Doped Nitrogen Atoms Research Articles

Nitrogen-doped graphene and conducting polymer PEDOT hybrids for flexible supercapacitor and electrochemical sensor

Nitrogen-doped graphene (NG) materials are highly desired for supercapacitors and sensors. Herein, we report nitrogen-doped graphene and conducting polymer PEDOT hybrids for the study of flexible supercapacitor and electrochemical sensor. Free-standing NG/PEDOT hybrids film electrodes were prepared by a flow-directed self-assembly strategy. Nitrogen doping validly exploit graphene's utilization by preventing graphene sheets’ stacking and introducing pseudocapacitance. The PEDOT component not only improves the hybrids’ conductivity and decreases NG's stacking, but also plays the role of binders to induce the hybrids to be free-standing film through simple vacuum filtration. The doping of nitrogen atoms and PEDOT endow the hybrids film with superior hydrophilicity, high conductivity, as well as good electrochemical capacitance (536 F g−1 at 0.5 A g−1). The hybrids films are simultaneously used as electrode materials, current collector, and mechanical support to fabricate flexible supercapacitor with the specific capacitance of 206 F g−1 at 0.25 A g−1. Moreover, the NG/PEDOT hybrids present giant potential in the electrochemical sensor area on account of its superior catalytic properties, hydrophilicity, and conductivity. The NG/PEDOT hybrids modified electrode presents high sensitivity (0.9 μA mM−1 cm−2), with a linear range from 0.2 μM to 90 μM, a detection limit of 54 nM (S/N=3) for dopamine detection.

Effect of graphene surface functionalization on the oxygen reduction reaction in alkaline media

Two types of few-layer graphene structures with different degrees of doping with nitrogen and with close surface concentrations of carbonyl groups were synthesized using the electrochemical exfoliation of graphite in the cathodic plasma mode. As for the concentrations of oxygen-containing functional groups and doping nitrogen atoms, pyridine N atoms make a dominating contribution to the electrocatalysis of oxygen reduction reaction on the synthesized structures.

Highly Efficient Hydrogenation of Nitroarenes by N-Doped Carbon-Supported Cobalt Single-Atom Catalyst in Ethanol/Water Mixed Solvent.

The cobalt single atoms supported on N-doped carbon (Co SAs/NC) were prepared by the direct pyrolysis of metal-organic framework (MOF) precursor. Compared with Co nanoparticle (NP) catalysts prepared by impregnation, the Co SAs/NC catalyst showed a much better performance in the selective hydrogenation of nitrobenzene, giving a specific activity 5.4 and 32.0 times higher than those of Co NPs supported on N-doped carbon and active carbon, respectively. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray absorption fine structure (XAFS), X-ray photoelectron spectra (XPS), N2 adsorption-desorption isotherms, and X-ray diffraction (XRD) characterizations revealed that the atomically dispersed Co species and doped nitrogen atoms in carbon support contributed to the high activity of Co SAs/NC. The reaction rate and aniline selectivity were further remarkably enhanced by introducing water into the reaction system. By adding 30% water to the solvent of ethanol, the activity was increased from 43.2 to 76.8 h-1 and the aniline selectivity was increased from 62.8 to 99.1%. Combining experimental results and density functional theory (DFT) calculations evidenced that the promoting effect of water addition was attributed to its differentiating ability in the competitive adsorption between nitrobenzene and aniline in the hydrogenation reaction. This catalytic system was highly efficient for the selective hydrogenation of various nitroarenes.

Phase inversion synthesis of Fe3O4@NC composites with superior lithium storage performance

The N-doped carbon coated Fe3O4 composites (Fe3O4@NC) are successfully fabricated on a polyacrylonitrile (PAN) phase inversion method and subsequently annealing. Compared with common electrospinning method, needing delicate equipment and strict reaction conditions, this method is facile and ingenious to synthesize PAN-based composites or carbon-coated materials. Applied to lithium ion batteries (LIBs) anode, the Fe3O4@NC composite exhibits a large specific capacity of 981 mAh g−1 at 0.2 A g−1 after 500 cycles, an outstanding rate capability and a superior long-term high-rate cycling performance (632 mAh g−1 at 1 A g−1 after 900 cycles). Its excellent electrochemical performance is attributed to the thin carbon layers on the surface of Fe3O4 nanoparticles, which can not only enhance the electron conductivity, but also buffer the volume change of Fe3O4 nanoparticles during lithiation/delithiation. Moreover, the doped nitrogen atoms derived from PAN can lead to more defects in electrode material, which benefits to the electrochemical performance of Fe3O4@NC composites.

