Study of Chemical and Morphological Transformations during Ni2Mo3N Synthesis via an Oxide Precursor Nitration Route

Chemical and morphological transformations during Ni2Mo3N synthesis were studied in this work. Nitride samples were synthesized from oxide precursors in H2/N2 flow and were analyzed by thermogravimetry, X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-ray spectroscopy methods. In addition, physical and chemical adsorption properties were studied using low-temperature N2 physisorption and NH3 temperature-programmed desorption. It was shown that nitride formation proceeds through a sequence of phase transformations: NiMoO4 + MoO3 → Ni + NiMo + MoO2 → Ni + NiMo + Mo2N → Ni2Mo3N. The weight changes that were calculated from the proposed reactions were in agreement with the experimental data from thermogravimetry. The morphology of the powder changed from platelets and spheres for the oxide sample, to aggregates of needle-like particles for the intermediate product, to porous particles with an extended surface area for the nitride final product. The obtained results should prove useful for subsequent Ni2Mo3N based catalysts production process optimization

Delaminated V2C MXene nanostructures prepared via LiF salt etching for electrochemical applications

Vanadium carbide MXenes have demonstrated both one of the highest theoretical capacities for Li and Mg storage among all members of the MXene family and a high performance as cathodes for high-energy-density Zn-ion batteries (ZIBs). However, V2C research has been limited because of the instability of delaminated V2C (d-V2C) in water suspension. Herein, we propose improvements of the HF-free synthesis of V2C MXenes via selective etching of the V2AlC MAX phase by a HCl and LiF mixture. A combination of etching in the closed environment of the hydrothermal autoclave under continuous stirring and thermal isolation of a reaction vessel and improved washing techniques result in high-quality d-V2C MXene nanostructures. High crystallinity and chemical purity of the as-synthesized materials is confirmed by X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and aberration-corrected high-resolution transmission electron microscopy. A high concentration of Li cations in the etching mixture results in significantly improved stability of d-V2C in water suspension. In addition, cyclic voltammetry analysis is conducted to gauge the electrochemical characteristics of fabricated d-V2C MXenes. Electrochemical tests confirm that fabricated MXenes are highly promising as cathode materials for aqueous ZIBs. Moreover, a charge storage mechanism of V2C MXenes can be tuned through the implementation of different synthetic methods as well as electrochemical activation protocols. </p

Optomechanical properties of MoSe2 nanosheets as revealed by in situ transmission electron microscopy

Free-standing few-layered MoSe2 nanosheet stacks optoelectronic signatures are analyzed by using light compatible in situ transmission electron microscopy (TEM) utilizing an optical TEM holder allowing for the simultaneous mechanical deformation, electrical probing and light illumination of a sample. Two types of deformation, namely, (i) bending of nanosheets perpendicular to their basal atomic planes and (ii) edge deformation parallel to the basal atomic planes, lead to two distinctly different optomechanical performances of the nanosheet stacks. The former deformation induces a stable but rather marginal increase in photocurrent, whereas the latter mode is prone to unstable nonsystematic photocurrent value changes and a red-shifted photocurrent spectrum. The experimental results are verified by ab initio calculations using density functional theory (DFT).</p

Carbon-Integrated Vanadium Oxide Hydrate as a High-Performance Cathode Material for Aqueous Zinc-Ion Batteries

