The extraordinarily high capacities delivered by lithium‐rich oxide cathodes, compared with conventional layered oxide electrodes, are a result of contributions from both cationic and anionic redox ...processes. This phenomenon has invoked a lot of research exploring new kinds of lithium‐rich oxides with multiple‐electron redox processes. Though proposed many years ago, anionic redox is now regarded to be crucial in further developing high‐capacity electrodes. A basic overview of the previous work on anionic redox is given, and issues related to electronic and geometric structures are discussed, including the principles of activation, reversibility, and the energy barrier of anionic redox. Anionic redox also leads to capacity loss and structural degradation, as well as voltage hysteresis, which shows the importance of controlling anionic redox reactions. Finally, the techniques used for characterizing anionic redox processes are reviewed to aid the rational choice of techniques in future studies. Important perspectives are highlighted, which should instruct future work concerning anionic redox processes.
Anionic redox plays an important role in obtaining high capacities in lithium‐rich layered oxide cathodes. Previous studies on anionic redox and related electronic‐ and geometric‐structure issues, as well as problems induced by anionic‐redox and suitable characterization techniques, are reviewed, in order to direct future work on high‐capacity electrodes that utilize anionic redox processes and widen the scope of these materials.
The first Ni-catalyzed C-O/P-H cross-coupling producing organophosphorus compounds is disclosed. This method features wide generality in regard to both C-O and P-H compounds: for C-O compounds, the ...readily available alcohol derivatives of aryl, alkenyl, benzyl, and allyl are applicable, and for P-H compounds, both >P(V)(O)H compounds (secondary phosphine oxide, H-phosphinate, and H-phosphonate) and hydrogen phosphines (>P(III)H) can be used as the substrates. Thus, a variety of valuable C(sp(2))-P and C(sp(3))-P compounds can be readily obtained in good to excellent yields by this new strategy.
Effective detection of small targets plays a pivotal role in infrared (IR) search and track applications for modern military defense or attack. Consequently, an effective small IR target detection ...algorithm based on a novel local contrast measure (NLCM) is proposed in this letter. Initially, difference of Gaussian band-pass filter is employed to enhance target and suppress background clutter. Then, a segmentation operation is implemented to obtain IR local regions of fixed size larger than general IR small target size. Finally, the salient map is obtained using the NLCM, and an adaptive threshold is applied to extract the target region. Experimental results on two real sequences show that the proposed method has better detection performance compared with conventional baseline methods.
A new inexpensive copper‐catalyzed denitrogenative C−P coupling reaction of pyridotriazoles with P(O)H compounds has been developed. The reaction proceeds via a process of copper‐catalyzed P(O)−H ...insertion into the pyridyl carbene intermediates generated in situ from pyridotriazoles. This reaction provides a new and effective method for the synthesis of a variety of 2‐picolylphosphoryl compounds.
4‐Methoxy‐3‐(trimethylphosphonio)phenolate was obtained from a regioselective addition of PMe3 to p‐quinone monoacetal. This compound undergoes hydrogen isotope exchange with D2O or CD3CN, and is ...capable of catalyzing H/D exchange of CD3CN with substrates bearing weakly acidic hydrogens. It exhibits similar reactivity to phosphorus ylides for olefinations of aldehydes. A possible tautomerization between the phosphonium phenolate zwitterion and phosphonium ylide is proposed for the first time to rationalize the unique reactivity.
A direct decarbonylative phosphorylation of benzoic acids catalyzed by palladium was disclosed. Under the reaction conditions, a wide range of benzoic acids coupled readily with all the three kinds ...of P(O)–H compounds, i.e. secondary phosphine oxides, H‐phosphinates and H‐phosphonates, producing the corresponding organophosphorus compounds in good to high yields. This reaction could be conducted at a gram scale and applied in the late‐stage phosphorylative modification of carboxylic acids drug molecules. These results well demonstrated the potential synthetic value of this new reaction in organic synthesis.
A direct decarbonylative phosphorylation of benzoic acids catalyzed by palladium was disclosed. Under the reaction conditions, a wide range of carboxylic acids coupled readily with all the three kinds of P(O)–H compounds, i.e. secondary phosphine oxides, H‐phosphinates and H‐phosphonates, producing the corresponding organophosphorus compounds in good to high yields. This reaction could be conducted at a gram scale and applied in the late‐stage phosphorylative modification of carboxylic acids drug molecules. These results well demonstrated the potential synthetic value of this new reaction in organic synthesis.
Despite the importance of P-chiral organophosphorus compounds in asymmetric catalysis, transition metal-catalyzed methods for accessing P-chiral phosphine derivatives are still limited. Herein, a ...catalytic enantioselective method for the synthesis of P-stereogenic alkenylphosphinates is developed through asymmetric hydrophosphorylation of alkynes. This process is demonstrated for a wide range of racemic phosphinates and leads to diverse P-stereogenic alkenylphosphinates directly.