Ag−Co3O4 @ Nr GO Material Synthesized by One‐pot Hydrothermal Method for Carcinoembryonic Antigen (CEA) Detection of Enzyme‐mimetic Electrochemical Immunosensor

AbstractA high‐sensitivity carcinoembryonic antigen immunosensor was successfully prepared via a one‐step hydrothermal method, wherein nitrogen‐doped graphene oxide (Nr GO) loaded Ag and Co3O4 nanomaterials were synthesized using ammonia as the nitrogen source. Doping nitrogen atoms into the graphene structure forms a new type of N‐type semiconductor with an increased number of graphene layers and more active sites for bonding with chemicals, thereby providing excellent in biocompatibility and good electrical conductivity. The electrical signal of the sensor is further amplified due to the good catalytic effect of Co3O4 and Ag NPs on H2O2. The signal probe requires neither pretreatment nor acid treatment, and can be easy to loaded with metal‐immobilized antibodies, which greatly simplifies the detection step not shorten the detection time. The sensor has good sensitivity to detecting carcinoembryonic antigen (CEA) and can easily operate, and requires mild reaction conditions. Under optimal experimental conditions, the linear range of the sensor is 0.001–200 ng ⋅ mL−1, the detection limit is 0.18 pg ⋅ mL−1, and the linear correlation coefficient is 0.991, which can be used for CEA determination of the actual sample.

Constructing flexible and self-standing electrocatalyst for oxygen reduction reaction by in situ doping nitrogen atoms into carbon cloth

Nitrogen doped carbon materials have attracted tremendous attention as the promising candidates for platinum-based catalysts toward oxygen reduction reaction (ORR). Herein, we report a facile preparation of N-doped carbon cloth (Co-N-OCC) as a flexible and self-standing electrocatalyst toward ORR by calcining oxidized carbon cloth coated with cobalt ions in ammonia atmosphere. The pyridinic N, Co-N and pyrrolic N, related to ORR activity, are the dominant configurations of nitrogen with an atomic ratio of 42.27%, 25.36% and 20.29% in the catalyst. The resulting Co-N-OCC shows favorable ORR activity with an onset potential of 0.87 V vs. RHE, an electron transfer number of 3.57, and good methanol tolerance in alkaline electrolyte. Co-N-OCC catalyst sheets were directly assembled in zinc-air battery as catalyst and current collector of cathode. The ORR catalytic performance of Pt/C is further boosted in a zinc-air battery by using the Co-N-OCC sheet as an electrode substrate.

High‐performance counter electrode based on nitrogen‐doped porous carbon nanoribbons for quantum dot‐sensitized solar cells

Nitrogen-doped porous carbon nanoribbons (NPCNs) are facilely prepared by carbonization of polypyrrole (PPy) nanotubes followed by a chemical activation process. NPCN counter electrodes are subsequently fabricated by depositing NPCNs onto Ti mesh for quantum dot-sensitized solar cells (QDSCs). Electrochemical tests are carried out to evaluate the electrocatalytic performance of obtained NPCN electrode. The data of electrochemical tests suggest that the NPCN electrode has a superior electrocatalytic ability towards polysulfide (S22−/S2−) electrolyte regeneration reaction and displays a high stability in polysulfide electrolyte. The excellent electrocatalytic performance of NPCN electrode can be ascribed to their large surface area, 2D porous nanoribbon morphology, and nitrogen atom doping, which provides abundant electrocatalytic active sites and facilitates the electrolyte diffusion. Consequently, a power conversion efficiency of 3.27% is obtained by using NPCN electrode as the counter electrode for QDSC. This efficiency is close to the QDSC assembled with commonly used PbS electrode (4.0%).

