Cobalt Fluorides Research Articles

Tri-metallic fluoride nanoplates immobilized on reduced graphene architectures as efficient oxygen evolution reaction catalyst

Exploring the transition metal fluoride-based catalysts with highly catalytic activity is of great importance to satisfy the electrochemical oxygen evolution reaction (OER). Herein, the tri-metallic (cobalt, iron, and nickel) fluorides immobilizing on reduced graphene oxide architectures (CoFeNiF-rGAs) are constructed by hydrothermal and low-temperature fluoridation. The hierarchical structure assembled by the π-π configuration of graphene can provide abundant channels for fast ion diffusion and guarantee the uniform loading of metal fluorides. Owing to the hierarchical morphology and the formation of metal fluorides/graphene interfaces, CoFeNiF-rGAs can show excellent OER performance. Only 238 mV of overpotential is required to achieve a current density of 10 mA cm−2 in alkaline electrolyte, and the Tafel slope (78.8 mV dec-1) and charge transfer resistance (13.6 Ω) are smaller than the control samples, respectively, implying a fast kinetic behavior during OER. The highly catalytic stability of CoFeNiF-rGAs is confirmed by 1000 cyclic voltammetry and chronoamperometry test for 20 h, and the boosted catalytic mechanism is elucidated by density function theory calculation.

Intimately mixed copper, cobalt, and iron fluorides resulting from the insertion of fluorine into a LDH template.

The advancement of lithium-ion batteries (LIBs) with high performance is crucial across various sectors, notably in space exploration. This advancement hinges on the development of innovative cathode materials. Our research is dedicated to pioneering a new category of cathodes using fluorinated multimetallic materials, with a specific focus on diverging from the traditional Ni, Co, and Mn-based NMC chemistries by substituting nickel and manganese with copper and iron which are more sustainable elements. Our goal is also to enhance the robustness of cathodes upon cycling by substituting oxygen with fluorine as the metal-ligand. To achieve this, an intimate composite blend of CuF2 and FeF3, through the multi-metallic template fluorination (MMTF) methodology using a layered double hydroxide (LDH) as a precursor has been designed. Each of these components was carefully selected for its distinct attributes, including high redox potential, elevated energy density, substantial theoretical capacity, and improved cyclability. The composition denoted as (Cu1.5Co0.5)2+(Fe0.75Al0.25)3+ has been selected for fluorination because it maximizes Fe3+ and Cu2+ amount in the screened LDHs. Subsequently, this particular LDH was fluorinated through solid-gas fluorination at different temperatures (200, 350, and 500 °C) using gaseous molecular fluorine (F2). A comprehensive characterization of these materials using various techniques, including X-ray diffraction (XRD), 57Fe Mössbauer spectrometry, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and inductively coupled plasma analyses (ICP-AES) was conducted, and the evolution of LDH upon fluorination has revealed an intermediate porous texture particularly sensitive to hydration. Two original crystallographic phases are else obtained by fluorination: one formed by the hydration of the amorphous intermediate compound: Cu3Fe1.5Al0.5F12(H2O)12 an anti-perovskite structure and another stabilized through the combination of solid gas fluorination and LDH precursor yielding an original CoFeF5-type phase. Raman operando during cyclic voltammetry measurement applied on a sample fluorinated at 500 °C and used as a cathode in front of lithium metal was finally conducted to validate redox activity and mechanism.

Redox Neutral Radical-Relay Cobalt Catalysis toward C-H Fluorination and Amination.

A redox neutral radical-relay cobalt-catalyzed intramolecular C-H fluorination of N-fluoroamides featuring the in situ formed cobalt fluorides as the latent radical fluorinating agents is reported. Moreover, the reactivity of such a cobalt catalysis could be diverted from C-H fluorination to amination by engineering substrates' conformational flexibility. Preliminary mechanistic studies (UV-vis spectroscopy, cyclic voltammetry studies and DFT calculations, etc.) support the reaction proceeding a redox neutral radical-relay mechanism.

Electron correlation effects in cobalt fluorides CoFn

AbstractThe molecular cobalt fluorides CoF2, CoF3 and CoF4 are studied and compared by employing different basis sets as well as Quantum Information Theory (QIT) to investigate their correlation effects. These prototypical monomers may be systematically extended in size yielding a novel quasi 1‐dimensional, strongly correlated model system consisting of cobalt atoms bridged by oxygen atoms and fluorine termination on both ends. Accurate correlation energies are obtained using Full Configuration Interaction (FCI) and Full Configuration Interaction Quantum Monte Carlo (FCIQMC) calculations and the results are compared to Coupled Cluster and Density Matrix Renormalization Group (DMRG) energies. The analysis indicates the cobalt atom requires a larger number of one‐electron basis functions than fluorine and the use of localized molecular orbitals may facilitate calculations for the extended systems.