The hydration of bilayer vanadium oxides has become the focus of several recent studies toward increasing the interlayer spacing and improving their structural stability, which is favorable for the reversible (de)insertion of Zn2+ions. However, there is limited understanding on the optimal level of H2O molecules to be incorporated within the vanadium oxide structure. Herein, we investigate the effects of the interlayer H2O content in a vanadium(IV,V) oxide-based cathode material toward the electrochemical performance of a zinc-ion battery (ZIB). A simple solvothermal synthetic route was employed to synthesize carbon-integrated hydrated vanadium oxides with varying H2O contents, CHVO (V5O12·2.7H2O) and CHVO-LW (V5O12·0.4H2O). CHVO material displays a high capacity of 396 mA h g-1at a specific current of 250 mA g-1and an excellent rate capability (187 W h kg-1at a high-power density of 4.5 kW kg-1). In contrast, CHVO-LW delivers a higher capacity of 582 mA h g-1at 200 mA g-1in the initial cycles, however, suffers a rapid capacity decay and cell failure in subsequent cycles. Electrochemical characterizations revealed that structural pillars, such as H2O molecules, can indeed provide significant structural stability, yet too many of them can block intercalation pathways leading to lower capacity. This study shows the importance of adjusting the hydration level to sustain a balance between the high capacity and long-term stability of hydrated vanadium oxide cathode-based ZIBs.</p

Mechanical properties of decellularized extracellular matrix coated with TiCaPCON film

For the first time the surface of decellularized extracellular matrix (DECM) was modified via deposition of a multicomponent bioactive nanostructured film for improvement of the DECM's mechanical properties. TiCaPCON films were deposited onto the surface of intact and decellularized ulna, radius, and humerus bones by magnetron sputtering of TiC<SUB>0.5</SUB> + 10%Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> and Ti targets in a gaseous mixture of Ar + N<SUB>2</SUB>. The film structure was studied using x-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopy. The films were characterized in terms of their wettability, as well as adhesion strength to the intact bone and DECM substrates. The mechanical properties of TiCaPCON-coated samples were investigated by compression testing. In addition, humerus bones were evaluated during three-point bending tests. The results indicate that the tightly adhered films, uniformly covering the DECM surfaces, possessed hydrophilic characteristics. A maximum improvement in mechanical properties (250%) was observed for coated humerus samples. In case of decellularized radius bones, the compressive strength also increased by 150% after coating. The positive role of TiCaPCON films was less noticeable for ulna bones because of large data scattering. These results clearly indicate that the films acted as a rigid frame that increased the material compressive strength. Compared with intact bones, fracture in the TiCaPCON-coated DECM samples was characterized by rarer and larger cracks generated under higher critical loads. As a result, the samples were crushed into several large pieces and numerous tiny fragments. Although the film deposition increased the bone stiffness, the bending tests revealed that the flexural strength of the coated samples became 20%–25% lower than the strength of the film-free samples

Optoelectronic and optomechanical properties of few-atomic-layer black phosphorus nanoflakes as revealed by in situ TEM

The optoelectronic signatures of free-standing few-atomic-layer black phosphorus nanoflakes are analyzed by in situ transmission electron microscopy (TEM). As compared to other 2D materials, the band gap of black phosphorus (BP) is related directly to multiple thicknesses and can be tuned by nanoflake thickness and strain. The photocurrent measurements with the TEM show a stable response to infrared light illumination and change of nanoflakes band gap with deformation while pressing them between two electrodes assembled in the microscope. The photocurrent spectra of an 8- and a 6-layer BP nanoflake samples are comparatively measured. Density functional theory (DFT) calculations are performed to identify the band structure changes of BP during deformations. The results should help to find the best pathways for BP smart band gap engineering via tuning the number of material atomic layers and programmed deformations to promote future optoelectronic applications.</p

Crystallography-derived optoelectronic and photovoltaic properties of CsPbBr3 perovskite single crystals as revealed by in situ transmission electron microscopy

Given the high importance of CsPbBr3 perovskite crystals for optoelectronic and photovoltaic device applications, surprisingly, relatively little work has been done to assess the impact of crystalline orientations and/or surface contacts on their performance. Herein, photocurrent and photovoltage properties of CsPbBr3 single crystals are selectively measured on (001) and (101) facets in pristine and compressed conditions using light-and-stress-compatible in situ high-resolution transmission electron microscopy (TEM). The photocurrent-to-dark-current ratios on (001) and (101) facets are found to be comparable, showing a minimal statistical discrepancy. The TEM-derived photocurrent spectroscopies revealed slight blue shifts of the cut-off wavelengths under crystal pressing. By contrast, the photovoltage values measured on the two regarded facets significantly differ, and this difference is sustained under in situ compression in the TEM. The higher values apparent for (101) facets provide valuable information for a smart device design and perovskite crystal applications in photoelectronic and photovoltaic fields