Simple multistep assembly of hybrid carbon material based microelectrode for highly sensitive detection of neurotransmitters

The miniature sensor has become one of the most popular tools for electroactive biomarker molecule sensing, but the challenge for preparing microelectrodes of hybrid materials still exists. In this contribution, we report a novel strategy for constructing a hybrid nitrogen-doped graphene microelectrode (NGR ME) to efficiently and reliably detect neurotransmitters. The construction procedure is a simple, green, easy-to-operate multistep assembly sequence coated on a customizable micro/nanoscale substrate. Meanwhile, polydopamine (PDA) is a biologically friendly polymer and playing multiple roles. It starts from classic adhesion ability on micro/nanoscale substrates, and its rich amino functional groups electrostatically adsorbed with graphene oxide (GO). Finally, it provided a nitrogen source for nitrogen atom doping in hybrid graphene materials. Since the self-assembled multilayers undergo a pyrolysis process, the synergistic interaction between the multilayers has endowed the microelectrodes excellent electrical conductivity and electrocatalytic performance. This work demonstrates our approach to designing microelectrodes with customizable sizes, proving that it can be used for neurotransmitter sensing with high sensitivity, excellent selectivity and low detection limit (0.69 nM for DA, 6.5 nM for 5-HT), and also can be implanted into a cannula to make a portable and micro-volume device for detecting real human serum samples, which demonstrates promising prospects in clinical diagnosis.

Tuning the binding behaviors of a protein YAP65WW domain on graphenic nano-sheets with boron or nitrogen atom doping.

In recent years, nanomaterials have attracted considerable research attention for biological and medical related applications due to their well-recognized physical and chemical properties. However, the deep understanding of the binding process at the protein–nanomaterial interface is essential to solve the concern of nano-toxicity. Here, we study the interactions between the recently reported graphenic nano-sheets, BC3 and C3N, and a prototypical protein (YAP65WW domain) via atomistic molecular dynamics simulations. Our simulations reveal that elemental doping is an effective way to tune the binding characteristics of YAP65WW with two nanomaterials. While YAP65WW can be attracted by two nanomaterials, the BC3 sheet is less able to disrupt the protein structure than C3N. From the energy point of view, this is because protein residues demonstrate a binding preference with the trend from electron rich nitrogen to electron deficient boron. Structural analyses of the bio-nano interface revealed the formation of an ordered water shell on the BC3 surface, which was compatible to the crystal pattern of BC3. When a protein binds with BC3, these interfacial water molecules protect the protein from being disrupted. We suggest that elemental doping is efficient to produce fruitful biological-effects of graphenic nanomaterials, which make it a prospective solution for the future design and fabrication of advanced nanomaterials with desired function.

Electronic structure variations of polar and nonpolar ZnO lattices with nitrogen-ion bombardment using synchrotron-based in situ photoemission and X-ray absorption spectroscopy.

Surface polarity with different crystal orientations has been demonstrated as a crucial parameter in determining the physical properties and device applications in many transition metal oxide and semiconductor compound systems. The influences of surface polarity on electronic structures in nitrogen-incorporated ZnO lattices have been investigated in the present work. The successful doping of nitrogen atoms in ZnO lattices is suggested by the existence of N-related chemical bonds obtained from X-ray photoelectron spectroscopy analysis where a pronounced N-Zn peak intensity has been observed in the (000\bar 1)-terminated polar ZnO compound compared with the (10\bar 10)-terminated nonpolar ZnO compound. An energy shift of the valence band maximum towards the Fermi level has been resolved for both polar and nonpolar ZnO lattices, whereas a charge redistribution of the O 2p hybridized states is only resolved for o-plane ZnO with a polar surface. Angular-dependent X-ray absorption analyses at the O K-edge reveal enhanced surface-state contributions and asymmetric O 2p orbital occupations in the (000\bar 1)-terminated o-plane ZnO compound. The results shed light on the efficient nitrogen doping in ZnO lattices with polar surfaces. The comprehensive electronic structure investigations of correlations between impurity doping and surface polarity in ZnO lattices may also offer guidance for the material design in other transition metal oxide and semiconductor systems.