Fluorination of Some Group IX and X Metals and Their Lower Fluorides by Monofluorine and Difluorine Mixtures

The fluorination of metallic platinum and of cobalt(II) and nickel(II) fluorides with nonequilibrium mixtures of F2 containing high percentages of F is considered in terms of the acquisition of thermodynamic equilibrium. The enthalpy of the reaction Ni2F5(cr) = 2NiF2(cr) + 1/2F2(g) was determined by an independent method to be ΔrH°(0) = –59.9 ± 1.5 kJ/mol, and the enthalpy of formation was verified: ΔfH°(Ni2F5(cr), 0 K). A correlation was shown between the experimentally determined sequences of reactions that occur inside a nickel effusion cell and their enthalpies.

Cobalt fluorides: preparation, reactivity and applications in catalytic fluorination and C-F functionalization.

Recent advances in the investigation of cobalt fluorides in organofluorine chemistry are highlighted. The preparation and reactivity of inorganic and organometallic cobalt fluorides are discussed. The in-depth understanding of the structures and reactivity of cobalt fluorides allows chemists to develop diverse innovative catalytic fluorination and C-F functionalization.

Combustion of Composites of Boron with Bismuth and Cobalt Fluorides in Different Environments

ABSTRACT Composite powders of boron and 50 wt-% of either bismuth or cobalt fluoride were prepared by arrested reactive milling. Particle combustion was studied in air, and in the products of air-hydrogen and air-acetylene flames, respectively. Combustion times, determined from 700 to 800 nm emission pulses, were correlated with particle sizes. Combustion temperatures were determined for select cases. In air, the composite particles burned faster than elemental boron with comparable combustion temperatures. However, the composite particles burned in one stage unlike the two-stage combustion pattern known for boron. In flame combustion products, the composite powders burned more slowly than elemental boron, but also in a single stage. Light emission was reduced compared to combustion in air, suggesting lower temperatures. Across all conditions, the B·BiF3 composites had shorter burn times compared to B·CoF2. Washing boron in acetonitrile prior to composite preparation to remove surface oxide/hydroxide had no significant effect on the combustion of the resulting composites.

Thermochemistry of Cobalt Trifluoride

The value ΔfH0° (CoF3(cr)) = –861 ± 10 kJ/mol is determined using the data on equilibria of the reactions involving crystalline cobalt(III) fluoride. The features of chemical and thermal behavior of this compound (in particular, its easy hydrolyzability due to hygroscopic properties and vaporization without decomposition to fluorine and difluoride) are explained. The enthalpies of formation of crystalline and gaseous cobalt fluorides CoFn (n = 2–4), as well as some of their negatively charged ions, and electron affinity energies of CoF3 and CoF4 (3.42 and 6.10 eV, respectively) are reported. Quantitative comparison of the efficiencies of iron, manganese, and cobalt trifluorides used as fluorinating agents to synthesize organic and inorganic compounds is performed.

A Study of Cobalt and Manganese Fluorides as Cathode Materials for Rechargeable Lithium Cells

This paper describes a study of the lithium/transition metal fluoride cells using nanocomposites of carbon with cobalt or manganese fluorides as cathode materials. The nanocomposite cathode materials were prepared by high energy milling of carbon and metal fluorides. It was, however, found that cobalt trifluoride reacted with carbon during the high energy milling process to form carbon fluoride. The Li/cobalt fluoride cells were, therefore, studied by using nanocomposite cathodes prepared by high energy milling of carbon, cobalt metal and lithium fluoride or cathodes prepared by mixing carbon and cobalt trifluoride without subjecting the mixture to the high energy milling process. The charge- discharge characteristics of lithium/transition metal fluoride cells were studied at 22oC and 50oC using a 1M LiPF6-sulfolane solution as the electrolyte. The cells were found to be electrochemically reversible but could not be completely charged due to simultaneous oxidation of the electrolyte at potentials above ~4.5 Volts.

