Prussian blue analogue Na2NiFe(CN)6 (Ni–PB) has been widely studied as a cathode material for sodium‐ion battery due to its excellent cycling performance. However, Ni–PB has a low theoretical ...capacity of 85 mAh g−1 because of the electrochemical inertness of Ni. Herein, ternary Ni–PB is successfully synthesized by double doping with Co and Fe at Ni‐site, and the effect of doping with Co and Fe on the electrochemical performance of Ni–PB is systematically investigated through theoretical calculations and electrochemical tests. The first principles calculations confirm that double doping with Co and Fe can significantly reduce the energy barrier and bandgap of Ni–PB. X‐ray diffraction and composition analysis results indicate that ternary NiCoFe–PB composite not only has good crystallinity and high Na content but also has low defects and crystal water. Electrochemical tests reveal that, besides the capacity contribution of high‐spin Co/Fe and low‐spin Fe, Co‐doping enhances the electrochemical activity of low‐spin Fe and Fe‐doping improves the activity of high‐spin Co; moreover, double doping can decrease the diffusion resistance of Na+ ions through solid electrolyte interface film, accelerate the kinetics for both ion diffusion process and Faradic reaction, and increase active sites. Under the synergistic effect of Co and Fe, this ternary NiCoFe–PB exhibits outstanding electrochemical performance with a high initial discharge capacity of 120.4 mAh g−1 at 20 mA g−1 and an extremely low capacity fading rate of 0.0044% per cycle at a high current density of 2 A g−1 even after 10,000 cycles, showing great application potential of ternary NiCoFe–PB in the field of large‐scale energy storage.
The effect of doping with Co and Fe on the electrochemical performance of Ni–PB has been systematically investigated through theoretical calculations and electrochemical performance tests. Density functional theory calculations confirm that double doping with Co and Fe can significantly reduce the energy barrier and bandgap of Ni–PB, and promote the migration of Na+ ions and electrons in NiHCF. Therefore, the ternary Ni–PB with double doping has superior sodium storage performance.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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•The structure of NiHCF has been regulated by K-doping for the first time.•K-doping induces the transformation of NiHCF from cubic to monoclinic.•K-doping improves the transport ...ability of sodium ions and electrons.•K+ ions can play a role of pillar in stabling the structure.•K-doped NiHCF shows excellent capacity performance and superior cycle stability.
Prussian blue analogs with unique open frame structure have aroused great concern because of their low cost, environmental friendliness and relatively easy synthesis. Especially, nickel hexacyanoferrate (NiHCF) attracts great attention due to its outstanding cycling stability. Herein, we regulate the structure of NiHCF by K-doping at Na-site and investigate the sodium storage performance by combining experiments with density functional theory calculations. Our results reveal that K-doping induces the transformation of NiHCF from cubic to monoclinic and provides more sodium storage sites. In addition, K+ ions can play a role of pillar in stabling the structure. More importantly, K-doping can improve the transport ability of sodium ions and electrons. As a result, the K-doped NiHCF electrode delivers an extremely high initial discharge capacity of 87.1 mAh g−1 at 10 mA g−1 with a very low capacity fading ratio of 0.016% per cycle at 800 mA g−1 over 1000 cycles. Such K-doped NiHCF composite shows its potential application prospects in the field of sodium-ion batteries.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The Fe-PB structure has been regulated by Zn substitution for the first time.•FeZn-PB has higher Na content, less vacancies and lower crystal water.•Zn-substitution accelerates ...electrons and sodium ions migration.•Zn-substitution enhances the activity of both low-spin Fe and high-spin Fe.•FeZn-PB has high capacity and superior cycle stability.
