In situ X-ray diffraction study of different graphites in a propylene carbonate based electrolyte at very positive potentials

Synchrotron based in situ X-ray powder diffraction was applied for the investigation of the PF₆⁻ intercalation behaviour into graphite of different particle size and various crystallinity at very positive potentials above 5 V vs. Li/Li⁺. In a propylene carbonate based electrolyte, small particles with low crystallinity show almost no anion intercalation and the particle structure remains intact. In graphite particles with increased particle size and/or higher crystallinity PF₆⁻ intercalation up to a stage 4 phase occurs but the reversibility is poor and exfoliation of graphene layers takes place as it was proven by post-mortem scanning electron microscopy. Thus, graphites with small particles and less crystallinity are preferred as conductive additive in positive “high voltage” cathodes in terms of structural integrity.     

An in situ Raman study of the intercalation of supercapacitor-type electrolyte into microcrystalline graphite

An initial Raman study on the effects of intercalation for aprotic electrolyte-based electrochemical double-layer capacitors (EDLCs) is reported. In situ Raman microscopy is employed in the study of the electrochemical intercalation of tetraethylammonium (Et₄N⁺) and tetrafluoroborate (BF₄⁻) into and out of microcrystalline graphite. During cyclic voltammetry experiments, the insertion of Et₄N⁺ into graphite for the negative electrode occurs at an onset potential of +1.0 V versus Li/Li⁺. For the positive electrode, BF₄⁻ was shown to intercalate above +4.3 V versus Li/Li⁺. The characteristic G-band doublet peak (E_2g2(i) (1578 cm⁻¹) and E_2g2(b) (1600 cm⁻¹)) showed that various staged compounds were formed in both cases and the return of the single G-band (1578 cm⁻¹) demonstrates that intercalation was fully reversible. The disappearance of the D-band (1329 cm⁻¹) in intercalated graphite is also noted and when the intercalant is removed a more intense D-band reappears, indicating possible lattice damage. For cation intercalation, such irreversible changes of the graphite structure are confirmed by scanning electron microscopy (SEM).     

Intercalated structure of polypropylene/in situ polymerization-modified talc composites via melt compounding

Talc was modified with methyl methacrylate (MMA) or butyl acrylate (BA) via in situ polymerization. The talc/isotactic polypropylene (PP) composites with nano-sized intercalated structure were formed by melt compounding of PP with the modified talc. The results showed that the talc layers were partially delaminated, aligned along the flow direction, and uniformly dispersed in the PP matrix. The thickness of the PMMA-modified talc layers in the PP matrix was in the range 80-240 nm, while the PBA-modified talc was even thinner. PMMA or PBA macromolecules attached on the surface of talc layers hindered the crystallization of the PP component. Moreover, the aligned pristine talc layers promoted the orientation of the PP crystals. However, the extent of PP crystal orientation decreased in the presence of PMMA or PBA-modified talc.     

Electrochemical lithium insertion into anatase-type TiO2: An in situ Raman microscopy investigation

Anatase type TiO₂ has been previously largely reported as a candidate negative electrode material for lithium-ion batteries. We report here for the first time the complete in situ Raman study of lithium insertion and de-insertion into three variously nano-sized TiO₂ anatase powders (Prolabo, ca. 80 nm, AK1, ca. 15 nm and MTi5 ca. 8 nm), of which AK1 and MTi5 show superior capacity and cyclability. From these measurements realized in a galvanostatic mode between 3 and 1 V versus Li/Li⁺, the phase transition from a tetragonal to an orthorhombic structure was clearly observed to take place at different quantities of x in Li_xTiO₂. These results confirm the extension of the solid solution domain as particle size is reduced. For the smaller TiO₂ nano-sized materials (AK1 and MTi5), a more pronounced decrease in band intensity when x > 0.3 for Li_xTiO₂, was observed and may be related to the decrease in the optical skin depth linked to the conductivity increase as lithiation proceeds.     