A Study of Cobalt and Manganese Fluorides as Cathode Materials for Rechargeable Lithium Cells

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Highly Selective Biaryl Cross-Coupling Reactions between Aryl Halides and Aryl Grignard Reagents: A New Catalyst Combination ofN-Heterocyclic Carbenes and Iron, Cobalt, and Nickel Fluorides

Combinations of N-heterocyclic carbenes (NHCs) and fluoride salts of the iron-group metals (Fe, Co, and Ni) have been shown to be excellent catalysts for the cross-coupling reactions of aryl Grignard reagents (Ar(1)MgBr) with aryl and heteroaryl halides (Ar(2)X) to give unsymmetrical biaryls (Ar(1)-Ar(2)). Iron fluorides in combination with SIPr, a saturated NHC ligand, catalyze the biaryl cross-coupling between various aryl chlorides and aryl Grignard reagents in high yield and high selectivity. On the other hand, cobalt and nickel fluorides in combination with IPr, an unsaturated NHC ligand, exhibit interesting complementary reactivity in the coupling of aryl bromides or iodides; in contrast, with these substrates the iron catalysts show a lower selectivity. The formation of homocoupling byproducts is suppressed markedly to less than 5% in most cases by choosing the appropriate metal fluoride/NHC combination. The present catalyst combinations offer several synthetic advantages over existing methods: practical synthesis of a broad range of unsymmetrical biaryls without the use of palladium catalysts and phosphine ligands. On the basis of stoichiometric control experiments and theoretical studies, the origin of the unique catalytic effect of the fluoride counterion can be ascribed to the formation of a higher-valent heteroleptic metalate [Ar(1)MF(2)]MgBr as the key intermediate in our proposed catalytic cycle. First, stoichiometric control experiments revealed the stark differences in chemical reactivity between the metal fluorides and metal chlorides. Second, DFT calculations indicate that the initial reduction of di- or trivalent metal fluoride in the wake of transmetalation with PhMgCl is energetically unfavorable and that formation of a divalent heteroleptic metalate complex, [PhMF(2)]MgCl (M = Fe, Co, Ni), is dominant in the metal fluoride system. The heteroleptic ate-complex serves as a key reactive intermediate, which undergoes oxidative addition with PhCl and releases the biaryl cross-coupling product Ph-Ph with reasonable energy barriers. The present cross-coupling reaction catalyzed by iron-group metal fluorides and an NHC ligand provides a highly selective and practical method for the synthesis of unsymmetrical biaryls as well as the opportunity to gain new mechanistic insights into the metal-catalyzed cross-coupling reactions.

Lithium-Ion Batteries: Thermal Reactions of Electrolyte with the Surface of Metal Oxide Cathode Particles

Thermal reactions between in 1:1:1 ethylene carbonate/dimethyl carbonate/diethyl carbonate and metal-oxide cathode particles were investigated by analyzing both the liquid electrolyte and solid cathode particles through the combined use of nuclear magnetic resonance spectroscopy, gas chromatography with mass selective detection, scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The reactions between the electrolyte and cathode particles inhibit the thermal decomposition of the electrolyte and modify the surface of the cathode particles. The on the surface of the metal oxides is removed and replaced by a complex mixture including poly(ethylene oxide), polycarbonate, , , and . Higher surface concentration of on allows a fragile temperature-dependent equilibrium to be established, accounting for the thermal stability of the electrolyte. Higher temperature leads to more and less on the surface. With , no equilibrium is established due to lower surface concentration of . Consequently, thermal reactions of the electrolyte with generate decomposition products, including and cobalt fluorides on the surface and bulk electrolyte decomposition. Independent addition of enhances the thermal stability of the -based electrolyte, confirming the thermal-stabilizing properties of surface films. The addition of a carbonate solution of to generates in the solution and on the surface.

The magnetic properties of mixed cobalt and zinc fluorides

An investigation of the magnetic properties of powder samples of Co x Zn 1- x F 2 for a complete range of compositions was undertaken using low field dc magnetic susceptibility and diffuse polarised neutron scattering measurements. The Néel temperature, as determined from the cusp in the powder susceptibility, was found to agree with percolation theory predictions. There was no evidence of spin glass behaviour from any of the measurements above 2.6 K for Co 0.26Zn 0.74F 2, or above 4.2 K for Co 0.2Zn 0.8F 2 and Co 0.1Zn 0.9F 2. All susceptibility data are fitted in the paramagnetic region with a simple molecular field model allowing for crystal field effects and spin-orbit coupling.

