Intercalation Of Bromine Research Articles

Water-Salt Oligomers Enable Supersoluble Electrolytes for High-Performance Aqueous Batteries.

Aqueous rechargeable batteries are highly safe, low-cost, and environmentally friendly, but restricted by low energy density. One of the most efficient solutions is to improve the concentration of the aqueous electrolytes. However, each salt is limited by its physical solubility, generally below 21-32molkg-1 (m). Here, a ZnCl2 /ZnBr2 /Zn(OAc)2 aqueous electrolyte with a record super-solubility up to 75 m is reported, which breaks through the physical solubility limit. This is attributed to the formation of acetate-capped water-salt oligomers bridged by Br- /Cl- -H and Br- /Cl- /O-Zn2+ interactions. Mass spectrometry indicates that acetate anions containing nonpolarized protons prohibit the overgrowth and precipitation of ionic oligomers. The polymer-like glass transition temperature of such inorganic electrolytes is found at ≈-70 to -60°C, without the observation of peaks for salt-crystallization and water-freezing from 40 to -80°C. This supersoluble electrolyte enables high-performance aqueous dual-ion batteries that exhibit a reversible capacity of 605.7mAhg-1 , corresponding to an energy density of 908.5Whkg-1 , with a coulombic efficiency of 98.07%. In situ X-ray diffraction and Raman technologies reveal that such high ionic concentrations of the supersoluble electrolyte enable a stage-1 intercalation of bromine into macroscopically assembled graphene cathode.

New application of intercalation on improving toughness of carbon/carbon composites

Toughness is one of the key mechanical properties of carbon/carbon composites for practical application. The present paper reports a new method to improve the toughness of carbon/carbon composites by intercalation of bromine into the graphite microcrystals of pyrolytic carbon. The intercalated pyrolytic carbon was characterized by X-ray diffraction (XRD), TG and DSC. The XRD results confirm that the graphite microcrystals of pyrolytic carbon could be intercalated by bromine, although the weight loss in TG measurement indicates a low content of the intercalation in the pyrolytic carbon. According to the three-point bending test, the flexural strength of carbon/carbon composites with bromine intercalation decreases 10%, while the flexural modulus and deflection increases 10 and 18%, respectively. At same time, a tough-like fracture mode can be observed in the intercalated carbon/carbon composites. The involved mechanism of the improving toughness of carbon/carbon composites will be discussed.

Aqueous electrochemical intercalation of bromine into graphite fibers

For the first time, graphite fibers have been electrochemically intercalated with Br − that have the same structure and properties as those intercalated from vapor phase Br 2. This was accomplished by intercalating pitch-based Thornel ® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br − is oxidized to aqueous Br 2 which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br 2 solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br 2 unless a voltage is applied.

Study of the bromination of pitch-based carbon fibres

The changes in the structure and properties of pitch-based carbon fibres (CF) brominated for different periods of time (up to 144 h) and the state of bromine in these fibres have been studied. Electrical conductivity in the temperature range from 10 to 300 K, IR and Raman spectra, and thermogravimetric analysis data are presented. The structural modifications in CF upon bromination, as indicated by these data, include the growth of the fine-crystalline phase, the degradation of the graphite structure, the emergence and growth of an amorphous phase, and an increase in the number of graphite layers adjacent to bromine. If the bromination time does not exceed 96 h, the process leads to the intercalation of bromine, i.e., the formation of charge-transfer complexes between the carbon network and bromine. More prolonged bromination results in the formation of C-Br chemical bonds.

Electrochemical intercalation of bromine into graphite in an aqueous electrolyte solution

By electrochemical oxidation of a graphite sheet in an aqueous solution of potassium bromide, the intercalation of bromine was observed. It was confirmed by the measurements of weight increase of about 10%, decrease in relative electrical resistivity down to 0.69, and enlargement of average interlayer spacing. On the graphite sheet pre-electrolyzed in KBr solution, the chronopotentiogram in K 2SO 4 aqueous solution showed some plateaux corresponding to the reduction of graphite intercalation compounds with bromine. The longest time on a plateau was observed on the graphite sheet pre-electrolyzed in a potential region of bromine gas evolution, where the most pronounced decrease in electrical resistivity of graphite sheet was detected.

