Metal Oxide Hollow Structures Research Articles

Construction of CoNi2S4 hollow cube structures for excellent performance asymmetric supercapacitors

Although the synthesis of transition metal oxide hollow structures has been relatively perfect, it is extremely challenging to prepare mixed transition metal sulfides with excellent structures and high specific capacitance as electrode materials for supercapacitors. Here, we report a simple ion-exchange method and hydrothermal treatment to synthesize a novel hollow structure of ternary metal sulfide, which is nickel-cobalt sulfide hollow cubes. First, a uniform ZIF-67 (Zeolitic Imidazolate Framework-67) cube is synthesized as a precursor, and then a CoNi2S4 hollow polyhedron is successfully realized through the chemical transformation without annealing. As the electrode materials of supercapacitors, the specific capacitance of the hollow cube CoNi2S4 is 2448 F g−1 at the current density of 1.0 A g−1. In addition, an asymmetric supercapacitor (ASC) device based on CoNi2S4 hollow cubes was also assembled. The asymmetric supercapacitor shows long-term cycling performance with a high energy density of 62.19 Wh kg−1 at the power density of 775 W kg−1. The simple synthesis process, low production cost and excellent electrochemical performance indicate that it has broad application prospects in high-performance electrochemical capacitors.

Coordination competition-driven synthesis of triple-shell hollow α-Fe2O3 microspheres for lithium ion batteries

Multi-shell hollow structure metal oxide materials, with the larger surface area and short diffusion lengths, are very promising for lithium-ion battery application as anode materials. However, the production of multi-shelled hollow structure is relatively cumbersome, and it is difficult to fabricate multi component metal oxide hollow structures. Herein, we developed a new one-step hydrothermal method for synthesizing α-Fe2O3 triple-shell hollow microspheres (TSHMs) by introducing urea as a coordination competitive agent. The triple-shell hollow structured α-Fe2O3 accommodates large volume change and provides abundant active sites enable it as an ideal material for lithium ion battery applications. We have demonstrated the high specific capacity of 903.6 mA h g−1 at a current density of 500 mA g−1 even after 1000 cycles by using the α-Fe2O3 TSHMs as anode material.

Hollow-Structured Metal Oxides as Oxygen-Related Catalysts.

Metal oxide hollow structures with large surface area, low density, and high loading capacity have received great attention for energy-related applications. Acting as oxygen-related catalysts, hollow-structured transition metal oxides offer low overpotential, fast reaction rate, and excellent stability. Herein, recent progress in the oxygen-related catalysis (e.g., oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and metal-air batteries) of hollow-structured transition metal oxides is discussed. Through a comprehensive outline of hollow-structured spinels, perovskites, rutiles, etc., a rational design strategy is provided for an enhanced oxygen-related catalysis performance from the viewpoint of crystal structures. Urgent challenges and further research directions are presented for hollow-structured transition metal oxides toward excellent oxygen-related catalysis.

Highly active CeO2 hollow-shell spheres with Al doping

Metal oxide hollow structures are of great interest in many current and emerging areas of technology. This paper presents a facile and controlled protocol for the synthesis of Al-doped CeO2 hollow-shell spheres (CHS), where the dopant confers enhanced stability and activity to the material. These Al-doped CeO2 hollow-shell spheres (ACHS) possess a controllable shell number of up to three, where the sizes of the exterior, middle, and interior spheres were about 250‒100 nm,150‒50 nm, and 40‒10 nm, respectively, and the average shell thickness was ~15 nm. The thermal stability of the ACHS structure was enhanced by the homogeneous incorporation of Al atoms, andmore active oxygen species were present compared with those in the non-doped congener. Au NPs supported on ACHS (Au/ACHS) showed superior catalytic performance for the reduction of p-nitrophenol. For the same Au NP content, the reaction rate constant (k) of the Au/ACHS was nearly twice that of the non-doped Au/CHS, indicating that Al doping is promising for improving the performance of inert or unstable oxides as catalyst supports.

Interface-modulated approach toward multilevel metal oxide nanotubes for lithium-ion batteries and oxygen reduction reaction

Metal oxide hollow structures with multilevel interiors are of great interest for potential applications such as catalysis, chemical sensing, drug delivery, and energy storage. However, the controlled synthesis of multilevel nanotubes remains a great challenge. Here we develop a facile interface-modulated approach toward the synthesis of complex metal oxide multilevel nanotubes with tunable interior structures through electrospinning followed by controlled heat treatment. This versatile strategy can be effectively applied to fabricate wire-in-tube and tube-in-tube nanotubes of various metal oxides. These multilevel nanotubes possess a large specific surface area, fast mass transport, good strain accommodation, and high packing density, which are advantageous for lithium-ion batteries (LIBs) and the oxygen reduction reaction (ORR). Specifically, shrinkable CoMn2O4 tube-in-tube nanotubes as a lithium-ion battery anode deliver a high discharge capacity of ~565 mAh·g−1 at a high rate of 2 A·g−1, maintaining 89% of the latter after 500 cycles. Further, as an oxygen reduction reaction catalyst, these nanotubes also exhibit excellent stability with about 92% current retention after 30,000 s, which is higher than that of commercial Pt/C (81%). Therefore, this feasible method may push the rapid development of one-dimensional (1D) nanomaterials. These multifunctional nanotubes have great potential in many frontier fields.