Conventional and in situ transesterification of castor seed oil for biodiesel production

In the present study, biodiesel production from Ricinus communis L. red and BRS-149 nordestina varieties seed oil is reported. Reactions were made through conventional and in situ processes using ethanol and evaluating the addition of n-hexane as co-solvent. The content of ethyl esters was quantified by ¹H NMR. The highest conversions were obtained from crude oil (conventional reaction) after pre-esterification, using ethanol and a molar ratio of alcohol to oil of 60; furthermore, the addition of n-hexane was not significant on yield. Under these conditions, best conversion was around 95% for both varieties.     

Electroreduction of oxygen on glassy carbon electrodes modified with in situ generated anthraquinone diazonium cations

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with in situ generated diazonium cations of anthraquinone (AQ) has been studied using the rotating disk electrode (RDE) technique. The electrografting of the GC electrodes was carried out in two different media: in acetonitrile and in an aqueous acidic solution (0.5 M HCl). 1- and 2-Aminoanthraquinone were used as starting compounds for the formation of the corresponding diazonium derivatives. The anthraquinone diazonium cations were generated by reaction of the aminoanthraquinones with tert-butyl nitrite and sodium nitrite in acetonitrile and in 0.5 M HCl, respectively. For comparison purposes, the previously synthesised and crystallised diazonium tetrafluoroborates of anthraquinone were used for the GC surface modification. Cyclic voltammetry was employed to determine the surface concentration of AQ in O₂ free 0.1 M KOH. The electrocatalytic behaviour towards O₂ reduction was similar for all the AQ-modified electrodes studied. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model. The rate constant of the reaction between the semiquinone radical anion of AQ and molecular oxygen was virtually independent of the point of attachment of the quinone to the electrode surface.     

Investigation of the peel behavior of polyethylene/polybutene-1 peel films using in situ peel tests with environmental scanning electron microscopy

The micro-deformation processes of sealed low-density polyethylene/isotactic polybutene-1 (PE-LD/iPB-1) films with different contents of iPB-1 up to 20 m.-% (mass-percentage) were investigated in this study.The peel process was analyzed in detail using in situ peel test measurements with environmental scanning electron microscopy (ESEM). This method enables the direct correlation of recorded force-elongation data with observed structural phenomena. Thus, important parameters, e.g., the peel initiation value, could be determined directly from in situ measurements. The dependence of the peel properties on the iPB-1 content was analyzed and the correlation between micro-structure and performance of the peel process was clarified.Furthermore, the structural reason behind the dependence of the peel properties on the peel angle was identified. The crack propagation types interlaminar and translaminar were analyzed in detail with the ESEM. The translaminar crack propagation was further characterized using a tilted microscope stage with a mounted tensile tester.The direct contact of the electron beam with the non-conductive sample surface can cause beam damage. The beam damage, indicated by the absorbancy band at 965 cm⁻¹ in the infrared spectrum, was investigated in dependence on the total irradiation time.     

Gelation and degradation characteristics of in situ photo-crosslinked poly(l-lactide-co-ethylene oxide-co-fumarate) hydrogels

The objective of this work was to determine the gelation kinetics, extent of swelling, sol fraction, and degradation kinetics of photo-crosslinked poly(l-lactide-co-ethylene oxide-co-fumarate) (PLEOF) hydrogels, with N-vinyl-2-pyrrolidone (NVP) crosslinker, as a function of composition as well as the time and intensity of UV radiation. The gelation process was monitored by in situ rheometry. The crosslinking was shown to be facilitated by increasing NVP concentration up to a certain value above which the hydrogel shear modulus did not increase with additional amount of NVP. Increasing the hydrophobicity of PLEOF macromer resulted in a decrease in the hydrogel swelling ratio and increase in sol fraction which was due to a reduction in the apparent reactivity of the PLEOF fumarate units. The degradation characteristics of PLEOF hydrogels depended on the ratio of PLA to PEG with PLEOF 30/70 (30% lactide) having the highest degradation rate.     

