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The alkaline hydrogen evolution reaction (HER) on Pt-based catalysts is largely retarded by the insufficient supply of dissociated hydrogen (*H) on Pt sites. Hydrogen spillover offers a promising solution to deliver reactive *H; however, the hydrogen migration process generally suffers from thermodynamic/kinetic obstacles. Herein, we demonstrate that hydrogen spillover on binary PtNi nanowires can be thermodynamically and kinetically boosted by P-doping, resulting in a substantially improved alkaline HER. A combination of experimental and theoretical investigations suggests the dual roles of the incorporated P heteroatoms in facilitating the hydrogen spillover, involving the increased *H coverage by promoting the water dissociation and the accelerated hydrogen migration across the Pt–Ni interface to the Pt sites by lowering the kinetic barrier. Benefiting from the enhanced *H supply on the Pt sites, the P-doped PtNi nanowires exhibit impressive alkaline HER performance (η10 = 12 mV, mass activity = 5.8 A mgPt−1 at 70 mV), outperforming most other state-of-the-art HER electrocatalysts. [ABSTRACT FROM AUTHOR]

We report the first successful covalent modification of fluorographene (FG) based on Suzuki–Miyaura reaction of the C–F bond. The origin of the reaction efficiency of the C–F bond can be linked to the two-dimensional structure of FG and the synergistic effect of a phosphine ligand. This extends the application of the Suzuki reaction of the C–F bond into two-dimensional chemistry. [ABSTRACT FROM AUTHOR]

Ideal microwave absorbing materials need high impedance matching and high attenuation capacity. Towards this goal, in this paper, we present a novel lightweight and broadband electromagnetic wave absorber prepared through facile hybridization of fluorinated single-walled carbon nanotubes (SWCNTs) and pristine SWCNTs. Fluorinated SWCNTs are conveniently oriented under the action of stress due to the strong electrostatic interaction. Thus, the fluorinated SWCNT arrays with low permittivity and high impedance matching can function as a transmission channel to allow the directional propagation of electromagnetic waves. The pristine SWCNT network can guarantee high attenuation capacity for electromagnetic waves. Benefiting from the combination of high impedance matching and high attenuation ability, the hybrids exhibit enhanced microwave absorption performance with a minimal reflection loss of −65.6 dB with only 4.8 wt% loading. The hierarchical structures also endow the hybrid with multiple reflection loss peaks and thus a wide efficient absorption region (5.1 GHz, RL ＜ −10 dB) at a thickness of only 1.45 mm. Besides, the hybrids display favorable low-frequency microwave absorption properties. We believe that the idea of constructing loss area and wave-transparent area can provide a guide to the design of other lightweight and broadband microwave absorbers. [ABSTRACT FROM AUTHOR]

Herein, we report the Friedel–Crafts reaction of fluorinated graphene with aryl molecules including methylbenzene, chlorobenzene and polystyrene. The reaction achieved the high-yield arylation functionalization of graphene under mild reaction conditions and extends the range of the Friedel–Crafts reaction to the field of two-dimensional materials. [ABSTRACT FROM AUTHOR]

A novel approach to prepare crystalline silica through calcination of the composite of silica and highly fluorinated graphene at a relatively low temperature is demonstrated. Silica and its composites with graphene and its derivatives (graphene, graphene oxide and graphene with various degrees of fluorination) were synthesized and then calcined at 900 °C in an air atmosphere. The results of X-ray-diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal that cristobalite was produced through calcining composites of silica and highly fluorinated graphene under ambient air at a relatively low temperature (900 °C), while for the composites of silica and graphene and its derivatives, the calcined products are all amorphous. Thermal gravimetric analysis results indicate that the maximum decomposition temperature of functional groups in highly fluorinated graphene at air temperature is 457 °C, which is higher than that in medium fluorinated graphene, lower fluorinated graphene and graphene oxide (411.3 °C, 313.4 °C and 238.9 °C). A high degradation temperature of highly fluorinated graphene contributes to strong residual hydrogen bonding interactions at high temperature. FTIR results further illustrate that many residual hydrogen bonding interactions in composites of silica and highly fluorinated graphene at higher temperature result in enough linear structures. As a consequence, stronger residual hydrogen bonding interactions at high temperature in composites of silica and highly fluorinated graphene restrain the self-condensation of Si–OH groups and promote the formation of crystalline structures. [ABSTRACT FROM AUTHOR]

