Nitrogen-doped Carbon Nanosheets Research Articles

Synthesis of Biomass-Derived Nitrogen-Doped Porous Carbon Nanosheests for High-Performance Supercapacitors

Graphene-like two-dimensional carbon nanosheets with properly modulated compositions and porosity are of particular importance for robust capacitance harvesting. Nevertheless, the large-scale and cost-effective production of such nanostructures still remains a great challenge. Herein, we innovatively produce nitrogen-doped porous carbon nanosheets using pine nut shells, an abundant biomass waste, as the precursor, under the synergetic effect of KOH and melamine during the activation process. The sole activation of the precursors with KOH can produce only traditional activated carbon particles of several micrometers, while interestingly, the extra introduction of melamine results in nitrogen-doped porous carbon nanosheets possessing high tunability. By construction of a two-electrode configuration, the supercapacitors with optimal nanosheets as the electrode materials can deliver a superior specific capacitance of 324 F g –1 at 0.05 A g–1, outstanding rate capability of 258 F g–1 at 20 A g–1, and extraordi...

Molten-salt strategy for fabrication of hierarchical porous N-doped carbon nanosheets towards high-performance supercapacitors

Abstract The efficient conversion of renewable biomass to advanced carbons with high porosity and heteroatoms doping is of huge significance towards energy-related applications. However, most of the resultant carbon materials are always bulk materials with low aspect ratio and unsatisfactory electronic properties owing to the severe activation process. In this work, the KNO3 modified molten-salt (KCl/LiCl) strategy is explored to fabricate two dimensional nitrogen-doped carbon nanosheets (NCNs) by using agaric as the precursor. Benefiting from its large surface area (1376 m2 g−1), high-ratio micro-porosity (72%), high-content N doping (4 at.%) and high graphitization, the optimized NCNs sample is endowed with exceptional electrochemical capacitances both in aqueous electrolyte (6 M KOH) and organic electrolyte (1 M tetraethylammonium tetrafluoroborate/acetonitrile), when evaluated as a competitive electrode for supercapacitors. It is strongly envisioned that the method developed here holds great potential for advanced porous heteroatom-doped carbons from natural biomass for next-generation supercapacitors.

Coordination-controlled single-atom tungsten as a non-3d-metal oxygen reduction reaction electrocatalyst with ultrahigh mass activity

Transition metal-nitrogen-carbon (M-N-C) catalysts have emerged as the most promising alternatives to their costly platinum–based counterparts for oxygen reduction reaction (ORR) catalysis, which are critical to renewable energy conversion and storage technologies. However, thus far, only 3d transition metals (Co, Fe, Ni, Mn, etc.) have often been good choices for the metal elements in such M-N-C catalysts, while other non-3d transition metals-based catalysts such as 5d tungsten (W) usually afford much inferior ORR activities in both bulk and nanoparticle form. Here, we report the atomically dispersed tungsten on nitrogen-doped carbon nanosheets with controlled W-N coordination numbers as efficient catalysts for ORRs, which are only formed through the deliberate modulation of the synthesis parameters, such as the pyrolysis atmosphere, temperature, and time, within a very narrow range. Instead of being considered to be almost inactive towards ORR, the single-atom tungsten electrocatalysts show remarkable, durable and coordination number-sensitive ORR catalytic ability. It is shown that single-atom tungsten with a W-N coordination number of 5 exhibits markedly high ORR catalytic activity in 0.1 M KOH with onset potential (∼1.01 V), half-wave potential (0.88 V) and a mass activity of 0.63 A/mg (at 0.9 V versus RHE), which even surpasses those of commercial Pt/C. Meanwhile, the WN5 catalyst catalyzes the ORR with a onset potential of 0.87 V and a half-wave potential of 0.77V in 0.1 M HClO4, both of which are nearly comparable to the benchmark Pt/C. In contrast, the single-atom tungsten electrocatalysts with W-N coordination numbers of 3 and 4 exhibit relatively poor ORR activity in both acidic and alkaline electrolytes. The DFT calculations suggest that the sharp increase in the ORR activity of the single-atom tungsten catalysts can be attributed to the moderate interaction between OH- and the single W atoms, which is probably caused by the optimal dz2-pz orbital hybridization and re-distribution of the charges.

