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•LDHs are promising candidates for high efficiency photocatalytic removal of organic pollutants.•LDHs are characterized by their morphological, compositional and electronic ...flexibilities.•Strategies in preparation of LDHs-based materials with maximized catalytic efficiencies are reviewed.•Challenges remain between research and practical application of LDHs-based photocatalysts.•LDHs-based photocatalysts are also applied in other important fields with promising performances.
Layered double hydroxides (LDHs) and their derivatives are a family of promising photocatalysts that have been widely used in photodegradation of organic pollutants. We review the most recent advances in visible-light driven photodegradation of organic pollutants using LDHs based materials with emphasis on the manipulation of their morphological, compositional, and electronic properties and the mechanistic understandings of the photocatalytic processes. Based on the characteristic structures of LDHs, i.e., stable layered structure, specific “memory effect”, switchable property of layered composites and high surface area, we overview the performance and mechanism of LDHs based catalysts for the photodegradation of common and persistent organic pollutants. First, LDHs-based photocatalysts were classified into five categories, LDHs-derived mixed metal oxides, supporting LDHs, intercalated LDHs, modified LDHs, and LDHs with unique structures (e.g., core-shell LDHs), and reviewed individually in terms of their synthetic methodologies, and structural, atomistic topological and electronic properties. Second, for mechanistic understandings of the photocatalytic processes, we summarize major factors that govern the performance of LDHs-based photocatalysts, including catalytically-relevant properties at the metal/LDHs heterojunctions, adsorption effect, acid-base pairs and the presence of vacancy sites. Third, depending on the photodegradation reactions, the targeting organic pollutants were classified into four types, azo dyes, phenols, persistent organic pollutants and other types of organic pollutants; LDHs-based photocatalysts with optimized performance for each type of molecule are summarized with mechanistic understandings. In addition, we review recent trend in the application of LDHs-based materials in new-emerging areas including CO2 reduction, hydrolysis to produce hydrogen, and photo-assisted organic synthesis with promising performances. Mechanistic details of the photocatalytic processes that lead to the different outcomes in terms of the efficiency, reaction routes and practically-relevant applications in energy harvesting and removal of organic pollutants are the primary focus of the present review. Outlook of major future directions in LDHs-based photocatalysis is outlined by the end.
MOF‐derived ZnO@ZnO Quantum Dots/C core–shell nanorod arrays grown on flexible carbon cloth are successfully fabricated as a binder‐free anode for Li‐ion storage. In combination with the advantages ...from the ZnO/C core–shell architecture and the 3D nanorod arrays, this material satisfies both efficient ion and fast electron transport, and thus shows superior rate capability and excellent cycling stability.
Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive platforms in next-generation nanoelectronics and optoelectronics for reducing device sizes down ...to a 10 nm scale. To achieve this, the controlled synthesis of wafer-scale single-crystal TMDs with high crystallinity has been a continuous pursuit. However, previous efforts to epitaxially grow TMD films on insulating substrates (e.g., mica and sapphire) failed to eliminate the evolution of antiparallel domains and twin boundaries, leading to the formation of polycrystalline films. Herein, we report the epitaxial growth of wafer-scale single-crystal MoS2 monolayers on vicinal Au(111) thin films, as obtained by melting and resolidifying commercial Au foils. The unidirectional alignment and seamless stitching of the MoS2 domains were comprehensively demonstrated using atomic- to centimeter-scale characterization techniques. By utilizing onsite scanning tunneling microscope characterizations combined with first-principles calculations, it was revealed that the nucleation of MoS2 monolayer is dominantly guided by the steps on Au(111), which leads to highly oriented growth of MoS2 along the ⟨110⟩ step edges. This work, thereby, makes a significant step toward the practical applications of MoS2 monolayers and the large-scale integration of 2D electronics.