Fe-based Prussian blue (Fe-PB) has attracted wide attention as cathode materials for sodium-ion batteries due to its open frame structure, abundant iron ore resources, and simple preparation. Nevertheless, the poor cycle performance caused by the Fe(CN)6 defects and crystal water hinders its practical application. Herein, the Fe-PB structure is regulated by Zn-substitution, and the effect of Zn-substitution induced structural regulation on sodium storage performance of Fe-PB is systematically investigated. The density functional theory calculation results confirm that Zn-substitution can reduce the bandgap and decrease the energy barrier of Na+ ions migration. Our experiment results further confirm the Zn-substituted Fe-PB composite (FeZn-PB) has a typical monoclinic structure with higher Na content, fewer Fe(CN)6 vacancies and lower crystal water. Moreover, Zn-substitution accelerates electrons and sodium ions migration and enhances the activity of both low-spin Fe and high-spin Fe. As a cathode material for sodium-ion batteries, the FeZn-PB electrode has a higher capacity and better cycle stability than Fe-PB. Especially, FeZn-PB delivers an initial capacity as high as 145.0 mAh g−1 with a capacity contribution of 60.5 mAh g−1 from low-spin Fe at 20 mA g−1. Even at a high current density of 1 A g−1, FeZn-PB still delivers a high initial capacity of 98.5 mAh g−1 with a very low capacity decay rate per cycle of only 0.05% over 500 cycles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Many plants grown with low‐millimolar concentration of NH4+ as a sole nitrogen source develop NH4+‐toxicity symptoms. To date, crucial molecular identities and a practical approach involved in the ...improvement of plant NH4+‐tolerance remain largely unknown. By phenotyping of upland cotton grown on varied nitrogen forms, we came across a phenomenon that caused sub‐millimolar concentrations of urea (e.g., up 50 μM) to repress the growth inhibition of roots and whole plant cultivated in a NH4+‐containing nutrient solution. A growth‐recovery assay revealed that the relief in NH4+‐inhibited growth required only a short‐term exposure (≧12 h) of the roots to urea, implying that urea could elicit an internal signaling and be involved in antagonizing NH4+‐sensitivity. Intriguingly, split‐root experiments demonstrated that low urea occurrence in one root‐half could efficaciously stimulate not only supplied root but also the root‐half grown in NH4+‐solution without urea, indicating the existence of urea‐triggered local and systemic long‐distance signaling. In the split‐root experiment we also observed high arginase activity, strong arginine reduction and remarkable upregulation of polyamine biosynthesis‐related genes (ADC1/2, SPDS and SPMS). Therefore, we suggest that external urea might serve as an effective cue (signal molecule) in an arginine‐/polyamine‐related process for ameliorating NH4+‐suppressed root growth, providing a novel aspect for deeper exploring and understanding plant NH4+‐tolerance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Global warming lowers the solubility of gases in the ocean and drives an enhanced hydrological cycle with increased nutrient loads delivered to the oceans, leading to increases in organic production, ...the degradation of which causes a further decrease in dissolved oxygen. In extreme cases in the geological past, this trajectory has led to catastrophic marine oxygen depletion during the so‐called oceanic anoxic events (OAEs). How the water column oscillated between generally oxic conditions and local/global anoxia remains a challenging question, exacerbated by a lack of sensitive redox proxies, especially for the suboxic window. To address this problem, we use bulk carbonate I/Ca to reconstruct subtle redox changes in the upper ocean water column at seven sites recording the Cretaceous OAE 2. In general, I/Ca ratios were relatively low preceding and during the OAE interval, indicating deep suboxic or anoxic waters exchanging directly with near‐surface waters. However, individual sites display a wide range of initial values and excursions in I/Ca through the OAE interval, reflecting the importance of local controls and suggesting a high spatial variability in redox state. Both I/Ca and an Earth System Model suggest that the northeast proto‐Atlantic had notably higher oxygen levels in the upper water column than the rest of the North Atlantic, indicating that anoxia was not global during OAE 2 and that important regional differences in redox conditions existed. A lack of correlation with calcium, lithium, and carbon isotope records suggests that neither enhanced global weathering nor carbon burial was a dominant control on the I/Ca proxy during OAE 2.
