Edge doping of graphene sheets

We present a direct comparison between two fundamental methods of chemically doping the 2-dimensional graphene sheet: (1) passivation of dangling σ-bonds resulting from a vacancy defect and (2) charge transfer from adsorption on the pristine basal plane. Using electron beam lithography and the negative tone resist hydrogen silsesquioxane, we are able to observe the doping contribution from the passivation of such defects that naturally reside along the edge of graphene sheets, and directly compare them to the doping limitations of basal plane adsorption methods. We demonstrate that the passivation of the edge is over three orders of magnitude more efficient for chemical doping than adsorption, in terms of conducting carriers donated per available C-atom. Moreover, as large-area graphene sheets are tailored into nanoscale devices, and the portion of C-atoms that occupy the edge increases, we demonstrate that edge decoration becomes a more pronounced method of chemical doping, exhibiting a scaling law that will induce vast carrier densities and dominance over adsorption techniques in the nanoscale.     

Thermal conductivity of graphene nanoribbons with defects and nitrogen doping

Thermal conductivity of defective graphene nanoribbons doped with nitrogen for different distributions around the defect edge at nanoscale is investigated using the reverse non-equilibrium molecular dynamics (RNEMD) method, which explores ways to improve thermal management. In addition, thermal conductivity of graphene nanoribbons with both defects and nearby nitrogen doping is investigated in comparison to that of nanoribbons with defects alone. The simulation results are analyzed from three perspectives: phonon match, concentration of N doping, and distribution of N doping. This approach reveals that a coupling effect is the cause of the observed results. Nitrogen doped graphene nanoribbons (both perfect and defective variants) perform better with thermal management than do graphene nanoribbons with defects alone, which is of considerable interest. Based on these investigations, a guide for graphene-interconnected circuits design is implied.     

Electrochemical studies on doping of polyacetylene

The mechanism for electrochemical doping of polyacetylene was studied using cyclic voltammetry. The I–V curve of a thin (CH)_x filme (<1 μm) electrode exhibited a redox peak with a formal redox potential of +0.65 V vs. sodium calomel electrode. Approximately 30% of the total charge that oxidized (CH)_x was not reversible when held at the open circuit voltage of the cell. A more negative potential was needed to recover the remaining charge. This large charge-trapping phenomenon was the consequence of the (CH)_x film being doped. Using a thick film (?50 μm) electrode or freestanding film (～0.1 mm) as an electrode, the I–V curve gave only a broad re-reduction peak at +0.4 V. The disappearance of the well-defined redox peak implies that the redox process revealed by the thin film data may not be the predominate mechanism for the doping process.     

Electrochemical chlorination of toluene by two-phase electrolysis

A simple method for the preparation of benzyl chloride from toluene by two-phase electrolysis is reported. The major product is benzyl chloride in contrast to chlorotoluenes in homogeneous electrolysis. Electrolysis was carried out at 30 °C in chloroform solvent. Toluene conversion ranges from 80 to 85% and the selectivity is as high as 95%. The effect of different electrodes, temperatures, and current density are studied and the optimum condition is reported.     

Radical-assisted chemical doping for chemically derived graphene

Carrier doping of graphene is one of the most challenging issues that needs to be solved to enable its use in various applications. We developed a carrier doping method using radical-assisted conjugated organic molecules in the liquid phase and demonstrated all-wet fabrication process of doped graphene films without any vacuum process. Charge transfer interaction between graphene and dopant molecules was directly investigated by spectroscopic studies. The resistivity of the doped graphene films was drastically decreased by two orders of magnitude. The resistivity was improved by not only carrier doping but the improvement in adhesion of doped graphene flakes. First-principles calculation supported the model of our doping mechanism.     

Electrochemical generation of hydrogenated graphene flakes

A cathodic electrochemical method for the exfoliation of graphite to produce hydrogenated graphenic flakes is introduced. The resulting solutions consist of micrometer-sized and predominantly 1–4 layers thick hydrogenated graphenic flakes. In contrast to oxygenation, chemisorption of hydrogen avoids the formation of structural vacancy defects in the exfoliated flakes. Thermal desorption of hydrogen therefore results in graphenic flakes with a low defect density and consequently good electrical conductivity. Cathodic electrochemical exfoliation offers a remarkably simple and effective technique for the production of high quality graphene flakes and their hydrogenated relatives.     

Electrochemical oxidation of toluene promoted by OH radicals

Benzaldehyde can be produced from toluene by an electrochemical process involving OH radicals. In the cathodic compartment of the electrolytic cell the reduction of molecular O₂ and of a metal ion M^ox, are simultaneously carried out in the presence of a toluene suspension. M^ox is the oxidized form of a redox couple such as V(V)/V(IV), V(IV)/V(III), Cu(II)/Cu(I); the electrogenerated H₂O₂ and the reduced metal ion generates OH radicals and M^ox, which is converted back to the reduced form at the electrode. The reactivity of the redox couples examined were compared from the point of view of their effectiveness for the toluene oxidation process. In some cases, current yields very close to the theoretical ones could be obtained.     

