Enhanced Redox Electrocatalysis in High‑Entropy Perovskite Fluorides by Tailoring d–p Hybridization

High-entropy catalysts featuring exceptional properties are,in no doubt,playing an increasingly significant role in aprotic lithium-oxygen batteries.Despite extensive effort devoted to tracing the origin of their unparalleled performance,the relationships between multiple active sites and reaction intermediates are still obscure.Here,enlightened by theoretical screening,we tailor a high-entropy perovskite fluoride(KCoMnNiMgZnF_(3)-HEC)with various active sites to overcome the limitations of conventional catalysts in redox process.The entropy effect modulates the d-band center and d orbital occupancy of active centers,which optimizes the d–p hybridization between catalytic sites and key intermediates,enabling a moderate adsorption of LiO_(2)and thus reinforcing the reaction kinetics.As a result,the Li–O2 battery with KCoMnNiMgZnF_(3)-HEC catalyst delivers a minimal discharge/charge polarization and long-term cycle stability,preceding majority of traditional catalysts reported.These encouraging results provide inspiring insights into the electron manipulation and d orbital structure optimization for advanced electrocatalyst.

High entropy fluorides as conversion cathodes with tailorable electrochemical performance

With the recent development of high entropy materials, an alternative approach to develop advanced functional materials with distinctive properties that show improved values compared to conventional materials has been provided. The high entropy concept was later successfully transferred to metal fluorides and high entropy fluorides(HEFs) were successfully synthesized. Owing to their high theoretical specific capacities in energy storage applications, HEFs were utilized as cathode materials for lithiumion batteries(LIBs) and their underlying storage mechanisms were investigated. Instead of a step-bystep reduction of each individual metal cation, the HEFs seem to exhibit a single-step reduction process,indicating a solid solution compound instead of merely a mixture of different metal fluorides. It was also observed that the electrochemical behavior of the HEFs depends on each individual incorporated element. Therefore, by altering the elemental composition, new materials that exhibit improved electrochemical properties can be designed. Remarkably, HEFs with seven incorporated metal elements exhibited a better cycling stability as well as a lower hysteresis compared to binary metal fluorides.These findings offer new guidelines for material design and tailoring towards high performance LIBs.

Largescale Preparation of Organic-Dispersible Lanthanide Fluorides Nanocrystals via Colloid-Extraction Route

Organic-dispersible lanthanide fluorides nanocrystals were synthesized at a large scale using colloid-extraction method, in the presence of dialkyl-dithiophosphinic acid (DDPA) as the extraction agent. The products were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transformation infrared (FTIR) spectroscopy. It was found that the synthesized lanthanide fluorides nanoparticles had high purity and crystallinity, and could be well dispersed in organic solvents such as chloroform, toluene etc., which could be closely related to the surface-capping of the nanocrystals by the DDPA molecules. Moreover, the nanocrystals before and after extraction by DDPA showed few differences in the microscopic morphologies. It was implied that DDPA as the extraction agent had good protection to the nanocrystals as well, which could be essential to the commercial application of the titled rare earth nanocrystals as novel multifunctional additives in the fields of lubrication.

Coprecipitation Synthesis of Fluorides Nanoparticles with Multiform Structures and Mechanisms Research

Fluoride nanoparticles with multiform crystal structures and morphologies were successfully synthesized by a facile, effective, and environmentally friendly coprecipitation method. Transmission electron microscopy (TEM) was used to characterize the nanoparticles. The nanoparticles were modified by PEI, CTAB, PAA and Ci, respectively. It was feasible for function by -COOH and -NH2 groups, due to the surface modification. Moreover, different surface modifications of the nanoparticles were examined. The possible formation mechanisms for fluoride nanoparticles with surface modification were presented in detail. More importantly, it is expected to be widely applied to biomedicine.

Electrolytic Codeposition of Y(Ⅲ) and Al(Ⅲ) and Surface Metalliding in Molten Fluorides—Oxides Systems

The mechanism of the electrolytic codeposition of Y Al alloy in molten LiF AlF 3 Al 2O 3 YF 3, LiF YF 3 Y 2O 3 AlF 3 and LiF YF 3 Y 2O 3 Al 2O 3 systems was investigated by means of cyclic voltammetry. The electrodeposited products were analysed by X ray diffraction. The results show that the electrolytic codeposition of Y Al alloy in the LiF YF 3 Y 2O 3 Al 2O 3 system without AlF 3 can be achieved at the same potential for Y(Ⅲ) and Al(Ⅲ) which have great difference in deposition potential. It is beneficial to codeposition of Y(Ⅲ) and Al(Ⅲ) when temperature rises. The potential of beginning codeposition is about -0.85 V ( vs Pt reference electrode), but only at the potential of -0.95 V or more negative can Y based Al alloy containing a great amount of yttrium be obtained.