Core@Shelled Co/CoO Embedded Nitrogen-Doped Carbon Nanosheets Coupled Graphene as Efficient Cathode Catalysts for Enhanced Oxygen Reduction Reaction in Microbial Fuel Cells

High-efficiency oxygen reduction reaction (ORR) catalysts are crucial for facilitating the large-scale exploitation of electrochemical energy storage and conversion technologies. Herein, we demonstrate a carbon-based metal hybrid, which offers a higher electrocatalytic activity than that of the individual composite by optimizing the electronic modulation effect from suitable microstructure. The resulting cobalt@cobalt oxide nanoparticles embedded in N-doped carbon shell couple with hierarchical porous graphene (GCN–Co@CoO), exhibiting a significantly enhanced ORR activity in alkaline solution and highlighting a synergistic effect between N-doped carbon shell and metallic Co species. More precisely, the GCN–Co@CoO hybrid pyrolyzed at 800 °C achieves a more positive half-wave potential of −0.194 V (vs SCE) and superior limiting current of 4.91 mA cm–2. Moreover, the GCN–Co@CoO composite also shows an outstanding tolerance to methanol crossover effects and long-term stability. Furthermore, based on the GCN–Co@CoO cathode catalyst, the self-assembled microbial fuel cells perform a maximum power density of 611 ± 9 mW m–2 at a high current density of 1869 ± 24 mA m–2.

Assembling Carbon Pores into Carbon Sheets: Rational Design of Three-Dimensional Carbon Networks for a Lithium-Sulfur Battery.

The conversion reaction-based lithium-sulfur battery features an attractive energy density of 2600 W h/kg. Nevertheless, the unsatisfied performance in terms of poor discharge capacity and cycling stability still hinders its practical applications. Recently, porous carbon materials have been widely reported as promising sulfur reservoirs to promote the sluggish reaction kinetics of sulfur conversion, tolerate volume expansion of sulfur, and suppress polysulfide shuttling. However, porous carbon with a simply designed nanostructure is hard to satisfy all of these aspects simultaneously. Herein, we have applied a dual-template strategy that assembles carbon pores into carbon sheets to prepare three-dimensional (3D) nitrogen-doped porous carbon nanosheets (N-PCSs) as the multifunctional sulfur host for the Li-S battery. By arranging carbon pores within an interconnected 3D architecture, the porous carbon sheets enable rapid electron/ion transfer. Moreover, the micro/mesopores and nitrogen dopant in N-PCS provide both physical and chemical restrictions to polysulfide species. With these advances, the N-PCS/S cathode delivers a large initial discharge capacity of 1360 mA h/g at 0.1 C. When performed at 0.5 C for 1000 cycles, the cathode can still remain ∼50% of its capacity with a low decay rate of 0.05% per cycle, showing the important role of the 3D carbon material in the Li-S battery.

ZrO2 nanoparticles anchored on nitrogen-doped carbon nanosheets as efficient catalyst for electrochemical CO2 reduction

Electrochemical reduction of CO2 to produce value-added feedstock chemicals using high-performance electrocatalysts is a promising protocol to address the excessive CO2 in the atmosphere and the energy crisis. However, the high overpotential, low current density, and poor product selectivity for CO2 electroreduction greatly impede their practical applications. In this work, we develop an efficient catalyst for CO2 reduction to CO consisting of well-dispersed ZrO2 nanoparticles tightly anchored on nitrogen-doped carbon nanosheets (ZrO2/N-C) for the first time. Importantly, the ZrO2 nanoparticles possess oxygen vacancies and defects, which regulate the electronic structure of catalyst and thus greatly enhance the electrocatalytic activity. Specifically, ZrO2/N-C demonstrates a high CO Faradaic efficiency (FE) of 64% at −0.4 V vs. the reversible hydrogen electrode (RHE) and a respectable current density of ∼2.6 mA cm−2 in CO2-saturated 0.5 M KHCO3 solution. This work opens a new avenue for developing excellent catalysts for CO2 electroreduction with metal oxide/heteroatom-doped carbon composite structure.