Thickness-dependent azobenzene doping in mono- and few-layer graphene

Doping effects on exfoliated graphenes induced by methyl orange (MO) have been studied by spatially resolved Raman spectroscopy. When the MO molecules were adsorbed on the top of graphenes, the charge transfer between them caused two outcomes simultaneously. One is the strong chemical doping in graphenes and the other is the enhanced Raman signals of MO molecules. Our finding provides a potential approach for manipulating the electronic properties of graphenes and investigating the vibrational properties of molecules. Moreover, the thickness-dependent doping effects in graphenes are unambiguous distinguished by Raman imaging. The possible origin was discussed and designated to the different band structures of graphenes and the screening effect.     

Radio-frequency characteristics of graphene monolayer via nitric acid doping

The radio-frequency, i.e. 0.5–40 GHz, characteristics of chemical vapor deposition-grown graphene monolayer via HNO₃ doping is experimentally investigated. According to the obtained results, the sheet resistance of HNO₃-treated graphene decreases about half compared to bare graphene. In the case of radio-frequency characteristics, the transmission coefficient and effective conductivity of the HNO₃-treated graphene are more enhanced than those of the bare graphene. Moreover, the intrinsic resistance and inductance of the HNO₃-treated graphene itself show diminishing tendency with frequency increase. As a result, it is verified that the direct current as well as high frequency characteristics of graphene are improved by using the chemical doping method.     

Vertically aligned epitaxial graphene nanowalls with dominated nitrogen doping for superior supercapacitors

For graphene-based electrode materials, N doping is one of the leading approaches for enhancing the performance of supercapacitors. However, such an outstanding performance is suppressed by the agglomeration of graphene and unspecified N incorporation. Here, we demonstrate a direct growth of vertically epitaxial graphene nanowalls (GNWs) on flexible carbon cloths (CCs) via microwave plasma-enhanced chemical vapor deposition, whereby predominantly N doping was sequentially achieved by introducing in situ NH₃ plasma, to form N-doped GNWs (NGNWs). The vertically aligned three-dimensional (3D) architecture of epitaxial NGNWs and their unique selectivity to the specific N dopants make such electrodes an ideal platform, not only for enhancing the capacitive performance but also for studying the role of the CN bonding configuration in its performance. Remarkably, NGNW supercapacitors exhibit an excellent specific capacitance of 991.6 F/g (estimation based on the actively contributing component) and an apparent area-normalized capacitance of 1488.9 mF/cm², at a specific current of 14.8 A/g. This approach allows us to achieve an energy density of 275.4 Wh/kg at a power density of 14.8 kW/kg (specific current of 14.8 A/g), and a power density of 74.1 kW/kg at an energy density of 232.6 Wh/kg (specific current of 74.1 A/g) in 1 M H₂SO₄.     

Tuning doping and strain in graphene by microwave-induced annealing

We propose microwave-induced annealing as a rapid, simple, and effective method of controlling surface doping and strain in graphene. Raman spectroscopy was used to confirm that heavy and uniform p-type (1.2 × 10¹³ cm⁻²) doping can be achieved within only 5 min without unintended defects by placing graphene onto a substrate with a sufficiently high dielectric constant and exposing graphene and its substrate to microwave irradiation. Further, we showed that ripples are formed in suspended graphene when it is exposed to microwave irradiation. Silicon has a sufficiently high dielectric constant (11.9) and graphene is commonly deposited on silicon-based substrates, so our proposed microwave-induced annealing technique can be used for the rapid manipulation of the properties of graphene at low cost.     

氧化石墨烯掺杂对低碳钢表面硅烷涂层性能的影响

利用浸渍法在Q235低碳钢表面制备了氧化石墨烯(GO)掺杂的双?[3?(三乙氧基)硅丙基]四硫化物(BTESPT)硅烷涂层.分别采用扫描电镜、傅里叶变换红外光谱仪、电化学工作站和摩擦磨损试验机研究了氧化石墨烯掺杂对硅烷涂层的表面形貌、相结构、耐蚀性和耐磨性的影响.结果表明:氧化石墨烯掺杂后硅烷涂层表面更加致密,耐蚀性和耐磨性得到提高.     

Stable p- and n-type doping of few-layer graphene/graphite

ZnMg and NbCl₅ were intercalated in graphite and the presence of such molecules between the graphene sheets results in n- and p-type doping, respectively. The doping effect is confirmed by Hall and Raman measurements and the intercalation process is monitored by scanning tunneling microscopy. After intercalation the carrier concentration increase almost an order of magnitude and reaches values as high as 10¹⁹and 10¹⁸ cm⁻³ for p- and n-type doping, respectively. For higher intercalation times, the intercalated graphite turns back to be as ordered as pristine one as evidenced by the reduction in the D peak in Raman measurements. Intercalation compounds show remarkable stability allowing us to permanently tune the physical properties of few-layer graphite. Our study has provided a new route to produce stable and functional graphite intercalation compounds and the results can be applied to other graphitic structures such as few-layer graphene on SiC.     

