N-doped Ordered Mesoporous Carbon Research Articles

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Defect engineering in N-doped OMC for lightweight and high-efficiency electromagnetic wave absorption

Developing low density and efficient dielectric loss materials has become a research hotspot, which can greatly meet the demands of modern radars and settle the problem of electromagnetic wave pollution. Herein, a series of N-doped ordered mesoporous carbon (OMC) materials with different nitrogen content were prepared via a modified self-assembly method and defect engineering in subsequent calcination treatment. It was discovered that the content and type of nitrogen doping can be effectively modulated by the amount of precursor dicyandiamide, resulting in the changes in porous structure, carbon defects, electromagnetic properties, microwave absorption (MA) performance and radar cross section (RCS) reduction values. Remarkably, as-fabricated OMC/N2.5 displays ideal MA performance, whose minimum reflection loss (RL(min)) value reaches −35.3 dB at 7.76 GHz (3.0 mm) and its effective absorption bandwidth reaches 3.52 GHz (10.64–14.16 GHz, 2.0 mm). Furthermore, the optimal RCS reduction values can be obtained as 12.01 dB·m2 when the detection theta is 30°, which validly reduces the chances of being detected by radar. Thus, this work opens up a novel way for the development of lightweight and high-efficiency MA materials.

Insight into the Evolution of Ordered Mesoporous sp2 Carbonaceous Material Derived from Self-Assembly of a Block Copolymer.

Block-copolymer-derived ordered mesoporous carbon (OMC) materials have great potential in many applications, such as adsorption, catalysis, and energy conversions; however, their formation process and the kinetic mechanism remain unclear. Herein, a N-doped OMC (N-OMC) with sp2-bonded C atoms is developed via self-assembly of the polystyrene-block-poly(4-vinyl pyridine) block copolymer. By correlating the external morphologies with the internal chemical states, the formation process can be concluded as follows: (1) pore evolution via polystyrene domain degradation and (2) regularization and graphitization of the residual carbon via the removal of sp3 C atoms. In addition, the thickness of the N-OMC shows a power function relationship with the spin-coating rate, and the N content can be incredibly increased up to 26.34 at. % in an NH3 carbonization atmosphere. With the as-prepared N-OMC as the support for loading of the pseudo-atomic-scale Pt (Pt/N-OMC), a high electrochemical active surface area value of 99.64 m2·g-1 and a half-wave potential (E1/2) of 0.850 VRHE are achieved, showing great potential in developing single-atom electrocatalysts.

Nanostructured Pt-Ru Catalyst Supported on Si-Containing Ordered Mesoporous Carbon Hollow Spheres for the Ethanol Oxidation Reaction

Pt-Ru nanoparticles were dispersed on N-doped Ordered Mesoporous Carbon Hollow Spheres containing Si (N-OMCHS-Si), to obtain the Pt-Ru/N-OMCHS-Si nanocatalyst. Its catalytic activity for the Ethanol Oxidation Reaction (EOR) was evaluated in acid media. Pt-Ru/N-OMCHS-Si showed a higher mass catalytic activity at more negative onset potential (Eonset) for the EOR than Pt-Ru/N-OMCHS (i.e., support without Si), Pt/C and Pt-Ru/C (where C is Vulcan XC-72). Pt-Ru/N-OMCHS-Si also demonstrated a high tolerance to CO, oxidizing the molecule at potentials of comparable negative values as Pt-Ru/C. Moreover, Pt-Ru/N-OMCHS-Si showed enhanced electrochemical stability after Accelerated Degradation Test (ADT) compared to Pt-Ru/C. The high performance of Pt-Ru/N-OMCHS-Si was ascribed to the formation of Pt-Ru alloyed phases and the presence of Si oxides at the hollow spheres.

Insight into the performance and stability of N-doped Ordered Mesoporous Carbon Hollow Spheres for the ORR: Influence of the nitrogen species on their catalytic activity after ADT

Novel N-doped Ordered Mesoporous Carbon Hollow Spheres (N-OMCHS) were successfully synthetized using two different nitrogen sources: i) 2-pyridinecarboxaldehyde (labeled as N1-OMCHS), and ii) pyrrole (labeled as N2-OMCHS). The catalytic activity of the synthesized N-OMCHS was evaluated towards the Oxygen Reduction Reaction (ORR) in alkaline media. Likewise, the effect of Accelerated Degradation Test (ADT) on the stability of the N-OMCHS was discussed. N2-OMCHS showed the best performance for the ORR (Eonset = 0.88 V, E½ = 0.82 V, H2O2 yield = 3.8% and n = 3.92, all potentials vs. RHE). Surprisingly, after evaluating the stability of each electrocatalyst by ADT, it was observed that the performance of N1-OCMHS improved with respect to that evaluated before ADT. N1-OCMHS had a better stability compared to N2-OMCHS. X-ray photoelectron spectroscopy (XPS) results before and after ADT demonstrated the chemical modification of nitrogen species on the surface of the electrocatalysts, which influenced a better performance towards the ORR. Therefore, N-OMCHS were considered as potential non-platinum electrocatalysts for Anion Exchange Membrane Fuel Cells (AEMFC) cathode applications.

