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This article studies the role of electrochemical parameters in controlling the morphology of oxidized TiO2 nanotubes and the electrochemical performance of modified TiO2 nanotubes. Humidity is a key factor for fabricating TiO2 nanotubes. When the relative humidity belows 70%, the TiO2 nanotubes can be successfully prepared. What's more, by changing the anodization voltage and time, the diameter and the length of TiO2 nanotubes can be adjusted. In addition, the TiO2 nanotubes are modified through electrochemical self-doping and loading Pt metal particles on the surface of the nanotubes, which promotes the performance of the supercapacitor. The sample anodized at 100 V for 3 h has a specific capacity of up to 2.576 mF/cm² at a scan rate of 100 mV/s after self-doping, and its capacity retention rate still remains at 89.55% after 5 000 cycles, demonstrating excellent cycling stability. The Pt-modified sample has a specific capacity of up to 3.486 mF/cm² at the same scan rate, exhibiting more outstanding electrochemical performance. [ABSTRACT FROM AUTHOR]

In recent years, metal compound‐based heterojunctions have received increasing attention from researchers as a candidate anode for lithium/sodium‐ion batteries, because heterojunction anodes possess unique interfaces, robust architectures, and synergistic effects, thus promoting Li/Na ions storage and accelerating ions/electrons transport. Exhilaratingly, the development of heterostructures has made rapid progress in the field of energy storage, greatly encouraging the industrialization of high energy and power density Li/Na ion batteries. However, there are few in‐detail and in‐depth reviews on the energy storage mechanism, synthesis routes, characterization methods and electrochemical performance of metal compound‐based heterojunction anodes. Herein, a deeper understanding of the correlation between the building blocks of heterojunctions and their enhanced electrochemical behaviors are summarized. Furthermore, various synthesis routes and characterization methods for heterostructure anodes are roundly reviewed. Finally, challenges and perspectives of heterojunction anodes in energy storage are presented in this work. [ABSTRACT FROM AUTHOR]

The surface plasmon resonance (SPR)‐generated electric field (E‐field) intensities around a Ag nanocube (NC) before and after it is covered by a BaTiO3 (BTO) layer (BTO@Ag NC) were calculated. It was observed that the theoretical E‐field intensities were reduced on BTO@Ag NCs, thus suggesting inferior catalytic activities under visible light illumination. However, BTO@Ag NCs experimentally displayed better photocatalytic performance than that of Ag NCs under illumination at 633 nm, both in ambient argon (Ar) and in ambient air, where p‐aminothiophenol (PATP) molecules were used to probe the conversion. The mechanism can be attributed to the surface polarization of the BTO layer trigged by a SPR effect of the Ag core. The oscillation of free electrons in the Ag core aroused appearance of surface polarization charge on the ferroelectric (FE) BTO surface, which resulted in the enhanced catalytic properties of BTO@Ag NCs. Therefore, our finding may provide a novel method to enhance visible‐light responsive photocatalytic activity of wide bandgap FE materials by depositing them on plasmonic metal nanostructures. [ABSTRACT FROM AUTHOR]

Among the electrode materials for supercapacitors (SCs), metal-organic framework (MOFs) is attracting huge research interest as a new type of energy storage electrode materia. However, due to their poor conductivity and stability, the practical application of original MOFs in the field of energy storage has been greatly hindered. Here, we demonstrate a special core-shell structure, which the synergistic action of NiCo2O4 and Ni-MOF forms a tight conductive network that speeds up electron transport and larger specific surface area, more active sites were obtained and mechanical stability that indicates its outstanding long life. The test results show that it has a high specific capacity of 4.23 F cm–2 at 5 mA cm–2, and the capacity retention rate is maintained at 97.5% after 8000 cycles. In addition, an asymmetric supercapacitor device, using NiCo2O4@Ni-MOF and activated carbon (AC) as anode and cathode, has a high specific capacity of 3.21 F cm–2 at 5 mA cm–2 and excellent cycling performance (83.8% retention over 8000 cycles at 10 mA cm–2). Our work demonstrates the possibility of using novel structured Ni-MOF-based hybrid arrays as electrodes for SCs with enhanced electrochemical performance compared to Ni-MOF and NiCo2O4, providing a reliable prospect for flexible energy storage devices. [ABSTRACT FROM AUTHOR]