Electrochemical reduction of graphene oxide in organic solvents

Graphene oxide (GO) cast on conductive substrates was electrochemically reduced in some organic solvents. The amount of electricity required for the almost complete reduction of GO was 2.0 C for 1 mg GO, corresponding to attaching of a one-electron reducible species to each benzene ring in graphene. The electrochemically reduced GO film gave an electrical conductivity of about 3 S cm⁻¹ and exhibited a relatively high specific capacitance of 147.2 F g⁻¹ in propylene carbonate. The electrochemical reduction of GO was feasible on Al foils as well.     

Electrochemical promotion of toluene combustion on an inexpensive metallic catalyst

Electrochemical promotion of the complete catalytic oxidation of toluene at 310 °C is reported, using a Ag/YSZ/Ag two electrode system where Ag films were deposited on YSZ from AgNO₃ aqueous solution followed by reduction in H₂. After on-stream activation, a non-negligible conversion (about 30%) at OCV is reached and then the rate of the catalytic toluene conversion into CO₂ and H₂O can be multiplied by a factor higher than 1.5, by application of a small negative current (about—4 μA cm⁻²). The associated Faradaic efficiency is very high and may exceed −13,000.     

Electrochemical production of OH. radicals and their reaction with toluene

The reaction between electrochemically generated Fenton's reagent and toluene was studied. The products arising from this reaction system were consistent with a primary hydrogen atom abstraction from the methyl group of toluene to give benzyl radicals.Benzaldehyde was obtained with a current yield higher than 60%; benzyl alcohol was also produced in smaller quantities in some experiments. The dependence of the yields on reagent concentrations, temperature and coulombs passed was examined. On the basis of the experimental results a mechanism is proposed involving peroxy and alkoxy radicals as intermediates.     

Site-dependent doping effects on quantum transport in zigzag graphene nanoribbons

We investigate the site-dependent effects of a substitutional nitrogen or boron atom on quantum transport in zigzag graphene nanoribbons from first principles and tight-binding model calculations. The former show three characteristics in transmission spectra: drops around the Fermi level, dips at the bottom of the second conduction (nitrogen) or valence (boron) band, and sharp peaks at the Fermi level. Comparing with the latter, the origins of the transmission features are revealed. The drops are attributed to the impurity onsite potential or its Coulomb interaction, depending on its location. The dips come from the interaction between the impurity and its neighbor atoms. The peaks are associated with the resonant long-rang components of the Coulomb interaction.     

Tuning sulfur doping in graphene for highly sensitive dopamine biosensors

S-doped graphene has attracted extensive interest in recent years due to its high catalytic activity. However, most of the previously reported S-doped graphene materials present diverse types of S-bonding configurations, it is hard to distinguish which configuration is mainly responsible for the catalytic activity. Here, homogeneous thiophene S-doped graphene can be synthesized through solid-state reaction between graphene oxide and sulfate, and the doping amount can be easily tuned by the sulfate dosage. More importantly, abundant micropores and some mesopores are formed in the surface of graphene sheets during S-doping. Due to its high S-loading mass, thiophenic sulfur species and unique porous structure, S-doped graphene shows high electrocatalytic activity toward the redox reaction of dopamine, such as high selectivity, high sensitivity and low detection limit (3.94 μM μA⁻¹, 1.5 × 10⁻⁸ M at S/N = 3).     

Band gap opening of graphene by doping small boron nitride domains

Boron nitride (BN) domains are easily formed in the basal plane of graphene due to phase separation. With first-principles calculations, it is demonstrated theoretically that the band gap of graphene can be opened effectively around K (or K') points by introducing small BN domains. It is also found that random doping with boron or nitrogen is possible to open a small gap in the Dirac points, except for the modulation of the Fermi level. The surface charges which belong to the π states near Dirac points are found to be redistributed locally. The charge redistribution is attributed to the change of localized potential due to doping effects. The band opening induced by the doped BN domain is found to be due to the breaking of localized symmetry of the potential. Therefore, doping graphene with BN domains is an effective method to open a band gap for carbon-based next-generation microelectronic devices.     

Designed nitrogen doping of few-layer graphene functionalized by selective oxygenic groups

Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxide. X-ray diffraction (XRD) pattern confirmed phase structure of the graphene oxide and reduced graphene oxide. Nitrogen doping content and bonding configuration of the graphene was determined by X-ray photoelectron spectroscopy (XPS), which indicated that different oxygenic functional groups were evidently different in affecting the nitrogen doping process. Compared with other oxygenic groups, carboxyl group played a crucial role in the initial stage of nitrogen doping while hydroxyls exhibited more evident contribution to the doping process in the late stage of the reaction. Formation of graphitic-like nitrogen species was controlled by a synergistic effect of the involved oxygenic groups (e.g., -COOH, -OH, C-O-C, etc.). The doping mechanism of nitrogen in the graphene was scrutinized. The research in this work may not only contribute to the fundamental understandings of nitrogen doping within graphene but promote the development of producing novel graphene-based devices with designed surface functionalization.