Effect Of Fluorine Content Research Articles

Effect of fluorine content in layered double hydroxide catalyzing oxygen evolution

Layered double hydroxides (LDHs) have been extensively studied in OER owing to their unique advantages. The mechanism of the effect of NH4F, a common and essential structural guide in the synthesis of LDH, on LDH is relatively ambiguous. Therefore, the solvothermal process synthesized a series of FeCoNi LDHs with different fluorine contents. Physical and chemical characterizations show that the fluorine content regulates the synthesis process, morphology, and electronic structure of the catalysts. The optimal catalyst required 196 mV overpotential to reach 10 mA cm-2, with a Tafel slope of 22 mV dec-1, and stable operation at a current density of 100 mA cm-2 for more than 120 h. XPS analysis demonstrated that the F- ions leached gradually during the OER reaction, promoting the formation of high-valent intermediates at the Co active site to enhance the catalyst activity. This work contributes to the subsequent study of LDH modification and NH4F.

Synthesis and characterization of low dielectric constant polybenzoxazines with different fluorine contents

AbstractThe rapid development of integrated circuits puts forward higher requirements for low dielectric constant polymers. In this study, two fluorinated benzoxazine monomers, bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isopropane (BA‐ftfa) and bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isoperfluoropropane (BAF‐ftfa), were successfully synthesized. Differential scanning calorimeter (DSC) was used to monitor the thermal curing behaviors of the monomers and their mixtures. Five groups of polybenzoxazine samples with different fluorine content (25% ~ 35%) were obtained by copolymerizing the two monomers with different mass ratios. The effects of fluorine content on dielectric properties were investigated and the results show that PBAF‐ftfa with the highest fluorine content has the lowest dielectric constant of 2.53 at 1 MHz. Furthermore, the results of thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) show that all polymers possess excellent thermal stability and exhibit high glass transition temperatures over than 180°C.

Fluorinated polyimide with triphenyl pyridine structure for 5G communications: Low dielectric, highly hydrophobic, and highly transparent

With the rapid development of 5G communications, the traditional interlayer dielectric material polyimide (PI) requires modification due to its intrinsically high dielectric constant (Dk), high dielectric loss (Df), and high moisture absorption, which make it difficult to meet the needs of the high-frequency communications industry. In this paper, a new strategy for the preparation of novel PI with intrinsically low Dk and Df is proposed from the perspective of molecular structure design, the modification effect of superimposing bulky triphenyl pyridine structures and strong electronegativity groups, combined with long-chain anhydride to reduce the density of the imide structure. Therefore, three bulk diamine monomers (BPAB, PBAB3F, PBAB6F) containing triphenyl pyridine structures were designed in this paper and polymerized with 4,4′-(4,4′-isopropyldiphenoxy) phthalic anhydride (BPADA) to obtain three new PIs (PI-H, PI-CF3, PI-2CF3) with different fluorine contents, focusing on the relationship between structure and properties, especially the effect of fluorine content on dielectric properties. The results of the study show that the dielectric and hygroscopic properties of PI improve with increasing fluorine content. Among them, PI-2CF3 has the best overall performance, showing low dielectric (Dk = 2.72@10 GHz & Df = 0.00233@10 GHz), high transparency (Cut-off wavelength (λ0) = 389 nm, Maximum transmittance (Tvia) = 89%) and low hygroscopicity (Water absorption (Ma) = 0.246%, Contact angle (Ca) = 111°).

Influence of fluorine content on crystallization and mechanical properties of SiO2–Li2O glass-ceramics

The effect of fluorine content on the crystallization, microstructure and mechanical properties of SiO2–Li2O glass-ceramics was investigated. Four parent glass samples with different fluorine content were prepared by melt quenching method. The glass-ceramic samples are obtained by heat treatment including nucleation and crystallization process. It was found that lithium disilicate (Li2Si2O5) is the main phase crystallizing in the course of heat treatment, while lithium metasilicate (Li2SiO3), petalite (LiAlSi4O10), and fluorapatite (Ca5(PO4)3F) appear in some of the samples as minor phases. The addition of fluorine increases the crystallinity and promotes the formation of Li2Si2O5 and Ca5(PO4)3F crystals, and thereby regulates the microstructure and mechanical properties. A proper amount of fluorine significantly enhanced mechanical properties. The SiO2–Li2O glass-ceramic sample with 0.5 mol% fluorine content has the highest Vickers hardness HV value of 6.64 GPa and highest fracture toughness KIC value of 0.932 MPa m1/2 after crystallization process at 670 °C for 8 h. The SiO2–Li2O glass-ceramic sample with 1.0 mol% fluorine content has the highest Young’s moduli E value of 102.1 GPa after crystallization process at 670 °C for 8 h.

