Nitrogen‐doped mesoporous carbon materials for oxidative dehydrogenation of propane

The CN‐15‐x series materials with different doses of SBA‐15 template and the CN‐y‐2.0 series materials with different hard templates were prepared by the hard template method with hexamethylenetetramine as the carbon and nitrogen source. The obtained mesoporous carbon materials were characterized by X‐ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The catalytic performance of propane oxidative dehydrogenation was determined. The characterization results indicate that the catalytic activity of CN‐15‐2.0 with a bipartite hexagonal ordered structure was higher than those of the other materials. The conversion of propane was 22.98%, and the selectivity toward propylene was 41.70%.     

Porous Nitrogen‐Doped Carbon Microspheres Derived from Microporous Polymeric Organic Frameworks for High Performance Electric Double‐Layer Capacitors

This research presents a simple and efficient method to synthesize porous nitrogen‐doped carbon microspheres (PNCM) by the carbonization of microporous poly(terephthalaldehyde‐pyrrole) organic frameworks (PtpOF). The common KOH activation process is used to tune the porous texture of the PNCM and produce an activated‐PNCM (A‐PNCM). The PNCM and A‐PNCM with specific surface area of 921 and 1303 m² g^?1, respectively, are demonstrated as promising candidates for EDLCs. At a current density of 0.5 A g^?1, the specific capacitances of the PNCM and A‐PNCM are 248 and 282 F g^?1, respectively. At the relatively high current density of 20 A g^?1, the capacitance remaining is 95 and 154 F g^?1, respectively. Capacity retention of the A‐PNCM is more than 92 % after 10 000 charge/discharge cycles at a current density of 2 A g^?1.     

One‐Step Hydrothermal Synthesis of Nitrogen‐Doped Carbon Nanotubes as an Efficient Electrocatalyst for Oxygen Reduction Reactions

A high amount of heteroatom doping in carbon, although favorable for enhanced density of catalytically active sites, may lead to substantially decreased electroconductivity, which is necessary for the electrochemical oxygen reduction reaction. Herein, a relatively low amount of nitrogen was successfully doped into carbon nanotubes (CNTs) by a hydrothermal approach in one step, and the synthesized nitrogen‐doped CNT (CNT‐N) materials retained most of the original, excellent characteristics, such as the graphitic structure, tubular morphology, and high surface area, of CNTs. The resultant CNT‐N materials, although containing a relatively low amount of nitrogen doping, exhibited high electrocatalytic ORR activity, comparable to that of 20 wt % Pt/C; long durability; and, more importantly, largely inhibited methanol crossover effect.     

Nitrogen‐Doped Carbon Monolith for Alkaline Supercapacitors and Understanding Nitrogen‐Induced Redox Transitions

A nitrogen‐doped porous carbon monolith was synthesized as a pseudo‐capacitive electrode for use in alkaline supercapacitors. Ammonia‐assisted carbonization was used to dope the surface with nitrogen heteroatoms in a way that replaced carbon atoms but kept the oxygen content constant. Ammonia treatment expanded the micropore size‐distributions and increased the specific surface area from 383 m² g^?1 to 679 m² g^?1. The nitrogen‐containing porous carbon material showed a higher capacitance (246 F g^?1) in comparison with the nitrogen‐free one (186 F g^?1). Ex situ electrochemical spectroscopy was used to investigate the evolution of the nitrogen‐containing functional groups on the surface of the N‐doped carbon electrodes in a three‐electrode cell. In addition, first‐principles calculations were explored regarding the electronic structures of different nitrogen groups to determine their relative redox potentials. We proposed possible redox reaction pathways based on the calculated redox affinity of different groups and surface analysis, which involved the reversible attachment/detachment of hydroxy groups between pyridone and pyridine. The oxidation of nitrogen atoms in pyridine was also suggested as a possible reaction pathway.     

ZIF‐8 Derived Graphene‐Based Nitrogen‐Doped Porous Carbon Sheets as Highly Efficient and Durable Oxygen Reduction Electrocatalysts

Nitrogen‐doped carbon (NC) materials have been proposed as next‐generation oxygen reduction reaction (ORR) catalysts to significantly improve scalability and reduce costs, but these alternatives usually exhibit low activity and/or gradual deactivation during use. Here, we develop new 2D sandwich‐like zeolitic imidazolate framework (ZIF) derived graphene‐based nitrogen‐doped porous carbon sheets (GNPCSs) obtained by in situ growing ZIF on graphene oxide (GO). Compared to commercial Pt/C catalyst, the GNPCSs show comparable onset potential, higher current density, and especially an excellent tolerance to methanol and superior durability in the ORR. Those properties might be attributed to a synergistic effect between NC and graphene with regard to structure and composition. Furthermore, higher open‐circuit voltage and power density are obtained in direct methanol fuel cells.     

