N-doped Graphene Research Articles

Single-Entity Electrochemistry of N-Doped Graphene Oxide Nanostructures for Improved Kinetics of Vanadyl Oxidation.

N-doped graphene oxides (GO) are nanomaterials of interest as building blocks for 3D electrode architectures for vanadium redox flow battery applications. N- and O-functionalities have been reported to increase charge transfer rates for vanadium redox couples. However, GO synthesis typically yields heterogeneous nanomaterials, making it challenging to understand whether the electrochemical activity of conventional GO electrodes results from a sub-population of GO entities or sub-domains. Herein, single-entity voltammetry studies of vanadyl oxidation at N-doped GO using scanning electrochemical cell microscopy (SECCM) are reported. The electrochemical response is mapped at sub-domains within isolated flakes and found to display significant heterogeneity: small active sites are interspersed between relatively large inert sub-domains. Correlative Raman-SECCM analysis suggests that defect densities are not useful predictors of activity, while the specific chemical nature of defects might be a more important factor for understanding oxidation rates. Finite element simulations of the electrochemical response suggest that active sub-domains/sites are smaller than the mean inter-defect distance estimated from Raman spectra but can display very fast heterogeneous rate constants >1cms-1. These results indicate that N-doped GO electrodes can deliver on intrinsic activity requirements set out for the viable performance of vanadium redox flow battery devices.

Computational Design of the Electronic Response for Volatile Organic Compounds Interacting with Doped Graphene Substrates

Changes in the work function provide a fingerprint to characterize analyte binding in charge transfer-based sensor devices. Hence, a rational sensor design requires a fundamental understanding of the microscopic factors controlling the modification of the work function. In the current investigation, we address the mechanisms behind the work function change (WFC) for the adsorption of four common volatile organic compounds (toluene, ethanol, 2-Furfurylthiol, and guaiacol) on different nitrogen-doped graphene-based 2D materials using density functional theory. We show that competition between the surface dipole moment change induced by spatial charge redistribution, the one induced by the pure adsorbate, and the one caused by the surface deformation can quantitatively predict the work function change. Furthermore, we also show this competition can explain the non-growing work function change behavior in the increasing concentrations of nitrogen-doped graphenes. Finally, we propose possible design principles for WFC of VOCs interacting with N-doped graphene materials.

Chemical Changes from N-doped Graphene and Metal-organic Frameworks to N-G/MOF Composites for Improved Electrocatalytic Activity

Chemical Changes from N-doped Graphene and Metal-organic Frameworks to N-G/MOF Composites for Improved Electrocatalytic Activity

Fe3O4 nanoparticles decorated on N-doped graphene oxide nanosheets for elimination of heavy metals from industrial wastewater and desulfurization

Finding an effective and excellent pertinent single catalyst material for multipurpose application for the purification of hydrocarbons in fuels (desulfurization), and for efficient removal of heavy metals from industrial effluent is greatly endowed. In the present work, a hybrid nanocomposite of ultrafine magnetite (Fe3O4) nanoparticle embedded on the surface of in-situ nitrogen doped layered GO (NGO) sheets were fabricated by sol-gel method and treatment with microwave irradiation technique is reported for the first time. The results show a high removal efficiency of 97 % for multiple heavy metals (Pb2+, Cd2+, Cu2+, Cr+2, Mn+2etc.) in industrial effluent and as well as in synthetic water with a very good retention performance of 99 %. The composites were tested against the elimination of sulfur from thiophene is 1.495 mmol g−1 is reported high is due to coupling and coordination of nitrogen with FeO and C. Recycling studies showed that the developed composites had excellent recyclability, with <82 % removal at the 5th cycle; its feasibility was evaluated using industrial effluent water and in synthetic water. Surface phenomena studies presented here revealed that the adsorptive removal processes of heavy metals involved π electron donor-acceptor interactions, ion exchange, and electrostatic interactions, along with surface complexation that showed an excellent synergism. A high stability, and retention performance is better than the pure Fe3O4 and NGO sheets. We hope that this study will motivate and give further scope for scientists working on magnetite-based graphene nanocomposites.

