In Situ Molecular Engineering Strategy to Construct Hierarchical MoS2 Double-Layer Nanotubes for Ultralong Lifespan "Rocking-Chair" Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc ion batteries (AZIBs) have gained considerable attention owing to their low cost and high safety, but dendrite growth, low plating/stripping efficiency, surface passivation, and self-erosion of the Zn metal anode are hindering their application. Herein, a one-step in situ molecular engineering strategy for the simultaneous construction of hierarchical MoS2 double-layer nanotubes (MoS2-DLTs) with expanded layer-spacing, oxygen doping, structural defects, and an abundant 1T-phase is proposed, which are designed as an intercalation-type anode for "rocking-chair" AZIBs, avoiding the Zn anode issues and therefore displaying a long cycling life. Benefiting from the structural optimization and molecular engineering, the Zn2+ diffusion efficiency and interface reaction kinetics of MoS2-DLTs are enhanced. When coupled with a homemade ZnMn2O4 cathode, the assembled MoS2-DLTs//ZnMn2O4 full battery exhibited impressive cycling stability with a capacity retention of 86.6% over 10 000 cycles under 1 A g-1anode, outperforming most of the reported "rocking-chair" AZIBs. The Zn2+/H+ cointercalation mechanism of MoS2-DLTs is investigated by synchrotron in situ powder X-ray diffraction and multiple ex situ characterizations. This research demonstrates the feasibility of MoS2 for Zn-storage anodes that can be used to construct reliable aqueous full batteries.

Alkali etching zinc and manganese silicates derived from natural green algaes for supercapacitors with enhanced electrochemical properties.

A facile novel method of alkali etching was proposed to enhance the application of metal-silicates in supercapacitors. First, 3D N, S, P-doped C-zinc-silicate (C-ZnSi), and C-manganese-silicate (C-MnSi) were derived from calcined green algaes (GAs) in a N2 atmosphere. Second, the synthesized products were soaked in a 3.0 M NaOH aqueous solution for alkali etching (soaked for 6, 12 and 24 h) to obtain the etching metal silicates (e-C-ZnSi and e-C-MnSi). This method can yield a higher specific surface area and more pores, and this in turn can improve the electrochemical performance. In the three-electrode system, e-C-ZnSi and e-C-MnSi, which were soaked in NaOH solution for 12 h, exhibited the highest specific capacitances and cycling performance. Solid-state hybrid supercapacitor (HSC) devices were manufactured using C-MSi, e-C-MSi (M = Zn and Mn), and activated carbon (AC) (denoted as C-MSi//AC and e-C-MSi//AC). In the two-electrode system, the e-C-MSi//AC HSC devices exhibited higher areal specific capacitances and energy densities and better cycle performance than those of C-MSi//AC, especially e-C-MSi//AC-12 h HSC devices, which exhibited the best electrochemical properties. This study demonstrated that the naturally polluted GAs can be used as a reusable silica source for the synthesis of supercapacitors. Furthermore, alkali etching can enhance the electrochemical performance of metal silicates and can be used to prepare electrode materials applied for high-performance supercapacitors.

Dual-cation-doped MoS2nanosheets accelerating tandem alkaline hydrogen evolution reaction.

Molybdenum disulfide (MoS2) nanosheets are promising candidates as earth-abundant and low-cost catalyst for hydrogen evolution reaction (HER). Nevertheless, compared with the benchmark Pt/C catalyst, the application of MoS2nanosheets is limited to its relatively low catalytic activity, especially in alkaline environments. Here, we developed a dual-cation doping strategy to improve the alkaline HER performance of MoS2nanosheets. The designed Ni, Co co-doped MoS2nanosheets can promote the tandem HER steps simultaneously, thus leading to a much enhanced catalytic activity in alkaline solution. Density functional theory calculations revealed the individual roles of Ni and Co dopants in the catalytic process. The doped Ni is uncovered to be the active site for the initial water-cleaving step, while the Co dopant is conducive to the H desorbing by regulating the electronic structure of neighboring edge-S in MoS2. The synergistic effect resulted by the dual-cation doping thus facilitates the tandem HER steps, providing an effective route to raise the catalytic performance of MoS2materials in alkaline solution.

A Highly Stable Photodetector Based on a Lead-Free Double Perovskite Operating at Different Temperatures.

In recent years, considerable breakthroughs have been achieved in the explored photodetectors with improved performance and stability. However, such devices suffer from the drifting parameters (photoresponsivity, response time, and specific detectivity) in the case of evident operating temperature changes. Here, a double perovskite Cs2NaBiCl6-based ultraviolet (UV) photodetector is developed free from thermal disturbance, exhibiting a steady photoresponsivity (≈ 67.98 mA/W) and response time (≈ 16.42 ms) within a wide temperature range (from 273 to 333 K). Further studies demonstrate that the stability of the crystal structure endows the superior photodetection capability. This result unambiguously highlights the great potential of such double perovskite Cs2NaBiCl6 compound as an environmentally friendly alternative for UV photodetectors.