Effect of Fluorine Concentration on Structural, Electrical and Optical Properties of SnO2:F Thin Films Orepared by Spray Pyrolysis Technique

Fluorine doped tin oxide, SnO2: F (FTO) thin films deposited on glass substrates at 405±2˚C have been prepared using Spray Pyrolysis Technique. Structural, electrical and optical properties of FTO thin films under different doping concentration (5, 15, 20, 25 and 30) wt% are investigated using XRD patterns, Hall effect measurement and UV–Vis spectrophotometry. X-ray diffraction studies of FTO films indicate that all films are polycrystalline with tetragonal structure. The lattice constants a and c vary from (4.7269 to 4.7557)Å and (3.2548 to3.2103) Å respectively. While the crystallite size D varies from 8.07 to 7.85 nm. Electrical measurements showed that all the films are of n-type conductivity. Carriers mobility (μ), concentration of carrier (n) and resistivity (ρ) reached 6.05 cm2/Vs, 5.62x1019cm-3 and 8.79x10-2 Ω cm, respectively. The energy gap decrease from 3.9 to 3.78 eV with increase fluorine concentration from (5-30) wt% respectively. FTO films can be used as conducting layers(Electrodes) in photovoltaic devices.

Fluorine patterning of graphene: effects of fluorine content and temperature.

In this paper we present a successful approach for the generation of partially fluorinated graphene structures. A computationally simple model optimized on a large density functional theory dataset quickly and precisely predicts experimentally observed structures. From the analysis of the structural diversity of fluorinated graphene in a wide range of synthesis temperatures, the general structural patterns are identified and the conditions for their achievement are determined. In addition, to facilitate further studies of fluorinated graphene, we present a ready-to-use GenCF code that implements the described structure generator.

Effect of fluorine doping concentration on efficiency of ZnO/p-Si heterojunction solar cells fabricated by spray pyrolysis

The paper reports the fabrication of fluorine-doped zinc oxide/p- silicon (ZnO/p-Si) heterojunction solar cells and the effects of fluorine content on efficiency of these solar cells. Fluorine-doped zinc oxide nanoparticles (FZO) were synthesized using sol–gel method and heterojunctions of n-FZO/p-Si solar cells were fabricated by the spray pyrolysis technique. FZO thin films were also deposited on the glass substrate under the same conditions for the investigation of their optical properties. The structural characterizations of FZO films were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Optical characterization of these thin films was studied by UV–Vis spectroscopy and transmittance values of over 84% were obtained at the visible region. The current–voltage characteristic of the n-FZO/p-Si heterojunction solar cells was measured at room temperature in the dark and under illumination (90 mW/cm2). Series resistance (Rs) values obtained from solar cells were found between 5.52 and 10.12 Ω. The conversion efficiency of the fabricated solar cell of between 3.82 and 6.74% was obtained.

Enhanced electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode by reducing lithium residue with low-temperature fluorination treatment

LiNi0.8Co0.15Al0.05O2 is considered as a representative layer-structured cathode material. Decreasing residual lithium (LiOH and Li2CO3) on its surface is the main challenge to improve cycling performance for commercial application. In this study, a dry and low-temperature fluorination (350 °C) method was proposed to modify LiNi0.8Co0.15Al0.05O2 cathode. The effects of fluorine content on the microstructure, surface composition and electrochemical properties of the cathode were extensively studied. The results showed that fluorination had multi-functions: (i) decreasing the lithium residues and generating amorphous LiF coating layer on the particle surface, (ii) restraining the diffusion of metal ions conveyed in the electrolyte, particularly at high temperature, (iii) retarding the increase of charge transfer impedance, and (iv) maintaining the structural stability of electrode during extended cycles. Electrochemical test results indicated that the sample fluorinated with 1.0 mol% F exhibited excellent cycling performance with the capacity retention of 93.9% after 100 cycles at 1 C, showing dramatical improvement compared with that of the pristine cathode (86.2%). This designed low-temperature dry fluorination process is expected to be practically applicable in other nickel-rich cathodes.