Interface engineering of heterostructural quantum dots towards high-rate and long-life lithium-sulfur full batteries

Despite being as next-generation energy storage systems with ultra-high theoretical energy density of 2600 Wh kg−1, lithium-sulfur (Li-S) batteries face serious hurdles due to the sluggish redox kinetics in S cathodes and uncontrollable growth of dendrites in Li anodes. To simultaneously address such issues, herein, we present an interface engineering strategy to develop a dual-functional host for S cathode and Li anode, which is constructed by heterostructural WC-WN0.67 quantum dots homogeneously embedded in N-doped graphene nanosheets (WC-WN0.67@NG). As a result, the Li-S full batteries deliver a high reversible capacity of 704 mA h g−1 even at a high rate of 4 C, and demonstrate a long-term cycling stability even at 2 C with a low degradation rate of 0.027 % over 1200 cycles. This work paves the way to facilitate the practical applications of Li-S batteries through interface engineering of dual-functional heterostructural quantum-dot host.

Ultrafine Mo2N Quantum Dots Embedded in N-Doped Graphene Sheets Enable Efficient Adsorption-Catalytic Transformation of Polysulfides.

Because of the high theoretical energy density of 2600 Wh kg-1, lithium-sulfur batteries (LSBs) are anticipated to be among the next generation of high-energy-density storage technologies. However, the practical application of LSBs has been severely hampered by the significant shuttle effect and slow redox kinetics of polysulfides (LiPSs). To address the above problems, in this paper, the concept of quantum dots (QDs) was introduced to design and synthesize Mo2N QD-modified N-doped graphene nanosheets (marked as Mo2N-QDs@NG), which were used as separator modification materials for LSBs. The experimental results demonstrated that the introduction of Mo2N QDs avoids stacking of graphene sheets and provides more active sites for the conversion of LiPSs. Moreover, Mo2N enhances the chemical fixation and catalyzes the liquid-solid conversion of soluble LiPSs by forming Mo-S and Li-N bonds with LiPSs. Additionally, establishing Mo-C bonds with Mo2N, N-doped graphene sheets can facilitate the transport of electrons and ions and physically prevent the diffusion of LiPSs, thus creating a highly conducting carbon structure to support electrochemical reactions. Benefiting from the synergistic effect of chemical immobilization and catalysis of Mo2N QDs with the physical confinement of NG, Mo2N-QDs@NG-PP batteries exhibit enhanced electrochemical performance.

Single-Atom Underpotential Deposition at Specific Sites of N-Doped Graphene for Hydrogen Evolution Reaction Electrocatalysis

Single-atom catalysts (SACs) have the advantages of good active site uniformity, high atom utilization, and high catalytic activity. However, the study of its controllable synthesis still needs to be thoroughly investigated. In this paper, we deposited Cu SAs on nanoporous N-doped graphene by underpotential deposition and further obtained a Pt SAC by a galvanic process. Electrochemical and spectroscopic analyses showed that the pyridine-like N defect sites are the specific sites for the underpotential-deposited SAs. The obtained Pt SAC exhibits a good activity in a hydrogen evolution reaction with a turnover frequency of 25.1 s−1. This work reveals the specific sites of UPD of SAs on N-doped graphene and their potential applications in HERs, which provides a new idea for the design and synthesis of SACs.

Modality-Tunable Exfoliated N-Doped Graphene as Effective Electrolyte Additive for High-Performance Lithium-Sulfur Batteries.