Self-assembly in the synthesis of shelled ZnO hollow spheres and their UV sensors performance

Herein, we reported a generalized and fundamental approach to molecular self-assembly synthesis of ZnO hollow spheres by rationally employing spherical reverse micelles. The formation mechanism of shelled structures was proposed in detail. The products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The as-prepared ZnO hollow spheres were then used to examine the photodetector performance under ultraviolet (UV) light irradiation, and the device exhibited excellent photoresponsivity and stability. This work should provide a new concept to design and fabrication of other shelled metal oxide hollow structures with enhanced properties for microelectronics, optoelectronics, and other applications.

Design of Metal Oxide Hollow Structures Using Soft-templating Method for High-Performance Gas Sensors

Abstract Semiconductor gas sensors based on metal oxide are widely used in a number of applications, from health and safety to energy effi-ciency and emission control. Nanomaterials including nanowires, nanorods, and nanoparticles have dominated the research focus in thisfield owing to their large number of surface sites that facilitate surface reactions. Recently, metal oxide hollow structures using soft tem-plates have been developed owing to their high sensing properties with large-area uniformity. Here, we provide a brief overview of metaloxide hollow structures and their gas-sensing properties from the aspects of template size, morphology, and additives. In addition, a gas-sensing mechanism and perspectives are presented. Keywords: Gas sensor, Soft-template method, Nanostructure, Hollow hemisphere, Metal decoration 1. INTRODUCTION The functional convergence of the Internet with radio frequencyidentification, sensors, and smart objects led to the era of theInternet of Things (IoT), which supplies and accesses all real-world information [1]. Sensor technology is the most importantfactor in IoT because sensors offer enormous amounts ofinformation for many types of environment. Accordingly, varioussensors such as gas, pressure, illumination, tilt, temperature, andmotion sensors have been heavily studied to more preciselymeasure and monitor changes in environments [2]. In particular,diverse applications of the gas sensor in broad fields including thedetection of air pollutants and gaseous hazards, homeland security,medical diagnosis, and fuel combustion control have acceleratedstudies for high-performance gas sensors [3-7]. Gas sensors for applications in the IoT should meet specialrequirements such as low cost, miniaturized size, ease ofintegration with electronic circuits, and high sensing performance[8]. Various gas sensors including optical, electrochemical, surfaceacoustic wave, and semiconductor metal oxide sensors have beenextensively studied to fulfill the needs of the IoT [9]. In particular,owing to their simplicity in operation, low cost, flexibility inproduction, small size, and easy integration with electroniccircuits, semiconductor gas sensors based on metal oxides arevery promising as sensing elements for IoT [10-12]. Generally, the gas-sensing properties of metal oxide aredetermined by three basic factors: utility factor, transducerfunction, and receptor function [13]. The first factor is related togas diffusion (porous structure), and the second factor is related tothe mechanism of electron transport between adjacent crystals(neck control). The receptor function is related to the ability of theoxide surface to interact with target gases (metal additives anddecoration). Over the past decade, metal oxide nanostructuressuch as nanoparticles, nanowires, nanotubes, and nanofibers withmetal catalysts have significantly improved the three basic factors,leading to high-performance gas sensors [14]. However, sincethese nanostructures are commonly synthesized using wetchemical methods or transfer methods, developing versatile andreproducible fabrication processes has remained a challenge [15]. An alternative method for achieving highly sensitive metaloxide gas sensors is a soft-template method consisting of polymermicrospheres, which is effective in fabricating long-range orderedsubmicron hollow structures of various metal oxides [16,17]. Inspite of their potential advantages, no review focused on the gas-sensing properties of metal oxide nanostructures fabricated by thesoft-template method has been published to the best of the

Multi-shelled NiO hollow spheres: Easy hydrothermal synthesis and lithium storage performances

Complex metal oxide hollow structures are mostly prepared by hard template-based multistep procedures. It is still desirable yet challenging to develop new efficient strategies to fabricate high-quality complex metal oxide hollow structures. Herein, uniform multi-shelled NiO hollow spheres were synthesized; especially quintuple-shelled NiO hollow spheres were synthesized for the first time by a simple shell-by-shell self-assembly capable of controlling the shell numbers, which are achieved by controlling the heat treatment. The research makes a significant contribution to the synthetic methodology of multi-shelled hollow structures and opens up new opportunities for deeper understanding formation mechanism of the shell-by-shell self-assembly. The obtained quadruple/quintuple-shelled NiO hollow spheres show promising electrochemical performance in anodic lithium storage for Li-ion battery.