The exact role of a defect structure on transition metal compounds for electrocatalytic oxygen evolution reaction (OER), which is a very dynamic process, remains unclear. Studying the ...structure–activity relationship of defective electrocatalysts under operando conditions is crucial for understanding their intrinsic reaction mechanism and dynamic behavior of defect sites. Co3O4 with rich oxygen vacancy (VO) has been reported to efficiently catalyze OER. Herein, we constructed pure spinel Co3O4 and VO-rich Co3O4 as catalyst models to study the defect mechanism and investigate the dynamic behavior of defect sites during the electrocatalytic OER process by various operando characterizations. Operando electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) implied that the VO could facilitate the pre-oxidation of the low-valence Co (Co2+, part of which was induced by the VO to balance the charge) at a relatively lower applied potential. This observation confirmed that the VO could initialize the surface reconstruction of VO–Co3O4 prior to the occurrence of the OER process. The quasi-operando X-ray photoelectron spectroscopy (XPS) and operando X-ray absorption fine structure (XAFS) results further demonstrated the oxygen vacancies were filled with OH• first for VO–Co3O4 and facilitated pre-oxidation of low-valence Co and promoted reconstruction/deprotonation of intermediate Co–OOH•. This work provides insight into the defect mechanism in Co3O4 for OER in a dynamic way by observing the surface dynamic evolution process of defective electrocatalysts and identifying the real active sites during the electrocatalysis process. The current finding would motivate the community to focus more on the dynamic behavior of defect electrocatalysts.
A novel and scalable synthesis approach to produce hierarchically aligned porous carbon nanotube arrays (PCNTAs) on flexible carbon fibers (CFs) is developed. The PCNTAs are obtained by catalytic ...conversion of ethanol on ZnO nanorod arrays and then reduction‐evaporation of ZnO nanorods, resulting in uniform and controllable wall thicknesses of the final PCNTAs. The 3D arrangement, the diameters, and the lengths of the PCNTAs can be tuned by adjusting the synthesis protocols of the ZnO nanorod arrays. The PCNTAs@CFs exhibit a high specific capacitance of 182 F g−1 at 40 A g−1 (188 F g−1 at 20 A g−1) in 6 m KOH. The symmetric supercapacitor shows an excellent cycling stability with only 0.0016% loss per cycle after 10 000 continuous cycles at the current density of 12 A g−1. These excellent electrochemical performances are ascribed to the unique structural design of hierarchical PCNTAs, which provide not only appropriate channels for enhanced electronic and ionic transport but also increased surface area for accessing more electrolyte ions. The structural design and the synthesis approach are general and can be extended to synthesizing a broad range of materials systems.
Radially aligned porous carbon nanotube arrays with desired mesopores and intimate contact with carbon fibers substrate facilitate fast transport of both electrons and electrolyte ions to provide high rate capability at high current density. Such unique hierarchical nanoarchitectures demonstrate excellent cycling stability and good mechanical properties, making them more applicable in flexible energy storage devices.
The rapid progress of micro/nanoelectronic systems and miniaturized portable devices has tremendously increased the urgent demands for miniaturized and integrated power supplies. Miniaturized energy ...storage devices (MESDs), with their excellent properties and additional intelligent functions, are considered to be the preferable energy supplies for uninterrupted powering of microsystems. In this review, we aim to provide a comprehensive overview of the background, fundamentals, device configurations, manufacturing processes, and typical applications of MESDs, including their recent advances. Particular attention is paid to advanced device configurations, such as two-dimensional (2D) stacked, 2D planar interdigital, 2D arbitrary-shaped, three-dimensional planar, and wire-shaped structures, and their corresponding manufacturing strategies, such as printing, scribing, and masking techniques. Additionally, recent developments in MESDs, including microbatteries and microsupercapacitors, as well as microhybrid metal ion capacitors, are systematically summarized. A series of on-chip microsystems, created by integrating functional MESDs, are also highlighted. Finally, the remaining challenges and future research scope on MESDs are discussed.