Vanadium-containing layered materials as high-performance cathodes for aqueous zinc-ion batteries

The world is currently in the midst of a climate crises and many across the globe are competing to find new technologies to create clean, and effective ways of harnessing renewable energy sources. However, this energy needs to be stored and the current systems simply would not last. Zinc-ion batteries (ZIBs) with vanadium-containing cathodes are a recently arising technology providing a cheap, safe, and eco-friendly alternative to the current systems. Vanadium is a material that has long been used for electrochemical systems due to its large range of stable oxidation states. Most common is the vanadium oxide (V2O5) renowned for its open layered framework and manipulatable structure. However, this is not the only vanadium-containing material that is proposed for use in ZIBs. The vanadium family is comprised of four main sub-categories under which materials can be classified: vanadium oxides, vanadium phosphates, vanadates, and O2-free vanadium compounds. This report delves into the specifics of each of these sub-families to further develop the understanding of their functionality by highlighting their structural and morphological characteristics, aptitude for modification, and the corresponding electrochemical properties. Through this investigation, the application of these materials in ZIB systems is highlighted and future development aims considered.</p

The effect of Ti3AlC2 MAX phase synthetic history on the structure and electrochemical properties of resultant Ti3C2 MXenes

The synthesis of MXenes is a lively area of research in today’s materials sciencecommunity. Pure carbide and nitride samples with tunable properties and crystal size are desirable for the implementation of these promising young materials in the wider economy. Herein, the preparation of Ti3AlC2 MAX phase has been studied with a view to improving the quality and purity of the resultant Ti3C2 MXene. Room temperature high-energy ball milling is exploited for the mechanical activation of elemental powder mixtures, which, along with adjusted input stoichiometry and heat treatment, achieves high-purity and highly crystalline Ti3AlC2 and Ti3C2 with rather quick and easy methodology. Several approaches are offered, as not all of these preparation steps are strictly necessary for acquiring MXene. The structure and properties of Ti3C2 are shown to depend on the preparation history and precursor characteristics. The MXene is additionally shown to perform well as a substrate for binder-free electrochemical cell electrodes; high electrical conductivity and cycling stability render this MXene@Zn anode a viable option for aqueous Zn-ion systems

Green plasma enhanced synthesis of multi-phase NiMnO3 cathode for aqueous Zn-ion batteries

Rechargeable Zn-ion batteries have the potential to address the need for cheap and widely accessible energy storage. Metal-doped manganese oxide cathodes are a common and effective choice for Zn-ion batteries. Zn-ion battery development can be advanced by overcoming the poor cycle life that many metal-doped Mn-oxide cathodes suffer from. Plasma-treated water (PAW) is created using low input power of 0.145 kWh per liter of PAW and is used to accelerate the reduction and precipitation of MnO4− and nickel acetate (Ni(Ac)) to form a multiphase NiMnO3 electrode with Ni2+ and Ni3+ doped into the MnO6 octahedra, which exhibits capacitance dominated charge storage mechanisms. The electrode shows initial specific capacitance of 60.1 F g−1 and a capacitance retention of 100.8% after 10,000 cycles and 92.2% after 12,000 cycles. The beneficial layer of nanoflake morphology is formed during cycling, which causes a rapid increase in specific capacitance due to the larger electrochemically active surface area and the associated surface adsorption-based (pseudo-capacitive) type charge storage. We also demonstrate the capability of our multiphase NiMnO3 electrode to be coupled with a Zn metal anode in a battery cell which exhibits 330 mAh g−1 peak specific capacity and capacity retention of 63.8% after 380 cycles. </div