Self-assembled hierarchical Au-loaded In2O3 hollow microspheres with superior ethanol sensing properties

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, hierarchical self-assembled Au-loaded In2O3 hollow microspheres have been synthesized via a template-free hydrothermal method. The growth mechanism of this complex nanostructure was proposed based on the characterization results of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) approach, TG-DSC analysis and X-ray photoelectron spectroscopy (XPS). With the large surface area, highly porous structure of the hierarchical and hollow architectures, and catalytic activity of Au nanoparticles, these unique hierarchical Au-loaded In2O3 hollow microspheres exhibit superior gas-sensing performances. The response value to 100ppm ethanol is 185at an operating temperature of 320°C. It is expected this Au nanoparticles-functionalized hierarchically porous and hollow nanostructure may provide a new pathway to develop advanced nanomaterials for applications in gas sensors.

Rational synthesis of metal–organic framework composites, hollow structures and their derived porous mixed metal oxide hollow structures

A chemical transformation method is used to synthesize unique MOF composites, MOF hollow and complex hollow structures. Moreover, porous mixed metal oxide hollow and complex structures are obtained by annealing the MOF hollow and complex hollow structures

A bubble-template approach for assembling Ni-Co oxide hollow microspheres with an enhanced electrochemical performance as an anode for lithium ion batteries.

Although significant advancements in the preparation of metal oxide hollow structures have been achieved, most synthesis routes have some complicated aspects such as requiring a hard-template, multistep procedures or other special reagents. This paper proposes a green and facile bubble-template approach to synthesize and organize Ni-Co hollow microspheres. The entire formation mechanism for the hollow spherical structures, including integration for nucleation, morphological tailoring and an Ostwald ripening process, has been elucidated based on time-dependent observations. The Ni-Co hollow microspheres revealed an excellent cycling stability (730 mA h g(-1) even after 140 cycles at 300 mA g(-1)) and good rate capability when evaluated as an anode material for lithium ion batteries (LIBs). The excellent electrochemical performance can be attributed to the rational design and organization of the hollow structures, which offer a large void space for accommodating volume changes, shorten the diffusion path for Li ions and electron transfer, as well as increase the contact area between the electrodes and electrolyte. Moreover, the synergistic effects of the nickel and cobalt ions with different lithiation potentials allowed the volume change to occur in a stepwise manner. The bubble-template strategy was convenient and very effective for constructing the hollow structures, and if well engineered, it could be extended to the synthesis of other advanced metal oxide anode materials for high energy storage devices and many other applications.

Self‐Templated Formation of Uniform NiCo2O4 Hollow Spheres with Complex Interior Structures for Lithium‐Ion Batteries and Supercapacitors

AbstractDespite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template‐based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed‐metal‐oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium‐ion batteries and supercapacitors. This approach can be an efficient self‐templated strategy for the preparation of mixed‐metal‐oxide hollow spheres with complex interior structures and functionalities.

Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities.

Porous Spinel Zn(x)Co(3-x)O(4) hollow polyhedra templated for high-rate lithium-ion batteries.

Nanostructured metal oxides with both anisotropic texture and hollow structures have attracted considerable attention with respect to improved electrochemical energy storage and enhanced catalytic activity. While synthetic strategies for the preparation of binary metal oxide hollow structures are well-established, the rational design and fabrication of complex ternary metal oxide with nonspherical hollow features is still a challenge. Herein, we report a simple and scalable strategy to fabricate highly symmetric porous ternary ZnxCo3-xO4 hollow polyhedra composed of nanosized building blocks, which involves a morphology-inherited and thermolysis-induced transformation of heterobimetallic zeolitic imidazolate frameworks. When tested as anode materials for lithium-ion batteries, these hollow polyhedra have exhibited excellent electrochemical performance with high reversible capacity, excellent cycling stability, and good rate capability.

Controlled synthesis of multi-shelled transition metal oxide hollow structures through one-pot solution route

Abstract As one type of promising candidates for environmental and energy-related systems, multi-shelled transition metal oxide hollow structures (MS-TMOHSs) have drawn great scientific and technical interest in the past few years. This article highlights recent advances in one-pot solution synthesis of MS-TMOHSs. We begin it with an overview of synthetic strategies that have been exploited to achieve these peculiar structures. We then focus on one-pot solution approaches in the following four sections: i) soft templates directed growth; ii) Ostwald ripening; iii) controlled etching; and iv) gas bubble assisted growth. After giving a brief discussion on the unique properties and applications of these multi-shelled hollow structures, we conclude this review with the general challenges and the potential future directions of this exciting area of research.

ChemInform Abstract: Metal Oxide Hollow Nanostructures for Lithium‐Ion Batteries

AbstractReview: 76 refs.

Metal Oxide Hollow Nanostructures for Lithium‐ion Batteries

Metal oxide hollow structures have received great attention because of their many promising applications in a wide range of fields. As electrode materials for lithium-ion batteries (LIBs), metal oxide hollow structures provide high specific capacity, superior rate capability, and improved cycling performance. In this Research News, we summarize the recent research activities in the synthesis of metal oxide hollow nanostructures with controlled shape, size,composition, and structural complexity, as well as their applications in LIBs. By focusing on hollow structures of some binary metal oxides (such as SnO 2 ,TiO 2 , Fe 2 O 3 , Co 3 O 4 ) and complex metal oxides, we seek to provide some rational understanding on the effect of nanostructure engineering on the electrochemical performance of the active materials. It is thus anticipated that this article will shed some light on the development of advanced electrode materials for next-generation LIBs.