Metastable monoclinic molybdenum trioxide (β-MoO 3 ) combined with perfect hexagonally-shaped MoS 2 and graphene nanosheets are fabricated by facile mechanochemical-molten salt treatment of irregularly-shaped molybdenum disulfide (MoS 2 ) and graphite in air. This hybrid nanostructure exhibits an excellent Li-ion storage performance, outperforming the nanocomposites made of conventional orthorhombic α-MoO 3 . To this end, ball-milled MoS 2 and graphite are treated in the presence of sodium chloride (NaCl) at 900–1200 °C, leading to the preparation of MoS 2 /MoO x @graphene (MSO@G) nanocomposites in an easily scalable and affordable way. The formation of β-MoO 3 is realized at 1100 °C (MSO@G-1100), outperforming the electrochemical performances of other samples and the initial MoS 2 . Moreover, the influence of binder on the electrochemical performance of MSO@G-1100 is studied, based on which polystyrene acrylic-acrylate (SAE) is found to provide a considerably low charge transfer resistance (27.59 Ω), outperforming conventional binders. The electrode exhibits a reversible Li-ion storage capacity of 878 mAh g −1 after 245 cycles at the current density of 100 mA g −1 . The capacitive contribution to the total Li-ion energy storage performance of MSO@G-1100/SAE is found to be significant with the value of around 62% at the potential scan rate of 0.3 mV s −1 . This article report on the facile, clean and sustainable preparation of β-MoO 3 based nanocomposites with remarkable electrochemical performance.
Organonitrogen chemicals with C=N bonds are one of the most important groups of chemicals with broad applications, but their synthesis via reductive coupling remains a great challenge, because of the favorable hydrogenation of C=N bonds into C–N bonds. In this study, a nitrogen-doped carbon-supported β-MoO 3 catalyst with abundant oxygen vacancies (O v ) was discovered to be robust in the reductive coupling of nitro compounds with biomass-derived alcohols toward the synthesis of organonitrogen chemicals, including imines and N -heterocycles with C=N bonds. The O v in β-MoO 3 serves a crucial role in the adsorption and activation of substrates via the electronic interaction between the negatively charged oxygen atoms in these substrates and the O v sites in β-MoO 3 . The presence of O v greatly lowers the energy barriers of the reductive coupling reaction, and the electron transfer from alcohols to nitro compounds is mediated by the Mo 5+ /Mo 6+ redox cycle. Our method demonstrates excellent selectivity to C=N bonds and is effective for a wide substrate scope including the highly inert methanol and ethanol. This study highlights the use of non-noble metal oxides as alternatives to traditional metal nanoparticles for various challenging organic transformations.
The transition metal oxides (TMOs) with high volumetric capacities are promising anodes for the future electronics, however, they usually suffer from severe capacity decay and poor rate capability. Carbon hybridization and nanosizing can resolve these challenges, yet these significantly compromise the volumetric capacity. Herein, both high capacity and long cycling stability are simultaneously achieved in the micrometer-sized Mo-based oxide particles by designing the dual conductive MoO 2 /β-MoO 3- x mosaics. The rational combination of the highly electronically conductive MoO 2 with the highly ionically conductive and open-structured β-MoO 3 achieves a promising volumetric capacity of 1742 mAh cm −3 , which is four times higher than the commercial graphite. Simultaneously, both stable cycling performance (87% retention after 500 cycles) and excellent rate capability (outperformed a majority of the MoO 2 -based anodes reported in literature) are obtained in the lithium-ion batteries. For the sodium-ion batteries, the composite exhibits three times higher Na + storage than pure MoO 2 . Moreover, the decisive role of the bond energy on the electrochemical performance of TMOs is also identified. This study may open up new perspectives for choosing and designing the TMO anodes with a high volumetric capacity for the practical applications.
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