Two-dimensional transition metal carbide/nitride MXenes have become a hot topic in the field of lithium-ion energy storage due to their unique surface chemistry and excellent electronic conductivity. However, electrodes made of multilayer MXenes suffer from low capacity, poor cycling performance, and slow lithiation kinetics. In this paper, the MoP2@Ti3C2Tx composite was prepared by adsorbing Mo cations on the surface of Ti3C2Tx followed by phosphatization. The uniformly distributed MoP2 nanostructure effectively increases the layer spacing, enlarges the specific surface area, and improves the structural stability of the material. At the same time, MoP2 and Ti3C2Tx are connected by a P−O bond, which accelerates the diffusion and migration of lithium ions and the charge transfer, and the strong covalent Ti−O−P bond can cause rapid charge transfer and stabilize the structure of the material. The electrochemical activity of MoP2 nanostructures also provides more active sites for lithium ions. The presence of the lamellar structure of Ti3C2Tx also inhibits to some extent the expansion of the transition metal phosphide volume with the cycling process, thus realizing more excellent lithium storage capacity. 1/2 MoP2@Ti3C2Tx material has a high reversible capacity of 165.7 mAh g−1 (172% improvement over the original material) at a current density of 3000 mA g−1. The assembled 1/2 MoP2@Ti3C2Tx//AC Li-ion hybrid capacitor LIC has 85.5% capacity retention after cycling at a current density of 1500 mA g−1. The ability of the assembled full battery to illuminate light-emitting diode (LED) light bulbs further confirms that the electrochemical reliability of the device meets the requirements of real-world applications. The results demonstrate that the strategy of constructing in situ-grown MoP2 nanostructures can effectively improve MXene high-energy-density applications in lithium-ion energy storage.
The Li 2 BaP 2 O 7 ceramics, synthesized through the solid-state reaction method, exhibit a pure monoclinic phase. Upon sintering at 750 °C, the ceramic achieves a high relative density of 97.3 %, which is indicative of an optimal microstructure conducive to the superior microwave dielectric properties: a ε r of 9.9, a Q × f of 86200 GHz, and a τ f of −95.4 ppm/°C. The variation in relative density is identified as the principal driver of changes in both the ε r and Q × f values for the Li 2 BaP 2 O 7 ceramics. The molecular polarizability is pivotal in determining the ε r of Li 2 BaP 2 O 7 ceramics. The P-V-L theory analysis elucidates that the P-O bond significantly surpasses other chemical bonds in contributing to the ionicity, lattice energy, and bond energy, thereby underscoring its dominance over the three principal microwave dielectric characteristics. Furthermore, Raman spectroscopy data demonstrate that the P-O bond vibration predominantly governs the overall vibrational spectrum.
You Zi,Songrui Wei,Zhihui Huang,Jun Zhu,Yi Hu,Mengke Wang,Han Zhang,Weichun Huang
Organophosphorus compounds display excellent chemical and biological properties that the S–P(O) bonds afford utility in various fields. Herein, we report for the first time on the utilization of zero-dimensional (0D) monoelemental bismuth (Bi) quantum dots (QDs) as photocatalysts for direct dehydrogenative phosphonylation under visible light irradiation. A tiny amount of 0D Bi QDs (1.5 mol%) show high photocatalytic efficiency in the direct formation of S–P(O) between thiols and H–P(O) compounds under visible light with simple protocol, amenable gram-scale synthesis and good reusability. The mechanism study and density functional theory (DFT) calculation demonstrate the sulfide radial generated on the surface of 0D Bi QDs. The DFT study also indicates that the as-synthesized 0D Bi QDs exhibit suitable adsorption energy and sufficient charge transfer to effectively promote phosphonylation. We believe that such unique transformation can pave the way to more sustainable organic photocatalytic transformations based on high-efficiency QDs or QD-related nanocomposites.
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