Nitrogen-doped Graphene Films Research Articles

Key role of graphitic-N in N-doped graphene coated Al alloy in corrosion resistance performance

In this study, nitrogen-doped graphene (NG) coated 6061 Al alloy (NG/Al) was prepared using a novel roll-coating technique. Through Raman and X-ray photoelectron spectroscopy analyses (XPS), the NG films with varying graphitic-N content obtained by plasma treatment was investigated. The electrochemical impedance spectroscopy, polarization curve, and immersion test were used to study the corrosion behaviors of the films. The results show that NG/Al exhibits enhanced corrosion resistance properties due to the enhanced adhesion between Al substrate and NG. In particular, the prepared NG/Al with the highest graphitic-N content shows superior resistance against both 0.5 M H2SO4 and 3.5 wt% NaCl.

Synthesis of N-doped graphene film with tunable graphitic and pyridinic doping content

Nitrogen-doped (N-doped) graphene films with up to a 17.39 at.% doping level were synthesized with the chemical vapor deposition growth method. An extensive range of tunable nitrogen doping levels was achieved by selecting organic molecules as precursors grown at a wide temperature range of 300 to 1000 °C. The benzene rings in the precursor significantly reduced the energy requirements of N-doped graphene. The incorporation of bridgehead nitrogen and amino groups ensured a high nitrogen doping level and offered the tunable modulation of nitrogen dopant concentrations. The influence of temperature on the nitrogen content was investigated, distinguishing the graphitic and pyridinic dopant types, each demonstrating unique trends considering the dopant stability and growth mechanism. Specifically, the proportion of graphitic doping could be modulated from 40 % to 100 %. Notably, the pyrrolic type was absent at lower temperatures and was nearly negligible at elevated temperatures. Therefore, we developed a synthesis method for N-doped graphene growth that allowed for the selective and prioritized tuning of nitrogen dopant types. This method is particularly favorable when specific nitrogen dopants at certain doping levels are required for electrical and chemical catalytic applications.

Growth of Low-Defect Nitrogen-Doped Graphene Film Using Condensation-Assisted Chemical Vapor Deposition Method.

It is significantly important to modulate the electrical properties of graphene films through doping for building desired electronic devices. One of the effective doping methods is the chemical vapor deposition (CVD) of graphene films with heteroatom doping during the process, but this usually results in nitrogen-doped graphene with low doping levels, high defect density, and low carrier mobility. In this work, we developed a novel condensation-assisted CVD method for the synthesis of high-quality nitrogen-doped graphene (NG) films at low temperatures of 400 °C using solid 3,4,5-trichloropyridine as a carbon and nitrogen source. The condensation system was employed to reduce the volatilization of the solid source during the non-growth stage, which leads to a great improvement of quality of as-prepared NG films. Compared to the one synthesized using conventional CVD methods, the NG films synthesized using condensation-assisted CVD present extremely low defects with a ratio of from D- to G-peak intensity (ID/IG) in the Raman spectrum lower than 0.35. The corresponding total N content, graphitic nitrogen/total nitrogen ratio, and carrier mobility reach 3.2 at%, 67%, and 727 cm2V-1S-1, respectively. This improved condensation-assisted CVD method provides a facile and well-controlled approach for fabricating high-quality NG films, which would be very useful for building electronic devices with high electrical performance.

Preparation of Nitrogen-Doped Graphene Films for Temperature Sensing by Crosslinking with Two-Dimensional Small Molecule

Graphene, as a typical zero band gap material, possesses excellent electrical conductivity and mechanical property, but is hardly applied in functional field directly. Hence, how to effectively modify the energy structure of graphene and apply it as functional material in physical signal sensing, information processing and energy management has become a widely attentional research field in recent decades. In this work, a two-dimensional (2D) organic molecular named 5, 10, 15, 20-tetra (4-aminopyenyl) porphyrin is selected to in-situ crosslink with graphene oxide (GO), and the nitrogen-doped graphene (NG) film is prepared through further graphitization. In this paper, the influence of the content of porphyrin molecular on the microstructure and nitrogen content of the NG film is mainly discussed. With the increasing of porphyrin content, the layer space of GO film rises gradually and the GO nanosheets are laid out more smoothly. After graphitization, nitrogen element is well preserved inside the NG film, and the electrical conductivity and Seebeck coefficient is greatly improved. Taking advantage of these properties, a NG film-based temperature sensor is prepared.