Earth-abundant metal-free carbon-based electrocatalysts for Zn-air batteries to power electrochemical generation of H2O2 for in-situ wastewater treatment

The overuse of fossil fuel has caused a serious energy crisis and environmental pollution. In this study, we rationally devised an integrated system, in which novel earth-abundant metal-free carbon-based electrocatalysts were used to catalyze oxygen reduction reaction (ORR) in Zn-air batteries for renewable energy storage as a power source for electrochemical generation of H2O2 as an oxidant for in-situ degradation of pollutants in wastewater. It was noted that the newly-developed ordered mesoporous carbon (OMC) and N-doped OMC (NOMC) exhibited high selectivity for 2e− ORR to produce H2O2 and high selectivity for 4e− ORR at the cathode of Zn-air batteries, respectively. The OMC electrode showed a H2O2 yield as high as 366.9 mg/L in 2 h at 0.5 V, leading to a high current efficiency ~73.6%, The subsequent use of thus-produced H2O2 for Rhodamine B (RhB) candidate pollutant degradation exhibited an 90% removal efficiency in 2 h, showing a great promise for practical wastewater treatment. This work represents a breakthrough in the development of a new concept and novel integrated systems to address the current energy and environmental changes.

Polyaniline-Derived N-Doped Ordered Mesoporous Carbon Thin Films: Efficient Catalysts towards Oxygen Reduction Reaction.

One of the most challenging targets in oxygen reduction reaction (ORR) electrocatalysts based on N-doped carbon materials is the control of the pore structure and obtaining nanostructured thin films that can easily be incorporated on the current collector. The carbonization of nitrogen-containing polymers and the heat treatment of a mixture of carbon materials and nitrogen precursor are the most common methods for obtaining N-doped carbon materials. However, in this synthetic protocols, the surface area and pore distribution are not controlled. This work enables the preparation of 2D-ordered N-doped carbon materials through the carbonization of 2D polyaniline. For that purpose, aniline has been electropolymerized within the porous structure of two different templates (ordered mesoporous Silica and ordered mesoporous Titania thin films). Thus, aniline has been impregnated into the porous structure and subsequently electropolymerized by means of chronoamperometry at constant potential. The resultant samples were heat-treated at 900 °C with the aim of obtaining 2D N-doped carbon materials within the template structures. Polyaniline and polyaniline-derived carbon materials have been analyzed via XPS and TEM and characterized by electrochemical measurements. It is worth noting that the obtained 2D-ordered mesoporous N-doped carbon materials have proved to be highly active electrocatalysts for the ORR because of the formation of quaternary nitrogen species during the heat treatment.

Highly Dispersed Pt Nanoparticles on N-Doped Ordered Mesoporous Carbon as Effective Catalysts for Selective Hydrogenation of Nitroarenes

Highly-dispersed Pt nanoparticles supported on nitrogen-modified CMK-3 mesoporous carbon (Pt/N-CMK-3) were first fabricated by a two-step impregnation route. The influences of N content on the catalyst porous structure, Pt nanoparticle size, surface properties, and interaction between Pt species and the support were investigated in detail using N2 sorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS). The N species acted as anchoring sites for the stabilization of Pt particles. Benefiting from the formation of ultrafine metal nanoparticles, the Pt/N-CMK-3 exhibited excellent catalytic activity and selectivity for the selective hydrogenation of nitro aromatics to the corresponding anilines with hydrogen. The Pt/N-CMK-3 catalyst could be reused eight times and keep its catalytic performance.