Phase change materials can enable temperature self-regulation due to their drastic changes in optical properties accompanying the phase transition. Significant reduction of the optical absorption after the transition is the key ingredient for an enhanced regulating performance. However, the absorptivity of unpatterned vanadium dioxide (VO2) thin films can hardly be reduced after phase transition at visual-to-infrared band. In this work, we combine the direct binary search (DBS) and particle swarm optimization (PSO) algorithms for an optimized design of temperature self-regulating nano-photonic devices on VO2 thin films. For a given incident wavelength, a pixelated structure is firstly inverse-designed by the DBS algorithm which maximizes the absorption contrast before and after the transition. To overcome fabrication challenges as pixel size is at deep sub-wavelength scale, the pixelated structure can then be replaced by geometric shapes which are more tractable in manufacturing processes. The geometrical parameters are optimized by the PSO algorithm where our optimized device brings the absorptivity down to 33% after the transition. These results provide an effective way for the inverse design of optimized nano-photonic structures based on phase change materials. [ABSTRACT FROM AUTHOR]

In this paper, NiMoO4@CoWO4 core–shell nanostructures have been synthesized by a hydrothermal process and annealing. Structural characterization and compositional analysis of the as-prepared NiMoO4@CoWO4 nanocomposites were performed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy. Here, NiMoO4@CoWO4 nanostructures were designed and synthesized on Ni foam. NiMoO4 nanorods would provide electron "superhighways" for charge storage and delivery, which could provide an effective electrical connection to the CoWO4 electrode material. In addition, the open space between these nanosheets can increase the active sites and the contribution of capacitive effects. Finally, NiMoO4@CoWO4 directly grown on Ni foam could avoid the "dead" volume caused by the tedious process of mixing active materials with polymer binders/conductive additives. As expected, NiMoO4@CoWO4 exhibited high specific capacity, good rate performance and excellent electrochemical stability. The results show that NiMoO4@CoWO4 exhibited a high specific capacity at a current density of 5 mA cm−2 and splendid electrochemical stability (88.5% retention after 4000 cycles). The great electrochemical performance could be ascribed to the unique core–shell architecture and the synergistic effect from the NiMoO4 nanorods and CoWO4. [ABSTRACT FROM AUTHOR]

As a multifunctional material, TiO2 shows excellent performance in catalytic degradation and lithium-ion storage. However, high electron-hole pair recombination, poor conductivity, and low theoretical capacity severely limit the practical application of TiO2. Herein, TiO2 nanotube (TiO2 NT) with a novel double-layer honeycomb structure were prepared by two-step electrochemical anodization. Honeycombed TiO2 NT arrays possess clean top surfaces and a long-range ordering, which greatly facilitates the preparation of high-performance binary and ternary materials. A binary TiO2 nanotube@Au nanoparticle (TiO2 NT@Au NP) composite accompanied by appropriately concentrated and uniformly distributed gold particles was prepared in this work. Interestingly, the TiO2 nanotube@Au nanoparticle (TiO2 NT@Au NP) composites not only showed the excellent catalytic degradation effect of methylene blue, but also demonstrated large lithium-ion storage capacity (310.6 μAh cm−2, 1.6 times of pristine TiO2 NT). Based on the realization of the controllable fabrication of binary TiO2 nanotube@MoS2 nanosheet (TiO2 NT@MoS2 NS) composite, ternary TiO2 nanotube@MoS2 nanosheet@Au nanoparticle (TiO2 NT@MoS2 NS@Au NP) composite with abundant defects and highly ordered structure was also innovatively designed and fabricated. As expected, the TiO2 NT@MoS2 NS@Au NP anode exhibits extremely high initial discharge specific capacity (487.4 μAh cm−2, 2.6 times of pristine TiO2 NT) and excellent capacity retention (81.0%). [ABSTRACT FROM AUTHOR]