N-doped graphene film prepared by rapid thermal shock for ultra-sensitive temperature reading

Graphene is restricted by its zero-band gap when applying in functional components. However, its band structure can be adjusted appropriately through nitrogen doping. At present, many nitrogen doping processes have been developed such as chemical vapor deposition, thermal annealing and plasma sputtering, but in general these methods are time-consuming and difficult to control the type of nitrogen atom doped. In this work, an in situ high-temperature thermal shock process, with an extremely fast rate of temperature change of more than 104 K/s, is developed and used to prepare the nitrogen doped graphene (NG) films. This novel N-doped process enables the preparation of NG films within 10 s, which is the fastest to the best of our knowledge. Moreover, the type and content of doped nitrogen atoms can be effectively regulated by controlling the composition of precursor films. Optimally, the nitrogen content of NG film reaches 2.26 %, and the proportion of graphite nitrogen is more than 60 %. The electrical conductivity and the average Seebeck coefficient of the NG film are 13,870 S·m−1 and −46.5 μV/K, respectively. Its thermoelectric power factor reaches 30 μW·m−1·K−1, indicating that the NG film has a good prospect of functional application. Furtherly, A NG film-based temperature reading device is developed, which shows ultra-high accuracy and sensitivity in temperature reading within a rather wide temperature range.

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method.

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.

High-quality nitrogen-doped graphene films synthesized from pyridine via two-step chemical vapor deposition

Modulation of the electrical properties of graphene is of significant importance in advancing graphene electronics: it can be achieved by a Fermi level shift induced by electron acceptor/donor doping. Suitable doping methods involving low-temperature processes and offering long-term stability are imperative to practical applications for such materials. Here, we demonstrate a two-step chemical vapor deposition (CVD) technique for direct synthesis of N-doped graphene film from a pyridine feed-stock at 300 °C under ambient pressure. We extended the synthesis—classified into nucleation and lateral growth steps—by controlling the carbon partial pressure in the processing gases. This led to large-area, continuous N-doped graphene films of excellent quality with full surface coverage: for example, a film size of 2 in2, optical transmittance of 97.6%, and electron mobility of 1400 cm2 V−1 s−1. Our modified CVD method is expected to facilitate the direct synthesis of N-doped graphene in device manufacturing processes toward practical applications while keeping the underlying devices intact.

Dependence of plasma power for direct synthesis of nitrogen-doped graphene films on glass by plasma-assisted hot filament chemical vapor deposition

Metal-free synthesis of nitrogen-doped (N-doped) graphene films on glass is important for modulating the properties of graphene glass but has so far met with limited success. In this study, direct synthesis of N-doped graphene films on glass with eco-friendly N2 dopant through a novel plasma-assisted hot filament chemical vapor deposition (HFCVD) approach was reported. Influence of plasma power on the structural and electrical properties of N-doped graphene films was investigated. The filament and plasma source were found to be both crucial for depositing high-quality N-doped graphene films with N2 dopant. With a small N2 flow of 5 sccm, the N content of graphene films synthesized by plasma-assisted HFCVD could be modulated from 0.6 to 3.0 at.% through adjusting the plasma power from 0 to 130 W. A lowest resistivity of 4.68 × 10−3 Ω cm was obtained at 130 W. Temperature-dependence of resistance measurement revealed that the carrier mobility of N-doped graphene films decreased by raising the plasma power, which was attributed to the increase of conductive activation energy. This work provides an alternative method for direct, controllable and green preparation of N-doped graphene films on glass.