While chemically doped graphene has shown great promise, the lack of cost-effective manufacturing has hindered its use. This study utilizes a facile fabrication approach for modality-tunable N-doped graphene via thermal annealing of aqueous-phase-exfoliated few-layered graphene from a Taylor-Couette reactor. This method demonstrates a high level of N-doping (27 atom % N) and offers modality tunability of the C-N bond without foregoing scalability and green chemistry principles. The resulting N-doped graphene, with varying N content and doping modality, is utilized in the lithium-sulfur battery electrolyte to address low ionic conductivity, lithium polysulfide (LiPS) shuttling, and Li anode instability. The study reveals that higher N content and pyridinic N modality graphene in the electrolyte positively influence battery performance. The results are 2-fold: higher overall N content improves capacity retention (73%) after 225 cycles at 0.2 C, and pyridinic-type nitrogen demonstrates the best performance at high C rates, exhibiting a 4-fold capacity increase relative to the reference cell at 2 C. Further, the computational study validates the adsorption affinity of LiPS to pyridinic nitrogen and improved Li+ mobility on the graphene backbone observed experimentally. This first experimental study on the impact of N-dopant concentration and modality on electrochemical performance provokes insights into tailoring N functionalization to achieve superior electrochemical performance.

Rare-earth metal neodymium anchored into graphene as a promising CO2 reduction electrocatalyst by regulating the coordination environment

Carbon-based single atom catalysts (SACs) are promising electrocatalysts in the field of carbon dioxide reduction reactions (CO2RR) due to their high efficiency and environmental friendliness, in which the coordination environment is the key factor determining their intrinsic catalytic activity. Furthermore, rare-earth-based SACs have shown great potential on CO2RR in recent years. Meanwhile, various studies have focused on combining metals with N-doped graphene, which together form potential Mx-Ny-C active sites. This work systematically investigates the impact of varying N/C coordination numbers on Nd atoms in graphene (Nd-NxC6-x, x = 0–5) on the CO2RR reaction mechanism and catalytic performance through density functional theory methods. Detailed Gibbs free energy calculation results indicate that most catalysts undergo a two-electron reduction pathway. For Nd-N3C3, Nd-N3C3–1, Nd-N3C3–2, Nd-N4C2, Nd-N4C2–1, Nd-N4C2–2, and Nd-N5C, HCOOH is the main product, with low UL values of -0.18, -0.17, -0.03, -0.10, -0.11, -0.09, and -0.10 V, respectively. In summary, our research results not only indicate that N atoms with different coordination numbers can improve the product selectivity and catalytic activity of catalysts, but also may provide valuable theoretical insights for studying the application of rare-earth-based SACs.

First-principles study of O3 molecule adsorption on pristine, N, Ga-doped and -Ga-N- co-doped graphene

The adsorption of O3 molecules (ozone) on graphene, N-doped graphene, Ga-doped graphene, and -Ga-N- co-doped graphene with an emphasis on O3 detection was examined in this work. The physical characteristics of -Ga-N-co-doped graphene are significantly altered upon O3 adsorption, which makes it a suitable choice for O3 detection molecular sensors. The interaction between the O3 molecule and the adsorbent is explained on the basis of their adsorption energy, adsorption distance and charge transfer. It was found that the adsorption of ozone molecules on the -Ga-N- co-doped graphene was more favorable in energy than that on the pristine one, representing the superior sensing performance of -Ga-N- co-doped system. In our work, we estimated the charge transfer between the O3 molecule and doped graphene nanostructures based on Mulliken population analysis. The calculated adsorption energy value shows the ozone molecule more firmly adsorbs on the surface of -Ga-N- co-doped graphene nanostructures (Eads = –1.74 eV) than that of pristine graphene (Eads = –0.41 eV), deriving from a stronger covalent bond between the ozone molecule and the -Ga- N- co-doped graphene nanostructures. Our findings thus suggest that -Ga-N- co-doped graphene could be a highly efficient gas sensor device for O3 detection in the environment.

