Strong adsorption and catalysis for lithium polysulfides (LiPSs) are critical toward the electrochemical stability of Li‐S batteries. Herein, a hollow sandwiched nanoparticle is put forward to ...enhance the adsorption‐catalysis‐conversion dynamic of sulfur species. The outer ultrathin Ni(OH)2 nanosheets not only confine LiPSs via both physical encapsulation and chemical adsorption, but also promote redox kinetics and accelerate the conversion of sulfur species, which is revealed by experiments and theoretical calculations. Meanwhile, the inner hollow polyaniline soft core provides a strong chemical bonding to LiPSs after vulcanization, which can chemically adsorpt LiPSs, and synergistically confine the shuttle effect. Moreover, the Ni(OH)2 nanosheets with a large specific area can enhance the wettability of electrolyte, and the flexible hollow sandwiched structure can accommodate the volume expansion, promoting sulfur utilization and structural stability. The obtained cathode exhibits excellent electrochemical performance with an initial discharge capacity of 1173 mAh g–1 and a small capacity decay of 0.08% per cycle even after 500 cycles at 0.2 C, among the best results of Ni(OH)2‐based materials for Li–S batteries. It is believed that the combination of adsorption‐catalysis‐conversion will shed a light on the development of cathode materials for stable Li–S batteries.
A sandwiched Ni(OH)2@S@P cathode is designed for stable Li–S batteries. The outer ultrathin Ni(OH)2 nanosheets enhance conversion kinetics of sulfur species, and endows a robust physical encapsulation and chemical adsorption for lithium polysulfides (LiPSs). The inner hollow polyaniline core provides a strong chemical bonding to LiPSs after vulcanization, synergistically inhibiting the LiPSs diffusion. The hollow/flexible structure accommodates volume expansion and improves sulfur utilization.
A series of remarkable crystalline compounds Cu2(BTC)4/3(H2O)26H n XM12O40·(C4H12N)2 (X = Si, Ge, P, As; M = W, Mo) were obtained from the simple one-step hydrothermal reaction of copper nitrate, ...benzentricaboxylate (BTC), and different Keggin polyoxometalates (POMs). In these compounds, the catalytically active Keggin polyanions were alternately arrayed as noncoordinating guests in the cuboctahedral cages of a Cu-BTC-based metal−organic framework (MOF) host matrix. X-ray crystallographic analyses, TG, FT-IR, UV−vis, N2 adsorption studies, and acid−base titration demonstrated their high stability and toleration for thermal and acid−base conditions. No POM leaching or framework decomposition was observed in our study. The representative acid catalytic performance of a compound containing PW12 species was assessed through the hydrolysis of esters in excess water, which showed high catalytic activity and can be used repeatedly without activity loss. Moreover, catalytic selectivity, which is dependent on the molecular size of substrates, and substrate accessibility for the pore surface were observed. It is the first time that the well-defined, crystalline, MOF-supported POM compound has behaved as a true heterogeneous acid catalyst. The unique attributes of MOF and well-dispersed level of POMs prohibited the conglomeration and deactivation of POMs, which allowed for the enhancement of their catalytic properties.
The lithium-selenium (Li-Se) battery has attracted growing interest recently due to its high energy density and theoretical capacity. However, the shuttle effect and volume change during cycling ...severely hinder its further application. In this work, we report a metal-organic framework (MOF)-derived nitrogen-doped core-shell hierarchical porous carbon (N-CSHPC) with interconnected meso/micropores to effectively confine Se for high-performance Li-Se batteries. The micropores were located at the ZIF-8-derived core and the ZIF-67-derived shell, while mesopores appeared at the core-shell interface after the pyrolysis of the core-shell ZIF-8@ZIF-67 precursor. Such a special hierarchical porous structure effectively confined selenium and polyselenides to prevent their dissolution from the pores and also alleviated the volume change. In particular, in situ nitrogen doping, which afforded N-CSHPC, not only improved the electrical conductivity of Se but also provided strong chemical adsorption on Li2Se, as confirmed by density functional theory calculations. On the basis of dual-physical confinement and strong chemisorption, Se/N-CSHPC-II (molar ratio of Co source to Zn source of 1.0 in the core-shell ZIF-8@ZIF-67 precursor) exhibited reversible capacities of up to 555 mA h g-1 after 150 cycles at 0.2 C and 462 mA h g-1 after 200 cycles at 0.5 C and even a discharge capacity of 432 mA h g-1 after 200 cycles at 1 C. Our demonstration here suggests that the carefully designed Se/C composite can improve the reversible capacity and cycling stability of Se cathodes for Li-Se batteries.
Utilization of nonprecious transition metals for high alcohols synthesis is of a great importance in heterogeneous catalysis. We synthesized successfully cobalt metal-carbide (Co–Co2C) catalysts, ...which present remarkable activity and selectivity for high alpha-alcohols via the Fischer–Tropsch reaction. The formation of the stable cobalt carbide and the Co–Co2C interface are found to be essential for the observed reactivity. Density functional theory calculations show that Co2C is highly efficient for CO nondissociative adsorption, behaving as noble-metal-like, whereas the Co metal is highly active for CO dissociative adsorption and the subsequent carbon-chain growth. The interface between the cobalt metal and its carbide phase, as well as the dual sites available at the interface for facile CO insertion to hydrocarbon, could be used to rationalize the design of the nonprecious transition metal catalysts for the oxygenates in syngas conversion.