Effect of Fe3O4‐Decorated N‐Doped Reduced Graphene Oxide Nanohybrid on the Anticorrosion Performance of Epoxy Composite Coating

AbstractThe present study explores the synergistic effect of Fe3O4 and heteroatom doped reduced graphene oxide (rGO) nanohybrid on anti‐corrosion performance of epoxy composite coating. In this connection, Fe3O4 nanoparticles were decorated over nitrogen doped rGO (Fe3O4‐NRG) and characterized by Fourier transform infrared spectroscopy (FT‐IR), Raman spectroscopy, X‐ray diffraction (XRD), X‐ray Photoelectron spectroscopy (XPS), and Thermogravimetric analysis (TGA). This approach to modulating the surface properties of graphene and hence the interaction with polymer matrix were quite distinct from traditional surface functionlization or decoration in a sense that the doped nitrogen atom facilitate the growth of Fe3O4 particles and at the same time augmented the interaction of rGO with polymer matrix. The prepared nanohybrid was dispersed in epoxy matrix through mechanical mixing and coated over mild steel surface via spin coating technique. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study revealed superior anti‐corrosion performance of Fe3O4‐NRG/epoxy coating in 3.5 wt% NaCl solution. The corrosion inhibition was found to improve by ∼ 98.5% with 0.5 wt% loading of Fe3O4‐NRG. We believe that this simple solvent free approach to prepare composite coating can be exploit for practical application and thus deserves special attention..

3D interconnected boron- and nitrogen-codoped carbon nanosheets decorated with manganese oxides for high-performance capacitive deionization

The boron- and nitrogen-codoped 3D interconnected carbon nanosheets were synthesized with chitosan hydrogel and boric acid as precursors. The obtained nanosheets were interconnected to form a 3D network with thin lamellae (thickness ∼30 nm) and abundant meso-pores. The successful doping of boron and nitrogen atoms was proved by X-ray photoelectron spectroscopy (XPS). Following the decoration of manganese oxides, the resultant B, N-codoped manganese oxide-containing 3D interconnected carbon nanosheets were highly favorable for ionic transportation and storage. The specific capacitance and desalination amount of the corresponding deionization device reached 249 F g−1 and 20.3 mg g−1, respectively. This nanosheet material exhibited a fast salt adsorption rate and high cycling stability, showing an average salt adsorption rate (ASAR) of 1.5 mg g−1 min−1 and the desalination retention of 90.3% after 50 cycles. B, N-dual doping introduces active sites for ion adsorption and improves the conductivity. In addition, MnO2 deposition contributes to the faradaic pseudocapacitance. This work provides a facile and novel strategy to fabricate 3D carbon nanosheets, by combination of B, N-doping and MnO2 decoration, for highly efficient deionization application.

Defect-Engineered MoS2 Nanostructures for Reactive Oxygen Species Generation in the Dark: Antipollutant and Antifungal Performances.

Meticulous surface engineering of layered structures toward new functionalities is a demanding challenge to the scientific community. Here, we introduce defects on varied MoS2 surfaces by suitable doping of nitrogen atoms in a sulfur-rich reaction environment, resulting in stable and scalable phase conversion. The experimental characterizations along with the theoretical calculations within the framework of density functional theory establish the impact of nitrogen doping on stabilization of defects and reconstruction of the 2H to 1T phase. The as-synthesized MoS2 samples exhibit excellent dye removal capacity in the dark, facilitated by a synergistic effect of reactive oxygen species (ROS) generation and adsorption. Positron annihilation spectroscopy and electron paramagnetic resonance studies substantiate the role of defects and associated sulfur vacancies toward ROS generation in the dark. Further, on the basis of its ample ROS generation in the dark and in the light, the commendable antimicrobial activity of the prepared MoS2 samples against fungal pathogen Alternaria alternata has been demonstrated. Thus, the present study opens up a futuristic avenue to develop newer functional materials through defect engineering by suitable dopants toward superior performances in environment issues.