A universal KOH-free strategy towards nitrogen-doped carbon nanosheets for high-rate and high-energy storage devices

A universal KOH-free strategy is developed to prepare nitrogen-doped carbon nanosheets (N-SCNSs) derived from edible oil residues with high specific surface area and high nitrogen content for application in high-rate and high-energy supercapacitors.

Ultrathin 2D nitrogen-doped carbon nanosheets for high performance supercapacitors: insight into the effects of graphene oxides.

Ultrathin 2D nitrogen-doped carbon nanosheets with a thickness of about 5 nm have been facilely synthesized from potato starch by using graphene oxides (GO) as the structure-directing agent. The pore structures and surface properties can be feasibly and rationally tailored by addition of a certain amount of GO in the precursor. The addition of GO to the potato starch can increase the surface areas and the pyridinic-N and pyrrolic-N ratios of the as-prepared 2D carbon nanosheets. The as-obtained ultrathin nitrogen-doped carbon nanosheets with the optimized amount of GO in potato starch (3 wt%) possess a unique 2D structure, a high N content, and high ratios of pyridinic-N and pyrrolic-N, exhibiting a high capacitance of 301 F g-1 at 0.5 A g-1, superior rate capability of 81% at 50 A g-1, and good cycling stability in 6 M KOH electrolyte. Experimental and theoretical results show that high pyridinic-N and pyrrolic-N ratios in the NCNSs are beneficial for improving the electrochemical performance. This work may provide helpful guidance for understanding the effect of the addition of GO to biomass precursors on the electrochemical performance of the 2D nitrogen-doped carbon electrodes for supercapacitors.

NiCo-layered double-hydroxide and carbon nanosheets microarray derived from MOFs for high performance hybrid supercapacitors

Exploring porous nano-structured materials has great significance for energy storage equipment. The metal-organic frameworks (MOFs) can be used as the outstanding sacrificial templates for electrode material of high performance supercapacitors due to their superior features that high specific surface area and tunable pore size distribution. However, the poor conductivity of MOFs is one of the biggest barriers to achieve high rate capacity and stable cycling performance. Herein, MOFs derived NiCo-layered double-hydroxide (NiCo-LDH) and nitrogen-doped carbon nanosheets (NC) on the flexible carbon nanotubes (CNTs) film are rationally designed, both of which as the binder-free electrodes can greatly improve the specific surface area and reaction sites. An asymmetric supercapacitor based on porous NiCo-LDH nanosheets on CNTs (CNT@NiCo-LDH) as the positive electrode and the NC nanosheets on carbon nanotubes film (CNT@NC) as the negative electrode exhibits the maximum energy density of 37.4 W h/kg at the power density of 750 W/kg, as well as a long-term cycling stability (94.5% capacity retention after 5000 cycles). Rationally design such combination is a meaningful process for energy storage equipment with excellent electrochemical performance.

Synthesis of nitrogen-doped mesoporous carbon nanosheets for oxygen reduction electrocatalytic activity enhancement in acid and alkaline media

In the present work, nitrogen-doped mesoporous carbon nanosheets (NMCNs) are prepared and extensively investigated for the oxygen reduction reaction. Initially, by using dual templates, viz. graphene oxide and a cationic surfactant, silica films (thickness: 1.0 nm) are synthesized and characterized using transmission electron microscope (TEM), nitrogen adsorption-desorption (N2 ad/des) measurements, and small-angle X-ray diffraction (SA-XRD).Morphology and structure of silica evolve along with graphene oxide concentration, while the co-operative assembly and the final structure are determined by the electrostatic interaction between the dual templates. The effect of silica template on the resultant NMCNs is investigated physicochemically by photoelectron spectroscopy (XPS), TEM, N2 ad/des and electrochemically by cyclic voltammetry (CV), and linear sweep voltammetry (LSV).NMCNs are featured of a high content of nitrogen dopant, high specific surface area (SSA) and ultrathin thickness (1.5 nm), favoring catalysis and facilitating the mass transport of the reactive species. From the electrochemical tests, it is confirmed that NMCNs yield a high oxygen reduction reaction (ORR) electrocatalytic activity in acid and alkaline environment; this activity is similar or even better as compared with the one measured over carbon supported platinum commercial catalyst (40 wt % Pt/C).