Intercalation of Potassium and Bromine into Carbon Blacks

Intercalation of potassium and bromine into furnace blacks with different heat-treatmenttemperatures (HTTs) has been investigated. Potassium can be intercalated into carbon blacks irrespective of their HTTs; the saturated compound has the stage 1 structure. The observed isotherms for carbon black-bromine system show that the amount of bromine fixed by carbon black is less than 10% of that by graphite. The electrical resistance of residue compounds is larger than that of pristine materials for HTT≤1500°C but smaller for HT≥2000°C Such behavior is discussed in connection with the structure of host carbon blacks.

Deterioration mechanism of the carbon-plastic electrode of the Zn-Br 2 battery

The reactivity of bromine with graphite and polyethylene was studied to clarify the deterioration mechanism of the carbon plastic (CP) electrode of the ZnBr 2 battery. At first, intercalation of bromine in highly oriented pyrolytic graphite (HOPG) was conducted in aqueous solution. Stages 2, 3, 4, and 5 bromine-graphite intercalation compounds (Br 2-GICs) were obtained in 19−3,2.9−0.8, 0.8−0.65, and 0.5 mol/1 Br 2 solutions, respectively, and analysed based on a linear diffusion theory. Apparent diffusion coefficients were found to be governed by the final stage structure. Bromine-GICs were electrochemically synthesised and decomposed in 3 mol/l ZnBr 2 solution. Bromine-GICs were ascertained to be generated and decomposed during charge/discharge cycles of the Zn-Br 2 battery. Repeated reaction of Br 2 with pyrolytic graphite (PG), polyethylene (PE), and CP led to C-Br bond formation, along with exfoliation and cracking on the surface. Consequently, this reaction must be the reason for the mechanical deterioration of the CP electrode in the Zn-Br 2 battery.

Intercalation of Bi 2Sr 2Ca n−1Cu nO y with iodine and other halogens

Intercalation of iodine and bromine into polycrystalline (n = 1,2,3) and single crystal (n + 2) specimens of Bi 2Sr 2Ca n−1Cu nO y has been examined. Intercalation of iodine is accompanied by an expansion of the c-axis of approximately 0.7nm in all 3 systems, while, for n·2, Br insertion leads to half this expansion. Susceptibility and resistivity measurements are discussed. An investigation of the Hall coefficient in an n=2 crystal suggests a modest charge transfer to the CuO 2 planes.

Bromination of graphitic pitch-based carbon fibers

Bromination of the du Pont E-130 pitch-based carbon fibers was found to degrade the tensile strength, tensile modulus and oxidation resistance. This degradation was greater when bromination was carried out by exposure to bromine vapor than by the electrochemical method, and is attributed to the physical damage of bromination. This degradation is in contrast to the beneficial effect of bromination of less graphitic fibers, such as Amoco's Thornel P-100. However, bromination decreased the electrical resistivity by up to a factor of 5. This effect is due to the intercalation of bromine, as indicated by the in-plane intercalate superlattice order at room temperature and up to 100°C, at which temperature inplane melting occurred for fibers brominated by either method. A sharp intercalate Raman peak was observed at 240 cm −1, in contrast to the large breadth of this peak in Thornel P-100 fibers.

Searching the evidence for the intercalation of bromine in high-rank coal

Similar to graphite, meta-anthracite absorbs bromine at room temperature to a concentration close to that of stage-2 graphite-bromine. Subsequent desorption at room temperature was incomplete, indicating that 88% of the bromine was loosely held and 12% was relatively strongly held in the meta-anthracite. The rate of bromine absorption and the amount and rate of bromine desorption were greater for meta-anthracite than for graphite. X-Ray diffraction, electron diffraction and differential scanning calorimetry showed the absence of intralayer or interlayer intercalate ordering in brominated meta-anthracite after desorption, hence yielding no evidence for intercalation. We conclude that the meta-anthracite was not intercalated. The ignition temperature of meta-anthracite was lowered by ≈ 80 °C by the bromination.