This paper presents a novel skin–core structured multiwalled carbon nanotube (MWCNTs) nanofiller to enhance the dielectric performance of epoxy resin through selective fluorination of the outer shell of the MWCNTs. The outer fluorinated shells not only guarantee good dispersibility of the fluorinated MWCNTs (F-MWCNTs) in epoxy, but also prevent the direct contact of the conductive inner tubes. As a result, the inner tubes in adjacent F-MWCNTs can form abundant microcapacitors, leading to an obvious improvement of the dielectric constant of the epoxy resin with low dielectric loss. When the filler content is 8 wt%, the dielectric constant of the F-MWCNTs/epoxy composite varies from 57 at 100 Hz to 44.9 at 1 MHz, about 11.9 times and 10.8 times that of neat epoxy resin, respectively. Simultaneously, the dielectric loss maintains low values of 0.043 at 100 Hz and 0.036 at 1 MHz, respectively. The broadband high-κ and low dielectric loss demonstrate the frequency-stable dielectric behavior of the F-MWCNTs/epoxy composites, which is attributed to the suppression of the space charge polarization induced by the grafting of the strongly electronegative element fluorine onto the outer shell. We believe that the convenient preparation process and special structure will provide a new design for fabricating broadband high-κ dielectric materials with low dielectric loss. [ABSTRACT FROM AUTHOR]

The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C–F bond, and a spin center was generated on the nanosheet and fluorine anion. Moreover, neither the SN1 nor SN2 mechanism was suggested to be appropriate for the substitution reaction of FG with a 2D structure due to the corresponding kinetics or thermodynamics disadvantage; hence, its nucleophilic substitution was proved to occur via a radical mechanism initiated by the defluorination step. The proposed substitution mechanism of FG demonstrates that nucleophilic substitution via a radical mechanism can also be applied to the attacking process of common nucleophiles without any particular conditions. Furthermore, it has been discovered that triethylamine without active hydrogen can be covalently attached to graphene nanosheets via a nucleophilic substitution reaction with FG; this further indicates a radical process for the nucleophilic substitution of FG rather than an SN1 or SN2 mechanism. The detailed process of the nucleophilic substitution reaction of FG was revealed to occur via a radical mechanism depending on the 2D structure of FG, which could also represent the typical characteristic of 2D chemistry. [ABSTRACT FROM AUTHOR]

The construction of heterostructures is always effective to achieve efficient microwave absorption (MA) properties. Herein, different from conventional hybrid techniques, a novel microwave absorber with an intrinsic heterostructure is fabricated via direct heating fluorination of SWCNTs (F-SWCNTs) utilizing F2/N2. The as-prepared inhomogeneous F-SWCNTs are confirmed to contain both fluorinated domains and aromatic domains at the nanoscale. The evolution of the fluorinated domains is closely related to the development of the C–F groups, whereas the –CF2 groups have no effect. For MA, it is proposed that the aromatic domains function as attenuation regions, whereas the fluorinated domains serve as microwave transparent regions. When the area of aromatic domains is almost equal to that of fluorinated domains, the complementarity between attenuation ability and impedance match endows F-SWCNTs (fluorine content equals of 6.8%) with a good MA performance. Specifically, with only 4.8 wt% loading, the minimum reflection loss (RL) reaches −64.3 dB at the thickness of 1.61 mm, and the effective absorption region (RL ＜ −10 dB) covers a range of 14.1–18 GHz at the thickness of 1.15 mm. The MA performances rely on the evolution of the physical heterostructure, instead of the introduced chemical bonds or fluorine-containing functional groups. The simplicity and feasibility of our design concept indicate the potential application of F-SWCNTs industrially. [ABSTRACT FROM AUTHOR]