Free-standing macro-porous nitrogen doped graphene film for high energy density supercapacitor

In this paper, a porous free-standing nitrogen-doped graphene (NG) film for high energy density supercapacitor is prepared via a facile hydrogel strategy. Taking advantage of the hydrogel behavior together with the mechanical stability of GO sheets, an interconnected macro-porous nitrogen-doped free-standing film is constructed. The nitrogen doping structure ensures sufficient pseudocapacitance and conductivity of the film, while the macro-porous structure favors fast ion adsorption. When assembled in a symmetric two-electrode supercapacitor, not any conductive agent or binder is used. The free-standing NG film shows specific capacitance of 455.4 F g−1 based on the mass of whole electrode, while no capacitance loss after 5000 cycles. Furthermore, an asymmetric supercapacitor is assembled with this NG film as negative electrode and a macro-porous graphene/polypyrrole composite film synthesized using the similar strategy as positive electrode. An energy density of 34.51 Wh kg−1 at a power density of 849.77 W kg−1 is obtained, suggesting great potential of this film for application in energy storage field.

Reversible Modification of Nitrogen-Doped Graphene Based on Se-N Dynamic Covalent Bonds for Field-Effect Transistors.

Temperature-dependent modification is an effective way to reversibly tailor graphene's electronic properties. We present the reversible modification of a uniform monolayer nitrogen-doped graphene (NG) film by the formation and cleavage of temperature-dependent Se-N dynamic covalent bonds. The increasing binding energy in X-ray photoelectron spectroscopy (XPS) indicates that phenylselenyl bromine (PhSeBr) bonds with pyridinic N and pyrrolic N rather than graphitic N by accepting the lone pair of electrons. The temperature dependence of Raman spectra (the increasing D band and the shifts of the 2D band) and XPS spectra (Se 3d and N 1s) indicates that the Se-N dynamic covalent bond is gradually cleaved by treatment at increasing temperatures and is also recovered by the reversible modification. Field-effect transistors (FETs) based on Se-NG exhibit a temperature-dependent change from n-type to p-type conduction and tunable electron and hole mobilities owing to the reversible formation or cleavage of Se-N dynamic covalent bonds. This result opens up opportunities for reversibly controlling electrical properties of FETs by optimizing dynamic covalent bonds.

Wet-spinning assembly of nitrogen-doped graphene film for stable graphene-polyaniline supercapacitor electrodes with high mass loading

Graphene-polyaniline (GP) composites are promising electrode materials for supercapacitors but possessing unsatisfied stability, especially under high mass loading, due to the low ion transmission efficiency and serious pulverization effect. To address this issue, we propose a scalable method to achieve highly wettable GP electrodes, showing excellent stability. In addition, our results demonstrate that the performance of electrodes is nearly independent of the mass loading, indicating the great potential of such GP electrodes for practical devices. We attribute the remarkable performance of GP to the delicate precursor of nitrogen doped graphene film assembled by wet-spinning technology. This report provides a strategy to promote the ion penetrating efficiency across the electrodes and deter the pulverization effect, aiming at the practical GP supercapacitor electrodes of high mass loading.

Designing Parameters of Surfactant-Free Electrochemical Sensors for Dopamine and Uric Acid on Nitrogen Doped Graphene Films

Electrochemistry studies on the derivatives of graphene have been in the forefront of chemical research in recent years. The large specific surface area, high electrical conductivity, fast electron transfer rate and excellent biocompatibility to biomolecules constitute a few of the underlying reasons for the extensive application of graphene derivatives in modern electrochemistry and related technologies. Much interest in graphene derivatives has been driven by the ease of intentional functionalisation of the carbon backbone of graphene with dopants, such as nitrogen. Doping enhances the electrical conductivity and biocompatibility of nitrogen-doped graphene (NGr) nanomaterials and aids in their potential applications in electrochemical sensing and spectroelectrochemical devices. Despite the application of NGr in electrochemical sensing devices, the major challenge for reproducible industrial application still lies in the use of surfactants and binders and the limited knowledge on the correlation between the N-configurations and the electrocatalytic performance of these NGr-based electrodes. Therefore, the purpose of this short review article is to highlight some recent progress on the application of NGr derivatives for electrochemical detection of biomarkers such as uric acid and dopamine. The paper will also illustrate design parameters for new surfactant-free two-dimensional (2D) N-doped graphene based electrochemical sensors with variable N-functionalities for the detection of dopamine and uric acid.

