Synergistic Effect of Charge Generation and Separation in Epitaxially Grown BiOCl/Bi₂S₃ Nano-Heterostructure

Nano-heterostructures are widely used in the field of optoelectronic devices, and an optimal proportion usually exists between the constituents that make up the structures. Investigation on the mechanism underlying the optimal ratio is instructive for fabricating nano-heterostructures with high efficiency. In this work, BiOCl/Bi₂S₃ type-II nano-heterostructures with different Bi₂S₃/BiOCl ratios have been prepared via epitaxial growth of Bi₂S₃ nanorods on BiOCl nanosheets with solvothermal treatment at different sulfuration temperatures (110–180 °C) and their photoelectrochemical (PEC) performances as photoanodes have been studied. Results indicate that the Bi₂S₃ content increases with the sulfuration temperature. BiOCl/Bi₂S₃-170 (i.e., sulfurized@170 °C) exhibits the highest PEC performance under visible-light illumination, whereas BiOCl/Bi₂S₃-180 with the maximum Bi₂S₃ content shows the highest visible-light absorption, i.e., possessing the best potential for charge generation. Further analysis indicates that the BiOCl/Bi₂S₃ heterojunction interface is also crucial in determining the PEC performance of the obtained heterostructures by influencing the charge separation process. With increasing Bi₂S₃ content, the interface area in the BiOCl/Bi₂S₃ nano-heterostructures increases first and then decreases due to the mechanical fragility of the nanosheet–nanorod structure and the structural instability in the [010] direction of Bi₂S₃ with higher Bi₂S₃ content. Therefore, the increasing content of the Bi₂S₃ does not necessarily correspond to higher heterojunction area. The optimal performance of BiOCl/Bi₂S₃-170 results from the maximum of the synthetic coordination of the charge generation and separation. This is the first time ever to figure out the detailed explanation of the optimal property in the nano-heterostructures. The result is inspiring in designing high-performance nano-heterostructures from the point of synthesizing morphological mechanically robust heterostructure and structurally stable constituents to reach a high interfacial area, as well as high light-absorption ability

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Supplementary material

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Reconstructed holographic image with both polarization dependent and independent color

Monoclinic ZIF‑8 Nanosheet-Derived 2D Carbon Nanosheets as Sulfur Immobilizer for High-Performance Lithium Sulfur Batteries

2D hierarchically porous carbon (2D-HPC) nanosheets with unique advantages are highly desired as host materials for lithium sulfur (Li–S) batteries and other energy storage devices. Herein, we propose a self-template and organic solvent-free approach to synthesize nanosheets of monoclinic ZIF-8 at room temperature from which 2D-HPC nanosheets (ZIF-8 nanosheets carbon denoted as ZIF-8-NS-C) are derived to be an efficient sulfur immobilizer for Li–S batteries for the first time. The anisotropic nanosheets are believed to relate to the symmetry of the monoclinic structure. The 2D ZIF-8-NS-C nanosheets with embedded hierarchical pores construct an effective conductive network through “plane-to-plane” modes to endow superior electron transfer and fast electrochemical kinetics. Moreover, the nitrogen-rich feature of ZIF-8-NS-C can increase the affinity/interaction of carbon host with lithium polysulfides, favoring the cyclic performance. The sulfur/ZIF-8-NS-C (S/ZIF-8-NS-C) cathode shows a superior rate capability with high capacities of 1226 mA h g^–1 at 0.2 <i>C</i> and 785 mA h g^–1 at 2 <i>C</i>, and a sustainable cycling stability with a capacity attenuation of 0.12% per cycle at 0.5 C for 300 cycles. The approach proposed here pioneers the controllable design of MOF-based structures to inspire the exploration of more variable MOF-derived porous materials for energy storage applications

Large-Scale Fabrication of Suspended, Aligned, and Strained Single-Walled Carbon Nanotube Networks

Large-scale fabrication of suspended single-walled carbon nanotubes remains a challenge, especially at specific locations and in specific directions. In this work, we demonstrate an effective, fast and large-scale technique to fabricate suspended, strained, and aligned SWNT networks, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between each two prefabricated palladium patterns in high temperature. The SWNTs are aligned in eight directions: up, down, left, right, upper right, lower right, upper left, and lower left. The simulated calculations show that the driving force leading the silver liquid motion on the substrate is around 0.66 μN. The Raman spectra of the SWNTs network were measured, and the downshift of the G+ band indicates that, for the suspended SWNTs, the uniaxial strain is around 0.13%. This technique could be extended to two-dimensional material systems and open the pathway toward better optoelectronic and nanoelectromechanical systems

Drastically Enhanced High-Rate Performance of Carbon-Coated LiFePO₄ Nanorods Using a Green Chemical Vapor Deposition (CVD) Method for Lithium Ion Battery: A Selective Carbon Coating Process

Application of LiFePO₄ (LFP) to large current power supplies is greatly hindered by its poor electrical conductivity (10^–9 S cm^–1) and sluggish Li⁺ transport. Carbon coating is considered to be necessary for improving its interparticle electronic conductivity and thus electrochemical performance. Here, we proposed a novel, green, low cost and controllable CVD approach using solid glucose as carbon source which can be extended to most cathode and anode materials in need of carbon coating. Hydrothermally synthesized LFP nanorods with optimized thickness of carbon coated by this recipe are shown to have superb high-rate performance, high energy, and power densities, as well as long high-rate cycle lifetime. For 200 C (18s) charge and discharge, the discharge capacity and voltage are 89.69 mAh g^–1 and 3.030 V, respectively, and the energy and power densities are 271.80 Wh kg^–1 and 54.36 kW kg^–1, respectively. The capacity retention of 93.0%, and the energy and power density retention of 93.6% after 500 cycles at 100 C were achieved. Compared to the conventional carbon coating through direct mixing with glucose (or other organic substances) followed by annealing (DMGA), the carbon phase coated using this CVD recipe is of higher quality and better uniformity. Undoubtedly, this approach enhances significantly the electrochemical performance of high power LFP and thus broadens greatly the prospect of its applications to large current power supplies such as electric and hybrid electric vehicles

Visible-Frequency Dielectric Metasurfaces for Multiwavelength Achromatic and Highly Dispersive Holograms

Dielectric metasurfaces built up with nanostructures of high refractive index represent a powerful platform for highly efficient flat optical devices due to their easy-tuning electromagnetic scattering properties and relatively high transmission efficiencies. Here we show visible-frequency silicon metasurfaces formed by three kinds of nanoblocks multiplexed in a subwavelength unit to constitute a metamolecule, which are capable of wavefront manipulation for red, green, and blue light simultaneously. Full phase control is achieved for each wavelength by independently changing the in-plane orientations of the corresponding nanoblocks to induce the required geometric phases. Achromatic and highly dispersive meta-holograms are fabricated to demonstrate the wavefront manipulation with high resolution. This technique could be viable for various practical holographic applications and flat achromatic devices