In situ growth of Ni-encapsulated and N-doped carbon nanotubes on N-doped ordered mesoporous carbon for high-efficiency triiodide reduction in dye-sensitized solar cells

A new micro-nanostructured composite (NOMC-Ni@NCNTs) of Ni-encapsulated and N-doped carbon nanotubes (Ni@NCNTs) pinned on N-doped ordered mesoporous carbon (NOMC) is constructed by a two-step synthesis strategy. The strategy involves the self-assembly preparation of water-soluble phenolic resin/F127 colloid by a hydrothermal route and the subsequent catalytic pyrolysis of as-prepared phenolic resin/F127 copolymer and melamine with nickel acetate as Ni source and self-generated catalyst, leading to the in situ growth of dispersive Ni@NCNTs pinned on NOMC through the Ni junction. In the resultant NOMC-Ni@NCNTs, the NOMC shows reduced particle size and shortened mesopore channel length of 15–30 μm compared to 850 μm-2 mm of pristine NOMC. The pinned Ni@NCNTs constructs a 3D conductive scaffold in the composite and the conductivity is correspondingly raised from 20.4 S cm−1 of pristine NOMC to 254.1 S cm−1 of NOMC-Ni@NCNTs. The particle size, mesoporosity and surface area of NOMC-Ni@NCNTs composite are also flexibly regulated by tailoring the relative content of Ni@NCNTs and NOMC. The new-structured NOMC-Ni@NCNTs composites are developed as counter electrode (CE) materials for DSSCs, which demonstrates an excellent catalytic activity towards I3- reduction. The optimum NOMC-Ni@NCNTs CE delivers a low charge-transfer resistance of 2.21 Ω and the assembled DSSC achieves a high power conversion efficiency of 8.39%. Moreover, the NOMC-Ni@NCNTs CE based DSSC also manifests a preeminent electrochemical stability in corrosiveI-/I3- electrolyte with a remnant efficiency of 7.82% after 72 h of illumination. The outstanding electrocatalytic performance is mainly correlated with their unique architecture, in which the pinned Ni@NCNTs conductive substrate accelerates the electron transportation among NOMC micron-particles, and the amorphous NOMC with short-range mesopores accelerates the electrolyte diffusion and supplies abundant ions-accessible defects for I3- reduction.

Synthesis of nitrogen-doped ordered mesoporous carbon with enhanced lithium storage performance from natural kaolin clay

N-doped ordered mesoporous carbon (N-OMC) samples with different N contents were synthesized by infiltrating molten melamine (the N source) into the framework of mesoporous silica–sucrose. The framework was prepared using an ordered mesoporous silica hard template derived from natural kaolin clay, subsequent carbonization in an inert gas atmosphere, and etching of the silica template. In this simple methodology, N-heteroatoms were incorporated into the C framework during the carbonization. The N-doping content of the prepared N-OMC was conveniently tuned by modifying the melamine/sucrose ratio. After the N-doping, the synthesized N-OMC exhibited remarkable Li storage properties; further, it demonstrated an initial discharge capacity of 1887 mA h g−1 at a current density of 0.1 A g−1. After 100 discharge–charge cycles, the electrode retained a reversible capacity of 648.7 mA h g−1, which is significantly higher than the theoretical capacity of the commercial graphite anode. The enhanced electrochemical performance of the N-OMC was attributed to the large number of defects introduced by N-doping as well as the abundant micropores and mesopores, which provided additional Li storage sites. The N-OMC anode material, which was synthesized by the hard template method using natural kaolin clay as the raw material, exhibited remarkable electrochemical properties including a long life cycle and superior rate of performance. Thus, this study demonstrates that natural kaolin clay exhibits considerable potential for application in Li-ion batteries.

Enhanced cyclic CO2/N2 separation performance stability on chemically modified N-doped ordered mesoporous carbon

The modification of ordered mesoporous carbon (OMC) via NH3 heat treatment and subsequent amine refluxing at increased temperature was investigated to improve their performances for cyclic CO2/N2 separation stability and kinetics. Characterizations conducted with nitrogen adsorption/desorption isotherm, Fourier transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy demonstrated that the porosity and surface chemistry of the OMCs were tuned by modification. Adsorption evaluation with volumetric and gravimetric methods under various conditions indicated that the resulting amine-introduced N-doped OMC presented a high CO2 adsorption capacity with fast kinetics, outstanding selectivity at 50 °C and maintained superior separation performance after 20 cycles. The presence of accessible amino groups in considerable amounts renders the modified mesoporous carbon a promising candidate for CO2 capture from flue gas by using the temperature swing adsorption.