High-temperature Reference Electrodes Used in Molten Fluorides

The thermodynamic and dynamic behaviour of Ni^(2+)|Ni couple in FLINAK melt is investigated by us- ing EMF measurement and micropolarization method.The couple shows the Nernstian reversibility and a large exchange current density(6 mA·cm^(-2)).A single crystal LaF_3 which is a fluoride ion conductor used as a membrane of the Ni^(2+)|Ni couple reference electrode is reliable in FLINAK melts at 973 K.The poten- tial of LaF_3 membrane reference electrode is constant within±2 mV.The boron nitride used as a salt bridge was not good in FLINAK melts.The platinum electrode is studied by using micropolarization.The equilibrium potential of Pt electrode is dependent on the absorption and the electrochemical reaction.The potential is stable for a constant composition at constant temperature.

REPLACED SITE OF Eu^(2+) ION IN THE COMPLEX FLUORIDES WITH THE PEROVSKITE CRYSTAL STRUCTURE

The replaced site of Eu^(2+) ion is dependent on the electronegativity difference of the cations in complex fluorides.In the mixed fluoride KMgF_3:Eu^(2+),Eu^(2+) ion occupies K^+ site,its emission spectrum is a sharp line and its valence-state is stable.

A Device for Measuring the Density and Liquidus Temperature of Molten Fluorides for Heat Transfer and Storage

An experimental device is constructed for measuring the density and liquidus temperature of molten fluorides by using the Archimedean and cooling curve methods respectively.Its operation is tested by measuring the density and liquidus temperature of NaCl salt.The accuracy of the liquidus temperature measurement is about±1 K.The density of NaCl measured is in good agreement with the widely recognized data and the deviation is less than 0.2%.The liquidus temperature and density of a typical heat transfer fluoride LiF-NaF-KF(46.5-11.5-42mol%)are investigated.

Hydrothermal Synthesis,Structure Characterization and Magnetic Studies of Perovskite-type Fluorides K_2 NaVF_6 and(NH_4)_3VF_6

Two perovskite-type fluorides K2NaVF6 and （NH4）3VF6 were synthesized under mild hydrothermal con- ditions. The structures of the compounds were determined by means of powder X-ray diffraction analysis. The Riet- veld refinement indicates that K2NaVF6 has a cubic elpasolite-type structure and crystallizes in space group Fm3m with lattice constant a=8.3180（2） nm. （NH4）3VF6 has a cubic cryolite-type structure and crystallizes in space group Fm3m with lattice parameter a=9.090（1） rim. The compounds were further characterized by scanning electron micro- scopy（SEM）, thermogravimetric（TG） and differential thermal analysis（DTA）. The variable temperature magnetic susceptibility of these two compounds was characterized for the first time and the result shows that the magnetic or- dering is related to the crystallographic features and isolated magnetic unit with the temperature decreasing.

Studies on the Transition Emission of Eu^（2＋） Ion in Complex Fluorides Using Neural Network

Quasi-Newton, fully-connected, and feed forward neural network were used to study the correlation between the spectral structure of the Eu2+ ion in complex fluorides and the structures of complex fluorides. The experimental results show that the neural network architecture (number of layers and number of nodes in each layer),the intial weights. and the organization of the data were all important factors affecting the performance of the neural network. The performance of the neural network was enhanced by adapting a test set to monitor the training process. Once trained, the neural network correctly classified 100% of the training set and 96.3% of the test set. These results offer tremendous improvement over previous pattern recognition methods.