A study of iodine adlayers on polycrystalline gold electrodes by in situ electrochemical Rutherford backscattering (ECRBS)

Iodine adsorption on a polycrystalline gold electrode was studied by in situ electrochemical Rutherford backscattering (ECRBS) using an ultrahigh vacuum (UHV)-electrochemical cell comprising of a thin-film silicon nitride window. The depth resolution of RBS allowed for measurement of nuclide concentration of the diffuse double-layer, electrode surface and near-surface regions. ECRBS measurements on the gold electrode, initially exposed to −500 mV vs. a platinum pseudo-reference electrode, in a potassium iodide solution, showed an increase in the 2.07 MeV iodine peak indicative of iodine adsorption. The surface concentration of the iodine adlayer was directly measured by ECRBS to be 1.3 ± 0.3 nmol/cm². ECRBS measurements on a gold electrode exposed to 1.5 V vs. a platinum pseudo-reference electrode, in a potassium iodide solution display a decrease in the 2.16 MeV gold peak and a shift to lower energies. Scanning electron microscopy images of electrodes studied by ECRBS displayed roughened surfaces consistent with gold dissolution. This work demonstrates the potential for in situ ECRBS using thin-film silicon nitride windows to become a powerful tool for the investigation of a wide range of electrochemical processes in areas such as corrosion, electrodeposition and electrocatalysis.     

Influence of stress-strain field on the dissolution process of polycrystalline nickel in H2SO4 solution: An original in situ method

Stress corrosion cracking (SCC) raises a lot of questions concerning complexity of stacked physical mechanisms. Synergy between electrochemical processes and mechanical field near the crack tip is now recognized. However, the influence of mechanical behaviour on corrosion processes is not well established and only few works dealt with this effect. Consequently, it seems to be necessary to determine the influence of the plastic strain on the surfaces reactivity in aqueous mediums. The great part of this work was devoted to the development of an electrochemical cell on a bench of mechanical test in order to carry out in situ measurements of current density. Three levels of interaction have been discussed taking into account the different expression of plastic deformation (dislocation density and distribution, slip bands emergence, stress field) in order to study the effect of mechanical state on dissolution, on passivation processes, and on stability of oxide film of polycrystalline nickel in H₂SO₄ solution.     

Influence of nanocrystallization on pitting corrosion behavior of an austenitic stainless steel by stochastic approach and in situ AFM analysis

The pitting corrosion behavior of an austenitic stainless steel nanocrystalline (NC) coating, fabricated by magnetron sputtering as well as that of the conventional polycrystalline (PC) alloy have been investigated in 3.5% NaCl solution by stochastic approach and in situ atomic force microscopy (AFM). The results indicate that the pitting corrosion resistance of the NC coating was much higher than that of the PC alloy with higher prevalence of metastable pits and lower rates of stable pit nucleation and growth. The influence of nanocrystallization on the pit initiation and pit growth processes has been discussed according to the in situ AFM observations.     

Investigation of the solidification behavior of Al2O3/YAG/YSZ ceramic in situ composite with off-eutectic composition

Directionally solidified Al₂O₃/YAG/YSZ ceramic in situ composite is an interesting candidate for the manufacture of turbine blade because of its excellent mechanical property. In the present study, two directionally solidified hypoeutectic and hypereutectic Al₂O₃/YAG/YSZ ceramic in situ composites are prepared by laser zone remelting, aiming to investigate the solidification behavior of the ternary composite with off-eutectic composition under high-temperature gradient. The results show that the composition and laser scanning rate significantly influence the solidification microstructure. The ternary in situ composite presents ultra-fine microstructure, and the eutectic interspacing is refined with the increase of the scanning rate. The Al₂O₃/YAG/YSZ hypoeutectic ceramic displays an irregular hypoeutectic network structure consisting of a primary Al₂O₃/YAG binary eutectic and fine Al₂O₃/YAG/YSZ ternary eutectic. Only at low scanning rate, homogeneous ternary eutectic-like microstructures are obtained in the hypoeutectic composition. Meanwhile, the Al₂O₃/YAG/YSZ hypereutectic ceramic shows homogeneous eutectic-like microstructure in most cases and the eutectic interspacing is finer than the ternary eutectic. Furthermore, the formation and evolution mechanism of the off-eutectic microstructure of the ternary composite are discussed.     

