Nitrogen-doped Graphenes Research Articles

Revision of the oxygen reduction reaction on N-doped graphenes by grand-canonical DFT.

Nitrogen-doped graphenes were among the first promising metal-free carbon-based catalysts for the oxygen reduction reaction (ORR). However, data on the most efficient catalytic centers and their catalytic mechanisms are still under debate. In this work, we study the associative mechanism of the ORR in an alkaline medium on graphene containing various types of nitrogen doping. The free energy profile of the reaction is constructed using grand-canonical DFT at a constant electrode potential in combination with an implicit electrolyte model. It is shown that the reaction mechanism differs from the generally accepted one and depends on the surface potential and doping type. In particular, as the potential decreases, coupled electron-proton transfer changes to sequential electron and proton transfer, and the potential at which this occurs depends on the doping type. It has been shown that oxygen chemisorption is the limiting step. The electrocatalytic mechanism of the nitrogen dopants involves reducing the oxygen chemisorption energy. Calculations predict that, at different potentials, different types of nitrogen impurities most effectively catalyze the ORR.

Sodium Intercalation in Nitrogen-Doped Graphene-Based Anode: A First-Principles Study

Density functional theory (DFT) and Monte Carlo (MC) simulations were performed to study the adsorption and distribution of Na ions on nitrogen-doped graphenes (NGs). DFT simulations revealed that both pyridinic and pyrrolic NGs enhanced Na adsorption even at higher Na concentrations by introducing electron-deficient vacancies. While Na ions tend to cluster on a pristine graphene, they separate when absorbed on pyridinic NGs due to stronger Na adsorption and Na-Na repulsion. Based on DFT energies, MC simulations were performed to study the distribution of Na on a pyridinic NG as a function of the pyridinic defect concentration and Na concentration. The average size of Na clusters decreases with increasing pyridinic defect concentration. The theoretical specific capacity increases monotonically as the pyridinic defect concentration is increased and reaches a maximum value at a concentration of ~7.5%. This theoretical study suggests that the pyridinic NGs hold promise as anode materials for sodium-ion batteries capable of enhancing Na adsorption, preventing Na clustering, and increasing the anode’s specific capacity.

Nitrogen-doped pyrogenic carbonaceous matter facilitates azo dye decolorization by sulfide: The important role of graphitic nitrogen

Pyrogenic carbonaceous matter (PCM) catalyzes azo dye decolorization by sulfide, but the nitrogen doping catalytic mechanisms are poorly understood. In this study, we found that stagnate time of azo dye methyl orange (MO) decolorization was reduced to 0.54-18.28 min in the presence of various nitrogen-doped graphenes (NGs), remarkably lower compared to graphene itself. Particularly, graphitic nitrogen played a critical role in NGs-catalyzed MO decolorization by sulfide. Gas chromatography-mass spectrometry and in-situ surface Raman analysis demonstrated that doping nitrogen, especially graphite one facilitated reactive intermediate polysulfides formation. This is attributed to the improved electron conductivity through graphitic nitrogen doping, and the enhanced interactions between sulfide and carbon atoms bonded to graphitic nitrogen. This study not only provides a better understanding of PCM impact on transformations and fates of organic pollutants in natural environments, but also offer a new regulation strategy for more efficient wastewater treatment processes in PCM-catalyzed engineering systems.

Boosting graphene electrocatalytic efficiency in oxygen reduction reaction by mechanochemically induced low-temperature nitrogen doping

Mechanochemically induced low-temperature preparation of nitrogen-doped few-layer graphenes (N-Gr) and their application as electrocatalysts of oxygen reduction reaction (ORR) in alkaline medium was shown. The proposed approach allowed achieving a high proportion of graphitic nitrogen atoms. Such doping of N-Gr caused healing of vacancies in its structure, and also lead to the increased charge carrier density and high reduction ability that support advanced electrocatalytic characteristics in ORR (the onset and half-wave potentials equal to 0.98 and 0.77 V vs RHE, the average electron transfer number close to four, the Tafel slope about 60 mV/dec), the absolute values of which are close to those of the platinum-based catalyst. A model of N-Gr-based zinc-oxygen cell could provide a discharge current density of ∼40 mA/cm2 at a potential of 1 V and peak power density about 100 mW/cm2, as well as high cathode stability during cycling.

