Role Of Nitrogen Doping Research Articles

Role of Nitrogen-doping in porous carbon for enlarging working voltage window of aqueous supercapacitors in neutral electrolyte

The fundamental mechanism on enlarging working voltage window of carbon-based aqueous supercapacitors is still unclear owing to the indistinct principles in inhibiting water splitting occurred at the electrochemical interface. Herein, we design a set of N, O co-doped porous carbon (NOPC) free-standing electrodes with adjustable N-doping level, and establish that N-doping (N-content and specific N-configuration) governs neutral HER and OER. The NOPC electrode with a lower N-doping level can possess a wide working potential window of − 1–1 V, and thus the corresponding aqueous symmetric supercapacitors showcase a wide working voltage window of 2 V in LiCl aqueous solution. In situ spectroscopy evidences and theoretical simulation demonstrate that the low N-doping (N-content and percentage of pyrrolic nitrogen) level can weaken the interaction between the electrode and interfacial water molecules and suppress the formation of *OOH intermediate during the charge–discharge process, and thus significantly decreasing the HER and OER activities to inhibit water splitting. The finding can shed light on the fundamental understanding of mechanism on enlarging working voltage window of carbon-based aqueous supercapacitor.

New insights into the role of nitrogen doping in microporous carbon on the capacitive charge storage mechanism: From ab initio to machine learning accelerated molecular dynamics

Fundamental understandings of the relationship between ion-electrode interaction and structural feature in porous carbon electrodes at a molecular level provides guidelines for the design of high-performance electric double layer supercapacitors. It is certified by experiments that porous carbon structures doped with nitrogen show enhanced capacitive performance. However, in the theoretical simulations, the fundamental charge storage mechanism is still elusive. In particular, the recent experimental result shows that the generally ignored nitrolic nitrogen (N5) in porous carbon exhibits a positive effect on capacitance, while graphitic nitrogen (N3) does the opposite, which is against with the simulation results based the 2D-modeled porous graphene structure. Here, we perform ab initio molecular dynamics simulations on the N3 and N5-doped carbon/electrolyte interfaces, including both 2D planar and 3D microporous carbon electrodes. Our calculation indicates that N3 in the 3D pore hinders the electrolyte transport, while N5-doped micropore still serves as an electrolyte transport channel through the formation of H-bond. The charge storage mechanism is further elucidated by the analysis of the well equilibrated interfaces obtained from the machine learning force field accelerated molecular dynamics. Our work provides a new insight into the effect of nitrogen doping in 3D porous carbon, which is exactly opposite to the 2D planar graphene. Therefore, we emphasize that differences in the electrochemical conditions of 2D planar and 3D microporous carbon electrodes should be fully considered when analyzing the effects of surface chemistry on charge storage mechanisms.

The Role of Nitrogen Doping in Modulating Ruthenium Nanocatalysts for Enhanced Electrochemical Hydrogen Evolution Reaction in Alkaline Medium

The Role of Nitrogen Doping in Modulating Ruthenium Nanocatalysts for Enhanced Electrochemical Hydrogen Evolution Reaction in Alkaline Medium

Improving Zinc-Ion Batteries’ Performance: The Role of Nitrogen Doping in V2O3/C Cathodes

This study presents the synthesis and electrochemical evaluation of nitrogen-doped vanadium oxide (N−V2O3/C) as a cathode material for aqueous zinc-ion batteries (AZIBs), using a hydrothermal method. Compared to undoped V2O3/C, N−V2O3/C exhibits enhanced electrical conductivity, capacity, and electrochemical kinetics, attributed to the incorporation of pyridinic and pyrrolic nitrogen. The initial charge–discharge cycles indicate phase transitions to amorphous vanadium oxides, enhancing conductivity. N−V2O3/C shows a high specific capacity of 168.4 mAh g−1 at 10 A g−1 and remarkable reversibility, highlighted by the transient existence of intermediate species during cycling. Optimal electrochemical performance is achieved with a vanadium-to-nitrogen molar ratio of 2:3, indicating the significant impact of the nitrogen doping concentration on the material’s efficiency. This work underscores the potential of N−V2O3/C as a superior cathode material for AZIBs.