A study on the electro-oxidation and electropolymerization of a new OPE linear molecule by EQCM and in situ FTIR spectroelectrochemistry

A novel symmetric conjugated oligo(phenylene-ethynylene) (OPE) linear molecule (1,4-bis(4-aminophenylethynyl)benzene); BAB) was synthesized by Sonogashira cross-coupling reactions. The structure and purity of the compound were confirmed by ¹H NMR, ¹³C NMR and infrared (IR) and mass spectrometry (MS). The electrochemical oxidation process and mechanism of BAB were investigated via in situ Fourier transform infrared (FTIR) spectroelectrochemistry and electrochemical quartz crystal microbalance (EQCM). The electrochemical oxidation mechanism of BAB was proposed. The studies revealed that the BAB concentration and oxidation potential had a significant influence on the growth of the polymer film. A densely packed polymer film, which exhibited nonelectroactivity, was formed when a high monomer concentration and a high oxidation potential were used. When the electropolymerization of BAB was conducted at a lower concentration, a new pair of redox peaks appeared, and the resultant thin film had better electroactivity. The in situ FTIR studies confirmed that BAB could be electro-oxidized into radical cations and then electropolymerized via para (N-N) and/or ortho (N-C) coupling reactions to form polymers with a larger conjugated π-electron system. The surface morphology of the poly-BAB was also investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM).     

An in situ scanning tunneling microscopic study of electrodeposition of bismuth on Au(1 1 1) in a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid: Precursor adsorption and underpotential deposition

In this article, the electrodeposition of Bi on Au(1 1 1) surface in the underpotential region in BMIBF₄ ionic liquid containing BiCl₃ is studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammogram shows several cathodic and anodic peaks associated with underpotential deposition (UPD) of Bi and dissolution of the UPD deposit, respectively, in the potential region between −0.38 and −0.7 V versus Pt quasi-reference electrode. In situ STM results indicate there is a BiCl₃ precursor adsorption stage prior to the Bi UPD. The adsorption of BiCl₃ leads to the formation of unique hexagonal and trigonal supramolecular assembly with a Au(1 1 1)(10 × 10) structure. The initial stage of Bi UPD proceeds with the formation of Au(1 1 1)(7 × 7) R21.8° adlayer structure composed of Bi trigonal clusters at −0.5 V. A structural transformation occurred at −0.6 V resulting in a unique “zipper-like” double-chain pattern composed of well-aligned Bi trigonal clusters which can be denoted by Au(1 1 1)(5 × 25√3/3) structural model. The trigonal clusters composed of six Bi atoms seem to be the main characteristic elemental units of Bi UPD adlayer regardless of underpotential shift. These features are dramatically different from those observed in Bi(III)-containing acidic aqueous solutions as well as in chloroaluminated ionic liquid, but are similar to those of Sb UPD in BMIBF₄ ionic liquid, which reveals profound solvent effects on the electrodeposition of semimetals.     

NiP^O and [Cp2ZrCl2/MAO] as a versatile dual-function catalyst system for in situ polymerization of ethylene to linear low-density polyethylene (LLDPE)

[Ni(Ph₂PCHCOPh)(Ph)(PPh₃)] (NiP^O) and Cp₂ZrCl₂/methylaluminoxane (MAO), well known as ethylene oligomerization and polymerization catalysts, respectively, are combined to produce LLDPE by in situ polymerization. Melting temperature (T_m), degree of crystallinity (χ_c), intrinsic viscosity, average molecular weight and ¹³C NMR analysis of copolymers confirm the insertion of α-olefins into the polyethylene chain. Variations in α-olefin concentration and ethylene pressure during the polymerization stage lead to changes in the degree of branching. The resulting copolymers have χ_c and T_m in the 25.8–65.2% and 114–132 °C ranges, respectively. Experimental results show the versatility of the dual-function catalyst.     

Dynamic behavior of nanometer-scale amorphous intergranular film in silicon nitride by in situ high-resolution transmission electron microscopy

We report about the dynamic behavior of a nanometer-scale amorphous intergranular film (IGF) in a Si₃N₄ ceramic by an in situ heating experiment in a high-resolution transmission electron microscopy (HRTEM). During the experiment the IGF gradually vanishes at 820 °C accompanied by the formation of crystal planes within the IGF. The IGF reappears after cooling back to room temperature. The results cannot be explained within the framework of a force balance model. We argue that the dynamic behavior of the IGF in our experiment originates from the open system observed.     

