Fluorinated Carbon Materials Research Articles

Fluorinated Hollow Porous Carbon Spheres as High-Performance Cathode Material for Primary Battery

Fluorinated carbon cathode materials have extremely high theoretical specific energy among known cathode materials of lithium primary batteries. Nevertheless, current fluorinated carbon cannot meet the performance demands of future applications due to the rate performance. This work innovatively applies hollow carbon spheres with a porous structure as carbon sources to prepare fluorinated hollow porous carbon spheres (FHPCS) with high energy density and power density. The porous structure provides more reaction sites for the fluorination process and also shortens the diffusion path of lithium ions during the discharge. Additionally, the hollow porous structure offers more interfacial contact areas and reduces volumetric expansion during discharge reactions. The Li/CFx primary battery has a maximum specific energy of 2007 Wh kg−1 and a maximum power density of 30,400 W kg−1 and can have a capacity retention rate of 80.8% at a current density of 16 A g−1. In addition, FHPCS also has the highest specific energy of 1999 Wh kg−1 and 1711 Wh kg−1 in Na/CFx and K/CFx primary batteries, respectively. The diffusion efficiency of an alkali metal ion is analyzed by the different discharge depths with electrochemical impedance spectroscopy and galvanostatic intermittent titration technique. This effort introduces a new high-performance fluorinated carbon featuring a hollow porous structure and puts forward an innovative approach to designing fluorinated carbon materials.

Direct Synthesis of Fluorinated Carbon Materials via a Solid‐State Mechanochemical Reaction Between Graphite and PTFE

AbstractFluorinated carbon materials (FCMs) have received significant attention, because of their exceptional stability, which is associated with the strong C‐F bonding, the strongest among carbon single bonds. However, the fluorination of carbon materials requires extremely toxic and moisture‐sensitive reagents, which makes it inapplicable for practical uses. Here, a straightforward and relatively safe method are reported for the scalable synthesis of FCMs, by mechanochemical depolymerization of polytetrafluoroethylene (PTFE) and fragmentation of graphite. The resultant FCMs are evaluated as anode materials for lithium‐ion batteries (LIBs). An optimized FCM delivered capacities as high as 951.6 and 329.3 mAh g −1 at 0.05 and 10 A g −1, respectively. It also demonstrated capacity retention as high as 76.6% even after 1000 cycles at 2.0 A g −1.

Fluorinated Carbon Materials and the Applications in Energy Storage Systems

Fluorinated Carbon Materials and the Applications in Energy Storage Systems

Rational Construction of Fluorescence Turn-Off Fluorinated Carbon Fiber/Ag Composites and Their Anticancer and Antibacterial Activities.

Although fluorinated carbon fiber/Ag composites possess unique structure and special charge distribution and exhibit great potential in numerous fields, their synthesis has long been a headache because of inert chemistry bonds, low surface energy, and easy aggregation. Herein, we first demonstrate a fresh concept of constructing the nanoscale hydrosoluble fluorinated carbon fiber oxide (FCO)/Ag composite and then integrate it as a highly effective targeting nanocarrier and photothermal therapy and antibacterial agent. Chemical introduction of oxygen allows us to controllably deposit Ag nanoparticles (AgNPs) for the first time and further facilitates surface modification with folic acid prelinked bovine serum albumin to induce targeted endocytosis toward tumor cells. The structure adjustment of FCO into nanosize and the decoration of AgNPs endow the composite with much better photothermal property than fluorinated carbon materials, and FCO/Ag also serves as an effective fluorescence quencher for doxorubicin, realizing visual monitor of drug adsorption processes by "turn-off" fluorescence. Meanwhile, both in vitro and in vivo results reveal greatly improved cancer therapeutic effects than single therapy. What is more is that the synergistic interactions of lipophilic fluorine and AgNPs also ensure highly effective antibacterial activity. Our study integrates FCO/Ag as an emerging drug carrier that exhibits excellent targeted efficiency and high photothemal property and reports its unprecedented experimental example in both antibacterial- and anticancer-combined chemo-photothermal therapy.

