N-doped rGO Research Articles

Nitrogen-Doped Reduced Graphite Oxide as a Support for CoSe Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

A nitrogen-doped reduced graphite oxide (rGO) has been prepared by high temperature pyrolysis from a Polypyrrole/GO composite yielding high nitrogen content, with specific graphitic and pyridinic bonding as electrochemically active sites for the oxygen reduction reaction. The effect of the N-doped GO supports for CoSe chalcogenide nanoparticles on the electrochemical properties was evaluated in both half-cell, and micro-laminar flow fuel cells (μLFFC) in alkaline medium. The improved performance toward the oxygen reduction reaction (ORR) can be attributed to the availability of active sites on the N-doped rGO specific morphology, and successful coordination of the nitrogen bonds on the carbon lattice.

Electron transfer number control of the oxygen reduction reaction on nitrogen-doped reduced graphene oxides for the air electrodes of zinc-air batteries and organic degradation

The mean electron transfer number (n) of the oxygen reduction reaction (ORR) on reduced graphene oxide (rGO) is controlled by nitrogen doping for the air electrodes of Zn-air batteries and electrochemical organic degradation. Melamine and pyrrole are employed as the nitrogen sources for fabricating N-doped rGO (N-rGO) by microwave-assisted hydrothermal synthesis (MAHS). The n value of the ORR is determined by the rotating ring-disk electrode (RRDE) voltammetry and is successfully controlled from 2.34 to 3.93 by preparation variables. The N-doped structures are examined by the x-ray photoelectron spectroscopic (XPS) analysis. The morphology and the defect degree of N-rGOs are characterized by high resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy. N-rGOs with high and low n values are employed as the air electrode catalysts of zinc-air batteries and in-situ hydrogen peroxide (H2O2) generation, respectively. The highest discharge cell voltage of 1.235 V for a Zn-air battery is obtained at 2 mA cm−2 meanwhile the current efficiency of H2O2 generation in 1-h electrolysis at 0 V (vs. RHE) reaches 43%. The electrocatalytic degradation of orange G (OG), analyzed by UV-VIS absorption spectra, reveals a high decoloration degree from the relative absorbance of 0.38 for the azo π-conjugation structure of OG.

Enhancing the charge-storage performance of N-doped reduced graphene oxide aerogel supercapacitors by adsorption of the cationic electrolytes with single-stand deoxyribonucleic acid

Single-stand deoxyribonucleic acid/N-doped reduced graphene oxide aerogel (ssDNA/N-doped rGO) composites were synthesized and used as the electrode materials for supercapacitors. The mass change of the electrolytes adsorbed on the ssDNA/N-doped rGO electrode during a charge/discharge process determined by an electrochemical quartz crystal microbalance (EQCM) at a cathodic potential range (−0.5 to −0.1 V vs. Ag/AgCl) is 10-fold higher than that at an anodic potential range (−0.1–0.3 V vs. Ag/AgCl). This is because the ssDNA having negatively charged phosphate and nitrogen-containing nucleobase groups prefers cationic electrolytes to anionic ones. An as-fabricated supercapacitor of the ssDNA/N-doped rGO with a coin-cell size (CR2016) provides 644 F/g at 0.5 A/g, which is 1.3-fold higher than that of the N-doped rGO device. The specific power and specific energy of the as-fabricated ssDNA/N-doped rGO device are ca. 30 Wh/kg and 4500 W/kg, respectively with a capacity retention of 94.1% over 2500 cycles. Two as-fabricated supercapacitor cells connected in series can supply electricity to the red LED over 10 min. The composite materials in this work may also be used in other applications where the functional groups of ssDNA can play an important role to the adsorption of the cationic electrolytes.

CNT Branching on the 3D Nitrogen-Doped Graphene Architecture for Lithium Ion Battery

The hybridization of 1D CNT with 3D graphene structure has recently attracted attention owing to their large specific surface area, high electronic conductivity, and structural integrity. These features of the hierarchical architectures can provide synergic affect on the energy storage such as supercapacitors, fuel cells and lithium-ion batteries. In addition, the performance has been further improved by doping with different heteroatoms like sulphur, boron, phosphorous and nitrogen because they can play a vital role in changing the local electronic density leading to improved electronic conductivity. In this work, we synthesize 3D nitrogen (N)-doped reduced graphene oxide (rGO) branched by CNT for applications into lithium ion batteries. The hierarchical architecture consisting of the CNT branching on 3D N-doped rGO was characterized by SEM and TEM images. Iron oxide nanoparticles acted as the catalyst for the growth of CNT as well as active materials for lithium storage. The crystalline structure of iron oxide nanoparticles and restacking inhibition of rGO were confirmed by the XRD analysis. The BET data indicate the presence of mesoporous structure with average pore diameter of 21 nm with 400 m2/g surface area. The XPS data identified the presence, composition, and bonding configuration of carbon, iron, nitrogen and oxygen. The electrochemical properties were characterized by cyclic voltametry, impedance spectroscopy, and galvanic charge/discharge curve for lithium ion battery application.