Fibrous catalyst based on atomic Pd and N-doped holey graphene functionalized cotton fiber for continuous-flow reaction

Continuous-flow catalysis bridges the gap between bench-scale laboratories and production-scale factories and thus should be a green and promising technology for the manufacture of value-added chemicals. Here, we present the construction of a continuous-flow catalytic system by integrating a tubular reactor with novel catalytic fibers, which are comprised of single-atomic Pd (Pd1) and nitrogen-doped holey graphene (NHG) functionalized cotton fibers (CFs). Due to the loosely packed structure, highly exposed dual-active sites (i.e., single-atomic PdN4 sites and activated C sites in the NHG carbocatalyst) of the CF@(Pd1/NHG) catalytic fibers, the corresponding flowing system exhibites remarkably high catalytic performance (activity and durability) and processing rate in organic reactions, including oxidative hydroxylation of phenylboronic acid and reduction of nitroarenes. Typically, the processing rate of the catalytic system toward 4-nitrophenol (a representative nitroarene) reduction can reach up to 2.46 × 10−3 mmol·mg−1·min−1, significantly higher than that of those packing catalysts reported in recent years.

Supported Cu3 cluster on N-doped graphene: An efficient triatom catalyst for CO electroreduction to propanol at low potential

Electroreduction of carbon monoxide into high-energy fuel is an excellent energy strategy for sustainable development, but the high yield of multi-carbon products remains a difficult challenge. Inspired by the successful synthesis of various trimer metal clusters and studies on electrocatalysis of CO to C3 products by Cu-based catalysts, Cu3 supported on N-doped graphene structures (Cu3@NG) are investigated as electrocatalysts for CORR toward propanol in this paper. Due to the appropriate Cu-Cu bond length, the moderate charge of the Cu site, mild CO adsorption energy, and 100 % CO coverage, the absorbed 3*CO substance can form the critical *CO-CO-CO intermediate with a rather low kinetic barrier of 0.25 eV. The limiting potential of the whole process for the formation of propanol is just −0.15 V. Our work not only showed that Cu3@NG is an excellent catalyst for the formation of propanol with high selectivity at low potential but also indicated that the *CO coverage can greatly reduce the CO hydrogenation potential and bonding of some intermediates such as *CH2O. This research will provide a new idea for the material design of products tending to multi-carbon.

Three-Supercenter Two-Electron Bonds in C16H10: Two-Dimensional Analogue of Halogen-Bridge Bonding.

Three-center two-electron bridging bonding plays a vital role in rationalizing structures and stabilities of certain molecules. Herein, the π electron rule of pyrene (C16H10) was unraveled based on a newly proposed two-dimensional (2D) superatomic-molecule theory, where the superatomic sextet rule was regarded as a π electron counting target. C16H10 can be taken as a ◊N2◊F2 superatomic molecule, where ◊N and ◊F denote 2D superatoms bearing 3π and 5π electrons, respectively. Interestingly, it represents the first 2D superatomic halogen-bridge molecule, which realizes π electronic shell-closure via two three-supercenter two-electron bridging bonds. Additionally, a N-doped nanoporous graphene with a wide band gap (1.22 eV) was designed based on C16H10, which can be considered as a periodic aggregate of 2D superatomic wires composed of 2π-◊C and bridging ◊F superatoms. This work enriches the 2D superatomic-molecule chemistry and provides a practicable bottom-up assemble approach to obtain 2D functional materials with tunable band gaps.

Impact of Nitrogen-Enriched 1T/2H-MoS2/CdS as an Electrode Material for Hybrid Supercapacitor.

Transition metal chalcogenides (TMX) have attracted energy researchers due to their role as high-performance electrode materials for energy storage devices. A facile one-pot hydrothermal technique was adopted to synthesize a molybdenum disulfide/cadmium sulfide (MoS2/CdS) (MCS) composite. The as-prepared samples were subjected to characterization techniques such as XRD, FT-IR, SEM, TEM, and XPS to assess their structure, morphology, and oxidation states. The MoS2/CdS (MCS) composites were prepared in three different ratios of molybdenum and cadmium metals. Among them, the MCS 1:2 (Mo:Cd) ratio showed better electrochemical performance with a high specific capacitance of 1336 F g-1 (high specific capacity of 185.83 mAh g-1) at a specific current of 1 A g-1 for half-cell studies. Later, a hybrid supercapacitor (HSC) device was fabricated with N-doped graphene (NG) as an anode and MCS (1:2) as a cathode, delivering a high specific energy of 34 Wh kg-1 and a specific power of 7500 W kg-1. The high nitrogen content in the MoS2 structure in MCS composites alters the device's performance, where CdS supports the composite structure through its conductivity and encourages the easy accessibility of ions. The device withstands up to 10 000 cycles with a higher Coulombic efficiency of 97% and a capacitance retention of 90.25%. The high-performance NG//MCS (1:2) HSC may be a potential candidate alternative to the existing conventional material.

