Theoretical Insight into the Multiple Roles of LiHMDS in Pd-Catalyzed Borylation of Fluorobenzene.

Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.

Three-Dimensional Porous Network Electrodes with Cu(OH)2 Nanosheet/Ni3S2 Nanowire 2D/1D Heterostructures for Remarkably Cycle-Stable Supercapacitors.

Developing advanced electrode materials with highly improved charge and mass transfer is critical to obtain high specific capacities and long-term cycle life for energy storage. Herein, three-dimensionally (3D) porous network electrodes with Cu(OH)2 nanosheets/Ni3S2 nanowire 2D/1D heterostructures are rationally fabricated. Different from traditional surface deposition, the 1D/2D heterostructure network is obtained by in situ hydrothermal chemical etching of the surface layer of nickel foam (NF) ligaments. The Cu(OH)2/Ni3S2@NF electrode delivers a high specific capacity (1855 F g-1 at 2 mA cm-2) together with a remarkable stability. The capacity retention of the electrode is over 110% after 35,000 charge/discharge cycles at 20 mA cm-2. The improved performance is attributed to the enhanced electron transfer between 1D Ni3S2 and 2D Cu(OH)2, highly accessible sites of 3D network for electrolyte ions, and strong mechanical bonding and good electrical connection between Cu(OH)2/Ni3S2 active materials and the conductive NF. Especially, the unique 1D/2D heterostructure alleviates structural pulverization during the ion insertion/desertion process. A symmetric device applying the Cu(OH)2/Ni3S2@NF electrode exhibits a remarkable cycling stability with the capacitance retention maintaining over 98% after 30,000 cycles at 50 mA cm-2. Therefore, the outstanding performance promises the architectural 1D/2D heterostructure to offer potential applications in future electrochemical energy storage.

Delicate control of crystallographic Cu2O derived Ni-Co amorphous double hydroxide nanocages for high-performance hybrid supercapacitors: an experimental and computational investigation.

The reasonable design of the composition and hollow structure of electrode materials is beneficial for promoting the electrochemical properties and stability of electrode materials for high-performance supercapacitors, and it is of great significance to understand the inherent effect of these features on their performance. In this paper, the amorphous Ni-Co double hydroxide nanocages with hollow structures (Ni-Co ADHs) including quasi-sphere, cube and flower are delicately tailored via a Cu2O template-assisted approach. By combining experimental characterization and density functional theory (DFT) calculations, we systematically study the morphological growth of Cu2O templates under different conditions and the electrochemical performance of Ni-Co ADHs. Due to the coordination and synergistic effect between different components, the unique hollow structure and the nature of amorphous materials, Ni-Co ADHs deliver a high specific capacitance of 1707 F g-1 at 1 A g-1. The DFT calculations demonstrate that Ni-Co ADH nanocages exhibit an optimal redox reaction energy barrier and immensely promote the performance. In addition, a hybrid supercapacitor assembled with Ni-Co ADHs as a cathode and active carbon (AC) as an anode shows a high energy density of 33.8 W h kg-1 at a power density of 850 W kg-1 and exhibits an excellent cycling performance with a retention rate of 98% after 50 000 cycles. The successful synthesis of Ni-Co ADH nanocages, combined with rational computational simulations, indicates the excellent electrochemical performance and the potential utilization of amorphous hollow nanomaterials as electrodes for supercapacitors.

Designed synthesis of nickel-cobalt-based electrode materials for high-performance solid-state hybrid supercapacitors.

Supercapacitors with high security, excellent energy and power densities, and superior long-term cycling performance are becoming increasingly essential for flexible devices. Herein, this study has reported a novel method to synthesize CoNi2S4, which delivered a high specific capacitance of 1836.6 F g-1 at 1 A g-1, with a slight fluctuation in the testing temperature rising up to 50 °C (1855.2 F g-1) or decreasing to 0 °C (1587.6 F g-1). In addition, the corresponding solid-state CoNi2S4//AC HSC could achieve a high energy density of 35.8 W h kg-1 at a power density of 800.0 W kg-1, with nearly no change when tested at 0 °C and 50 °C, and possessed excellent long-term electrochemical cycling stability of 132.3% after 50 000 cycles; the solid-state hybrid supercapacitor using biomass-derived carbon (BC) as the negative electrode (CoNi2S4//BC HSC) could also deliver a high energy density of 38.9 W h kg-1 at a power density of 850.0 W kg-1 and the specific capacitance retention was 101.2% after cycling for 50 000 times. This work has provided a promising method to prepare high-performance electrode materials for solid-state hybrid supercapacitors with superior cycling stability and energy density.

Modeling the crystallization of magnesium ammonium phosphate for phosphorus recovery.

The crystallization of magnesium ammonium phosphate (MAP) is one of the main processes for recovering P and N from wastewater. Chemically defined solution systems were designed; the saturation indices (SIs) of the solution systems with respect to MAP were derived by using a geochemical aqueous model Program, PHREEQC 2.11; the effects of the solution conditions were evaluated using thermodynamic theories. The concentrations of P and Mg in the tested solutions were 10-600 mg l(-1) and 24-720 mg l(-1), respectively, the molar ratios of N/P and pH values of the solutions varied in the ranges of 1-40 and 6.0-12.0, respectively. The temperature of all the tests was set at 25 degrees C. The test results show that the SI value of MAP is the logarithmic functions of the concentrations of P, ammonium-N and Mg, and increases with the increase of the concentration of each element. The SI value of MAP is a polynomial function of pH value of the solution, and the optimum pH value for the crystallization of MAP is 9.0 but increases slightly with the increase of the N/P. Moreover, the SI value of MAP is a power law function of the ionic strength of solutions but decreases with its increase. The adjustment of the Mg concentration and the control of solution pH are two effective methods for the control of the crystallization of MAP. The results obtained from the research can be used to guide the design and control of MAP crystallization process for the removal and recovery of P.