Synthesis and characterization of Nitrogen-doped &CaCO3-decorated reduced graphene oxide nanocomposite for electrochemical supercapacitors

Alone, it is expected, and also was experimentally proved, that calcium carbonate and reduced graphene oxide do have negligible specific capacitance due to the chemical composition of both materials. However, synthesis of CaCO3 on the form of very thin sporadic layer attaching rGO results in dramatic increase in the specific capacitance of the obtained composite due to formation of the electrochemical double layer at the interfacial area. Moreover, the specific capacitance could be further enhanced by nitrogen-doping of the rGO sheets. Typically, a novel N-rGO/CaCO3 composite has been successfully synthesized by heat reflux strategy with graphite powder, calcium acetate and urea as raw materials.The composite was characterized by X-Ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FESEM), coupled with rapid EDAX (energy dispersive analysis of X-Ray) and X-ray photoelectron spectroscopy. The utilized physiochemical characterizations indicated that the final prepared composite can be demonstrated as N-doped rGO decorated by very thin discrete layer from calcium carbonate. Supercapacitive performance of N-rGO/CaCO3 composite has been investigated by cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy in 1M KOH solution. The results reveal that the N-rGO/CaCO3 composite delivers a large specific capacitance of as high as 214Fg−1 and 188Fg−1 at 5mVs−1and 1.0Ag−1, according to CV and galvanostatic charge-discharge tests, respectively; while the CaCO3, rGO, rGO/CaCO3, N-rGO based electrodes has a poor electrochemical performance at the same conditions. Moreover, the as-prepared composite exhibited excellent long cycle stability with about 88.7% specific capacitance retained after 10,000 cycles.

Nickel phosphide nanoparticles-nitrogen-doped graphene hybrid as an efficient catalyst for enhanced hydrogen evolution activity

Development of hybrid catalysts with high activity, good stability and low cost is extremely desirable for hydrogen production by electrolysis of water. In this work, a hybrid composed of Ni2P nanoparticles (NPs) on N-doped reduced graphene oxide (NRGO) is synthesized via an in situ thermal decomposition approach for the first time and investigated as a catalyst for the hydrogen evolution reaction (HER). The as-synthesized Ni2P/NRGO hybrid exhibits an enhanced catalytic activity with low onset overpotential (37 mV), a small Tafel slope (59 mV dec−1), a much larger exchange current density (4.9 × 10−5 A cm−2), and lower HER activation energy (46.9 kJ mol−1) than Ni2P/RGO hybrid. In addition, the Ni2P/NRGO hybrid maintains its catalytic activity for at least 60′000 s in acidic media. The enhanced catalytic activity is attributed to the synergistic effect of N-doped RGO and Ni2P NPs, the charged natures of Ni and P, as well as the high electrical conductivity of Ni2P/NRGO hybrid. This study may offer a new strategy for improving the electrocatalytic activity for hydrogen production.

Sulfur and Nitrogen Co-Doped Graphene for Metal-Free Catalytic Oxidation Reactions.

Sulfur and nitrogen co-doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal-free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first-order kinetic model, S-N co-doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min(-1) , which is 86.6, 22.8, 19.7, and 4.5-fold as high as that over graphene oxide (GO), rGO, S-doped rGO (S-rGO), and N-doped rGO (N-rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co-doping. Co-doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp(2) -hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal-free catalyst for green remediation of organic pollutants in water.

Microwave Enabled One-Pot, One-Step Fabrication and Nitrogen Doping of Holey Graphene Oxide for Catalytic Applications.

The unique properties of a holey graphene sheet, referred to as a graphene sheet with nanoholes in its basal plane, lead to wide range of applications that cannot be achieved by its nonporous counterpart. However, the large-scale solution-based production requires graphene oxide (GO) or reduced GO (rGO) as the starting materials, which take hours to days for fabrication. Here, an unexpected discovery that GO with or without holes can be controllably, directly, and rapidly (tens of seconds) fabricated from graphite powder via a one-step-one-pot microwave assisted reaction with a production yield of 120 wt% of graphite is reported. Furthermore, a fast and low temperature approach is developed for simultaneous nitrogen (N) doping and reduction of GO sheets. The N-doped holey rGO sheets demonstrate remarkable electrocatalytic capabilities for the electrochemical oxygen reduction reaction. The existence of the nanoholes provides a "short cut" for efficient mass transport and dramatically increases edges and surface area, therefore, creates more catalytic centers. The capability of rapid fabrication and N-doping as well as reduction of holey GO can lead to development of an efficient catalyst that can replace previous coin metals for energy generation and storage, such as fuel cells and metal-air batteries.