Key Points
Upper ocean oxygenation levels are highly dynamic across OAE 2
A shallow O2 oasis in proto‐Atlantic is supported by proxy and model
I/Ca is a proxy for local redox, not for weathering and carbon burial
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Attapulgite (ATT) has never been used as a barrier additive in polypropylene (PP). As a filler, ATT should be added in high content to PP. However, that would result in increased costs. Moreover, the ...compatibility between ATT and the PP matrix is poor due to the lack of functional groups in PP. In this study, carboxylic groups were introduced to PP to form a modified polypropylene (MPP). ATT was purified, and a low content of it was added to MPP to prepare MPP/ATT nanocomposites. The analysis from FTIR indicated that ATT could react with MPP. According to the results of oxygen and water permeability tests, the barrier performance of the nanocomposite was optimal when the ATT content was 0.4%. This great improvement in barrier performance might be ascribed to the following three reasons: (1) The existence of ATT extended the penetration path of O2 or H2O molecules; (2) O2 or H2O molecules may be adsorbed and stored in the porous structure of ATT; (3) Most importantly, –COOH of MPP reacted with –OH on the surface of ATT, thereby the inner structure of the nanocomposite was denser, and it was less permeable to molecules. Therefore, nanocomposites prepared by adding ATT to MPP have excellent properties and low cost. They can be used as food packaging materials and for other related applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The effects of the Si-substrate doping concentration on electrical characteristics of back-gate (BG) and top-gate (TG) MoS 2 field-effect transistors (FETs) are investigated. The experimental results ...show that MoS 2 FETs fabricated on different-concentration Si substrates using the same processing have similar interface characteristics and surface roughness of gate dielectric but exhibit different carrier mobility, and the higher the doping concentration, the higher the carrier mobility. This is because the carriers in Si substrate can screen the phonon scattering from the low-energy surface optical phonon produced by the soft Hf-O bonds in HfO 2 dielectric, which will couple with the carriers in MoS 2 channel, resulting in the reduction of the mobility, and the higher the Si-substrate concentration, the better the screening effect. Also, it is found that the BG dielectric scattering will impact on the mobility of the TG transistor, which causes a similar change trend of carrier mobility to that of the BG MoS 2 FET as the Si-substrate concentration increases. Therefore, it can be revealed that the Si-substrate concentration has an important influence on the carrier mobility of MoS 2 FETs, and the high Si-substrate concentration is beneficial for fabricating high-performance BG and TG MoS 2 FETs.
We report an efficient copper-catalyzed dehydrogenation method for the synthesis of aroyl triazines from arylmethyl triazines with water in the absence of additional oxidants or hydrogen acceptors. ...The use of substrates with both electron-donating and electron-withdrawing groups resulted in moderate to good yields. Using liquid chromatography–mass spectrometry, 18O-labeled-water reactions and hydrogen capture experiments confirmed that water was the only oxygen donor and hydrogen was the by-product. This oxidation strategy provides a new approach for the synthesis of aroyl triazines with a broad substrate scope.
Micro visualization has become an important means of solving colloid and interface scientific problems in enhanced oil recovery. It can establish a relationship between a series of performance ...evaluations of an oil-water interface under macroscopic dimensions and the actual application effect in confined space, and more truly and reliably reflect the starting and migration behavior of crude oil or emulsion in rock pores. In this article, zwitterionic surfactant alkyl sulfobetaine (ASB) and anionic extended surfactant alkyl polyoxypropylene sulfate (A145) were employed as flooding surfactants. The macroscopic properties of the surfactant solutions, such as the oil-water interfacial tension (IFT), the interfacial dilational rheology and the viscosity of crude oil emulsions, have been measured. At the same time, we link these parameters with the oil displacement effect in several visual glass models and confirm the main factors affecting the migration ability of emulsions in micro-scale pores. The experimental results show that ASB reduces the IFT through mixed adsorption with crude oil fractions. The flat arrangement of the large hydrophilic group of ASB molecules enhances the interactions between the surfactant molecules on the oil-water interface. Compared with sulfate, betaine has higher interfacial membrane strength and emulsion viscosity. A145 has a strong ability to reduce the IFT against crude oil because of the larger size effect of the PO chains at the oil side of the interface. However, the membrane strength of A145 is moderate and the emulsion does not show a viscosity-increasing effect. During the displacement process, the deformation ability of the front emulsions or oil banks is the main controlling factor of the displacement efficiency, which is determined by the membrane strength and emulsion viscosity. The strong interfacial membrane strength and the high emulsion viscosity are not conducive to the migration of droplets in pore throats and may result in low displacement efficiency.
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