Nitrogen-doped graphene/graphitic carbon nitride with enhanced charge separation and two-electron-transferring reaction activity for boosting photocatalytic hydrogen peroxide production

Pyrrolic nitrogen-doped graphenes with high surface activity of selective catalysis boost the photocatalytic hydrogen peroxide production of graphitic carbon nitride.

Effects of pyridine and pyrrole moieties on supercapacitive properties of imine-rich nitrogen-doped graphene

In this study, a series of imine-rich nitrogen-doped graphenes (IR-NGs), where pyridine and pyrrole functionalities were selectively incorporated in the near vicinity of imine groups, were synthesized, and used as electrode materials for supercapacitors. The facile acid-catalyzed dehydration reactions of graphene oxide (GO) with 6-aminoquinoline and 5-aminoindole could produce specific pyridine- and pyrrole-modified IR-NGs, respectively, denoted as PD-NG and PR-NG, respectively. In addition, aniline was reacted with GO to obtain the reference AN-NG, which only contains imine groups. The compositional and structural features of these three IR-NG compounds were confirmed using various spectroscopic and microscopic measurements. The specific capacitances of these IR-NGs in 6 M aqueous KOH solution as an electrolyte gradually increased as follows: PD-NG < AN-NG < PR-NG. The highest capacitance of 174 F g−1 was obtained from PR-NG at the current density of 1.0 A g−1, whereas the capacitances of PD-NG and AN-NG were limited to 125 and 138 F g−1, respectively, under the same conditions. These results indicated that the contributions of the pyridine and pyrrole moieties on the supercapacitive properties of IR-NGs were significant.

Transition-metal single atoms in nitrogen-doped graphenes as efficient active centers for water splitting: a theoretical study.

Highly active single-atom catalysts (SACs) have recently been intensively studied for their potential in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Due to the existence of many such SAC systems, a general understanding of the trend and designing principle is necessary to discover an optimal SAC system. In this work, by using density functional theory (DFT), we investigated a series of late single transition metals (TM = Fe, Co, Ni, Cu, and Pd) anchored on various N doped graphenes (xN-TM, x = 1-4) as electrocatalysts for both the HER and OER. Solvent effects were taken into account using an implicit continuum model. Our results reveal that the catalytic activity of SACs is determined by the local coordination number of N and TM in the catalysts. Among the considered catalysts, a low-coordinated Co site, i.e. a triple-coordinated Co, exhibits a high catalytic activity toward the HER with a calculated hydrogen adsorption free energy of -0.01 eV, whereas a high-coordinated Co center, i.e. a quadruple-coordinated Co is a promising candidate for the OER with a low computed overpotential of -0.39 V, which are comparable to those of noble metal catalysts, indicating superior HER and OER performance of N-Co co-doped graphenes. The results shed light on the potential applications of TM and N co-doped graphenes as efficient single-atom bifunctional catalysts for water splitting, thereby functioning as promising candidates for hydrogen/oxygen production.

Metal-N4/graphene as an efficient anchoring material for lithium-sulfur batteries: A computational study

Despite their high theoretical capacity, the practical commercialization of lithium-sulfur batteries have continued to face obstacles of low cycle stability and low efficiency, which stem from the dissolution and diffusion of lithium polysulfides intermediates in the electrolyte. Here, by means of comprehensive density functional theory computations, we exploited the potentials of the experimentally available metal-nitrogen/graphene as the anchoring material for high-performance Li-S batteries. Our results revealed that Cr-, Mn-, Fe-, Co-, and Cu-nitrogen/graphenes exhibit optimal interaction with soluble lithium polysulfides due to the synergistic effects between the metal and N atoms, which not only effectively traps the soluble lithium polysulfides to suppress the shuttle effects, but also well keeps their cyclic structures intact. Especially, the electronic properties of metal-nitrogen/graphenes are well preserved, and the computed voltages of discharge processes are larger than those of the well-established nitrogen-doped graphenes. Thus, the metal-nitrogen/graphene could present a kind of quite promising anchoring material for lithium sulfur battery cathodes to suppress the lithium polysulfides shuttle effect.