Metal Fluorides Produced Using Chlorine Trifluoride Gas

For developing coating materials, the fluorides of scandium, lanthanum, strontium, barium, magnesium and aluminum were produced from their oxides and chlorides by means of exposure to chlorine trifluoride gas at temperatures between room temperature and 700°C. The metal chlorides could be easily fluorinated even at room temperature, while the metal oxides required temperatures higher than 300?C. After the heating in ambient hydrogen at 1100°C, the fluorides of lanthanum and barium showed very low weight losses at 1100°C, although the weights of the other fluorides significantly decreased. These materials may work as protective films against corrosive and high temperature environments, particularly when using the chlorine trifluoride gas.

Designing mesostructured iron (Ⅱ) fluorides with a stable in situ polymer electrolyte interface for high-energy-density lithium-ion batteries

As high-energy cathode materials,conversion-type metal fluorides provide a prospective pathway for developing next-generation lithium-ion batteries.However,they suffer from severe performance decay owing to continuous structural destruction and active material dissolution upon cycling,which worsen at elevated temperatures.Here,we design a novel FeF2 cathode with in situ polymerized solid-state electrolyte systems to enhance the cycling ability of metal fluorides at 60 C.Novel FeF2 with a mesoporous structure(meso-FeF2)improves Liþdiffusion and relieves the volume change that typically occurs during the alternating conversion reactions.The structural stability of the meso-FeF2 cathode is strengthened by an in situ polymerized solid-state electrolyte,which prevents the pulverization and ion dissolution that are inevitable for conventional liquid electrolytes.Under the double action of this in situ polymerized solid-state electrolyte and the meso-FeF2's mesoporous structure,the active material maintains an intact SEI layer and part of the mesoporous structure after long charge–discharge cycling,showing excellent cycling stability at high temperatures.

A General Electrochemical Synthesis of Sulfonimidoyl Fluorides,Azides,and Acetates

Sulfonimidoyl fluorides,the aza-bioisostere of sulfonyl fluorides,are emerging as a promising linkage agent in the sulfur(VI)fluoride exchange reaction(SuFEx).However,conventional synthetic approaches typically require the use of either unstable sulfonimidoyl chlorides,toxic and corrosive sulfur fluorides,or expensive electrophilic fluorinating agents.Herein,we report an electrochemistry-enabled oxidative nucleophilic fluorination of readily available and bench-stable sulfinamides using a commercially available and easy-to-handle triethylamine trihydrofluoride.With other nucleophilic agents,this electrochemical approach also serves as a general approach to diverse sulfonimidoyl derivatives,including sulfonimidoyl azides and acetates.

Reviewing metal fluorides as the cathode materials for high performance Li batteries

Exploring high‐energy density rechargeable lithium(Li)batteries is urgently needed to meet the demand of the large‐scale electric vehicle market.Conversion‐type metal fluorides(MFx)have been considered as desirable cathode materials for next‐generation rechargeable batteries because of their high operational voltages,environmental non‐toxicity,low cost,and high thermal stability.In this review,we present the most promising and feasible MFx applied in rechargeable Li batteries in terms of capacity,discharge po-tential,volume change,fabricated methods,crystal structure,and cost/abun-dance.The electrochemical performance is briefly illustrated,and the recent advances in mechanisms focused on MFx cathodes upon cyclic processes are noted and discussed in detail.Finally,prospects for the current challenges and possible research directions,with the aim to provide some inspiration for the development of MFx‐based cathodes are presented.

Enhancing charge storage of O-doped perovskite fluorides via in-situ electrochemical oxidation for high-performance potassium-ion capacitors

Potassium ion capacitors(PICs)are regarded as promising large-scale aqueous energy storage systems.However,due to the poor K^(+)transport kinetics and the structural instability of the cathode materials,the key issues of limited energy density and poor cyclic stability are obstacles to the in-depth growth of PICs.Herein,a novel O-doped perovskite fluoride is demonstrated via an in-situ electrochemical oxidation strategy as the cathode for PICs,introducing additional defects that improve the capacitance and facilitate the reaction kinetics of the electrode.During the electrochemical oxidation process,it is discovered that the perovskite fluoride crystal tends to transform into disordered O-doped KMnF 3(K_(x)MnF_(y)O_(z)),realizing a structural reconstruction at the electrode material/electrolyte interface.The First-principles calculations based on density functional theory(DFT)are performed to confirm that the improved electrical conduc-tivity and low ionic adsorption energy may be ascribed to the substitution of oxygen for fluorine.The obtained K_(1.14)MnF_(1.17)O_(1.26) cathode achieves a high specific capacitance of 694 F g^(-1) at 1 A g^(-1),as well as high capacitance retention of 91.3%after 10,000 charge/discharge cycles in mild K_(2)SO_(4) electrolyte.This study provides an effective strategy to improve the capacitive performance of perovskite fluoride cathode materials in electrochemical energy storage.