Role of nitrogen doping and pore volume for CO2 capture in metal-organic framework derived ultramicroporous carbon material

We report the synthesis of four MOF-derived nitrogen and oxygen co-doped ultramicroporous/microporous carbon (MNOUCs) at different carbonization temperatures and their applications as adsorbents for efficient CO2 capture. MNOUC-900, carbonized at 900 ℃ having the highest surface area of 1320 m2/g and highest ultramicropore volume of 0.205 cm3 g−1 showed the maximum CO2 uptake of 4.65 mmol g−1 at 0 ℃ and 1 bar. Contrary to this, MNOUC-600, which was synthesized at 600 ℃ showed the highest CO2/N2 selectivity of 31. This study revealed that CO2 uptake had been found to be correlated with ultramicropore volume while selectivity (CO2 vs N2) improves with increasing basic nitrogen functionalities such as pyridinic and pyrollic. The heat of adsorption values was found to be 25–40 kJ mol−1 suggesting the physisorption nature of the interaction. Dynamic CO2 uptake experiment was performed for MNOUC-900, which revealed its good efficiency to be used as a CO2 adsorbent.

Atomically well-defined nitrogen doping for cross-plane transport through graphene heterojunctions.

The nitrogen doping of graphene leads to graphene heterojunctions with a tunable bandgap, suitable for electronic, electrochemical, and sensing applications. However, the microscopic nature and charge transport properties of atomic-level nitrogen-doped graphene are still unknown, mainly due to the multiple doping sites with topological diversities. In this work, we fabricated atomically well-defined N-doped graphene heterojunctions and investigated the cross-plane transport through these heterojunctions to reveal the effects of doping on their electronic properties. We found that a different doping number of nitrogen atoms leads to a conductance difference of up to ∼288%, and the conductance of graphene heterojunctions with nitrogen-doping at different positions in the conjugated framework can also lead to a conductance difference of ∼170%. Combined ultraviolet photoelectron spectroscopy measurements and theoretical calculations reveal that the insertion of nitrogen atoms into the conjugation framework significantly stabilizes the frontier molecular orbitals, leading to a change in the relative positions of the HOMO and LUMO to the Fermi level of the electrodes. Our work provides a unique insight into the role of nitrogen doping in the charge transport through graphene heterojunctions and materials at the single atomic level.

Platinum Deposited Nitrogen-Doped Vertically Aligned Carbon Nanofibers as Methanol Tolerant Catalyst for Oxygen Reduction Reaction with Improved Durability

Nitrogen doping in carbon materials can modify the employed carbon material’s electronic and structural properties, which helps in creating a stronger metal-support interaction. In this study, the role of nitrogen doping in improving the durability of Pt catalysts supported on a three-dimensional vertically aligned carbon nanofiber (VACNF) array towards oxygen reduction reaction (ORR) was explored. The nitrogen moieties present in the N-VACNF enhanced the metal-support interaction and contributed to a reduction in the Pt particle size from 3.1 nm to 2.3 nm. The Pt/N-VACNF catalyst showed better durability when compared to Pt/VACNF and Pt/C catalysts with similar Pt loading. DFT calculations validated the increase in the durability of the Pt NPs with an increase in pyridinic N and corroborated the molecular ORR pathway for Pt/N-VACNF. Moreover, the Pt/N-VACNF catalyst was found to have excellent tolerance towards methanol crossover.