Atomic force microscopy studies of surface and dimensional changes in LixCoO2 crystals during lithium de-intercalation

An in situ electrochemical atomic force microscopy (EC-AFM) cell was developed to study surface and dimensional changes of individual Li_xCoO₂ crystals during lithium de-intercalation. Discrete Li₂CO₃ particles having 50-250 nm in diameter and 5-15 nm in height were observed on the surface of stoichiometric LiCoO₂ crystals and they were shown to gradually dissolve into the LiPF₆-containing electrolyte. The dimensional change of individual Li_xCoO₂ crystals along the c_hex. axis was monitored in situ during lithium de-intercalation. Evidence of surface instability or structural instability was not found in Li_xCoO₂ single crystals upon de-intercalation to 4.2 V versus Li.     

In situ mid-IR and UV-visible spectroscopies applied to the determination of kinetic parameters in the anionic copolymerization of styrene and isoprene

In situ MIR and UV-visible spectroscopies have been combined in a set-up that has been used to monitor anionic (co)polymerizations of styrene and isoprene. This experimental set-up gives access to the simultaneous and real time concentrations of monomers and actives species during the polymerization, through optical fibers probes immersed in the reaction medium. This method allows fast, accurate and reproducible measurements of the rate constants of the (co)polymerizations investigated even if it does not resort to high vacuum. The influence of some experimental factors has been examined using this method. Among the kinetic parameters governing the (co)polymerization of styrene and isoprene initiated by sec-butyllithium, the influence of the nature of solvent was investigated. It appears that the only reaction to depend on the nature of the aromatic solvent (k_ss,toluene > k_{ss,ethylbenzene}) is the propagation step of styrene.     

In situ X-ray absorption spectroscopic study for the electrochemical delithiation of a cathode LiFe0.4Mn0.6PO4 material

The electronic and local atomic structural characterization of a promising cathode material, LiFe_0.4Mn_0.6PO₄, for a lithium rechargeable battery was performed by in situ X-ray absorption fine structure (XAFS) on both Mn and Fe K-edges. Upon delithiation, the X-ray absorption near edge structure (XANES) spectra analysis showed that the Fe²⁺/Fe³⁺ electrochemical reaction was two times faster than that of Mn²⁺/Mn³⁺. The Fe and Mn K-edge extended X-ray absorption fine structure (EXAFS) spectra were effectively altered with different spectral behaviors for the local atomic structure near Fe and Mn during delithiation. Alternatively, the EXAFS spectra of LiFePO₄ changed significantly and those of LiMnPO₄ were constant through all delithiations for the corresponding reference materials of LiFePO₄ and LiMnPO₄. The present study with XAFS characterization demonstrates that initially delithiated Fe-rich domains at 3.5 V can promote more effective local structural change of the neighboring Mn-rich domains during the next second plateau at 4.1 V, which can ease delithiation in the Mn-rich domains through more flexible reaction of the local structure in the Mn octahedra.     

In situ FTIR study of the decomposition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ionic liquid during cathodic polarization of lithium and graphite electrodes

In this work we analyzed the cathodic reactions of an important ionic liquid (IL) based electrolyte solution, namely lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/N-methyl-N-methylpyrrolidinium (BMP) TFSI. In situ FTIR spectroscopy was used for the analysis of gaseous products of the electrochemical decomposition of this IL solution during cathodic polarization of lithium metal and graphite electrodes. The main volatile product of the reductive decomposition of the anion in these BMPTFSI solutions is trifluoromethane. BMP cations decompose to mixtures of tertiary amines and hydrocarbons. The composition of the products is influenced by the nature of the anode material. Graphite possesses a catalytic activity in the electroreduction process of BMP cations which occurs along with their intercalation into the graphite structure. The liquid phase after cathodic polarization of graphite electrodes was analyzed by multinuclear NMR spectroscopy coupled with FTIR spectroscopy. ¹⁵N NMR and FTIR spectra revealed an increase in the Li cations content in the electrolyte solution, as a result of BMP cations decomposition during repeated cycling of graphite electrodes.