Nickel-catalyzed hydromonofluoromethylation of unactivated alkenes for expedient construction of primary alkyl fluorides

A nickel-catalyzed direct hydromonofluoromethylation of unactivated olefins with industrial raw fluoroiodomethane is developed,furnishing various primary alkyl fluorides in a step-economic manner.The key factor to success is the use of pyridine-oxazoline as ligand and(MeO)_(2)MeSiH as the hydrogen source.This transformation demonstrates high efficiency,mild conditions,good functional-group compatibility and great potential in the drug discovery.

Synthesis of L-Hexopyranosyl Fluorides Enabled by Radical Decarboxylative Fluorination: Assembly of a Pentasaccharide Repeating Unit Corresponding to Extracellular Polysaccharide S-88

L-Hexoses are key components of many biologically relevant natural products and pharmaceuticals.As rare sugars,L-hexoses are not readily obtained from natural sources.Access to L-hexose building blocks from commercially available and inexpensive D-sugars is highly desirable from the viewpoints of organic synthesis and drug discovery.As demonstrated by the convenient preparation of L-glucosyl,L-galactosyl,and L-mannosyl fluorides from readily availableβ-D-C-glucosyl,β-D-C-mannosyl,andβ-D-C-galactosyl derivatives,we describe a novel and efficient approach to the demanding L-glycosyl fluorides.

Oxidation of Difluorocarbene by Pyridine N-Oxide and Ensuing Access to Carbamoyl Fluorides

A practical one-pot preparation of carbamoyl fluorides from easily obtained pyridine N-oxide,commercially available secondary amines and synthetically versatile difluorocarbene precursors(Ruppert-Prakash reagent or Chen's reagent)was developed herein,which dexterously resorted to the oxidation of difluorocarbene by external pyridine N-oxide to produce the toxic and gaseous fluorophosgene in situ.Notable features of this method include nice functionality tolerance,late-stage modification of drug molecules and the recoveryand recycle of quinoline.

Nanosized complex fluorides based on Eu^(3+) doped Sr_2LnF_7(Ln=La, Gd)

A simple co-precipitation approach taking place between Ln3＋, Sr2＋ cations and F anions, led to the formation of nanocrystalline Eu3＋ doped Sr2LnF7 （Ln-La and Gd） complex fluorides. The reaction was carried out in the presence of polyeth- ylene glycol, PEG 6000 as a surfactant/surface modifier, providing small size and homogeneity of the products. The synthesized compounds were composed of small nanoparticles with an average size of 15 nm. All obtained Eu3＋ doped compounds exhibited an intensive red luminescence. In the case of gadolinium based compounds, the energy transfer phenomena could be observed from Gd3＋ ions to Eu3＋ ions. In order to study the structure and morphology of the synthesized fluorides, powder X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed. Also FT-IR spectra of the products were re- corded, revealing the presence of PEG molecules on the nanoparticles suN＇ace. A spectrofluorometry technique was applied to examine optical properties of the synthesized nanoparticles. Excitation and emission spectra as well as luminescence decay curves were measured and analysed. The performed analysis revealed a red luminescence, typical for the Eu3＋ ion situated in the inorganic, highly symmetric matrix. Concentration quenching phenomena and lifetimes shortening, together with an increasing of the Eu3＋ doping level, were observed and discussed. Judd-Ofelt analysis was also performed for all doped samples, in order to support the registered spectroscopic data and examine in details structural and optoelectronic properties of the synthesized nanomaterials.

Hydrothermal synthesis of mixed rare earth-alkali metal or ammonium fluorides

The recent results on hydrothermal synthesis of mixed rare earth-alkali or ammonium fluorides were presented. The initial ratios of the starting materials, pH value and reaction temperature were the critical factors for obtaining the single-phase product. Four main types of complex rare earth fluorides, AREF4, A2REF5, ARE2F7 and ARE3F10 (A=Na+, K+, Rb+, NH4+), appeared in the primary hydrothermal reactions. The correlation between cation sizes and the formation of mixed rare earth fluorides under mild hydro...