Charge‐transfer‐induced spin transition occurs cooperatively and reversibly in the isolated FeIII2CoII chains of {Fe(pzTp)(CN)32Co(4‐styrylpyridine)2}⋅2 H2O ⋅2 CH3OH (1). When 1 is irradiated with ...532 nm light, it shows single‐chain magnetic behavior with no antiferromagnetic ordering after irradiation (see picture; C gray, N blue, B yellow; LS=low spin, HS=high spin).
•When the advection velocities of all plankton are the same, the plankton community remains relatively stationary, and the advection at the same speed will not change the stability of the system but ...transfer the algae ecosystem as a whole.•When the system is Hopf stable and Turing stable, if the advection velocities of phytoplankton and zooplankton are different, there is a wave bifurcation, the smallest convection speed difference that drives the system Wave unstable.•When the system is Hopf stable but Turing unstable, We assign an advection speed zero and the other nonzero, there is a traveling bifurcation, the smallest convection speed difference that results in Traveling patterns.
We studied a spatial plankton community, comprising phytoplankton (prey) and zooplankton (predators), with advection. If the advection velocities of all plankton are the same, the plankton community remains relatively stationary. If the convection velocities are different, the speed difference will make the system unstable. When the original system without advection is Turing stable, due to the advection speed difference, there should be a Wave bifurcation, which will drive the system with advection Wave instability. If the original system without convection becomes Turing unstable, the system with advection will always be of Wave instability. Numerical simulations validated our analysis of stabilaity and showed more phenomena. When the original system without advection is Turing unstable, we keep the coefficient of one advection term zero and the other nonzero, the advection speed difference will produce traveling patterns (patterns on the traveling waves). If the speed difference is small enough, the patterns remain stationary, and if the speed difference increases, the traveling patterns appear. Therefore, there should be a Traveling bifurcation that separates stationary patterns and the traveling ones. The analysis and simulation experiments enrich the dynamics in the plankton models and contribute to a better understanding of the planktonic ecosystem in the real environment.
Sodium‐ion batteries (SIBs) are considered as a promising large‐scale energy storage system owing to the abundant and low‐cost sodium resources. However, their practical application still needs to ...overcome some problems like slow redox kinetics and poor capacity retention rate. Here, a high‐performance ZnSe/carbon fibers (ZnSe‐CFs) anode is demonstrated with high electrons/Na+ transport efficiency for sodium‐ion half/full batteries by engineering ZnSe/C heterostructure. The electrochemical behavior of the ZnSe‐CFs heterostructure anode is deeply studied via in situ characterizations and theoretical calculations. Phase conversion is revealed to accelerate the “Zn‐escape” effect for the formation of robust solid electrolyte interphase (SEI). This leads to the ZnSe‐CFs delivering a superior rate performance of 206 mAh g−1 at 1500 mA g−1 for half battery and an initial discharge capacity of 197.4 mAh g−1 at a current density of 1 A g−1 for full battery. The work here heralds a promising strategy to synthesize advanced heterostructured anodes for SIBs, and provides the guidance for a better understanding of phase conversion anodes.
A ZnSe/carbon fibers (ZnSe‐CFs) anode with high electrons/Na+ transport efficiency by engineering ZnSe/C heterostructure is designed for high performance sodium‐ion half/full batteries. Phase conversion is found to accelerate the “Zn‐escape” effect for the formation of robust solid electrolyte interphase, providing the guidance for a better understanding of phase conversion anodes for high‐performance sodium‐ion batteries.
A light change: A linear cyanido‐bridged Fe2Co compound (see picture) exhibits a reversible, thermally induced cooperative charge transfer transition accompanying spin transition and polar–nonpolar ...transformation in the trinuclear cluster. The change in magnetic properties and polarity could also be induced by irradiation with light.
We proposed and demonstrated that PT symmetric metamaterials could be used to achieve enhanced spin Hall effect (SHE) of light. We find that when laser mode is excited in PT symmetric system, the ...enhanced SHE could be obtained in both transmitted and reflected beams. In addition, as exceptional points (EPs) of PT symmetric system can happen for both p- and s-polarizations, the enhanced SHE of reflected light can function for both horizontally and vertically polarized incident beams. Particularly, these EPs can lead to unidirectional reflectionlessness, asymmetric SHE with maximum contrast ratio of 48 is obtained by launching light beams near EPs. Our work opens up a new path to obtain enhanced transverse displacement for both reflected and transmitted light and enables more opportunities in manipulating photonic SHE.
Chloramphenicol was chosen as the imprinting molecule and the methacrylic acid was chosen as the functional monomer to prepare molecularly imprinted polymers. Ethylene glycol dimethacrylate, ...pentaerythritol triacrylate, and trimethylolpropane trimethylacrylate were used as the cross‐linking agents, respectively. The interaction processes between chloramphenicol and methacrylic acid were simulated by using the ωB97XD/6‐31G (d,p) method. The self‐assembled configuration, bonding sites, binding number, binding energy, and interaction principle of stable complex formed by chloramphenicol and methacrylic acid with different molar ratios have been studied. The selectivity of the most stable complex formed from chloramphenicol and methacrylic acid was discussed with the thiamphenicol and florfenicol as the analogues of chloramphenicol. The results showed that chloramphenicol and methacrylic acid were interacted through the hydrogen bonds. When the molar ratio was 1:10 and pentaerythritol triacrylate as the cross‐linking agent, the ordered complex formed by chloramphenicol and methacrylic acid has the largest amount of hydrogen bonds and the lowest binding energy. Scatchard analysis showed that the maximum apparent adsorption capacity was 173.3 mg/g (0.536 mol/g), and the selection factor of florfenicol was the largest. This study provides a reliable theoretical and experimental basis for the design, preparation, and characterization of chloramphenicol molecularly imprinted polymers.