A brief review for fluorinated carbon: synthesis, properties and applications

AbstractFluorinated carbon (CFx), a thriving member of the carbonaceous derivative, possesses various excellent properties of chemically stable, tunable bandgap, good thermal conductivity and stability, and super-hydrophobic due to its unique structures and polar C-F bonding. Herein, we present a brief review of the recent development of fluorinated carbon materials in terms of structures, properties and preparation techniques. Meanwhile, the applications in energy conversions and storage devices, biomedicines, gas sensors, electronic devices, and microwave absorption devices are also presented. The fluorinated carbon contains various types of C-F bonds including ionic, semi-ionic and covalent C-F, C-F2, C-F3 bonds with tunable F/C ratios. The controllable designing of C-F bonding and F/C ratios play a key role to optimize the properties of fluorinated carbon materials. Until now, the potential issues and future opportunities of fluorinated carbon are proposed. The present review will provide a direction for tuning C-F bonding and F/C ratios, developing a safe and efficient fluorination method and popularizing the applications of fluorinated carbon materials.

New Fluorinated Carbon Materials for Binder-Free Ultra-High Capacity Cathodic Materials

Low capacity of current cathodic materials is a bottle-neck for the next generation electrochemical energy storage devices. LiMO2, LiMPO4, and mixed metal oxide lithium salts are commonly used in current lithium batteries. The heavy nature of these transition metal elements limits their capacity below 300 mAh/g. Fluorinated carbon materials are mainly used in primary lithium batteries since the 1970s. It is a high capacity cathodic material that surfers low conductivity and slow electron transfer kinetics. The preparation method, high temperature reaction between graphite and fluorine gas, also possesses significant safety threat for the production of current carbon fluoride materials. To solve the low conductivity and low discharge rate problem for carbon fluoride based cathodic materials, we designed a new type of fluorinated carbon materials that integrate conducting polymers, electron-transfer catalysts, and energy storage units, yet still have the similar composition of carbon fluoride to maintain the high specific capacity. Thus, this materials does not require additional mechanical binder and conducting materials for the cathode. The materials were characterized by electrochemical, spectroscopic, and scanning electron microscopic (SEM) methods. Electrochemical experiments were done in an Argon filled glovebox with residual O2 level less than 1 ppm. Three electrode systems were used for the characterization of this carbon fluoride cathodic materials on glassy carbon (GC) and aluminium electrodes in both 1,2-difluorobenzene (DFB)/TBAPF6 and propylene carbonate (PC)/LiPF6solution. Figure 1 shows galvanostatic discharge curve of the new carbon fluoride materials on GC WE in PC/1.0 M LIPF6 with two pieces of Li foil as CE and RE respectively at C/8 rate. The discharge result shows that this new cathodic material possesses specific capacity of 1.03 Ah/g with average voltage of 2.1 V (vs. Li+/Li) at 0.125 C rate, giving specific energy of 2.16 Wh/g. We also observed that the galvanostatic discharge of this material does not involve an initial voltage dipping as observed with current carbon fluoride materials. Searching and optimizing the electrolyte solution for rechargeable application is currently underway in this laboratory. We hope that this presentation will shed new light to the discovery of new cathodic materials. Figure 1

Fluorine Patterning in Room-Temperature Fluorinated Graphite Determined by Solid-State NMR and DFT

Fluorination of graphite at room temperature allows producing graphite fluoride compounds with a controlled content of fluorine. Here we combine solid-state NMR spectroscopy and DFT calculations to study the structure and reveal the fluorine patterning in graphite fluorides C2Fx intercalated with acetonitrile. Two major chemical states of carbon, namely the atoms covalently bound to fluorine and the bare atoms, are detected by 13C MAS NMR irrespective of the degree of fluorination. The data indicate that although all graphene sheets were subjected to fluorination, the near-planar configuration is preserved. The interaction between host C2Fx matrix and acetonitrile molecules is of van der Waals character. Decomposition of the 19F MAS NMR spectra reveals occurrence of at least six fluorine environments in each sample. By DFT calculations distinct 19F chemical shifts are attributed to isolated, end chain, “linked” (which include midchain, cyclic, and branched) CF groups and infinite CF arrays. The assignment is confirmed by 19F RFDR, which is sensitive to dipolar coupling. Analyzing the data for C2Fx samples with different degrees of fluorination x, an evolution of the fluorine pattern is proposed. The reported calculated 19F NMR shielding parameters provide classification criteria for assignment of 19F NMR chemical shifts in fluorinated carbon materials.