Structural, elastic and electronic properties of atomically thin pyridyne: theoretical predictions.

In this paper, we propose a new acetylenic carbon material called pyridyne, which is composed of acetylenic linkages and pyridine rings. From first-principles calculations, we investigate the structural, elastic and electronic properties of pyridyne. It is found that the structure of pyridyne is stable at 300 K and its stability is comparable to experimentally synthesized graphdiyne and graphtetrayne. Compared with graphene or graphyne, pyridyne possesses more diverse pores and reduced delocalization of electrons. The in-plane stiffness of pyridyne is 183 N m-1 with a Poisson's ratio of 0.304. Pyridyne is found to be a semiconductor with a direct band gap of 0.91 eV. The intrinsic electron mobility can reach 6.08 × 104 cm2 V-1 s-1, while the hole mobility can reach 1.82 × 104 cm2 V-1 s-1.

Heterostructured Electrocatalysts for Hydrogen Evolution Reaction Under Alkaline Conditions.

The hydrogen evolution reaction (HER) is a half-cell reaction in water electrolysis for producing hydrogen gas. In industrial water electrolysis, the HER is often conducted in alkaline media to achieve higher stability of the electrode materials. However, the kinetics of the HER in alkaline medium is slow relative to that in acid because of the low concentration of protons in the former. Under the latter conditions, the entire HER process will require additional effort to obtain protons by water dissociation near or on the catalyst surface. Heterostructured catalysts, with fascinating synergistic effects derived from their heterogeneous interfaces, can provide multiple functional sites for the overall reaction process. At present, the activity of the most active known heterostructured catalysts surpasses (platinum-based heterostructures) or approaches (noble-metal-free heterostructures) that of the commercial Pt/C catalyst under alkaline conditions, demonstrating an infusive potential to break through the bottlenecks. This review summarizes the most representative and recent heterostructured HER catalysts for alkaline medium. The basics and principles of the HER under alkaline conditions are first introduced, followed by a discussion of the latest advances in heterostructured catalysts with/without noble-metal-based heterostructures. Special focus is placed on approaches for enhancing the reaction rate by accelerating the Volmer step. This review aims to provide an overview of the current developments in alkaline HER catalysts, as well as the design principles for the future development of heterostructured nano- or micro-sized electrocatalysts.

Preparation and Characterization of Mo Doped in BiVO4 with Enhanced Photocatalytic Properties.

Molybdenum (Mo) doped BiVO4 was fabricated via a simple electrospun method. Morphology, structure, chemical states and optical properties of the obtained catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), N2 adsorption-desorption isotherms (BET) and photoluminescence spectrum (PL), respectively. The photocatalytic properties indicate that doping Mo into BiVO4 can enhance the photocatalytic activity and dark adsorption ability. The photocatalytic test suggests that the 1% Mo-BiVO4 shows the best photocatalytic activity, which is about three times higher than pure BiVO4. Meanwhile, 3% Mo-BiVO4 shows stronger dark adsorption than pure BiVO4 and 1% Mo-BiVO4. The enhancement in photocatalytic property should be ascribed to that BiVO4 with small amount of Mo doping could efficiently separate the photogenerated carries and improve the electronic conductivity. The high concentration doping would lead the crystal structure transformation from monoclinic to tetragonal phase, as well as the formation of MoO3 nanoparticles on the BiVO4 surface, which could also act as recombination centers to decrease the photocatalytic activity.

The photosensitivity of carbon quantum dots/CuAlO2 films composites.

Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

Enhanced microwave absorption performance of hollow alpha-MnO2 nanourchins.

Three dimensional (3D) hierarchical nanostructures are expected to provide enhanced microwave absorption properties for nanomaterials. In this report we prepared hollow urchinlike alpha-MnO2 nanostructures and dispersed alpha-MnO2 nanorods via a facile hydrothermal method. The complex permittivity and permeability of the hollow alpha-MnO2 nanourchins/paraffin wax composites with different manganese dioxide loadings were investigated in the range of 2-18 GHz, based on which the corresponding reflection loss were simulated. A minimum reflection loss of -36 dB was obtained from the composites with 50 wt% MnO2 nanostructures. Furthermore, the microwave absorption properties of dispersed alpha-MnO2 nanorods were studied for comparison, which indicate the unique morphology of the hollow urchinlike nanostructures is of significant effect to their microwave absorption properties.