Role of nitrogen doping in stoichiometric and defective carbon nano-onions: Structural diversity from DFT calculations

Carbon nano-onions (CNOs) and their modified forms have been utilised recently as active catalysts, capacitors, and anode materials. In this study, the structural and electronic properties and the thermodynamic stability of both stoichiometric and defective (mono- and divacancy) N-doped CNOs were elucidated from a theoretical perspective. We examined numerous structures with an increasing nitrogen content, including different distribution patterns using density functional theory calculations. Our findings facilitate a deeper understanding of nitrogen active sites and their relative stability. It was shown that the most stable nitrogen positions were located in five-membered rings, while the nitrogen distribution for mono- and divacancy-containing CNOs was different. In this case, the most attractive positions were pyridinic sites and those in the pentagon rings. We also demonstrated the influence of doping level and defect type on thermodynamic stability. It was observed that the type of defect and doping level ambiguously determined the energy band gap. For monovacancy-containing N–CNOs, the reduction of band gap was moderate, whereas for divacancy systems, the band gap increased.

Highly efficient oxygen photosensitization of carbon dots: the role of nitrogen doping

Photosensitization is a promising avenue of oxygen activation, which can overcome the spin selection rule to transform the ground state oxygen (3O2) into a highly reactive singlet oxygen (1O2). Carbon dots (CDs) are a promising type of carbon-based photosensitizer, and nitrogen doping can further improve the oxygen photosensitization performance. Although the roles of nitrogen doping in tuning the optical properties (mainly absorption and fluorescence) of CDs have been well-studied, their association with oxygen photosensitization has not been reported. Herein, using the well-developed synthetic protocol of hydrothermal treatment of citric acid and ethylenediamine, we prepared nitrogen-doped CDs (N-CDs) of varied nitrogen contents. The oxygen photosensitization performances of the N-CDs were first confirmed by ROS investigation with TMB oxidation as the ROS probe and EPR. After XPS analysis of the surface nitrogen doping speciation, it was found that the changes of graphitic N and pyrrolic N correlated well with the oxygen photosensitization performances of N-CDs. Further theoretical calculations indicated that the two key factors for oxygen photosensitization, namely triplet activation and oxygen adsorption, are mainly associated with graphitic N and pyrrolic N, respectively. The results in this work help further understanding of the oxygen photosensitization mechanism of N-CDs, and are expected to be useful in the future design of carbon-based photosensitizers.

Exploring the role of nitrogen incorporation in ZrO2 resistive switching film for enhancing the device performance

The role of nitrogen doping on the resistive switching (RS) performance in nitrogen doped ZrO2 memristive device is investigated. The Pt/N:ZrO2/TiN resistive random access memory (RRAM) shows smaller switching voltage, larger memory window as well as improved uniformity. Moreover, the multilevel storage capability can be successfully obtained by varying the compliance current in the SET process for the memory cell. It is considered that the connection and rupture of conducting oxygen vacancy filaments (CF) can be localized and the oxygen ions (O2−) migration randomness is depressed due to nitrogen doping in ZrO2 film. Combining with the first-principle method, we theoretically calculate the formation energy (Evf), migration energy (Em) and density of states for oxygen vacancy (VO). Both Evf and Em values show noticeable decrease in N doped 2 × 2 × 2 ZrO2 supercell, which are related to the lower forming voltage and operating voltage. The density of states indicates that the oxygen vacancy midgap defect states can be eliminated as a result of N dopant, which neutralizes the excess defects in ZrO2 switching layer and may reduce the densities of the potential filaments. Herein the uniformity can be improved. All the theoretical results show reasonable agreement with the improved experimental RS performance for Pt/N:ZrO2/TiN device.