Enhancing sulfacetamide degradation by peroxymonosulfate activation with N-doped graphene produced through delicately-controlled nitrogen functionalization via tweaking thermal annealing processes

Nitrogen-doped graphenes (NG) fabricated through thermal annealing of graphene oxide (GO) and urea was applied to activate peroxymonosulfate (PMS) for sulfacetamide (SAM) degradation. The contents of reactive functional groups (graphitic N, pyridinic N, pyrrolic N, nitric oxide and CO) and catalytic performance of NG were delicately controlled by adjusting thermal annealing temperature. Thermal annealing temperature of ≥500°C was required to produce the NG endowed with catalytic activity for SAM degradation via PMS activation. NG600 (NG prepared at 600°C) with a high N doping level (16.0wt%) and a most optimum amount of pyridinic N (38.4%N), pyrrolic N (31.8%N), graphitic N (25.9%N) and CO groups (43.7%O) exhibited the most outstanding catalytic activity to activate PMS. NG600 with the controlled N bonding configurations possessed a higher SAM degradation efficiency than NGs prepared via other optimized synthesis methods The specific surface area (SSA) contributed less significantly than N doping to the SAM degradation performance. Increments in the PMS dosage and catalyst loading were both conducive to the catalytic performance of NG. The presence of NO3− in the NG600/PMS system had a negligible influence on SAM degradation but Cl− and humic acid decreased the SAM degradation rate. Experiments using chemical scavengers and electron paramagnetic resonance (EPR) study revealed that SAM degradation process follows predominantly the radical pathway with sulfate radical (SO4−) as the main reactive oxygen species over the non-radical pathway. Density functional theory (DFT) calculations suggest that graphitic N can facilitate PMS adsorption on the NG and SAM degradation. This study improves the understanding on the role of different surface N functional groups of NG in the PMS activation.

Fabrication of nitrogen-doped graphenes by pulsed laser deposition and improved chemical enhancement for Raman spectroscopy

In this letter, we report the in situ growth of N-doped graphene (NG) thin films by ultraviolet pulsed laser deposition (PLD) in the presence of nitrogen. Based on this approach, the concentration of nitrogen-doping can be easily controlled via the nitrogen gas pressure during the PLD process. XPS results confirm that the nitrogen atoms have been successfully doped into graphene lattice. Moreover, the NGs show improved chemical enhancement for Raman spectra of absorbed Rhodamine 6G (R6G) molecules as compared to the pristine graphene (PG). The relative enhancement factor varies with the nitrogen content in the graphene, and the maximum value is about 2.5. The results show that the NG is a promising material for applications in chemical and biological detection because of its excellent enhanced Raman scattering performance.

A mechanistic study on the carrier properties of nitrogen-doped graphene derivatives using thermoelectric effect

For graphene to find wide applicability in various nanoelectronic applications, it must be synthesized in bulk with reliable n- and p-type electrical properties. Most nitrogen-doped graphenes show p-type character despite their high nitrogen contents, leading to a lack of the n-type graphene. Here, we demonstrate that the reason why the pristine n-type graphene derivatives exhibit p-type character is due to unintentional hole doping by water and oxygen molecules from surroundings, which was firstly confirmed by understanding the electrochemical potential of graphene and water/oxygen layer. Furthermore, we show that this unintentionally p-doped graphene derivative can be changed to air-stable n-type by the surface charge transfer doping using polyethylenimine with the electron donating groups. The carrier properties of graphene derivatives were investigated using thermoelectric effects. These results demonstrate that the mechanistic and systematic study proposed here for controlling the carrier properties of graphene derivatives has great potential for further development of graphene-based electronic and energy devices.