High-performance asymmetric micro-supercapacitors based on electrodeposited MnO2 and N-doped graphene

In-plane asymmetric micro-supercapacitors using nitrogen-doped graphene (NG) film as negative electrode and MnO2 nanostructures as positive electrode are fabricated onto a plastic substrate coated with Ni/Cu film. A laser-scribing machine is employed to make interdigital finger electrodes in the plastic substrate coated with NG film via a slurry coating process. MnO2 nanosheets are electrochemically deposited onto pre-coated NG film. In LiCl-based gelled electrolyte, the NG//MnO2 cell exhibits excellent electrochemical performance and a broad voltage window up to 1.8 V. The maximum specific capacitance of a single cell is measured to be 13 mF cm−2. In addition, several cells in series can be easily fabricated by combining the laser-scribing technique and the electrodeposition of MnO2 electrodes. As a proof of concept, four cells in a compact configuration and with high voltage output up to 7.2 V are demonstrated.

Electroanalytical Performance of Nitrogen-Doped Graphene Films Processed in One Step by Pulsed Laser Deposition Directly Coupled with Thermal Annealing.

Graphene-based materials are widely studied to enable significant improvements in electroanalytical devices requiring new generations of robust, sensitive and low-cost electrodes. In this paper, we present a direct one-step route to synthetize a functional nitrogen-doped graphene film onto a Ni-covered silicon electrode substrate heated at high temperature, by pulsed laser deposition of carbon in the presence of a surrounding nitrogen atmosphere, with no post-deposition transfer of the film. With the ferrocene methanol system, the functionalized electrode exhibits excellent reversibility, close to the theoretical value of 59 mV, and very high sensitivity to hydrogen peroxide oxidation. Our electroanalytical results were correlated with the composition and nanoarchitecture of the N-doped graphene film containing 1.75 at % of nitrogen and identified as a few-layer defected and textured graphene film containing a balanced mixture of graphitic-N and pyrrolic-N chemical functions. The absence of nitrogen dopant in the graphene film considerably degraded some electroanalytical performances. Heat treatment extended beyond the high temperature graphene synthesis did not significantly improve any of the performances. This work contributes to a better understanding of the electrochemical mechanisms of doped graphene-based electrodes obtained by a direct and controlled synthesis process.

Barrier mechanism of nitrogen-doped graphene against atomic oxygen irradiation

Nitrogen-doped graphene (NG) exhibited a good activity as an electrocatalyst of oxygen reduction reaction while there was no experimental example to investigate the catalytic ability and barrier performance of the NG to atomic oxygen (AO). Here we explored the effect of AO on the structure and barrier properties of pristine graphene (PG) and NG coated Cu foils. AO with high energy and strong oxidizing capacity reacts with graphene and then the graphitic structures are broken down into smaller parts, leading to the oxidation of underlying Cu. Miraculously, AO irradiation causes little damage of NG films and the oxidation degree of NG coated Cu is significantly reduced than that of PG coated. Density functional theory calculations show NG can catalyze the bonding of adsorbed oxygen atom with a second oxygen atom to form O2. And eventually, O2 molecule moves away from the NG surface and the damage of NG film is slow down.

Direct growth of nitrogen-doped graphene films on glass by plasma-assisted hot filament CVD for enhanced electricity generation

N-Doped graphene glass was prepared through a novel plasma-assisted HFCVD approach, which exhibited significantly enhanced voltage generation for energy harvesting.