Nanoforest of hierarchical Co3O4@NiCo2O4 nanowire arrays were synthesized via a facile strategy for electrochemical supercapacitors. The smart combination of Co3O4 and NiCo2O4 nanostructures in the ...nanowire arrays shows a promising synergistic effect for capacitors with greatly enhanced performance. A high areal capacitance of 2.04Fcm−2 at the scan rate of 5mVs−1 and 0.79Fcm−2 (almost 2.5 times as high as that of pristine Co3O4) even at 30mAcm−2 after 6000 cycles with varying current densities were achieved. Particularly, when the current turned back to 10mAcm−2 after the above cycles with large current, 1.18Fcm−2, corresponding to 83.7% of the initial capacitance, can be recovered and maintains for another 1500 cycles without noticeable decrease. These results show that the nanoforest of hierarchical Co3O4@NiCo2O4 nanowire arrays could be a promising electrode material for high-performance electrochemical capacitors.
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•Synthesis of hierarchical Co3O4@NiCo2O4 nanoforest with a facile fabrication strategy.•Hierarchical nanoforest structures greatly enhanced the performance of supercapacitors.•Large specific surface areas and extra electronic transmission channels can enhanced the performance of supercapacitors.
Focused ion beam (FIB) milling is a versatile maskless and resistless patterning technique and has been widely used for the fabrication of inverse plasmonic structures such as nanoholes and nanoslits ...for various applications. However, due to its subtractive milling nature, it is an impractical method to fabricate isolated plasmonic nanoparticles and assemblies which are more commonly adopted in applications. In this work, we propose and demonstrate an approach to reliably and rapidly define plasmonic nanoparticles and their assemblies using FIB milling via a simple “sketch and peel” strategy. Systematic experimental investigations and mechanism studies reveal that the high reliability of this fabrication approach is enabled by a conformally formed sidewall coating due to the ion-milling-induced redeposition. Particularly, we demonstrated that this strategy is also applicable to the state-of-the-art helium ion beam milling technology, with which high-fidelity plasmonic dimers with tiny gaps could be directly and rapidly prototyped. Because the proposed approach enables rapid and reliable patterning of arbitrary plasmonic nanostructures that are not feasible to fabricate via conventional FIB milling process, our work provides the FIB milling technology an additional nanopatterning capability and thus could greatly increase its popularity for utilization in fundamental research and device prototyping.
Developing high-performance anode materials is essential for advanced next-generation lithium ion batteries. ZnO-based nanomaterials have been considered promising candidates owing to their high ...theoretical specific capacity, environmental friendliness, and relatively low cost. However, major problems, including inherent poor conductivity and huge volume expansion, have severely impeded ZnO-based nanomaterials from being viable. Here, we first present a brief review of the most effective strategies to improve the lithium ion storage performance of ZnO-based anodes. In addition, recent advances in other novel Zn-based nanomaterials are also summarized and discussed. Finally, we describe the challenges and prospects of future research trends for Zn-based nanomaterials.
Recent progress, including storage mechanisms, synthetic methods, advanced strategies and electrochemical performance of Zn-based anodes in LIBs, is reviewed.
In many high-speed electrical machines, centrifugal forces within the rotor can be first-order constraints on electromagnetic optimization. This can be particularly acute in interior permanent magnet ...(IPM) machines in which magnets are usually retained entirely by the rotor core with no additional mechanical containment. This study investigates the nature of the trade-off between mechanical and electromagnetic requirements within the context of an eight-pole, 100 kW IPM machine with a base speed of 4000 rpm and an extended speed range up to 12,000 rpm. A series of mechanical and electromagnetic models are used to estimate the level of shaft interference, mechanical stress in critical regions of the rotor and the impact of various features and dimensions within the machine on electromagnetic torque. A systematic exploration of the design space is undertaken for rotor diameters from 120 mm to 180 mm, with optimal designs in terms of torque per unit length established at each diameter while meeting the constraints imposed on mechanical stress. The final preferred design has a rotor of 165 mm and an axial length of 103 mm long with a fractional slot winding in a 30-slot stator. The overall machine has an active mass of 42.3 kg, which corresponds to ~2.4 kW/kg. This paper describes the optimization study in detail and draws on the results to explore the nature of the design trade-offs in such rotors and the impact of core properties.
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