalt manganate (CoMn₂O₄/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NO_x removal.

Facile controllable hydrothermal route for a porous CoMn2O4 nanostructure: synthesis, characterization, and textile dye removal from aqueous media

We herein report the synthesis of a pure sphere-like spinel CoMn₂O₄ nanostructure using a facile and surfactant-free hydrothermal approach followed by a thermal decomposition of the as-prepared CoCO₃/MnCO₃ composite precursor.

Yolk/shell nanoparticles: classifications, synthesis, properties, and applications

Core/shell nanoparticles were first reported in the early 1990s with a simple spherical core and shell structure, but the area is gradually diversifying in multiple directions such as different shapes, multishells, yolk/shell etc., because of the development of different new properties of the materials, which are useful for several advanced applications. Among different sub-areas of core/shell nanoparticles, yolk/shell nanoparticles (YS NPs) have drawn significant attention in recent years because of their unique properties such as low density, large surface area, ease of interior core functionalization, a good molecular loading capacity in the void space, tunable interstitial void space, and a hollow outer shell. The YS NPs have better properties over simple core/shell or hollow NPs in various fields including biomedical, catalysis, sensors, lithium batteries, adsorbents, DSSCs, microwave absorbers etc., mainly because of the presence of free void space, porous hollow shell, and free core surface. This review presents an extensive classification of YS NPs based on their structures and types of materials, along with synthesis strategies, properties, and applications with which one would be able to draw a complete picture of this area.

General formation of tin nanoparticles encapsulated in hollow carbon spheres for enhanced lithium storage capability

A new simple process for synthesis of heterogeneous yolk-shell microspheres is introduced. The core/shell-structured microspheres are prepared by a one-pot spray pyrolysis process. The removal of one kind of metal oxide by a dry process produces heterogeneous yolk-shell microspheres. The yolk-shell Sn@C microspheres show superior electrochemical properties as anode materials for lithium-ion batteries.

Electrochemical properties of micron-sized, spherical, meso- and macro-porous Co3O4 and CoO-carbon composite powders prepared by a two-step spray drying process

Micron-sized, spherical, meso- and macro-porous Co3O4 and CoO-carbon composite powders were prepared via a simple two-step spray drying process. The CoO-carbon composite powders, in which homogeneous mixing of the metal oxide and carbon components was achieved using the first spray drying process, were wet milled to produce the slurry for the second spray drying process. Co3O4 and CoO-carbon composite powders with mean particle sizes of 4.4 and 4.7 μm were respectively obtained by spray-drying the slurry after post-treatment at 400 °C under air and nitrogen atmospheres. Meso- and macro-pores were uniformly distributed inside the Co3O4 and CoO-carbon composite powders. The CoO-carbon composite powders exhibited discharge capacities of 882 and 855 mA h g(-1) at a high constant current density of 1400 mA g(-1) for the 2(nd) and 100(th) cycles. The discharge capacities of the Co3O4 powders at the 2(nd) and 100(th) cycles were 970 and 644 mA h g(-1). With stepwise increment in the current density from 500 to 5000 mA g(-1), the discharge capacities of the CoO-carbon composite powders decreased slightly from 985 to 698 mA h g(-1). The superior rate and cycling performances of the CoO-carbon composite powders are ascribed to their meso- and macro-porous structures and carbon components.

Recent advances in Mn-based oxides as anode materials for lithium ion batteries

The Mn-based oxides including MnO, Mn₃O₄, Mn₂O₃, MnO₂, CoMn₂O₄, ZnMn₂O₄and their carbonaceous composite/oxide supports with different morphologies and compositions as anode materials are reviewed.

Hierarchical CoNiO2structures assembled from mesoporous nanosheets with tunable porosity and their application as lithium-ion battery electrodes

Mesoporous CoNiO₂structures can be considered as alternative materials for application in the design of energy storage devices.

One-pot synthesis of Fe2O3 yolk-shell particles with two, three, and four shells for application as an anode material in lithium-ion batteries

Fe2O3 yolk-shell particles with two, three, and four shells are prepared by one-pot spray pyrolysis. The discharge capacity of the Fe2O3 yolk-shell particles with two shells showing the best electrochemical properties is as high as 848 mA h g(-1) after 80 cycles at a current density of 300 mA g(-1).