•The effect of steel-polypropylene hybrid fiber on the flexural behavior of concrete was investigated.•Favorable improvements in failure modes, flexural loads, toughness and ductility of HFRC were ...observed.•The synergy of hybrid fibers with various fiber parameters was analyzed.
This paper presents an experimental study on the flexural behavior of steel-polypropylene hybrid fiber reinforced concrete (HFRC) using four-point bending tests on 51 samples. Three types of steel fibers, i.e., straight, hooked-end and corrugated fiber, and a type of monofilament polypropylene fiber are considered. The flexural behavior in terms of load-deflection curves, load and deflection characteristics, toughness, cracking properties as well as the synergetic effect of hybrid fibers is studied. The results show that synergetic effect is observed for all the three types of steel fiber with the combination of polypropylene fiber on improving the flexural behavior of HFRC. Specimens with hooked-end fibers show the best flexural performance. However, the combination of straight steel and polypropylene fibers presents the most obvious synergy. Moreover, an increase in volume fractions of both steel and polypropylene fibers leads to an increase in the compressive, splitting tensile and flexural strengths of concrete. The post-peak ductility of concrete is improved and the strength degradation is alleviated with increasing fiber volume fraction and steel fiber aspect ratio. In addition, specimens with corrugated and hooked-end fibers exhibit a better failure behavior than specimens with straight fibers, with multiply micro-cracks induced by mechanical interlocks of deformed steel fibers observed at the main cracks. Finally, based on a comprehensive fiber reinforcing index, analytical equations for flexural loads, deflections, and toughness of HFRC are developed with varying fiber parameters taken into consideration.
Electrochemical reduction of N2 to NH3 is a promising method for artificial N2 fixation, but it requires efficient and robust electrocatalysts to boost the N2 reduction reaction (NRR). Herein, a ...combination of experimental measurements and theoretical calculations revealed that a hybrid material in which ZnO quantum dots (QDs) are supported on reduced graphene oxide (ZnO/RGO) is a highly active and stable catalyst for NRR under ambient conditions. Experimentally, ZnO/RGO was confirmed to favor N2 adsorption due to the largely exposed active sites of ultrafine ZnO QDs. DFT calculations disclosed that the electronic coupling of ZnO with RGO resulted in a considerably reduced activation‐energy barrier for stabilization of *N2H, which is the rate‐limiting step of the NRR. Consequently, ZnO/RGO delivered an NH3 yield of 17.7 μg h−1 mg−1 and a Faradaic efficiency of 6.4 % in 0.1 m Na2SO4 at −0.65 V (vs. RHE), which compare favorably to those of most of the reported NRR catalysts and thus demonstrate the feasibility of ZnO/RGO for electrocatalytic N2 fixation.
ZnO/RGO can fix it: A hybrid material, in which ZnO quantum dots are supported on reduced graphene oxide (ZnO/RGO), was synthesized by a facile, one‐step, microwave‐assisted solvothermal method and found to be a highly active and stable catalyst for the electrochemical reduction of dinitrogen to ammonia (see figure) under ambient conditions, which is a promising method for artificial nitrogen fixation.
The strong interface is an essential requirement to ensure the effective load transfer of graphene/Cu composites. Here we attempted to improve the interface adhesion and mechanical properties of ...reduced graphene oxide (RGO)/CuCr composites by matrix-alloying with ∼0.2 at.% Cr. It was found that a trace amount of Cr7C3 layers/nanoparticles was in-situ formed at the RGO-CuCr interface, which contributed to the dramatically improved interfacial bonding of the composites. The 2.5 vol% RGO/CuCr composite exhibited a tensile strength of 352 MPa, 82% and 19% higher than that of unreinforced CuCr and 2.5 vol% RGO/Cu composite without Cr alloying, respectively. The enhanced strength of RGO/CuCr composite was ascribed to the dual role of Cr7C3 layers/nanoparticles that not only enhanced the load transfer efficiency, but also promoted the dislocation strengthening ability of RGO itself. Furthermore, we proposed the possible Cr7C3 formation/evolution mechanism that involved the four steps of amorphous carbon formation, Cr7C3 nucleation in amorphous carbon, Cr7C3 growth and Cr7C3 coalescence. The formation of medium sized Cr7C3 layers/nanoparticles at 1053 K resulted in the highest strength of RGO/CuCr composite with a satisfactory strength-ductility combination. This study provides new insights into the interface structure, strengthening mechanism and carbide formation/evolution mechanism of graphene/CuX composites.
Display omitted
PDF