Measures against global warming and assessments of environmental impact for fluorinated carbon materials

Global warming countermeasures have been evaluated using the global warming potential (GWP). However, since GWP shows only one aspect of global warming, the alternative indicator, carbon dioxide equivalent warming number (CEWN), which is based on the removal rate of each greenhouse gas from the atmosphere, is explained here. The latest CEWN values are shown, and the life cycle climate performance results of car air-conditioning, recovery and recycling of R-22 refrigerant and semiconductor cleaning process, where fluorinated carbon compounds are used, are evaluated with those CEWN values. The results reveal that fluorinated carbon compounds are beneficial in coping with global warming. In addition, carbon resources are also evaluated with new concept, and consequently it is shown that fluorinated carbon compounds are beneficial in conserving carbon resources.

Measures against global warming and assessments of environmental impact for fluorinated carbon materials

Global warming countermeasures have been evaluated using the global warming potential (GWP). However, since GWP shows only one aspect of global warming, the alternative indicator, carbon dioxide equivalent warming number (CEWN), which is based on the removal rate of each greenhouse gas from the atmosphere, is explained here. The latest CEWN values are shown, and the life cycle climate performance results of car air-conditioning, recovery and recycling of R-22 refrigerant and semiconductor cleaning process, where fluorinated carbon compounds are used, are evaluated with those CEWN values. The results reveal that fluorinated carbon compounds are beneficial in coping with global warming. In addition, carbon resources are also evaluated with new concept, and consequently it is shown that fluorinated carbon compounds are beneficial in conserving carbon resources.

Fluorinated nanocarbons using fluorinating agent: Strategies of fluorination and applications

The fluorination method strongly influences the physical properties of the resulting fluorinated carbon materials. Two fluorination ways, direct fluorination under pure fluorine gas and controlled fluorination by the decomposition of TbF4, have been used for the fluorination of particular nanocarbons: carbon nanofibers and a mixture of carbon nanodiscs and nanocones. Then, fluorocarbon matrix structures have been determined owing to solid state 19F NMR for MAS conditions at a spinning speed of 30 kHz. It reveals that the fluorination mechanism depends on the fluorination conditions but not on the starting nanocarbons morphology, i.e. tubular or planar. Finally, the electrochemical properties of carbon nanofibers fluorinated by the two ways are detailed. Controlled fluorination allows an increase of the power densities of fluorinated carbon nanofibers used as electrode in primary lithium batteries.

Fabrication of electrochemically stable fluorinated nano-carbon film compared with other fluorinated carbon materials

We fabricated electrochemically stable fluorinated nano-carbon film that had an sp 2 and sp 3 hybrid nanocrystalline structure formed using the electron cyclotron resonance (ECR) sputtering method. This fluorinated ECR (F-ECR) nano-carbon film prepared with a short CF 4 plasma treatment has a high fluorine content (F/C:0.20) and a low oxygen content (O/C:0.02) on its surface and retains its original morphology. This F-ECR nano-carbon is capable of a lower capacitance current, and a wider potential window than untreated ECR nano-carbon. The electron transfer rates at an F-ECR electrode are as high as those of untreated carbons for Ru ( NH 3 ) 6 2 + / 3 + , whereas they are much slower than those of untreated ECR nano-carbon for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - owing to its selective sp 2 fluorination. These slow electron transfer rates for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - are maintained during potential cycles due to its robust nanocrystalline structure. In contrast, these slow electron transfer rates were easily recovered for fluorinated glassy carbon under same condition. Furthermore, a smaller fluorination effect was observed for polycrystalline boron-doped diamond owing to the low reactivity of its sp 3 bonds. Our ECR nano-carbon film is suitable for the effective fabrication of a fluorinated surface while maintaining a relatively active electrochemical interface and excellent stability.