Nitrogen doped nanographene structures; study on the adsorption of nucleobases, nucleotides, and their triphosphate derivatives using mixed docking, MD, and QM/MM approaches.

The interactions of the nucleobases, nucleotides, and their triphosphate derivatives in both neutral and anionic forms with the nitrogen doped graphenes (NG) were studied using docking and molecular dynamic simulation methods. In docking studies, based on binding energy results, the anionic species and nucleobases were showing the most and the least tendency toward the surface of the NG, respectively. The molecular mechanic/Poisson-Boltzmann surface area results revealed similar results, except for the anionic species; in these studies, the anionic species showed a lesser affinity toward the NG. The time-dependent density functional theory studies were carried out to investigate the effects of the NG on the electronic nature of the investigated ligands; a red-shift in all of the cases was observed. The results of binding energy decomposition and atoms in molecules studies showed that the interactions are van der Waals in nature. The graphitic, pyridinic, and pyrrolic nitrogen atoms which were considered in this study behaved similar to each other.

3-D mesoporous nitrogen-doped reduced graphene oxide as an efficient metal-free electrocatalyst for oxygen reduction reaction in alkaline fuel cells: Role of π and lone pair electrons

Nitrogen-doped graphenes are promising oxygen reduction reaction (ORR) electrocatalysts for replacement of Pt-based electrocatalysts. In this paper, 3-D mesoporous nitrogen-doped reduced graphene oxides (NRGOs) with different nitrogen contents (1.0–4.7%) were hydrothermally synthesized through manipulation of relative amount of the graphite oxide (GtO) and melamine. Eight characterization techniques including FESEM, TEM, BET, XRD, Raman, FTIR, UV–vis, and XPS were used to evaluate the structural and electronic properties of the prepared nanomaterials. The ORR performance of NRGOs and commercial 20wt% Pt/C were examined in three electrode cell and direct methanol fuel cell (DMFC) setups. It was revealed that N-content of NRGOs (regardless of their bonding configurations) promotes ORR performance at lower potentials due to activation and strengthen of π-electrons of graphene framework while pyridinic-N content has significant role in ORR at higher potentials because of activation of their lone pair electrons. Furthermore, the DMFC with NRGO containing 4.1% (4.6wt%) nitrogen as cathode electrocatalyst, due to its higher selectivity towards ORR, presents superior output power compared to the commercial 20wt% Pt/C one.

Nitrogen-doped graphene supporting PtSn nanoparticles with a tunable microstructure to enhance the activity and stability for ethanol oxidation

In this work, a series of nitrogen-doped graphenes (NGs) were prepared by deriving from pyrolysis of graphite oxide (GO) with urea at different temperatures and high-dispersed PtSn nanoparticles with tunable size were then deposited onto nitrogen-doped graphene (PtSn/NG) by an easy-controlled template-free method. The PtSn/NG and undoped graphene (PtSn/G) were carried out as anode catalysts for the electrooxidation of ethanol. The microstructure and morphology of the synthesized catalysts were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. The electrocatalytic performance toward ethanol oxidation was evaluated by cyclic voltammetry and chronoamperometry. It is found that the pyrolysis temperature is an important factor which influenced the contents of nitrogen and functional groups of nitrogen. And then, the functional groups of nitrogen affect the distribution, size, and contents of PtSn nanoparticles. The as-obtained optimal PtSn/NG-600 sample with narrower size distribution and high content of PtSn exhibits higher electrocatalytic activity and stability compared with the other samples, implying the potential application for ethanol fuel cells.

Boron and Nitrogen Doped Graphene via Microwave Exfoliation for Simultaneous Electrochemical Detection of Ascorbic Acid, Dopamine and Uric Acid

AbstractBoron and nitrogen doped graphenes show opposite effect on the electronic structure, one with electron withdrawing and another one with electron donating effects. It is of high importance to investigate the influence of B or N doping on biomarkers detection and compare it to non‐doped graphene. Here we show that B‐doped graphene shows significant enhancement in detection currents in the cyclic voltammetry of the above mentioned compounds.