Fluorinated graphene (FG) can be regarded as the representative two-dimensional (2D) material to study the characteristics of “2D chemistry”, whereas its derivative reaction mechanism is still required to be revealed for the destination of deciduous fluorine atoms after defluorination of FG. Herein, we proposed a particular derivative reaction of FG by employing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as the attacking reagent, and the products were characterized via Electron Paramagnetic Resonance Spectroscopy (EPR), Mass Spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the defluorination caused by TEMPO occurred in a radical mechanism, thus leading to formations of new spin centers on graphene nanosheets as well as C=C bonds. More importantly, the deciduous fluorine atoms after defluorination, which existed in TEMPO fluoride molecules, have been detected for the first time. Meanwhile, some TEMPO molecules were covalently grafted on the nanosheet, which resulted from the coupled reaction between TEMPO radical and the spin center on the FG nanosheet. These findings deepen the research of derivative reactions of FG, meanwhile providing a particular view to investigate the chemistry characteristics of 2D materials from a radical mechanism. [ABSTRACT FROM AUTHOR]

The investigation of the dispersion behavior of fluorinated MWCNTs (F-MWCNTs) is very important to understand their structure and take full advantage of their good properties. In this present paper, the dispersion behavior of F-MWCNTs with a low content and a high content of fluorine (denoted as lF-MWCNTs and hF-MWCNTs) was explored in 18 kinds of common solvents. The surface of hF-MWCNTs is considered to be a heterostructure consisting of fluorinated regions and aromatic regions, while lF-MWCNTs are inclined to be a homogeneous structure on the basis of their dispersion behavior. According to dispersion theory based on surface energy and Hansen solubility parameters (HSPs), it was indicated that the corresponding preferable solvents are different for different regions. As a result, good solvents of hF-MWCNTs are distributed in a quite wide scope while lF-MWCNTs can be dispersed only in a significantly narrow range of solvents. The HSPs of lF-MWCNTs and hF-MWCNTs are determined to be δD = 17.6 MPa1/2, δP = 11.8 MPa1/2, δH = 8.8 MPa1/2 and δD = 16.9 MPa1/2, δP = 9.3 MPa1/2, δH = 13.5 MPa1/2, respectively. As a result, mixed solvents of acetone and water were carefully tuned to be compatible with hF-MWCNTs. The dispersion behaviors of lF-MWCNTs and hF-MWCNTs in epoxy were also predicted according to HSPs. It was found that hF-MWCNTs maintain a stable dispersion in epoxy due to their heterogeneous structure at elevated temperatures. [ABSTRACT FROM AUTHOR]

Considering practical applications, the thermal/thermal oxidative stability of fluorinated graphene should be given sufficient attention. Herein, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were used to investigate in detail the differences in the thermal stabilities of two types of fluorinated samples, fluorinated graphene (FG) and fluorinated porous graphene (FPG) with various fluorine contents, respectively, as well as the reasons for these differences. It was demonstrated that the thermal stability of FG and FPG was improved upon increasing the fluorine content, which was mainly caused by the enhancement of bond energy of the covalent C–F bonds. Moreover, compared to that of the raw graphene samples, the thermal oxidative stability of FG was reduced due to the defects brought by fluorination, while the thermal oxidative stability of FPG was improved, originating from the inflaming retarding effect of the fluorine element. Interestingly, the thermal oxidative stability of the fluorinated samples was even better than their thermal stability. Using a comparison of the two types of fluorinated samples and support from the computational simulations of the model molecules, it was suggested that a greater amount of CFn (n = 2, 3) groups or defects in the FG samples resulted in its relatively worse thermal stabilities. Furthermore, electron paramagnetic resonance (EPR) spectroscopy was introduced to analyze the thermal stabilities of the fluorinated graphene samples as a novel method. The changes in the spin centers in samples after thermal treatment were studied, which indicated that the lower amount of the more stable spin centers of FPG was another reason leading to its more outstanding thermal stabilities in comparison to FG samples. [ABSTRACT FROM AUTHOR]