Tuning capacitance of graphene films via a robust routine of adjusting their hierarchical structures

In this work, the nitrogen doped graphene films with hierarchical network structures have been successfully fabricated via a robust routine of adjusting the content of large- and small-sized reduced graphene oxide (RGO) sheets in the graphene films, where the large-sized RGO sheets act as the backbone to form the well-connected network structures and small-sized RGO sheets act as the interlayer and interpore linkers to connect the large-sized RGO sheets and large pores. A maximum capacitance of 429.7 F g−1 is obtained for the optimized RGO electrode with small-sized RGO content of 40 wt%, which is 61.9% improvement compared to the RGO electrodes with pure large-sized RGO sheets. While, the specific surface area and electrical conductivity of the optimized RGO electrode are 36.1% and 26.2% improvement compared to the pure large-sized electrode. Therefore, we attribute the improved capacitance primarily comes from the increasing of specific surface area due to the formation of fine hierarchical structures and the better connection of the network structures (the increasing of electrical conductivity) for the optimized RGO electrode. Besides, the optimized RGO electrode exhibits good cycle, rate performance, power and energy density compared to the previous carbon based supercapacitor. Herein, we can precisely control the specific surface area and electrical conductivity of RGO electrode by simply adjusting the content of large- and small-sized RGO, which may shed useful insight for the design of high performance supercapacitors and Li-ion batteries.

Investigating the electrochemical behaviour and detection of uric acid on ITO electrodes modified with differently doped N-graphene films

Sensitive and selective electrochemical sensors based on indium-doped tin oxide electrodes (ITO) modified with differently nitrogen-doped graphene (NGr) films were successfully developed for the individual and simultaneous determination of uric acid (UA) in the presence of ascorbic acid (AA). The influence of the contents of various N-configurations on the detection of UA on the NGr/ITO based sensors is herein reported for the first time. The contents of various N-configurations on the NGr/ITO electrodes displayed varying promotional effects of the electro-oxidation of UA; attributed to the unique properties of the NGr films arising from the N-configurations. In particular, three N-doped materials prepared with varying amount of graphitic-N, pyrrolic-N, and pyridinic-N allowed the individual detection of UA, in the presence of AA, in the concentration range from 2 to 320μM with the detection limits of 0.043μM to 0.19μM. Finally, the NGr/ITO-based sensors exhibited successful simultaneous detection of UA and AA, depicting detection limits of 0.051–0.19μM and 0.93–5.1μM within the concentration ranges of 6–280μM and 8–800μM, for the detection of UA and AA, respectively. The study provided insight into an understanding as to how the different contents of N-configurations influenced the electrocatalytic activity of NGr/ITO electrodes for the individual and simultaneous detection of uric acid.

One-step synthesis of nitrogen-doped graphene from a sole aromatic precursor

A cheap aromatic precursor (1,10-phenanthroline) with heteroatom and planar-structure was designed to synthesize large-scale, continuous and mostly single-layer nitrogen-doped graphene (NG) films by one-step chemical vapor deposition method. The NG sheets can be obtained even at 600 °C. The results indicated that the content and type of doped N are intensely relied on the growth temperature. Our fabrication approach provides an economic synthetic route and potentially promotes the practical application of graphene-based materials.

Modification of N-doped graphene films and their applications in heterojunction solar cells

A two-step growth process was developed to synthesis N-doped graphene films by using pentachlorop-yridine as nitrogen source and methane as carbon source. The configuration and compositions of modified graphene films were characterized by X-ray photoelectron spectroscopy (XPS), and its bonding properties were obtained with Raman spectroscopy. The films were found to be N-doped graphene films with the N/C ratio of 2.5%–4%. The electronic properties of the films have been tested by using Hall Effect Measurement System. The nitrogen doped graphene film exhibits lower resistance (7.26 × 10−6 Ω·cm) but smaller mobility (521.8 cm2/V·S). Current density-voltage feature of solar cells with different structures were measured to research the photovoltaic characteristic of Graphene/n-Si solar cells. It was found that solar cells with N-doped graphene layer shown better performance of photovoltaic in illumination. The maximum energy conversion efficiency achieved was 6.24%. The inserted nitrogen atoms can effectively reduce the resistivity of graphene films, thus solve the problem of carrier recombination which caused by slow transmission speed. As a result, N-doped graphene film can highly facilitate the transmission and exportation of current, along with the improvement of short-circuit current density, which further enhance the overall efficiency of the solar cells. This work can promote the development of graphene film in application of transparent conductive electrode fields.