RESUMEN
In this paper, a cobalt-based sulfide nanosheet structure (Co9S8/NC) was successfully synthesized by topochemical and phase transformation processes from a dodecahedral cobalt-based imidazole skeleton (ZIF-67) as a self-template. The 2D sheet structure facilitates full contact of electrode materials with the electrolyte and shortens the diffusion distance for electrons and ions. In addition, the nitrogen-doped carbon framework derived from ZIF-67 promotes electron transfer and provides a reliable skeleton to buffer volume expansion during discharging and charging. Finally, Co9S8/NC exhibits excellent rate capability and stable cycling performance for the anode of a sodium ion battery, delivering a specific capacity remaining at 530 mA h g-1 after 130 cycles at a current density of 1 A g-1.
RESUMEN
Herein, a well-designed hierarchical architecture of bimetallic transition sulfide FeIn2S4 nanoparticles anchoring on the Ti3C2 MXene flakes has been prepared by cation exchange and subsequent high-temperature sulfidation processes. The introduction of MXene substrate with excellent conductivity not only accelerates the migration rate of Na+ to achieve fast reaction dynamics but provides abundant deposition sites for the FeIn2S4 nanoparticles. In addition, this hierarchical structure of MXene@FeIn2S4 can effectively restrain the accumulation of MXene to guarantee the maximized exposure of redox active sites into the electrolyte, and simultaneously relieve the volume expansion in the repeated discharging/charging processes. The MXene@FeIn2S4 displays outstanding rate capability (448.2 mAh g-1 at 5 A g-1) and stable long cycling performance (428.1 mAh g-1 at 2 A g-1 after 200 cycles). Moreover, the Nay-In6S7 phase detected by ex-situ XRD and XPS characterization may be regarded as a "buffer" to maintain the stability of the Fe-based components and enhance the reversibility of the electrochemical reaction. This work confirms the practicability of constructing the hierarchical structure bimetallic sulfides with the promising electrochemical performance.
RESUMEN
Development of multitudinous heteroatoms co-doped carbon nanomaterials with pleasurable electrochemical behavior for sodium ion batteries is still an enormous challenge. Herein, high dispersion cobalt nanodots encapsulating into N, P, S tri-doped hexapod carbon (H-Co@NPSC) have been victoriously synthesized via H-ZIF67@polymer template strategy with using poly (hexachlorocyclophos-phazene and 4,4'-sulfonyldiphenol) as both carbon source and N, P, S multiple heteroatom doping sources. The uniform distribution of cobalt nanodots and the Co-N bonds are conducive to form a high conductive network, which synergistically increase a lot adsorption sites and lessens the diffusion energy barrier, thereby improving the fast Na+ ions diffusion kinetics. Consequently, H-Co@NPSC delivers the reversible capacity of 311.1 mAh g-1 at 1 A g-1 after 450 cycles with 70% capacity storage rate, while obtains the capacity of 237.1 mAh g- 1 after 200 cycles at the elevated current densities of 5 A g-1 as an excellent anode material for SIBs. These interesting results pave a generous avenue for the exploitation of promising carbon anode materials for Na+ storage.
RESUMEN
We experimentally and numerically investigate amplified spontaneous emission (ASE) in the presence of radiation reabsorption by using an end-pumped ruby laser. From the fluorescence time decay in the axial direction, we find that the average path length of ASE is much larger than the reabsorption length and exhibits sharp variation near the semi-concentric cavity configuration; however, the side lifetime is independent of cavity configuration. In addition, an axial power bump corresponding to a side power valley and the enhanced fluorescence R-line spectrum are observed and explained.
RESUMEN
Panonychus ulmi Koch is one of the important pest insects of apple production in China. To clarify the spatiotemporal dynamics of P. ulmi on the apple tree crowns in an apple orchard of Liaoning, Northeast China, an investigation with random sampling was conducted on the pest mite number at each direction and each layer of the crowns in the whole growth season from May to November 2007. The spatial distribution pattern and time series dynamics of P. ulmi were analyzed by calculating the indices of aggregation and using the parameters of Iwao model. In the early and mid growth periods of apple tree, P. ulmi within whole crown fitted negative binomial distribution, presented an aggregated pattern, and its fundamental component was the group composed of several individuals that attracted each other. The aggregation intensity showed a negative fluctuation with population density, namely, high population density but low patchiness density, and low population density but high patchiness density, and there existed definite differences at different crown directions and layers, i. e., the patchiness density was the highest in south direction and the lowest in west direction, and was higher in mid and lower layers than in upper layer, and in inner layer than in outer layer.