Kinetics and thermodynamics of intercalation of bromine in graphite—II. Theory

A theory that describes the diffusion of an intercalate within graphite in a multiphase situation is presented. The theory was applied to the intercalation of bromine in graphite. Single-phase diffusion represents the intercalation of bromine in graphite as well as multiphase diffusion due to the dominance of the final stage.

Kinetics and thermodynamics of intercalation of bromine in graphite—I. Experimental

The intercalation of bromine in highly oriented pyrolytic graphite was performed at various combinations of temperature T (20–160°C) and bromine vapor pressure P (0.01–20 atm). The phase diagram ( logP vs 1 T ) for the formation of various stages showed that the enthalpies of reaction were −10.0, −10.8 and −11.0 kcal mol −1 Br 2 for stages 2, 3 and 4, respectively, and that the entropies of reaction were −29.9, −30.8 and −30.6 cal mol −1 Br 2 K −1 for stages 2, 3 and 4, respectively. The progress of intercalation was monitored in situ by optical measurements and ex situ by gravimetry, X-ray absorption and X-ray diffraction. The kinetic data yielded the first time-temperature-transformation diagram for intercalation. In particular, the rate of formation of stage 2 or 3 was found to first increase and then decrease as the reaction temperature increased and the thermal phase boundary (70°C for stage 2, 120°C for stage 3) was approached. In addition, the intercalation rate was determined as a function of the bromine potential, thereby yielding a time-concentration-transformation diagram.

124. Model of intercalation of bromine in graphite

124. Model of intercalation of bromine in graphite

The intercalation of bromine fluorosulfates into graphite

The action of bromine(1)fluorosulfate on graphite has led to the synthesis of several novel intercalation compounds. The intercalation of bromine(1)fluorosulfate at room temperature results in a first stage compound, C12BrSO3F, while at higher temperatures (~110 °C) C20BrF(SO3F)2 forms instead. Oxidation of C12BrSO3F with S2O6F2 yields C16Br(SO3F)3 and this reaction can be reversed by reacting the latter with an excess of Br2.Graphite trifluoromethylsulfate C12SO3CF3 is formed in the solvolysis of C12BrSO3F with an excess of trifluoromethyl-sulfuric acid. First stage nature of these compounds has been confirmed by the X-ray identity period along C axis and [Formula: see text], vibrational lattice mode in the Raman spectra. The use of 19F nmr in identifying the chemical species in the inter-lamellar space has been demonstrated. The planar electrical conductivity of these compounds has been observed to be three to six times higher than that of graphite.

Intercalate displacement and exchange in graphite

The mechanism of intercalate transport in graphite was studied by sequential intercalation of bromine and iodine monochloride. It was found that the transport involved solid-state intercalate displacement such that the first intercalate molecule to enter an interlayer space is the first to reach the center of the graphite sample. Upon exposure of stage-2 graphite-bromine to ICI, the in-plane superlattice diffraction pattern was observed to change from that of graphite-bromine to that of graphite-ICl, while the ICl intercalate distributed itself uniformly at a concentration level above that of the bromine intercalate. This is interpreted as the expulsion of bromine by the in-coming ICl, which dissolved the remaining bromine to form a solid solution with the ICl in-plane structure.