Role of nitrogen doping at the surface of titanium nitride thin films towards capacitive charge storage enhancement

Abstract We recently reported an impressive cycling stability (over 20,000 cycles) of titanium nitride (TiN) electrodes with high specific capacitance. It is anticipated that nitrogen (β−N) doping in the oxidized surface of TiN film plays a crucial role in charge storage mechanism and stability of this material. In this work, we offer an evidence on the effect of β−N doping on improvement in specific capacitance of vacuum annealed TiN thin films. The annealing of the TiN films leads to the diffusion of the excess β−N from sub-surface to oxidized TiN film surface without further oxidation of the electrode surface. We demonstrate an increase in the TiN areal capacitance upon an increase in the amount of β−N dopant. The areal capacitance of the annealed films was enhanced by 3-fold (8.2 mF cm−2 in K2SO4 aqueous electrolyte) without sacrificing the cycling stability of the electrodes after more than 10,000 consecutive charge/discharge cycles.

The role of nitrogen doping in ALD Ta2O5 and its influence on multilevel cell switching in RRAM

The role of nitrogen doping on the stability and memory window of resistive state switching in N-doped Ta2O5 deposited by atomic layer deposition is elucidated. Nitrogen incorporation increases the stability of resistive memory states which is attributed to neutralization of electronic defect levels associated with oxygen vacancies. The density functional simulations with the screened exchange hybrid functional approximation show that the incorporation of nitrogen dopant atoms in the oxide network removes the O vacancy midgap defect states, thus nullifying excess defects and eliminating alternative conductive paths. By effectively reducing the density of vacancy-induced defect states through N doping, 3-bit multilevel cell switching is demonstrated, consisting of eight distinctive resistive memory states achieved by either controlling the set current compliance or the maximum voltage during reset. Nitrogen doping has a threefold effect: widening the switching memory window to accommodate the more intermediate states, improving the stability of states, and providing a gradual reset for multi-level cell switching during reset. The N-doped Ta2O5 devices have relatively small set and reset voltages (< 1 V) with reduced variability due to doping.

One-step hydrothermal synthesis of nitrogen doping graphene based cobalt oxide and its supercapacitive properties

Abstract Nitrogen doping is considered to be a promising way to improve the performance of graphene-based supercapacitors. It is crucial to discuss that the role of nitrogen doping in regulating the electronic properties. Herein, we chose urea, NH3·H2O and N2H4·H2O as the nitrogen sources to modify the graphene based cobalt oxide composites to compare which nitrogen source made a great improvement on the supercapacitive performance of the composites. When the urea is used as the nitrogen source, the electrochemical performance was the best among the nitrogen-doped (N-doped) graphene based cobalt oxide composites (334.8 F g−1 at a current density of 5 A g−1 in 2 M KOH aqueous solution). Nitrogen doping worked as a modification to control the structure of graphene sheet and effectively improved the electrochemical performances.

Charting the Outer Helmholtz Plane and the Role of Nitrogen Doping in the Oxygen Reduction Reaction Conducted in Alkaline Media Using Nonprecious Metal Catalysts

This study was focused on elucidating the origin of the catalytic activity displayed by non-precious-metal-based oxygen reduction reaction (ORR) catalysts before and after heat treatment. Electrochemical measurements were recorded using a series of metal phthalocyanines calculated to exhibit varying oxygen adsorption energies before and after heat treatment at a temperature sufficiently high to facilitate degradation. Collectively, the results indicate that while the oxygen adsorption is germane to the catalytic activity before heat treatment, the ORR appears to proceed through a different pathway that is not dependent on adsorption energy after heat treatment. These conclusions help to explain the high catalytic activities exhibited by carbon- or nitrogen-based materials containing metal ions after heat treatment and may lead to the realization of substitutes for ORR catalysts that utilize precious transition metals.