Reactions of cobalt fluorides with hydrazine

Reactions of cobalt fluorides with hydrazine

Polyfluroheterocyclic compounds. Part XXIII. Monoenes and dienes derived by the fluorination of hexafluorobenzene and of perfluoro- and chlorofluoro-heteroaromatic compounds. A mechanism for fluorination by cobalt fluorides

Hexafluorobenzene, pentafluoro-, 3- and 4-chlorotetrafluoro-, and 3,4- and 3,5-dichlorotrifluoro-pyridines have been fluorinated with a mixture of cobalt(III) and calcium fluorides. Reaction conditions can be adjusted so that hexafluorobenzene gives only octafluorocyclohexa-1,4-diene and decafluorocyclohexene. Pentafluoro-, 3-chlorotetrafluoro-, and 3,5-dichlorotrifluoro-pyridines give only perhalogeno-1-azacyclohex-1-enes together with small amounts of acyclic aza-alkenes when fresh fluorinating agent is used. When there is a chlorine atom on position 4 of the ring system, cyclic dienes are also produced and may be the main products. If a much depleted fluorinating agent is used, pentafluoropyridine gives a trace of heptafluoro-1-azacyclohexa-1,3-diene. The latter can also be prepared from the 4-chloro- and 3,4-dichloro-cyclic aza-monoenes by dechlorination or by the action of fluoride ion on the 4-chloro-diene.When tetrafluoropyrazine is fluorinated, the only product is hexafluoro-1,4-diazacyclohexa-1,3-diene.Calculations of the charge and spin densities on the atoms in the ring system at various stages in the fluorinaton have been made and a mechanism for the process involving, at each stage, the quenching of the first formed radical cation by fluoride ion and then by a fluorine atom, is suggested. The mechanism is supported by the isolation of a dimer from the fluorination of tetrafluoropyrimidine.

Magneto‐Optical Investigation of Antiferromagnets (Manganese and cobalt carbonates and fluorides)

AbstractAn experimental study is made of the effect of high magnetic fields on the structure of the optical absorption spectra of Mn2+ and Co2+. The study uses single crystals of antiferromagnetic fluorides and carbonates of the ions and also single crystals of fluorides of mixed content, containing both ions simultaneously. The investigations are carried out at 20.4 and 4.2 °K, which is significantly lower than the temperature of antiferromagnetic ordering (TN). Magnetic fields of up to 1.7 · 105 Oe are used. The magneto‐optical effects found in the fluorides are connected with spin‐flipping of the magnetic sublattices by the external field. This may be due to a significant spin‐orbital exchange in states (the final states for the optical transitions responsible for the absorption bands) which respond to the re‐establishment of the antiferromagnetic structure by the external field. Zeeman splitting and shift of some absorption lines is observed in antiferromagnetic carbonates in which the magnetic structure cannot be changed by the external field. This is accounted for on the basis that the internal field HE, perpendicular to the C3‐axis of the crystal, effects some excited states of Mn2+ and Co2+ significantly less than the external field H parallel to C3‐axis although H ≪ HE.

Fluoride catalysis at 175°C. of the reaction: Glycerol plus fatty acid

Summary In uncatalyzed reactions the esterification of stearic, oleic, and linolenic acid proceeded at the same general rate though the speed was somewhat enhanced as the degree of unsaturation of the fatty acid increased. None of the reactions went to completion, after 15 hours being 72%, 83%, and 84%, respectively, completed. Only a small fraction of the distearate was converted to the triglyceride; a greater amount of the dioleate was esterified to the trioleate and about half the dilinolenate was changed to the trilinolenate. Of 15 metallic fluorides studied, all afforded some catalysis, but only antimony trifluoride and zinc and cobalt fluorides were outstanding. Antimony trifluoride was the most active although in large amount it caused severe decomposition and charring of the products. Zinc fluoride had the best general properties, approaching antimony trifluoride yet causing practically no decomposition even in high concentration. Its activity was enhanced with an increase in amount, the best concentration apparently being 0.1 mole per 100 grams fatty acid. Antimony trifluoride was also better in larger amount within limits, but cobalt fluoride did not exhibit this property. With zinc fluoride as catalyst the reactions of stearic, oleic and linolenic acids after 15 hours were 95%, 94%, and 92%, respectively, completed. At least three‐fourths of the diglycerides were converted to triglycerides. From a study of reaction velocities, zinc fluoride caused the monoglyceride to form at a rate approximately four times that of the uncatalyzed reaction and the diglyceride at a six‐fold rate. The triglyceride was formed at an almost undiminished rate whereas in the uncatalyzed reaction the formation of triglyceride was diminished rapidly. Unsaturation and viscosity were not affected seriously in the presence of the fluorides except antimony trifluoride. Certain other fluorides caused severe darkening but without accompanying serious decomposition.