In-situ fabrication of nitrogen-doped carbon nanosheets containing highly dispersed single iron atoms for oxygen reduction reaction

Iron and nitrogen co-doped carbons show great potential for high-performance electrochemical oxygen reduction reaction. However, the rational design of atomically dispersed iron over nitrogen-doped carbons with activity comparable to that of Pt-C is still challenging. Herein, we develop a new approach that enables the direct formation of intrinsically nitrogen-functionalized two-dimensional sheet-like carbons containing a high concentration of single Fe atoms. This strategy only involves one-step pyrolysis of both, guanine and iron nitrate, without using any guiding agent and sacrificial template. The electrochemistry tests demonstrate an excellent ORR performance of the prepared Fe-Nx-C catalyst with a half-wave potential of 0.85 V and a limited current density of −6.5 mA/cm2 in alkaline medium, outperforming the commercial Pt-C and most of previously reported Fe-Nx-C catalysts. We believe that the emergence of superior ORR performance is mostly attributed to the uniform dispersion of single Fe atoms at the molecular level and the formation of abundant coordinated Fe-Nx sites. In addition, the high surface area, optimal porosity and defective structure (particularly the defects at the edge) of the two-dimensional carbons are also beneficial for the improved ORR activity.

Two-dimensional covalent organic frameworks as self-template derived nitrogen-doped carbon nanosheets for eco-friendly metal-free catalysis

Heteroatom-doped carbon materials with superior physico-chemical properties and high stability are potential candidates for environmentally friendly metal-free catalysis. In this study, mesoporous carbon materials with high N content and lattice defects were successfully fabricated via self-templated carbonization of a two-dimensional covalent organic framework (2D COF). The ordered structure and clear composition of intrinsic COF precursors aid the understanding of the specific role of dopants in the as-prepared N-doped mesoporous carbon materials. Based on the obtained experimental results and characterizations, graphitic N and its related defects were found to be closely associated with catalytic activity, indicating they are probably the main active sites. In addition, the obtained catalyst showed remarkable catalytic performance in both hydrogenation of nitroarenes and Knoevenagel condensation of aromatic aldehyde derivatives in aqueous solution. This study is expected to provide a new inspiration for the synthesis of heteroatom-doped carbon materials from cost-effective COFs via self-templated carbonization for eco-friendly metal-free catalysis.

Two-dimensional covalent-organic-framework-derived nitrogen-rich carbon nanosheets modified with small Pd nanoparticles for the hydrodechlorination of chlorophenols and hydrogenation of phenol

Heteroatom-doped carbon materials have attracted immense attention for heterogeneous catalysis applications because of their excellent physicochemical properties. In this work, we prepared a cost-effective triazinyl-containing two-dimension COFs (2D-COFs), and then the 2D-COFs was self-templated carbonized to fabricate 2D nitrogen-doped carbon nanosheets (NCNs). NCNs were modified with highly dispersed small palladium nanoparticles (Pd NPs), affording the Pd/NCNs catalyst. The as-prepared NCNs and Pd/NCNs exhibited a smoke-like morphology, a large specific surface area, and mesoporous and macroporous structures, which can enhance reactants diffusion and mass transfer. The obtained Pd/NCNs catalyst exhibited excellent activity, stability, and recyclability in the aqueous-phase hydrodechlorination (HDC) of organic hazardous substances chlorophenols (CPs). Meanwhile, outstanding activity and high selectivity were observed for the subsequent hydrogenation of the HDC product phenol to cyclohexanone. The excellent activity of the Pd/NCNs catalyst was related to the synergistic effect of Pd NPs and the nitrogen atoms doped in the NCNs. Thus, this study offers a novel, facile route for fabrication heteroatom-doped carbon materials derived from cost-effective COFs materials to prepare highly dispersed small noble-metal-NP-modified catalysts for various catalytic applications.