Enhanced charge storage in supercapacitors using carbon nanotubes and N-doped graphene quantum dots-modified (NiMn)Co2O4

The integration of ternary metal oxides into carbon materials is anticipated to significantly boost the electrochemical performance of supercapacitor electrodes. This article synthesized carbon nanotubes (CNT)/(NiMn)Co2O4 composite materials using a straightforward hydrothermal method and subsequently prepared composite thin films of CNT/P-(NiMn)Co2O4@NGQD by phosphating and incorporating nitrogen-doped graphene quantum dots (NGQD). These films served as the functional electrode material for supercapacitors, enhancing their performance capabilities. The specific capacity of CNT/P-(NiMn)Co2O4@NGQD was measured at 2172.0 F g−1 at a current density of 1 A g−1, maintaining a capacitance of 1954.0 F g−1 at 10 A g−1, thus demonstrating excellent rate performance. Electrochemical impedance spectroscopy (EIS) further revealed enhancements in electrolyte flow dynamics and capacitance behavior post-NGQD introduction. The energy density of the composite material reached 94.4 Wh kg−1 at power density of 800 W kg−1, demonstrating superior electrochemical performance. The enhancement in these electrochemical properties is attributed to the high specific surface area and active sites of CNT/P-(NiMn)Co2O4@NGQD films, along with the synergistic effects of NGQD and metal ions facilitating rapid electrons and charge transfer. This work provides new insights into developing high-performance supercapacitors.

Regulating the evolution of interfacial species via B, N-codoped Pt sites for oxygen reduction electrocatalysis

The sluggish kinetics of the oxygen reduction reaction (ORR) poses significant limitations to the widespread application of the ORR in advanced energy systems. Here, we present a composite catalyst consisting of Pt nanoparticles immobilized on 3D B, N-doped graphene oxide (Pt/GO-BCN). Through X-ray absorption fine structure spectroscopy and synchrotron radiation infrared spectroscopy analyses, we discovered that the codoping of B and N significantly regulates the electronic structure of graphene and enhances the interaction between Pt nanoparticles and the supports. The electronic state-optimized 3D support promotes the uniform distribution of Pt nanoparticles with small size, forming a low-resistance interfacial environment to accelerate the cleavage of the *OOH species during the reaction process. The ORR activity and selectivity of Pt/GO-BCN significantly surpass those of commercial Pt/C catalysts, and excellent durability under long-term operation is achieved. These results provide a new avenue for the design of advanced Pt-based catalysts.

CO2 adsorption on 3d transition metal-alloyed Pt clusters supported on pyridinic N-doped graphene

CO2 adsorption on Pt4 and on Pt2M2 (M = Co, Ni, and Cu) clusters supported on N-doped graphene (PNG) was analyzed using density functional theory. The Pt2M2 (M = Co, Ni) clusters supported on PNG had the maximum binding energy and charge transfer. Furthermore, the adsorption energy and charge transfer of CO2 were high for Pt2M2 (M = Co, Ni, and Cu) supported on PNG. In addition, bond elongation and bending angle were observed in the CO2 molecule after it was adsorbed on metal clusters supported on PNG. Non-covalent interaction contours revealed a repulsive interaction due to the steric effect between Pt2M2 (M = Co, Ni, and Cu) and PNG, whereas the Pt4/PNG composite showed a combination of repulsive and van der Waals interactions. This investigation proved that Pt2M2 (M = Co, Ni, and Cu) clusters supported on PNG are promising candidates for CO2 adsorption and activation.