Nitrogen-Doped Hierarchical Porous Hollow Carbon Microspheres for Electrochemical Energy Conversion

Nitrogen-doped hierarchical porous hollow carbon microspheres (N-HPHCS) are synthesized using melamine-formaldehyde (MF) resin as carbon and nitrogen sources, sulfonated polystyrene microspheres (SPS) as the core template, and SiO2 nanoparticles as the mesopore forming agent. The obtained microspheres are composed of SPS core and MF/SiO2 composite shell (SPS@MF/SiO2). This SPS@MF/SiO2 is then calcined and acid-treated to obtain N-HPHCS. During the calcination, SPS core is removed, and the micropores are formed on the shell owing to the thermal decomposition of the MF resin. After chemical etching of the SiO2 nanoparticles, mesopores are generated on the carbon shell. The as-prepared sample of N-HPHCS has high surface area and large pore volume, and exhibits catalytic activity toward oxygen reduction reaction (ORR). The electrocatalytic performance of N-HPHCS can be ascribed not only to the doped nitrogen atoms, but also to the hierarchical porous structure.

Cobalt-Phosphate Catalysts with Reduced Bivalent Co-Ion States and Doped Nitrogen Atoms Playing as Active Sites for Facile Adsorption, Fast Charge Transfer, and Robust Stability in Photoelectrochemical Water Oxidation.

A cobalt-phosphate (Co-Pi) catalyst having octahedral CoO6 molecular units as reaction sites is a key component in photoelectrochemical (PEC) water oxidation systems, but its limited adsorption sites for oxygen-evolving intermediates (*OH, *OOH), slow charge transfer rates, and fast degradation of reaction sites are yet to be overcome. Here, we report that Co-Pi nanoparticles with low-coordinate Co ions and doped nitrogen atoms could be decorated on hematite nanorod arrays to form N-CoPi/hematite composites. Moreover, the local atomic configuration and bond distance studies show that trivalent Co3+ states are partially reduced through nitrogen radicals in the plasma to low-coordinate bivalent Co2+ states playing as the facile adsorption sites of oxygen-evolving intermediates due to the decreased activation barrier for water oxidation. Electron transport is also reinforced by nitrogen species due to the formation of hybridizing N 2p orbitals that give the acceptor levels in the bandgap. As a result, both the incident photon-to-electron conversion efficiency and the charge transfer resistance on N-CoPi/hematite outperform those on a bare hematite by about 3 fold. Furthermore, N-CoPi/hematite gives high activity retention over 90% after the long operation of water oxidation, in support of the reaction sites on N-CoPi not degrading during the successive water oxidation.

Fabrication of Core‐Shell Ni2P@N, P−Co‐Doped Carbon/Reduced Graphene Oxide Composite as Anode Material for Lithium‐ and Sodium‐Ion Batteries

AbstractCommonly, carbon layer was a suitable choice to enhance the conductivity and reduce the large volume effect of Ni2P nanoparticles (NPs) in electrochemical applications. The doped nitrogen (N) and phosphorous (P) atoms in carbon could further improve its performance. In this paper, core‐shell structure Ni2P@N, P‐co‐doped carbon (Ni2P@N, P−C) NPs were loaded onto reduced graphene oxide nanosheets (GN) to form new composite serial Ni2P@N, P−C/GN, which was designed for the combination of these merits and successfully obtained by two‐step method (firstly hydrothermal process and secondly phosphorization process). As anodes for LIBs and SIBs, the responding electrochemical studies showed the Ni2P@N, P−C/GN‐0.4 electrode exhibited an outstanding specific capacity of 450 mA h g−1 at 5 A g−1 after 2000 cycles in lithium‐ion batteries (LIBs) and maintained 110 mA h g−1 at 2 A g−1 after 3000 cycles in sodium‐ion batteries (SIBs), respectively. These results showed that Ni2P@N, P−C/GN material could be an excellent candidate for energy storage area.