Preparation of N-doped ordered mesoporous carbon and catalytic performance for the pyrolysis of 1-chloro-1,1-difluoroethane to vinylidene fluoride

N-doped ordered mesoporous carbons (NOMC) were prepared with mixed solution of urea and sucrose as carbon source and nitrogen source. SBA-15 was adopted as the hard template. The effect of urea to sucrose molar ratio on NOMC was investigated. NOMC samples were characterized by techniques such as BET, TEM, XPS and TG. The catalytic performances of NOMC catalysts were evaluated for the pyrolysis of 1-chloro-1,1-difluoroethane (HCFC-142b, CH3CClF2) to vinylidene fluoride (VDF, CH2=CF2). The catalytic reactions were carried out at 400 °C and space velocity of 600 h−1 (based on HCFC-142b). The results indicate that NOMC exhibits a stable activity at 400 °C with high HCFC-142b conversion and selectivity to VDF. The textural parameters of NOMC play a major role in VDF selectivity and N species over the carbon surface are responsible for NOMC catalytic performance. Compared with the temperatures of industrial manufacture of VDF at 650–700 °C, the NOMC catalysts provide a promising pathway to produce VDF at much lower temperatures (below 400 °C).

N-doped ordered mesoporous carbon prepared by solid–solid grinding for supercapacitors

Abstract

Microwave Electromagnetic and Absorption Properties of N-Doped Ordered Mesoporous Carbon Decorated with Ferrite Nanoparticles

Lightweight nitrogen-doped ordered mesoporous carbon (NOMC) with high specific surface area and pore volume have been prepared through self-assembly and subsequent heat treatment route. The spherical NOMC particles are decorated with CoFe2O4 nanoparticles via coprecipitation method to enhance their microwave absorption property. The electromagnetic parameters of the NOMC and CoFe2O4/NOMC composites are measured and the microwave reflection loss properties are evaluated in the frequency range of 0.5–18 GHz. The results show that both the real part and imaginary part of permittivity of NOMC totally decline and the real part of permeability increases with the introduction of ferrite. However, the negative values of the imaginary part of the complex permeability appear for the CoFe2O4/NOMC composites, which may be caused by enhanced eddy current effect due to the introduction of ferrite. The reflection loss results exhibit that the CoFe2O4/NOMC composites have excellent microwave absorption performances. The ...

N-Doped Ordered Mesoporous Carbon Originated from a Green Biological Dye for Electrochemical Sensing and High-Pressure CO2 Storage.

Herein, a series of nitrogen-doped ordered mesoporous carbons (NOMCs) with tunable porous structure were synthesized via a hard-template method with a green biological dye as precursor, under various carbonization temperatures (700-1100 °C). Compared with the ordered mesoporous silica-modified and unmodified electrodes, the use of electrodes coated by NOMCs (NOMC-700-NOMC-1100) resulted in enhanced signals and well-resolved oxidation peaks in electrocatalytic sensing of catechol and hydroquinone isomers, attributable to NOMCs' open porous structures and increased edge-plane defect sites on the N-doped carbon skeleton. Electrochemical sensors using NOMC-1000-modified electrode were fabricated and proved feasible in tap water sample analyses. The NOMCs were also used as sorbents for high-pressure CO2 storage. The NOMC with the highest N content exhibits the best CO2 absorption capacities of 800.8 and 387.6 mg/g at 273 and 298 K (30 bar), respectively, which is better than those of other NOMC materials and some recently reported CO2 sorbents with well-ordered 3D porous structures. Moreover, this NOMC shows higher affinity for CO2 than for N2, a benefit of its higher nitrogen content in the porous carbon framework.

N-doped ordered mesoporous carbons prepared by a two-step nanocasting strategy as highly active and selective electrocatalysts for the reduction of O2 to H2O2

A new, two-step nanocasting method was developed to prepare N-doped ordered mesoporous carbon (NOMC) electrocatalysts for the reduction of O2 to H2O2. Our strategy involves the sequential pyrolysis of two inexpensive and readily available N and C precursors, i.e. aniline and dihydroxynaphthalene (DHN), inside the pores of a SBA-15 hard silica template to obtain N-doped graphitic carbon materials with well-ordered pores and high surface areas (764 and 877m2g−1). By tuning the ratio of carbon sources to silica template, it was possible to achieve an optimal filling of the pores of the SBA-15 silica and to minimise carbon species outside the pores. These NOMC materials displayed outstanding electrocatalytic activity in the oxygen reduction reaction, achieving a remarkably enhanced kinetic current density compared to state-of-the-art N-doped carbon materials (−16.7mAcm−2 at −0.35V vs. Ag/AgCl in a 0.1M KOH solution as electrolyte). The NOMC electrocatalysts showed high selectivity toward the two-electron reduction of oxygen to hydrogen peroxide and excellent long-term stability.

N-Doped ordered mesoporous carbon grafted onto activated carbon fibre composites with enhanced activity for the electro-Fenton degradation of Brilliant Red X3B dye

N-Doped ordered mesoporous carbon (N-OMC) was successfully prepared using dicyandiamide (C2H4N4) as the nitrogen source and was grafted onto activated carbon fibres (ACFs) to form carbon composites (ACF@N-OMC).