Highly efficient nitrogen-doped graphene coupled eosin-B photocatalyst for fixation and regeneration of N2 and NADH cofactors under visible light

Achieving nitrogen fixation in visible light-driven using metal-free and eco-friendly semiconductors at acceptable temperature and pressure still remains a big challenge. In the field of artificial photosynthesis, reported semiconductors for nitrogen fixation have large band gap around 3.0 eV and requires high temperature and pressure which results the catalytic nitrogen fixation is navigate under visible light, consume supply of global energy, and emit global greenhouse gas. In conflict this report illustrates a metal free catalyst EBCNDG with a band gap of ∼2.64 eV at room temperature and pressure indicate photocatalytic campaign toward nitrogen fixation in visible light without producing any harmful gases. The EBCNDG photocatalyst has a vacancy of high active oxygen which helps adsorb and stabilize the intermediate and increases the rate of nitrogen fixation. The EBCNDG photocatalyst was prepared by coupling of an eosin B (EB) with N-doped graphene (NDG) via amide linkage. This unique combination opens a new trial for nitrogen fixation as well as NADH regeneration under acceptable conditions using visible energy. The amount of ammonia obtained by EBCNDG is 0.513 mM and the regeneration yield of NADH is 90.3%.

Potential of graphene as an adsorbent for HSSS· radical – A DFT investigation

The sulfane sulfur molecules are known to regulate many biological processes for the normal functioning of cells. Herein, the interactions of pristine, B-doped, N-doped, BN-codoped, monovacancy defected, and Stone-Wales (SW) defected graphene with HSSS· radical have been investigated theoretically in the framework of density functional theory (DFT) with an aim to understand if pristine or modified graphene can be used as an adsorbent for HSSS· radical. The analysis based on the structural details, Wiberg bond, ZPE-corrected adsorption energies, reaction enthalpies, reaction free energies and density of states (DOS) reveal that the pristine, BN-codoped, monovacancy defected and SW defected graphene would serve as potential adsorbents for adsorption of HSSS· radicals; the monovacancy defected graphene could be the best choice for this job. It is found that the B-doped graphene would act as a weak adsorbent but the N-doped graphene would not at all be suitable for adsorption of HSSS· radicals.

Theoretical Study on the Electrocatalytic CO2 Reduction Mechanism of Single-Atom Co Complexed Carbon-Based (Co-Nχ@C) Catalysts Supported on Carbon Nanotubes.

Electrocatalytic CO2 reduction serves as an effective strategy to tackle energy crises and mitigate greenhouse gas effects. The development of efficient and cost-effective electrocatalysts has been a research hotspot in the field. In this study, we designed four Co-doped single-atom catalysts (Co-Nχ@C) using carbon nanotubes as carriers, these catalysts included tri- and dicoordinated N-doped carbon nanoribbons, as well as tri- and dicoordinated N-doped graphene, respectively denoted as H3(H2)-Co/CNT and 3(2)-Co/CNT. The stable configurations of these Co-Nχ@C catalysts were optimized using the PBE+D3 method. Additionally, we explored the reaction mechanisms of these catalysts for the electrocatalytic reduction of CO2 into four C1 products, including CO, HCOOH, CH3OH and CH4, in detail. Upon comparing the limiting potentials (UL) across the Co-Nχ@C catalysts, the activity sequence for the electrocatalytic reduction of CO2 was H2-Co/CNT > 3-Co/CNT > H3-Co/CNT > 2-Co/CNT. Meanwhile, our investigation of the hydrogen evolution reaction (HER) with four catalysts elucidated the influence of acidic conditions on the electrocatalytic CO2 reduction process. Specifically, controlling the acidity of the solution was crucial when using the H3-Co/CNT and H2-Co/CNT catalysts, while the 3-Co/CNT and 2-Co/CNT catalysts were almost unaffected by the solution's acidity. We hope that our research will provide a theoretical foundation for designing more effective CO2 reduction electrocatalysts.