Two-step fabrication of lanthanum nickelate and nickel oxide core-shell dandelion-like materials for high-performance supercapacitors.

LaNiO3 and NiO are promising materials for supercapacitor applications. However, it is still challenging to design special structures based on these materials to improve the electrochemical performances of supercapacitor electrodes. In this work, a two-step method with low cost and convenient operation was developed to prepare dandelion-shaped LaNiO3/NiO (CSD-LaNiO3/NiO) with core-shell structure. The as-obtained CSD-LaNiO3/NiO showed high conductivity due to the core LaNiO3, which helped to provide an efficient electron transmission path for the shell NiO, producing a strong synergistic effect. The results of electrochemical properties of CSD-LaNiO3/NiO, LaNiO3 and NiO samples revealed the superior specific capacitance of CSD-LaNiO3/NiO (326.8 F g-1) at 1 A g-1 compared to LaNiO3 (166.5 F g-1) and NiO (44.2 F g-1). The as-obtained CSD-LaNiO3/NiO material was then mixed with activated carbon and assembled into an asymmetric supercapacitor, which exhibited a wide potential window of 1.8 V, energy density of 30.4 Wh kg-1 at 1800 W kg-1, and specific capacity retention of 97.7% after 3000 cycles. In sum, the as-obtained core-shell nanostructure prepared by the proposed synthesis method is very promising for future development of high-performance supercapacitors.

Investigation of High-Temperature Normal Infrared Spectral Emissivity of ZrO2 Thermal Barrier Coating Artefacts by the Modified Integrated Blackbody Method.

Zirconium oxide (ZrO2) is widely used as the thermal barrier coating in turbines and engines. Accurate emissivity measurement of ZrO2 coating at high temperatures, especially above 1000 °C, plays a vital role in thermal modelling and radiation thermometry. However, it is an extremely challenging enterprise, and very few high temperature emissivity results with rigorously estimated uncertainties have been published to date. The key issue for accurately measuring the high temperature emissivity is maintaining a hot surface without reflection from the hot environment, and avoiding passive or active oxidation of material, which will modify the emissivity. In this paper, a novel modified integrated blackbody method is reported to measure the high temperature normal spectral emissivity of ZrO2 coating in the temperature range 1000 °C to 1200 °C and spectral range 8 µm to 14 µm. The results and the associated uncertainty of the measurement were estimated and a relative standard uncertainty better than 7% (k = 2) is achieved.

Controllable Epitaxial Growth of MoSe2 Bilayers with Different Stacking Orders by Reverse-Flow Chemical Vapor Deposition.

The stacking order plays a critical role in the electronic and optical properties of two-dimensional materials. It is however of great challenge to achieve large-size and homogeneous bilayer crystals with precisely controlled stacking orders. Here, we demonstrate an optimized chemical vapor deposition strategy to grow MoSe2 bilayers with controlled AA or AB stacking sequences. Reverse gas flow effectively suppresses the random nucleation centers, leading to uniform growth of the second layer of MoSe2 on the first monolayer. A customized temperature profile selectively activates the growth of the MoSe2 bilayer with different stacking orders: the AA stacking MoSe2 bilayer tends to form at 810 °C, and the AB stacking MoSe2 bilayer prefers to grow at a higher temperature of 860 °C. A series of characterization methods confirm that MoSe2 bilayers with different stacking orders exhibit distinct crystal structures and physical properties. Our results demonstrate a robust and effective route for the controllable synthesis of transition metal dichalcogenide bilayers, which will benefit the development of two-dimensional materials and van der Waals heterostructures.

Synthesis of silicon nitride nanowires by the pyrolysis of perhydropolysilazane.

Silicon nitride nanowires synthesized by the pyrolysis of perhydropolysilazane without using any catalysts are reported. After pyrolysis at 1073 K in N2/NH3 atmosphere, the synthetic nanowires are discrete and curly with diameters about tens of nanometers and lengths of hundreds of nanometers. While after post-treatment at 1873 K in N2 atmosphere, the nanowires are continuous and randomly distributed with diameters about tens of nanometers and several microns in length. There are no bulbs or droplets on the tips of the nanowires, and two gas-solid mechanisms are proposed to explain their growth.