Gas adsorption, energetics and electronic properties of boron- and nitrogen-doped bilayer graphenes

We study stabilities and electronic properties of several environmental polluting or toxic gas molecules (CO, CO2, NO, and NO2) adsorbed on B and N atoms in bilayer graphene using first-principles electronic-structure calculations. We find that NO and NO2 molecules can be bound chemically on B-doped bilayer graphene with large adsorption energies, while CO and CO2 molecules are not adsorbed chemically on B-doped one. In the case of the N-doped graphene, all four gases do not bind with chemical bonds but adsorb rather physically with small adsorption energies at long distances between gases and graphene. The adsorptions of NO and NO2 molecules on B-doped bilayer graphene induce the acceptor states above the Fermi energy, and we also find that the charge transfer takes place when the NO and the NO2 molecules are adsorbed. Thereby, the B-doped bilayer graphene is expected to be useful for NO and NO2 gas sensor materials.

Tuning the Electrochemical Reactivity of Boron- and Nitrogen-Substituted Graphene.

The structural modification of nanomaterials at the atomic level has the potential to generate tailor-made components with enhanced performance for a variety of tasks. The chemical versatility of graphene has been constantly employed to fabricate multi-functional doped 2D materials with applications encompassing energy storage and electrocatalysis. Despite the many reports on boron- and nitrogen-doped graphenes, the possible synergy that arises from combining these electronically complementary elements has yet to be fully understood and explored. The techniques used for the fabrication of these nanomaterials are reviewed, along with the most recent reports on the benefits of B, N singly doping and co-doping in the electrocatalysis for oxygen reduction reactions and for energy storage in supercapacitors and lithium secondary batteries. The investigation of bulk co-doped materials has intrinsic limitations in fully understanding the real role of heteroatoms in the above applications. Ultimately, the design and creation of substituted monolayers with controlled compositions might hold the key for carbon-based energy-related applications.

Nitrogen-doped graphenes as efficient electrocatalysts for the selective reduction of carbon dioxide to formate in aqueous solution

We report the first example of metal-free nitrogen-doped graphene-based materials for the electrochemical reduction of CO2to formate. The synthesized catalysts are highly active and stable in the electrocatalytic reduction of CO2to formate in an aqueous electrolyte.

Nitrogen doped porous graphene as counter electrode for efficient dye sensitized solar cell

Nitrogen doped graphenes (NGs) were synthesized by pyrolysis of graphene polypyrrole composites (G-PPys) for application as counter electrode (CE) in dye sensitized solar cells (DSSCs). The as-prepared NGs demonstrate mesoporous texture with large specific surface areas, high N doping level with homogeneous distribution, as well as moderate graphitization phase, all of these structural and interfacial features are beneficial for abundant active sites and well conductivity, therefore can effectively promote the electrocatalytic reduction of I3⿿ and improve the photovoltaic performances of pertinent DSSCs. The optimized sample, denoted as NG2, used as CE of DSSC exhibit high power conversion efficiency (PCE) (6.8%) with high reliability and durability, which is comparable to that of Pt CE (7.0%). Given the cost effective synthesis and the high electrochemical performance, NG2 herein is a promising non-Pt CE alternative material in DSSC.

First-Principles Calculation of Quantum Capacitance of Codoped Graphenes as Supercapacitor Electrodes

Because of their many advantages, graphene and graphene-based materials are used in supercapacitor electrodes. The main limitation of these electrodes is their low quantum capacitance, which is a direct result of the shortage of states near the Fermi level. Using first-principles density functional theory calculations, this report explored the quantum capacitances of Si-, S-, and P-doped graphenes and the same materials codoped with nitrogen. The findings imply that using phosphorus- and nitrogen-doped graphenes as electrode materials for supercapacitors could be a worthwhile strategy. Quantum capacitance calculations confirmed the greater advantage of some codoped graphenes compared with doped and pristine graphene.