Highly porous nanostructures with large surface areas are typically employed for electrical double-layer capacitors to improve gravimetric energy storage capacity; however, high surface area carbon-based electrodes result in poor volumetric capacitance because of the low packing density of porous materials. Here, we demonstrate ultrahigh volumetric capacitance of 521 F cm−3 in aqueous electrolytes for non-porous carbon microsphere electrodes co-doped with fluorine and nitrogen synthesized by low-temperature solvothermal route, rivaling expensive RuO2 or MnO2 pseudo-capacitors. The new electrodes also exhibit excellent cyclic stability without capacitance loss after 10,000 cycles in both acidic and basic electrolytes at a high charge current of 5 A g−1. This work provides a new approach for designing high-performance electrodes with exceptional volumetric capacitance with high mass loadings and charge rates for long-lived electrochemical energy storage systems.
Highly uniform single-crystal ultrathin Pt nanowires (UTPtNWs) with a diameter of ~1.8 nm and a superhigh aspect ratio of >10(4) were fabricated using insulin amyloid fibrils (INSAFs) as sacrificial templates. The use of INSAFs to build the UTPtNWs allowed for the preferential exposure of low-energy crystal facets that would be highly advantageous for the methanol oxidation reaction. The UTPtNWs displayed a large electrochemical active surface area of 71.34 m(2)/g, which is much higher than that of a commercial Pt/C catalyst. The UTPtNWs also maintained excellent electrochemical durability under repeated cyclic voltammetry scans. Because of its exciting high electrochemical activity, UTPtNWs is a promising material for the design of next-generation electrocatalysts and would also be useful in sensing, biomedical, and other electrochemical applications.
Using first-principles total energy calculations we investigate the structural, elastic, and electronic properties of OsB2 and OsB, respectively. The calculated equilibrium structural parameters of OsB2 are in agreement with the available experimental results. The calculations indicate that OsB in tungsten carbide is more energetically stable under the ambient condition than the metastable cesium chloride phase of OsB. Results of bulk modulus show that they are potential low compressible materials. The hardness of OsB2 is estimated by employing a semiempirical theory. The results indicate that OsB2 is an ultraincompressible material, but not a superhard material. The method designing superhard materials is different from one creating ultraincompressible materials.
The compressible behaviors of the selected 5d transition metal carbides MC (M=W,Re,Os,Ir) with hexagonal tungsten carbide-type structure were studied by first-principles calculations. Results indicate that the incompressibility of ReC exceeds that of diamond under higher pressure. The calculated method for hardness of crystals with partial metallic bonding is suggested and the calculated results indicate that hexagonal ReC crystal possesses excellent mechanical properties.
Two-dimensional molybdenum disulfide (2D MoS) has drawn persistent interests as one of the most promising alternatives to Pt catalysts for the hydrogen evolution reaction (HER). It is generally accepted that the edge sites of 2D MoS are catalytically active but the basal planes are inert. Activating the MoS basal plane is an obvious strategy to enhance the HER activity of this material. However, few approaches have sought to activate the basal plane. Here, for the first time, we demonstrate that the inert basal planes can be activated via the synergistic effects of nitrogen and fluorine codoping. Our first-principles calculations reveal that nitrogen in the basal plane of the fluorine- and nitrogen-codoped MoS (NF-MoS) can act as a new active and further tuneable catalytic site. The as-prepared NF-MoS catalyst exhibited an enormously enhanced HER activity compared to that of pure MoS and N-doped MoS due to the chemical codoping effect. This work will pave a novel pathway for enhancing the HER activity using the synergistic effects of chemical codoping.
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