Thermodynamics of Lithium Intercalation into Fluorinated Carbon Materials

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Syntheses and Properties of Fluorinated Carbon Materials

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Heteronuclear dipolar recoupling using Hartmann–Hahn cross polarization: A probe for 19F– 13C distance determination of fluorinated carbon materials

A NMR determination of the C–F bond length in fluorinated carbon materials using dipolar recoupling is described. To this end Hartmann–Hahn cross polarization with magic angle spinning (inverse cross polarization sequence) is used. A description of the corresponding 13C magnetization evolution as a function of the evolution time and its simulation for typical fluorinated samples are realized. The procedure is applied to 15 different materials having different bonding (semi-covalent or covalent) and from various carbon allotropic varieties. The distance evolves from 0.138 ± 0.002 nm for covalent bonding to 0.1445 ± 0.002 nm for semi-covalent bonding. Other parameters may affect the C–F bond length e.g. steric hindrance which leads for fluorinated fullerenes to an increase of this distance up to 0.146 ± 0.002 nm .

Electrochemical applications of fluorinated carbon materials

Electrochemical applications of fluorinated carbon materials

Property control of carbon materials by fluorination

Fluorination is one of the most effective chemical methods to modify and control physicochemical properties of carbon materials. The method is rather straightforward, but the interpretation of the results are not necessarily facile. The complication lies in the diversity of carbon materials and the wide-range C–F bond nature. This conversely gives an opportunity to control properties of carbon materials in a wide range, either gradually or drastically. In this review, recent topics in the field of fluorinated carbon materials are covered with an emphasis on the recent research developments in our laboratories and in Japan.

Carbon and Fluorinated Carbon Materials for Fuel Cells

ABSTRACTCarbon and fluorinated carbon materials are major constituents of phosphoric acid fuel cells and PEM fuel cells and the stability of these materials is critical for long life operation. Laboratory corrosion studies of separator plate materials were correlated with separator plate changes in commercial PAFC fuel cells. The addition of thin films of Teflon™ to the separator plates extends the life of the separator plates to 60,000+ hours through the formation of a temporary hydrophobic barrier. ESCA studies show the loss of hydrophobicity with time of PAFC electrodes to be a result of delamination of the Teflon from the carbon and not corrosion of the Teflon by phosphoric acid. The projected life of PAFC power plants has been confirmed by commercial operation of power plants for over 40,000 hours.

On the nature of CF bonds in various fluorinated carbon materials: XPS and TEM investigations

Abstract The different types of CF interactions have been evidenced from XPS investigations on fluorinated carbonaceous materials. The respective amount of the C1s and F1s components depends on several factors, including the nature of the host material, the thermal treatments which increase the graphitization level and the fluorination conditions. TEM images and corresponding Fourier transforms of high temperature-treated pitch-based and PAN-based fibres have shown that only stage-1 compounds and graphitic-type domains are detectable in the experimental conditions. In particular, no interlayer spacing corresponding to higher stage materials has been noticed. The observed results can be correlated to the ratio of semi-ionic to covalent FC bonding determined by XPS.

Chemical properties of new fluorinated carbon materials from pitch

In previous work, new fluorinated carbon materials were synthesized by direct fluorination of various coal tar pitches. But there were always problems in that process because of large generation of heat. Then we try to control the reaction temperature by flow rate of F 2 and cooler set in the reactor. As a result, two types of fluorinated pitches were synthesized at different reaction temperatures, a low-temperature type (L) and a high temperature type (H). The result of elemental analysis showed that F/C ratio of the type (H) is larger than that of the type (L). The type (H) shows whiter color than the type (L). This result seems to be concerned with the amount of the residual double-bonds in the fluorinated pitch. 19FNMR spectra showed that the type (H) has more amount of −CF2 CF3 chemical shift. It is considered by the ring-opening reaction because starting pitch has few ethyl-chain. Therefore the high temperature condition seems to produce the more ring-opening reaction. Mean molecular weights by VPO measurement showed that Mw. of the type (H) is about 3,000. That value is in accordance with the estimated value by Mw. of starting pitch and F/C. On the other hand, that of the type(L) reaches about 5,000, which indicates a form of recombinations of cleaved bonds through low temperature condition and stable fluoination.