Nitrogen Doped Carbon Nanosheets Encapsulated in situ Generated Sulfur Enable High Capacity and Superior Rate Cathode for Li-S Batteries.

Lithium-sulfur batteries (LSBs), with large specific capacity (1,675 mAh g−1), are regarded as the most likely alternative to the traditional Lithium-ion batteries. However, the intrinsical insulation and dramatic volume change of sulfur, as well as serious shuttle effect of polysulfides hinder their practical implementation. Herein, we develop three-dimensional micron flowers assembled by nitrogen doped carbon (NC) nanosheets with sulfur encapsulated (S@NC-NSs) as a promising cathode for Li-S to overcome the forementioned obstacles. The in situ generated S layer adheres to the inner surface of the hollow and micro-porous NC shell with fruitful O/N containing groups endowing both efficient physical trapping and chemical anchoring of polysulfides. Meanwhile, such a novel carbon shell helps to bear dramatic volume change and provides a fast way for electron transfer during cycling. Consequently, the S@NC-NSs demonstrate a high capacity (1,238 mAh g−1 at 0.2 C; 1.0 C = 1,675 mA g−1), superior rate performance with a capacity retention of 57.8% when the current density increases 25 times from 0.2 to 5.0 C, as well as outstanding cycling performance with an ultralow capacity fading of only 0.064% after 200 cycles at a high current density of 5.0 C.

Nitrogen-doped carbon nanosheets containing Fe3C nanoparticles encapsulated in nitrogen-doped graphene shells for high-performance electromagnetic wave absorbing materials

Nitrogen-doped carbon sheets containing Fe3C nanoparticles encapsulated in nitrogen-doped graphene shells are fabricated through heating the mixture of urea and ferric acetylacetonate and the subsequent treatment in hot acid solution. The nitrogen-doped carbon sheets have a lateral length ranging from hundred nanometers to several micrometers, while the Fe3C nanoparticles encapsulated in nitrogen-doped graphene have a diameter of approximately 60 nm. The nitrogen-doped carbon sheets exhibit excellent electromagnetic wave absorption property. Typically, the optimal sample has the effective absorption bandwidth of 6.0 GHz at the absorber thicknesses of only 2.0 mm, favorably comparable to those of the magnetic absorbers reported previously. The excellent electromagnetic wave absorption property of nitrogen-doped carbon sheets containing Fe3C nanocapsules encapsulated in the nitrogen-doped graphene shells can be explained by their better impedance matching character and enhanced dielectric loss.

Quantum Effects Allow the Construction of Two-Dimensional Co3 O4 -Embedded Nitrogen-Doped Porous Carbon Nanosheet Arrays from Bimetallic MOFs as Bifunctional Oxygen Electrocatalysts.

In terms of promising candidates for high-performance fuel cells and water splitting electrocatalysts, two-dimensional (2D) materials refer to a class of materials with high electrical conductivity along 2D conducting channels and possessing abundant active sites in the form of surface atoms and edge sites. Herein, we report an ammonia-modulated method for the synthesis of nanosized bimetallic ZnCo-ZIF, and owing to quantum effects, the nanosized ZnCo-ZIF can be transformed into novel 2D nanosheet arrays, which can be used as a bifunctional electrocatalyst. The size of the ZnCo-ZIF crystals can be controlled to less than 10 nm by increasing the ammonia amount. The products from the nanosized particles through calcination have a distinct structure from the microsized nanoparticles owing to quantum effects and appear to be well-aligned 2D mono-crystalline Co3 O4 -embedded nitrogen-doped porous carbon nanosheet arrays (2D-MCo3 O4 -NCNAs). These novel 2D nanosheet arrays lead to large active surface areas, enhanced mass/charge transport capability, numerous active sites, and strong structure stability. When used as bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the 2D-MCo3 O4 -NCNAs exhibit superior ORR activity as well as efficient OER activity in alkaline electrolyte, in comparison to the state-of-the-art precious metal catalysts.

Hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets as an efficient bifunctional catalyst for Zn–air battery

Rational design of low-cost, highly electrocatalytic activity, and stable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been a great significant for metal–air batteries. Herein, an efficient bifunctional electrocatalyst based on hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets (Co/N-Pg) is fabricated for Zn–air batteries. A low-cost biomass peach gum, consisting of carbon, oxygen, and hydrogen without other heteroatoms, was used as carbon source to form carbon matrix hosting hollow cobalt oxide nanoparticles. Meanwhile, the melamine was applied as nitrogen source and template precursor, which can convert to carbon-based template graphitic carbon nitride by polycondensation process. Owing to the unique structure and synergistic effect between hollow cobalt oxide nanoparticles and Co-N-C species, the proposal Co/N-Pg catalyst displays not only prominent bifunctional electrocatalytic activities for ORR and OER, but also excellent durability. Remarkably, the assembled Zn–air battery with Co/N-Pg air electrode exhibited a low discharge-charge voltage gap (0.81 V at 50 mA cm–2) and high peak power density (119 mW cm–2) with long-term cycling stability. This work presents an effective approach for engineering transition metal oxides and nitrogen modified carbon nanosheets to boost the performance of bifunctional electrocatalysts for Zn–air battery.

Synthesis of Carbon Nanosheets and Nitrogen-Doped Carbon Nanosheets from Perylene Derivatives for Supercapacitor Application

The development of an economical, eco-friendly, and easy method for the production of carbon nanosheets and heteroatom-doped carbon nanosheets has been a challenge for material scientists. In this study, we developed a method for the synthesis of carbon nanosheets (CNS) and nitrogen-doped carbon nanosheets (NCNS) of high quality from organic compounds. We exploited the electrostatic interaction among ionic crystals (NaCl in the present case) and polarized aromatic molecules (3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and 3,4,9,10-perylene tetracarboxylic diimide (PTCDI) in this work) to obtain uniform coverage of the latter over the surface of the ionic crystal. This NaCl-PTCDA/PTCDI assembly, on pyrolysis at 700 °C followed by washing with water, yields high-quality CNS and NCNS depending on the aromatic precursor employed. The sheets obtained consist of minimum 2–3 layers (∼2 nm) as observed from atomic force microscopy. The process demonstrated is highly scalable, economical, eco-friendly, n...

Dicyandiamide and iron-tannin framework derived nitrogen-doped carbon nanosheets with encapsulated iron carbide nanoparticles as advanced pH-universal oxygen reduction catalysts

The development of an efficient and cost-effective electrocatalyst toward the oxygen reduction reaction (ORR) is of critical importance for diverse renewable electrical energy techniques. Herein, a dicyandiamide and iron-tannin framework-derived nitrogen-doped carbon nanosheet with encapsulated iron carbide nanoparticle (Fe3C/N-CNS) is developed. Particularly, dicyandiamide is the key to achieve this two-dimensional nitrogen-doped lamellar carbon nanosheet. Owing to the synergistic characteristics including composition and structure, the optimal catalyst exhibits the comparable or even better catalytic activity, as well as superior methanol tolerance and stability compared with platinum/carbon catalyst over the whole pH range. More notably, the current approach can be potentially extended to synthesize additional two-dimensional structured transition-metal/carbon composites for various energy conversion and storage technologies.

Fe1-xC decorated porous nitrogen doped carbon matrix as anode for sodium ion battery

ABSTRACTFe1-xC decorated Nitrogen doped carbon nanosheets (Fe1-xC@C) with a highly porous nanostructure are successfully synthetized through a facile two-step process: fabricating Fe1-xC@C nanosheets by pyrolysis polyacrylonitrile (PAN) and subsequently etched by acid. The as-prepared Fe1-xC@C composites delivers a reversible capacity of 125.2 mAh g−1 at the current density of 500 mA g−1. As anode of sodium ion battery, the capacity retention 88.5% after 800 cycles, and a rate capability is 75 mAh g−1 at 3A g−1. This simple scalable and low cost synthesis approach will provide a new strategy for the fabrication of NIBs anode.