Facile Synthesis of Nitrogen‐Containing Mesoporous Carbon for High‐Performance Energy Storage Applications

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen‐containing mesoporous carbon with high SSA (1390 m² g^?1), a suitable pore size distribution (1.5–8.1 nm), and a nitrogen content of 4.7 wt % through a facile one‐step self‐assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium–sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g^?1 at 1 A g^?1 and an excellent rate capability (180 F g^?1, 10 A g^?1). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium–sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g^?1 at 837.5 mA g^?1 and an extraordinary cycling stability with 70.3 % capacity retention after 100 cycles.     

Nitrogen‐Doped Carbon Nanomaterials: Synthesis,Characteristics and Applications

Nonmetallic carbon‐based nanomaterials (CNMs) are important in various potential applications, especially after the emergence of graphene and carbon nanotubes, which demonstrate outstanding properties arising from their unique nanostructures. The pristine graphitic structure of CNMs consists of sp² hybrid C?C bonds and is considered to be neutral in nature with low wettability and poor reactivity. To improve its compatibility with other materials and, hence, for greater applicability, CNMs are generally required to be functionalized effectively and/or doped with heteroatoms in their graphitic frameworks for feasible interfacial interactions. Among the various possible functional/doping elements, nitrogen (N) atoms have received much attention given their potential to fine tune the intrinsic properties, such as the work‐function, charge carrier concentration, surface energy, and polarization, of CNMs. N‐doping improves the surface energy and reactivity with enhanced charge polarization and minimal damage to carbon frameworks. The modified surface energy and chemical activity of N‐doped carbon nanomaterials (NCNMs) can be useful for a broad range of applications, including fuel cells, solar cells, Li‐ion batteries, supercapacitors, chemical catalysts, catalyst supports, and so forth.     

Template‐ and Metal‐Free Synthesis of Nitrogen‐Rich Nanoporous “Noble” Carbon Materials by Direct Pyrolysis of a Preorganized Hexaazatriphenylene Precursor

The targeted thermal condensation of a hexaazatriphenylene‐based precursor leads to porous and oxidation‐resistant (“noble”) carbons. Simple condensation of the pre‐aligned molecular precursor produces nitrogen‐rich carbons with C₂N‐type stoichiometry. Despite the absence of any porogen and metal species involved in the synthesis, the specific surface areas of the molecular carbons reach up to 1000 m² g^?1 due to the significant microporosity of the materials. The content and type of nitrogen species is controllable by the carbonization temperature whilst porosity remains largely unaffected at the same time. The resulting noble carbons are distinguished by a highly polarizable micropore structure and have thus high adsorption affinity towards molecules such as H₂O and CO₂. This molecular precursor approach opens new possibilities for the synthesis of porous noble carbons under molecular control, providing access to the special physical properties of the C₂N structure and extending the known spectrum of classical porous carbons.     

Cationic Nitrogen‐Doped Helical Nanographenes

Herein, we report the design and synthesis of a series of novel cationic nitrogen‐doped nanographenes (CNDNs) with nonplanar geometry and axial chirality. Single‐crystal X‐ray analysis reveals helical and cove‐edged structures. Compared to their all‐carbon analogues, the frontier orbitals of the CNDNs are energetically lower lying, with a reduced optical energy gap and greater electron‐accepting behavior. Cyclic voltammetry shows all the derivatives to undergo quasireversible reductions. In situ spectroelectrochemical studies prove that, depending on the number of nitrogen dopants, either neutral radicals (one nitrogen dopant) or radical cations (two nitrogen dopants) are formed upon reduction. The concept of cationic nitrogen doping and introducing helicity into nanographenes paves the way for the design and synthesis of expanded nanographenes or even graphene nanoribbons with cationic nitrogen dopants.     

Metal‐Nitrogen‐doped Porous Carbons Derived from Metal‐Containing Ionic Liquids for Oxygen Reduction Reaction

This study describes a self‐doping and additive‐free strategy for the synthesis of metal‐nitrogen‐doped porous carbon materials (CMs) via carbonizing well‐tailored precursors, metal‐containing ionic liquids (M‐ILs). The organic skeleton in M‐ILs serves as both carbon and nitrogen sources, while metal ions acts as porogen and metallic dopants. A high nitrogen content, appropriate content of metallic species and hierarchical porosity synergistically endow the resultant CMs (MIBA‐M‐T) as effective electrocatalysts for the oxygen reduction reaction (ORR). MIBA‐Fe‐900 with a high specific surface area of 1567 m² g^?1 exhibits an activity similar to that of Pt/C catalyst, a higher tolerance to methanol than Pt/C, and long‐term durability. This work supplies a simple and convenient route for the preparation of metal‐containing carbon electrocatalysts.     