A facile way to prepare fluorinated graphene (FG) with a high fluorine content and controllable structure is important to achieve its full potential application. In this work, it was found that the fluorine to carbon (F/C) ratio of fluorinated graphene oxide (FGO) was nearly twice as much as that of fluorinated chemically reduced graphene oxide (FCrGO) after fluorination at the same temperature. Concerning the detailed effects of oxygenic groups on the fluorination and structure of fluorinated graphene (FG), graphene oxides with different oxygen contents were fluorinated under the same conditions. It was shown that oxygenic groups promote the fluorination reaction by activating the surrounding aromatic regions and taking part in the substitution reaction with fluorine radicals, among which, hydroxyls and carbonyls tend to be replaced by fluorine atoms. Moreover, the fluorination mainly occurs at the edges and defects of graphene sheets with a low oxygen content, while the highly oxidized graphene sheets are fluorinated both at the edges and basal planes simultaneously. This indicates that the quantity and location of the C–F bonds in FGO can be controlled by adjusting the species and content of oxygenic groups in the precursor graphene oxide. [ABSTRACT FROM AUTHOR]

The attachment of fluorine to graphene is a facile means to activate the carbon bonds for subsequent covalent bonding to other molecules for the preparation of desired graphene derivatives. Therefore, an insight into the chemical reactivity of fluorinated graphene (FG) is very essential to enable precise control of the composition and structure of the final products. In this study, FG has been treated with various mass amounts of poly(oxypropylene)diamine (PEA) ranging from starvation to saturation to explore the dependence of a substitution reaction of diamines on the nature and location (attached onto the basal planes or along defects or edges) of C–F bonds. X-ray photoelectron spectroscopy directly tracked the atomic percentage of fluorine present and the carbon 1s bonding state, showing that the grafting ratio of diamines gradually increases with increased diamine mass ratio. The varying of the types and orientation of C–F bonds characterized by polarized attenuated total reflectance Fourier transform infrared spectroscopy indicates that “covalent” C–F bonds are more sensitive to the substitution reaction of diamines than ‘‘semi-ionic’’ C–F bonds, and the C–F bonds attached onto basal planes more preferably participate in the functionalization reaction of diamines than that of C–F bonded on non-coplanar regions (edges or defects). The one-dimensional expansion along the graphene c-axis shown by wide angle X-ray diffraction provides further evidence on the preferred functionalization reaction of C–F attached on the basal planes, resulting in a change of the average intersheet distance by various magnitudes. [ABSTRACT FROM AUTHOR]

The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C-F bond, and a spin center was generated on the nanosheet and fluorine anion. Moreover, neither the S N 1 nor S N 2 mechanism was suggested to be appropriate for the substitution reaction of FG with a 2D structure due to the corresponding kinetics or thermodynamics disadvantage; hence, its nucleophilic substitution was proved to occur via a radical mechanism initiated by the defluorination step. The proposed substitution mechanism of FG demonstrates that nucleophilic substitution via a radical mechanism can also be applied to the attacking process of common nucleophiles without any particular conditions. Furthermore, it has been discovered that triethylamine without active hydrogen can be covalently attached to graphene nanosheets via a nucleophilic substitution reaction with FG; this further indicates a radical process for the nucleophilic substitution of FG rather than an S N 1 or S N 2 mechanism. The detailed process of the nucleophilic substitution reaction of FG was revealed to occur via a radical mechanism depending on the 2D structure of FG, which could also represent the typical characteristic of 2D chemistry.