Fabrication of spray derived nanostructured n-ZnO/p-Si heterojunction diode and investigation of its response to dark and light

Abstract Fluorine doped ZnO thin films were grown by chemical spray pyrolysis technique of zinc acetate and ammonium fluoride, and the effect of fluorine content on structural, optical and electrical properties were evaluated. The structural, morphological, optical properties of ZnO films were investigated by XRD (X-ray diffraction), AFM (Atomic force microscopy), SEM (Scanning electron microscop) and UV–Vis spectroscopy, respectively. According to results, it was observed that all films had polycrystalline texture with hexagonal wurtzite crystal structure and film surface were made up of nano-scale grains, varied by fluorine content. Optical properties showed that optical band gap energy of ZnO changed from 3.28 to 3.24 eV with F content. Shrinkage effect was assessed as the cause in the variation of optical band gap values. Finally, current-voltage (I-V) analysis was performed in Au/ZnO:F/p-Si device in dark and light conditions and certain diode parameters such as ideality factor, barrier height and series resistance were calculated and discussed in detail.

Cr3+ and F− co-doped lithium manganese oxide cathode for medium-temperature reserve primary cell

Medium-temperature molten salt reserve primary cell utilizes low-melting nitrate electrolyte, that is considered suitable for geothermal borehole as well as oil and gas exploration. In this work, Cr3+ and F− ions were introduced into spinel lithium manganate oxides by high-temperature solid-state method and verified by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of fluorine content on the morphology and discharge performance of the LiCr0.1Mn1.9O4−xFx (0 ≤ x ≤ 0.5) have been studied in LiCr0.1Mn1.9O4−xFx/LiNO3-KNO3-Ca(NO3)2/Li-Mg-B system. Fluoride-doped samples have a significant improvement in discharge performance at the condition of 10 mA·cm−2 and 250 °C because of the stabilization of the crystal structure. Factors of operating temperature and current density have a significant effect on battery discharge performance, and the surroundings of 10 mA·cm−2 and 200–250 °C contributes the battery to achieve high performance. That indicates the LiCr0.1Mn1.9O4−xFx/LiNO3-KNO3-Ca(NO3)2/Li-Mg-B battery shows great potential in geothermal borehole as well as oil and gas exploration environment.

Improving the Degradation Resistance and Surface Biomineralization Ability of Calcium Phosphate Coatings on a Biodegradable Magnesium Alloy via a Sol-Gel Spin Coating Method

Bioactive calcium phosphate (CaP) coatings have been applied on biodegradable magnesium (Mg) and its alloys to provide a suitable degradation rate for orthopedic applications. However, the porous CaP coatings formed in the aqueous solution owns poor degradation resistance and thus short in vivo valid life. This paper reports a sol-gel spin coating method to prepare hydroxyapatite (HA, Ca10(PO4)6(OH)2) and fluorine doping HA sealing coatings on a porous CaP coating. The effects of fluorine content on the degradation and biomineralization behaviors of the composite coatings were studied. It reveals that the homogeneous and stable sol-gel coating, especially the fluorapatite coating could significantly improve the degradation resistance and surface biomineralization ability of the porous CaP coating on the Mg alloy.

Surface and mechanical properties of waterborne polyurethane films reinforced by hydroxyl-terminated poly(fluoroalkyl methacrylates)

Novel waterborne fluorinated polyurethane (WFPU) based on hydroxyl-terminated poly(fluoroalkyl methacrylates) (HTPFMA) was prepared successfully. The microstructures and micro-phase separation of WFPU were evaluated through infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic mechanical analysis (DMA), and scanning electron microscope (SEM). FT-IR revealed that the H-bonded carbonyl in hard domains increased with the increasing of fluorine content, resulting in enhancing the extent of micro-phase separation between hard and soft segments. XRD results indicated that the crystallinity of hard segment was enhanced with the increasing of fluorine content. The direct visual microstructures by SEM showed that the micro-phase separation was more significant when the fluorine content increased. DMA also revealed strengthened micro-phase separation with increasing fluorine content. The studies of mechanical properties confirmed that WFPU based on HTPFMA had outstanding mechanical properties. The effects of fluorine content on the static contact angles, surface free energy, and surface composition were also studied. The static contact angles of the WFPU films against water and methylene iodide reached around 108° and 84°, respectively. X-ray photoelectron spectroscopy (XPS) confirmed that the fluorine surface enrichment factor in the outermost 10 nm depth was about 10–18 fold higher than its bulk level.