Probing the active sites of site-specific nitrogen doping in metal-free graphdiyne for electrochemical oxygen reduction reactions

The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology. Herein, the site-specific nitrogen doping of graphdiyne (GDY) including grap-N, sp-N(I) and sp-N(II) GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory (DFT). Our results indicate that the doped nitrogen atom can significantly improve the oxygen (O2) adsorption activity of GDY through activating its neighboring carbon atoms. The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction (ORR) in both O2 dissociation and association mechanisms. It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates. Especially, sp-N(II) GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V. This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY.

Single cobalt atom anchored on N-doped graphyne for boosting the overall water splitting

Developing inexpensive and high-active electrocatalysts for overall water splitting is important to the development of future clean energy technologies. Many non-noble metal single-atom catalysts (SACs) present unsatisfactory water-splitting catalytic performance because of their intrinsic electronic structures. Here, through the density functional theory calculations, a nitrogen atom doping strategy is applied to directly tune the electronic structure of the SAC and boost their catalytic activities towards both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). By precisely manipulating N doping modes in graphyne supported single Co atom catalyst (Co@GY), the stability, electronic properties, and HER, as well as OER catalytic activities of these N-doped Co@GY catalysts are investigated. It is found that the N-induced charge redistribution on the surface of the N-doped Co@GY catalysts greatly affects their HER and OER performances. The N-induced charge density not only increases the number of active sites of Co@N1-GY and enhances its catalytic activity for HER, but also weakens the chemisorption of oxygenated species and decreases distinctly the over-potential for OER, making Co@N1-GY a promising bifunctional electrocatalyst for water splitting. This work offers a feasible strategy for experimental groups to properly tune the electronic structures of catalysts and improve catalytic activity.

Hierarchical porous carbon pellicles: Electrospinning synthesis and applications as anodes for sodium-ion batteries with an outstanding performance

N-doped hierarchically structured carbon pellicles (CZIF-8/PAN) were prepared from the carbonization of zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile (PAN) composite fibers which were fabricated by electrospinning technique. The resultant free-standing nanofiberic pellicles can be cut into membrane disks and directly used as anode materials without any binder and additive. As an anode for sodium-ion batteries (SIBs), the CZIF-8/PAN nanofiberic carbon pellicles showed superior reversible capacities of 186.2 mAh g−1 at high current density of 1.0 A g−1 and an excellent cyclic stability (93.5% remaining after 600 cycles) compared to other similar reported carbonaceous anode materials for SIBs. The improved electrochemical performance of CZIF-8/PAN carbon pellicles is mainly attributed to the hierarchical porous structures produced by introducing large ZIF-8 particles as a template, which greatly promotes the large sodium cation transportation and electron transfer rates due to the enlarged pores and increased contact area between the electrode and electrolyte. In addition, the enhanced electrochemical performance of CZIF-8/PAN nanofiberic anodes also benefits from the doping of nitrogen atoms which enhance the conductivity and increase the active sites.

Tuning Nitrogen Species in Two‐Dimensional Carbon through Pore Structure Change for High Supercapacitor Performance

AbstractCarbonaceous materials have long been a key component of supercapacitor energy storage systems, and exploring nitrogen atom doping and its role is currently the focus of carbon‐based electrode development. However, achieving a high proportion of pyridinic N (active N) in N‐doped carbon is still a big challenge. Here, by introducing a triblock copolymer F127 into the phenolic resin, the pore structure of the two‐dimensional carbon material is successfully adjusted, thereby increasing the probability of generation of active nitrogen. We found that this two‐dimensional porous structure is beneficial to the formation of pyridinic N. Through the change of pore structure, the ratio of pyridinic N to the total N was further increased by 13.9 %. Therefore, it provides a large specific capacitance (220 F g−1), excellent cycle stability (93.6 %) and high rate performance (71.2 %) in the alkaline KOH electrolyte. To further increase the energy density, we constructed an symmetrical supercapacitor device using an ionic liquid electrolyte (equal amount of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate and acetonitrile). As a result, since the electrolyte has a voltage window of up to 3 V, the energy density is as high as 37.5 Wh kg−1. This superior performance indicates that adjusting the ratio of pyridinic N provides a promising method for preparing excellent N‐doped carbon materials for energy storage systems.