Nitrogen-doped graphene for generation and evolution of reactive radicals by metal-free catalysis.

N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8-11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the N-doped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin-unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on N-doped graphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS activation processes and pathways of phenol degradation on nanocarbons. It was observed that both (•)OH and SO4(•-) existed in the oxidation processes and played critical roles for phenol oxidation.

Electronic interaction between platinum nanoparticles and nitrogen-doped reduced graphene oxide: effect on the oxygen reduction reaction

Confirmed by DFT, a significant amount of platinum atoms are chemically bound to N of N-doped RGO.

Silver/Nitrogen-Doped Graphene Interaction and Its Effect on Electrocatalytic Oxygen Reduction

Three types of silver/reduced graphene oxide (Ag/rGO) nanocomposites (one doped with nitrogen and another two without) are synthesized to investigate their atomic structures and the oxygen reduction reaction (ORR) performance with them as the electrocatalysts. For the first time, the bonding interaction between Ag and N in N doped rGO (N-rGO) is confirmed by both high resolution X-ray photoelectron spectroscopy (XPS) and surface enhanced Raman spectroscopy (SERS). The Ag/N-rGO shows excellent ORR performance, including very high onset potential and current density, which outperforms those Ag/rGOs without N doping. Detailed electrochemical analysis shows that the ORR mechanism on Ag/N-rGO is different from both Ag and N-rGO, and its excellent performance is caused by the Ag–N bonding which alters the electronic structure of N-rGO.

Enhanced thermal oxidation stability of reduced graphene oxide by nitrogen doping.

Nitrogen-doped reduced graphene oxide (N-doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.

A promising photoelectrochemical sensor based on a ZnO particle decorated N-doped reduced graphene oxide modified electrode for simultaneous determination of catechol and hydroquinone

This paper describes the two-step synthesis of a nitrogen-doped reduced graphene oxide–ZnO (N-doped RGO–ZnO) nanocomposite and its photo electrochemical application.

Co2Nx/nitrogen-doped reduced graphene oxide for enzymeless glucose detection

Co2Nx/nitrogen-doped reduced graphene oxide (Co2Nx/NG) is synthesized by electrostatic co-precipitation of Co and rGO followed by high-temperature nitridation, which can serve as an efficient catalyst for sensitive glucose detection due to the unique electrocatalytic property of Co2Nx and synergistic effect between Co2Nx and N-doped rGO.

Synthesis of Highly n‐Type Graphene by Using an Ionic Liquid

n-Type graphene: A new, easy, and cheap method to produce n-type reduced graphene oxide was developed by synthesizing a partially reduced intermediate containing nitrogen (PrGO-IL, see scheme) by treating graphene oxide (GO) with an ionic liquid (IL) at 160 °C followed by rapid thermal annealing (RTA) at temperatures ranging from 400 to 1000 °C. A high N-doping level of 6 % was achieved and the N-doped rGO exhibits n-type behavior with a Dirac point at −38 V at 400 °C. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Microwave-assisted hydrothermal synthesis of Mn3O4/reduced graphene oxide composites for high power supercapacitors

Crystalline hausmannite nanocrystals/reduced graphene oxide composites (denoted as Mn3O4/RGO) are synthesized by means of the microwave-assisted hydrothermal synthesis (MAHS) route for the application of symmetric and asymmetric supercapacitors. Effects of the Mn3O4 content on the microstructure and electrochemical performances of nanocomposites are systematically investigated. The morphology and crystalline structure of composites are examined by scanning electron microscopic (SEM) and X-ray diffraction (XRD) analyses. Thermogravimetric analysis (TGA) is used to determine the mass content of RGO in the Mn3O4/RGO composites. The results indicate that the composite with about 82.4 weight percents (wt%) Mn3O4 (denoted as GMn80) shows the largest total specific capacitance (∼193 F g−1), which is employed for the tests of supercapacitors of both symmetric and asymmetric types. An aqueous asymmetric supercapacitor, consisting of a GMn80 cathode and an N-doped RGO anode (reduced from a GO-NH4OH solution through the MAHS method), with a cell voltage of 2 V is demonstrated in this work, which shows the device energy and power densities of 11.11 Wh kg−1 and 23.5 kW kg−1, respectively.