Influence of fluorine doping on the microstructure, optical and electrical properties of SnO2 nanoparticles

Tin dioxide (SnO2) is one of the most promising functional semiconductor materials; it has stimulated considerable research interest for its wide applications such as optoelectronic devices and solar cells technology. Undoped and fluorine doped tin oxide aerogel nanoparticles have been successfully synthesized by sol–gel route and dryed under supercritical conditions of ethanol. The effect of fluorine concentration on SnO2 nanoparticles properties was systematically investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, UV–Vis–IR spectroscopy and impedance spectroscopy. Characterization data showed that both pure SnO2 and FTO aerogels have a polycrystalline tetragonal rutile structure with a highly (110) plane preferred orientation. The grain sizes in the range of 11–25 nm were obtained depending on the elaboration conditions. Raman spectra show the fundamental peaks at 477, 632, and 782 cm−1, corresponding to the Eg, A1g, and B2g vibration modes, respectively, in good agreement with those for the rutile bulk SnO2. The optical band gap value of tin oxide decreases from 3.88 to 3.44 eV with the increase of fluorine content. Impedance spectroscopy results indicate that the electrical properties are strongly dependent on temperature and doping rate. These results show the strong correlation between the structural, morphological, optical and electrical properties of the samples depending on doping content which was well reflected on the quality of the nanoparticles.

Effect of fluorine (an anionic dopant) on transparent conducting properties of Sb (a cationic) doped ZnO thin films deposited using a simplified spray technique

By adding fluorine, an anionic co-dopant with antimony, a cationic dopant, Sb+F doped ZnO films are prepared using a simplified spray technique and the effect of fluorine concentration (0, 5, 10 and 15 at.%) on electrical, optical, structural and surface morphological properties are studied. The results show that the resistivity of ZnO:Sb:F film decreases gradually with the increase in F doping level, reaches a minimum value of 7.27ÿ10⿿3Ωcm at 10 at.% and starts increasing thereafter. The possible mechanisms for this variation in resistivity are addressed. The optical transmittance slightly improves due to F doping. The surface morphological studies reveal that the shape and size of the grains are affected remarkably by Sb doping but not affected appreciably by the additional F doping. The XRD, XPS and EDAX analyses confirm the formation of hexagonal wurtzite ZnO structure and the presence of the expected elements in the final product.

Development of transparent conductive indium and fluorine co-doped ZnO thin films: Effect of F concentration and post-annealing temperature

In the present work ZnO, In doped ZnO and In-F co-doped ZnO (IFZO) films were synthesized on heated glass substrates (350°C) by the chemical spray technique. The effect of fluorine concentration on the structural, morphological, optical and electrical properties was studied. It was observed from X-ray diffraction (XRD) that the films have a polycrystalline structure and the intensity of the peaks depend on the doping and co-doping concentration. No diffraction peak related to dopants in XRD patterns along with shift in peaks angles to ZnO proved that In and F ions were doped into ZnO thin films. The Raman spectra confirm the hexagonal structure of the as-deposited films, and demonstrated an enhancement of the surface phonon mode of doped and co-doped films as compared to undoped films. The as-deposited films showed an average transmittance above 70%, in the wavelength range of 400–800nm. A minimum electrical resistivity, in the order of 5.2×10−2Ωcm was obtained for the IFZO thin film with 5at.% F doping. Moreover, the electrical properties of doped and co-doped films were enhanced after post-deposition annealing. It was found that post-annealed thin films at 350°C showed a decrease of one order of magnitude of the resistivity values. Such a transparent and conducting thin film can be suitable for optical and electrical applications owing to their low resistivity combined with high transmittance in the visible range.

Effect of Fluorine Content in Thienothiophene-Benzodithiophene Copolymers on the Morphology and Performance of Polymer Solar Cells

A new family of polythienothiophene-co-benzodithiophene copolymers with different amounts of fluorine decoration (PBFx) had been successfully synthesized. Detailed structure–property investigations covering physical properties, morphology, and solar cell performance with respect to the fluorine content in the polymers were performed by a series of structural characterization techniques. A PCE of 8.75% was obtained with the highest fluorinated polymer; the morphological trends, as well as the crystalline structure, were also investigated, shedding light on this important material modification.