Abstract Novel hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays were fabricated on silicon substrates by a one-step thermal evaporation of CdS powder. The as-grown products were characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Studies reveal that a typical hierarchical Cd4SiS6/SiO2 heterostructure nanowire is composed of a single crystalline Cd4SiS6 nanowire core sheathed with amorphous SiO2 sheath. Furthermore, secondary nanostructures of SiO2 nanowires are highly dense grown on the primary Cd4SiS6 core-SiO2 sheath nanowires and formed hierarchical Cd4SiS6/SiO2 based heterostructure nanowire arrays which stand vertically on silicon substrates. The possible growth mechanism of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays is proposed. The optical properties of hierarchical Cd4SiS6/SiO2 heterostructure nanowire arrays are investigated using Raman and Photoluminescence spectroscopy.

The ground and first singlet excited state absorption in distyrylbenzene (DSB) is simulated based on linear-response time dependent density functional theory (LR-TDDFT). It is found that distyrylbenzene shows a strong reverse saturable absorption effect around the near-infrared range. Combining the calculations of cubic response functions to simulate the three-photon absorption in distyrylbenzene, we are able to show that distyrylbenzene is a promising ultrafast optical limiter for the light with wavelengths around 775 nm. The primary mechanism for the optical limiting behavior can be well understood by the three-photon induced excited state absorption (3PA-ESA). This result in that DSB has high transmittance for low-intensity ambient light levels and the ultrafast response of optical-limiting. In addition, the limited optical window can be tuned by changing the length of the π-electron conjugated structure. It was also discovered that the molecular aggregation has an inhibitory effect on the optical limiting efficiency of distyrylbenzene. The present results may serve as a theoretical guideline for the design of distyrylbenzene-based optical limiting materials. [ABSTRACT FROM AUTHOR]

In this study, α-MnO2 and Fe2O3 nanomaterials are prepared on a carbon fiber modified with carbon nanotubes to produce the nonbinder core–shell positive (α-MnO2@CNTs/CC) and negative (Fe2O3@CNTs/CC) electrodes that can be operated in a wide voltage window in ultrafast asymmetrical flexible supercapacitors. MnO2 and Fe2O3 have attracted wide research interests as electrode materials in energy storage applications because of the abundant natural resources, high theoretical specific capacities, environmental friendliness, and low cost. The electrochemical performance of each electrode is assessed in 1 M Na2SO4 and the energy storage properties of the supercapacitors consisting of the two composite electrodes are determined in Na2SO4 and EMImBF4 electrolytes in the 2 V and 4 V windows. The 2 V supercapacitor can withstand a large scanning rate of 5000 mV S−1 without obvious changes in the cyclic voltammetry (CV) curves, besides showing a maximum energy density of 57.29 Wh kg−1 at a power density of 833.35 W kg−1. Furthermore, the supercapacitor retains 87.06% of the capacity after 20,000 galvanostatic charging and discharging (GCD) cycles. The 4 V flexible supercapacitor shows a discharging time of 1260 s and specific capacitance of 124.8 F g−1 at a current of 0.5 mA and retains 87.77% of the initial specific capacitance after 5000 GCD cycles. The mechanical robustness and practicality are demonstrated by physical bending and the powering of LED arrays. In addition, the contributions of the active materials to the capacitive properties and the underlying mechanisms are explored and discussed [ABSTRACT FROM AUTHOR]

Investigations of two-dimensional ( 2D ) / one-dimensional ( 1D) van der Waals ( vdW) heterojunctions have attracted significant attention due to their excellent properties such as the smooth heterointerface, the highly gate-tunable bandgap, and the ultrafast carrier transport. However, the complicated method of manufacturing vdW heterojunction represents a major problem that severely limits their practical applications. Herein, we develop onestep hydrothermal method and use it to synthesize 2D PbI2 / 1D Pb5S2I6 vdW heterojunction. The PbI2 / Pb5S2I6 vdW heterojunction photodetector(PD) displays lower dark current (<20 pA), higher responsivity (up to 134 mA·W-1), self-powered and wider response spectrum in comparison with that of pristine PbI2 PD and Pb5S2I6 PD. This one-step hydrothermal method provides a new idea for preparing other mixed-dimensional heterojunction. [ABSTRACT FROM AUTHOR]