Role of Nitrogen Doping on the Performance of Carbon Nanotube Catalysts: A Catalytic Wet Peroxide Oxidation Application

AbstractFour magnetic carbon nanotube (CNT) samples (undoped, completely N‐doped, and two selectively N‐doped) were synthesized by chemical vapor deposition. The materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4‐nitrophenol solutions (4‐NP, 5 g L−1). Relatively mild operating conditions were considered (atmospheric pressure, T=50 °C, pH 3), using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4‐NP. N‐doping was identified to influence considerably the CWPO performance of the materials. In particular, undoped CNTs, with a moderate hydrophobicity, favor the controllable and efficient decomposition of H2O2 into highly reactive hydroxyl radicals (HO.), thus showing high catalytic activity for 4‐NP degradation. On the other hand, the completely N‐doped catalyst, fully hydrophilic, favors a quick decomposition of H2O2 into nonreactive O2 and H2O species. The selectively N‐doped amphiphilic catalysts, that is, hybrid structures containing undoped sections followed by N‐doped ones, provided intermediate results, namely, a higher N content favored H2O2 decomposition towards nonreactive H2O and O2 species, whereas a lower N content resulted in the formation of HO., increasing 4‐NP mineralization. Catalyst stability and reusability were also investigated by consecutive CWPO runs.

The right kind of dopant

Electrochemisty The oxygen reduction reaction is an important step in fuel cells and other electrochemical processes but is still largely dependent on precious metal-containing catalysts. Recently explored alternatives include carbon materials that are doped with different, preferably non-precious metal, atoms. Guo et al. studied model graphite catalysts to try to understand the role of nitrogen doping and to elucidate the active catalytic sites. A nitrogen atom bound to two carbons formed an active catalyst site with an activity rivaling that of N-doped graphene catalysts. Science , this issue p. [361][1] [1]: /lookup/doi/10.1126/science.aad0832

Controllable nitrogen introduction into porous carbon with porosity retaining for investigating nitrogen doping effect on SO2 adsorption

Chemical doping of nitrogen into carbon framework has been demonstrated effective for gas molecules (e.g. CO2, SO2, NOx) adsorption. Here we report a series of nitrogen-doped porous carbons with controllable doping level (4.25–10.23%) and consistent pore structure (surface area around 1000m2/g) by a co-assembly method. Based on the unique structure, SO2 was used as probe molecule to independently study the N doping effect on the SO2–carbon surface interactions from both experimental and calculation aspects. The results indicate that SO2 adsorption capacities are proportional to the nitrogen contents and the sample with 10.2% nitrogen content gives the highest SO2 adsorption capacity of 48.3mg/g, 2.95 times higher than non-doped carbon. Moreover, combining the literature data with our studies indicates that both pore structure and N species play a contribution in SO2 adsorption process. For the NPC materials with similar pore structure, the increase of N contents improves the SO2 adsorption area in pores of N doped carbon mainly by enhancing the physisorption on various locations of carbon surface including basal plane and edge positions. Density functional theory (DFT) calculations indicate that nitrogen atom itself cannot serve as active site for SO2 adsorption. The role of nitrogen doping is to remodel the local electronic density, the polarity of carbon atoms as well as charge distribution of carbon surface, which induces the enhanced SO2 adsorption.

H2 purification by functionalized graphdiyne – role of nitrogen doping

Nitrogen doping into graphdiyne leads to a reduced H2 diffusion barrier and hence an enhanced hydrogen purification capability.

Effect of thickness on structural, optical and mechanical properties of Mn doped ZnO nanocrystalline thin films RF sputtered in nitrogen gas environment

Thin films of Zn0.95Mn0.05O were synthesized by RF- sputtering in nitrogen gas environment. Structural, optical and mechanical properties of the films with thickness ranging from 398 to 1650nm are studied. The X-ray diffraction (XRD) results show that the as- deposited films are oriented along the (002) direction with hexagonal wurtzite structure. The field emission scanning electron microscopy (FESEM) studies show an increase in grain size with increase in thickness. Optical transmission studies show band gap values in the range 3.03–3.37eV. The values of hardness and Young’s modulus are found to be in the range 14–18GPa and 122–167GPa at an indentation depth of 100nm respectively. The role of nitrogen doping on the microstructure and properties of films is discussed.

The Role of Nitrogen Doping on Durability in the Pt-Ru/HOPG System

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