Thermodynamics Of Intercalation of Bromine in Graphite

ABSTRACTThe thermodynamics of intercalation of bromine in highly oriented pyrolytic graphite had been studied by determining the pressure-temperature equilibrium diagram for stages 2–4. The standard heat and entropy of reaction for the transformation from stage n to stage n−l (n=5, 4, 3) were found to be roughly the same, though the enthalpy of reaction became slightly more negative as the stage number increased. The heat and entropy of formation from pure graphite were thus found to be −10.9 kcal mol-1 Br2 and −30.4 cal mol−1 Br2 K−1 respectively for stage 2, −11.32 kcal mol−1 Br2 and −30.6 cal mol−1 Br2 K−1 respectively for stage 3, and −11.5 kcal mol−1 Br2 and −30.6 cal mol−1 Br2 K−1 respectively for stage 4.

Intercalation of bromine into natural graphite the effect of oxidation and residual bromine on the rate and amount of uptake

Intercalation of bromine at 20°C into spectroscopic grade SP-1 natural graphite flakes oxidized previously to four levels of burn-off has been studied. The threshold pressure, equilibrium amounts taken up at relative pressures up to 0.95, and the diffusion coefficient for bromine uptake are little affected by graphite oxidation at all burn-off s studied (up to 46.1%). However the time after bromine exposure at the threshold pressure at which rapid bromine intercalation commences monotonically decreases with increasing burn-off. It is suggested that during this initial time period, bromine entering the graphite is essentially fully ionized, whereas bromine entering later, and rapidly, is not ionized. Oxidation affects the subsequent thermal stability of the intercalated bromine and the composition of the residue compound formed following heating to 950°C. Rates of uptake and amount of bromine intercalated subsequently on the residue compounds are dependent upon their Br C ratio and how the residual compounds were formed.

The intercalation of bromine in graphitized carbon fibers and its removal

When the bromine residue in graphite is heated and cooled between 20° and 900°C there is an emission of Br 2 over certain relatively small temperature ranges on both heating and cooling. It is shown that two of these emissions are associated with observed decreases in X-ray diffraction spacing between carbon layers—one on heating around 175°C and one on cooling around 100°C. The intercalation isotherms of Br 2 and of ICl on graphitized carbon fibers show that the threshold pressure on the residue is lower than on the original fiber. This is believed to be caused in fibers by the production of microscopic cracks in the interlocking amorphous carbon networks between the graphitized domains during the initial intercalation. Hence, when again exposed to Br 2 the compresssion-tension builds to a lower value so that the threshold pressure is lower and the rate of intercalation is higher. The anomalous bromine emission behavior in fiber is attributed to differential dimensional changes of the isotropic carbon network and the anisotropic crystallites. In natural graphites the anomalous emission originates in a differential dimensional change between the polycrystalline structure of the total sample of graphite and the anisotropic single crystal components of the graphite.

Influence of graphite structure on rates of intercalation

Rates of intercalation of bromine and of nitric acid are remarkably sensitive to the structure and preferred orientation of the graphite employed. Apparent diffusion coefficients, Dapp, for nitration of a series of cylindrical pyrographites, graphite foils, and graphitic carbon fibers, differ by a factor exceeding 1000, and diffusion coefficients for bromination of the same series of graphites differ by a factor of 20. The largest diffusion coefficients are obtained during intercalation of graphite foils and highly-oriented pyrolytic graphite. These large variations are attributable, in part, to difference in diffusion path lengths associated with orientation of graphite basal planes with respect to the diffusion axis. When diffusion coefficients are corrected for preferred orientation, D corr for nitration of pyrographites exceed those for nitration of graphitic carbon fibers by a factor of 20, but D corr for bromination of graphitic carbon fibers exceeds that for bromination of pyrographites by a factor of 5. The duration of the initial “induction period” which preceeds diffusion of intercalant increases as D app increases and as the mean strain of graphite crystallites increases. The duration of the induction period is not related to the degree of orientation or to the basal plane stack height L c, of graphite. The amount of intercalant absorbed during the induction period depends upon the structure of the graphite and upon the intercalant chosen.

116. A. Magnetic and gravimetric study of the kinetics of the first intercalation of bromine into a pyrocarbon

116. A. Magnetic and gravimetric study of the kinetics of the first intercalation of bromine into a pyrocarbon