Controllable Sulfur,Nitrogen Co‐doped Porous Carbon for Ethylbenzene Oxidation: The Role of Nano‐CaCO3

Heteroatom‐doped porous carbon materials have exhibited promising applications in various fields. In this work, sulfur, nitrogen co‐doped carbon materials (SNCs) with abundant pore structure were prepared by pyrolysis of sulfur, nitrogen‐containing porous organic polymers (POPs) mixed with nano‐CaCO₃ at high temperature. Among the resultant materials, SNC‐Ca‐850 possesses a relatively high level of doped heteroatoms and exhibits an excellent catalytic performance for the selective oxidation of benzylic C?H bonds. It is noteworthy that nano‐CaCO₃ increases the doped sulfur content in the synthesized carbon materials to a large extent and impacts the existence modes of sulfur. In addition, it enhances the porous structure and specific surface area of the resultant SNCs significantly. This work provides a viable strategy to promote the doping of sulfur into carbon materials during the pyrolysis process.     

Synthesis of Nitrogen‐Containing Rubicene and Tetrabenzopentacene Derivatives

Carbon‐based materials, such as acenes, fullerenes, and graphene nanoribbons, are viewed as the potential successors to silicon in the next generation of electronics. Although a number of methodologies provide access to these materials’ all‐carbon variants, relatively fewer strategies readily furnish their nitrogen‐doped analogues. Herein, we report the rational design, preparation, and characterization of nitrogen‐containing rubicenes and tetrabenzopentacenes, which can be viewed either as acene derivatives or as molecular fragments of fullerenes and graphene nanoribbons. The reported findings may prove valuable for the development of electron transporting organic semiconductors and for the eventual construction of larger carbonaceous systems.     

Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen‐Doped Carbon Composites For High‐Performance Lithium–Sulfur Battery Cathodes

Despite the high theoretical capacity of lithium–sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon‐nanotube‐interpenetrated mesoporous nitrogen‐doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g^?1 after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer‐sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm^?2) with a high sulfur loading of approximately 5 mg cm^?2, which is ideal for practical applications of the lithium–sulfur batteries.     

Sulfur‐Doped Graphene Derived from Cycled Lithium–Sulfur Batteries as a Metal‐Free Electrocatalyst for the Oxygen Reduction Reaction

Heteroatom‐doped carbon materials have been extensively investigated as metal‐free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li–air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene‐based sulfur composites have been recently developed to prolong the cycling life of Li–S batteries, one of the most attractive energy‐storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li–S batteries. Herein, we report a green and cost‐effective method to prepare sulfur‐doped graphene, achieved by the continuous charge/discharge cycling of graphene–sulfur composites in Li–S batteries. This material was used as a metal‐free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.     

Three‐dimensional Nitrogen‐Doped Reduced Graphene Oxide/Carbon Nanotube Composite Catalysts for Vanadium Flow Batteries

The development of vanadium redox flow battery is limited by the sluggish kinetics of the reaction, especially the cathodic VO₂⁺/VO²⁺ redox couples. Therefore, it is vital to develop new electrocatalysts with enhanced activity to improve the battery performance. Herein, we synthesized the hydrogel precursor by a facile hydrothermal method. After the following carbonization, nitrogen‐doped reduced graphene oxide/carbon nanotube composite was obtained. By virtue of the large surface area and good conductivity, which are ensured by the unique hybrid structure, as well as the proper nitrogen doping, the as‐prepared composite presents enhanced catalytic performance toward the VO₂⁺/VO²⁺ redox reaction. We also demonstrated the composite with carbon nanotube loading of 2 mg/mL exhibits the highest activity and remarkable stability in aqueous solution due to the strong synergy between reduced graphene oxide and carbon nanotubes, indicating that this composite might show promising applications in vanadium redox flow battery.     

A Ratiometric Luminescent Thermometer Co‐doped with Lanthanide and Transition Metals

Herein, we report the fabrication of a sensitive ratiometric and colorimetric luminescent thermometer with a wide operating‐temperature range, from cryogenic temperatures up to high temperatures, through the combination of lanthanide and transition metal complexes. Benefiting from the transition metal complex as a self‐reference, the lanthanide content in the mixed‐coordination complex, Eu_0.05(Mebip‐mim bromine)_0.15Zn_0.95(Mebip‐mim bromine)_1.9, was lowered to 5 %.     

One‐Pot Synthesis of Nitrogen‐doped TiO2 Nanowires with Enhanced Photocurrent Generation

A nitrogen‐doped TiO₂ (N‐TiO₂) nanowire film was synthesized via a one‐pot hydrothermal method using triethylamine as nitrogen source. The effect of the concentration of the triethylamine on the films was evaluated. In addition, the N‐TiO₂ nanowires were characterized using field‐emission scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet–visible spectroscopy. A 3.2× enhancement of the photocurrent for N‐TiO₂ (0.6) was achieved over the as‐prepared TiO₂ nanowire, under AM1.5G solar illumination. This was due to nitrogen doping, which could narrow the bandgap of titania to extend the adsorption of the catalyst to the visible light region.