Synthesis and performance of fluorine substituted Li1.05(Ni0.5Mn0.5)0.95O2−xFx cathode materials modified by surface coating with FePO4

Abstract The F-doped layered cathode materials Li 1.05 (Ni 0.5 Mn 0.5 ) 0.95 O 2− x F x (0 ≤ x ≤ 0.1) with ball-like shape were successfully synthesized by carbonate co-precipitation method, followed by a high temperature calcination process. The effects of fluorine content on the crystal structure, morphology and electrochemical performance were extensively investigated. The XRD results reveal that all the materials synthesized have typical hexagonal structure without impurity. Fluorine-doped materials could have improved cycling performance compared with Li 1.05 (Ni 0.5 Mn 0.5 ) 0.95 O 2 , and Li 1.05 (Ni 0.5 Mn 0.5 ) 0.95 O 1.95 F 0.05 shows the best electrochemical property. In addition, 3 wt% FePO 4 -coated Li 1.05 (Ni 0.5 Mn 0.5 ) 0.95 O 1.95 F 0.05 has significantly improved rate capability and better thermal stability compared with pristine sample. Electrochemical impedance spectroscopy (EIS) measurements reveal that both fluorine substitution and FePO 4 coating could suppress the increase of charge transfer resistance with cycling. Overall, the combination of fluorine doping and FePO 4 coating was effective in improving both cycling performance and rate capability of Li 1.05 (Ni 0.5 Mn 0.5 ) 0.95 O 2 .

Improved electrochemical performance of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material by fluorine incorporation

High capacity cathode materials Li[Li0.2Mn0.54Ni0.13Co0.13]O2−xFx (x=0, 0.05 and 0.10) have been synthesized by a sol–gel method using NH4F as F source. The effects of fluorine content on the structure, morphology and electrochemical performance of the Li[Li0.2Mn0.54Ni0.13Co0.13]O2−xFx have been extensively studied. With fluorine doping, cycling stability of Li[Li0.2Mn0.54Ni0.13Co0.13]O2−xFx is significantly improved because of the stabilization of the host structure. Li[Li0.2Mn0.54Ni0.13Co0.13]O1.95F0.05 shows a capacity retention of 88.1% after 50 cycles at 0.2C at room temperature, much higher than that of 72.4% for pristine one. The improvement mechanism of fluorine doping has been investigated by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The results demonstrate that fluorine incorporation stabilizes the electrode/electrolyte interface by suppressing the formation of poorly conducting LiF in the SEI layer and thus maintains stable interfacial resistances. As compared to the enhanced material structure, the stabilized electrode/electrolyte interface is the primary factor contributing to the improved electrochemical performance. In addition, the thermal stability of fully delithiated electrode is also greatly improved by fluorine doping.

The Effect of the Two-Step Sintering Process on Consolidation of Fluoridated Hydroxyapatite and its Mechanical Properties and Bioactivity

The aim of this work was to evaluate the effect of the two-step sintering process on consolidation of fluoridated hydroxyapatite (FHA). In addition, the effect of fluorine content on sinterability, mechanical properties, and bioactivity of FHA bulks was studied. Nanostructured FHA bulks were obtained under the conditions of 1000 and 900°C for the initial and secondary temperatures, respectively, without any structural decomposition. In addition, by increasing the fluorine content, the sinterability of FHA bulks was decreased and the hardness of FHA bulks was improved. Moreover, FHA bulks showed acceptable bioactivity.

The enhanced electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials by low temperature fluorine substitution

Layered oxy-fluoride LiNi0.6Co0.2Mn0.2O2−zFz (0≤z≤0.06) cathode materials have been synthesized by a low temperature (450°C) fluorination with NH4F of the corresponding LiNi0.6Co0.2Mn0.2O2 oxides that were synthesized by hydroxide co-precipitation method. The effect of fluorine content on the structure and electrochemical performance of the LiNi0.6Co0.2Mn0.2O2−zFz has been extensively studied. The XRD results reveal that LiNi0.6Co0.2Mn0.2O2−zFz (0≤z≤0.06) has typical hexagonal structure without impurity. The composition analysis and XPS verify fluorine incorporation in the particle. The electrochemical results indicate that the initial discharge capacity slightly decreases with increasing the content of fluorine. However, cycling performance and rate capability are improved by the fluorine substitution. In addition, after stored at 90°C for 5h in fully charged state, fluorine substituted materials exhibit better cycling performance than pristine materials. Electrochemical impedance spectroscopy shows that fluorine substitution can reduce the charge transfer resistance. Overall, fluorine substitution has a positive effect on the electrochemical performance of layered LiNi0.6Co0.2Mn0.2O2.