Content Of Pyridinic Nitrogen Research Articles

Urea-treatment of CoOx carbon nanofibers to improve the electrochemical performance of supercapacitor using aqueous electrolytes

Supercapacitors (SCs) play a crucial role in flexible electronics, necessitating innovative approaches to enhance surface faradaic reactions and minimize faradaic diffusion while using aqueous electrolytes. Thus, the urea treatment of cobalt oxide (CoOx)-decorated carbon nanofibers (CNFs) is proposed in this study to decrease the contribution of faradaic diffusion-limited current. Flexible CoOx/CNF electrodes were obtained by annealing ZIF-67-grafted polyacrylonitrile (PAN) fibers via a wet chemical method. The urea treatment of CoOx/CNFs increased the content of sp2-hybridized carbon and pyridinic nitrogen, as confirmed by X-ray photoelectron spectroscopy, effectively enhancing conductivity and pseudocapacitive charge storage capability via nitrogen doping. Notably, urea-treated CoOx/CNF electrode samples exhibited a capacitance of 750 mF cm−2 at a scan rate of 10 mV s−1, while retaining more than 81 % capacitance at a higher scan rate of 100 mV s-1. The cyclic voltammetry curves during variable bending angle testing (0°, 45°, and 90°) exhibited negligible changes, indicating the excellent flexibility of the SCs. The CoOx/CNFs and urea-treated CoOx/CNFs exhibited 80 % and 91 % capacitance retentions, respectively, after 10,000 galvanostatic charge and discharge cycles. Furthermore, the attained energy densities of 76 and 61 µWh cm−2 at the respective power densities of 2 and 20 mW cm−2 indicated the excellent electrochemical performance of the optimal urea-treated CoOx/CNF electrode.

Synergistic effects of hierarchical porous structures and ultra-high pyridine nitrogen doping enhance the oxygen reduction reaction electrocatalytic performance of metal-free laminated lignin-based carbon

Construction of non-metallic biomass-carbon based catalysts for fuel cell air cathode applications has attracted great attention in recent years. In this work, a convenient and clean technique was developed to fabrication nitrogen-doped lignin-based hierarchical porous lamellar carbon (N-LHPC) via lignin as the carbon precursor, melamine/urea as the nitrogen source and ZnC2O4.2H2O as the chemical activator. The N-LHPC has a high specific surface area (491.5 m2 g−1) and macroporous/mesoporous/microporous structures. The nitrogen doping of N-LHPC can reach 16.37 wt%, with a high pyridinic nitrogen content of 41.39 at.%. N-LHPC exhibits a high half-wave potential (0.87 V) and a large limiting current density (5.75 mA cm−2) in 0.1 mol KOH media which is comparable to the commercial Pt/C catalysts. Furthermore, N-LHPC was assembled as air cathode catalyst for Zn-air batteries to evaluate its practical catalytic performance, and the power density was as high as 191 mW cm−2, which was superior to the 20 wt% Pt/C electrocatalyst. This research demonstrates that lignin is a promising carbon source for the fabrication of high catalytic activity and economical electrocatalysts for energy storage systems.

Chemically tuned nitrogen-doped sulfur host for a reversible and stable room-temperature sodium-sulfur batteries

The fast transition of long-chain polysulfide to short-chain polysulfide causes a sharp decay in the performance of room-temperature sodium sulfur (RT-Na/S) batteries. The nitrogen-doped sulfur host is identified as effective in slowing the transition process by entrapping the sodium polysulfide. However, precise control over the amount of nitrogen remained a challenge. We report a chemical route to fine-tune nitrogen doping in the sulfur host. The nitrogen content in the sulfur host is identified to vary from 7 to 19 at. % by varying the reaction time from 4 to 12 h. The optimized reaction time of about 8 h results in the highest pyridinic and pyrrolic nitrogen content. In addition to nitrogen doping, the sulfur host with a hierarchical pore structure could be achieved with 8 h of reaction time. The as-developed sulfur host serves as a sulfur cathode and is used to fabricate an RT-Na/S battery. The cell could function stably for over 500 cycles at 1C, with a high Coulombic efficiency of ~99.5 % and a capacity decay of 0.28 mAh g−1 per cycle at 1C. The cell could function reversibly and stably at various C-rates (0.2C – 2C). This study paves a path for the researcher to revisit the design of the sulfur host to construct a stable cathode for RT-Na/S batteries.

Multifunctional G@UC3N4 modified separator for high-performance Li-S batteries

Lithium-sulfur batteries (LSBs) are known for their outstanding theoretical energy density and low cost. However, low sulfur utilization and shuttle effect of the lithium polysulfides (LiPSs) dissolved in the electrolyte seriously limit its commercialization. Herein, graphene@carbon nitride (G@UC3N4) composite modified separator is designed as a multifunctional barrier to enhance the performance of LSBs. UC3N4 with high specific surface area and high pyridinic nitrogen (N) content is prepared by simple secondary heat treatment method, achieving a double physical-chemical limitation for the shuttle of LiPSs. Meanwhile, graphene as a carrier for UC3N4 not only enhances the conductivity of the entire electrode but also accelerates the diffusion of Li+ and the penetration process of the electrolyte. LSBs assembled with G@UC3N4 polypropylene separator exhibit high initial specific capacity (1216.46 mAh g−1 at 1 C) and stable long cycling capability (average decay rate of only 0.047% after 1000 cycles at 2 C, with a coulombic efficiency consistently above 99%).

Nitrogen Self-Doped Metal Free Catalysts Derived from Chitin via One Step Method for Efficient Electrocatalytic CO2 Reduction to CO

In this study, a facile one-step method via pyrolysis was used to prepare nitrogen self-doped metal free catalysts derived from inexpensive biomass-chitin for an electrochemical CO2 reduction reaction (CO2RR). The microstructure, surface area, defect and N type in the catalysts were analyzed by BET, Raman, XPS, SEM and TEM. The sustainable chitin-based electrocatalyst prepared under optimized conditions has a surface area of 1972 m2/g and can convert CO2 into CO with FECO of ~90% at a potential of −0.59 V (vs. RHE). This good CO2RR performance results from plentiful active sites due to a high surface area, rich ultra-micropores that are beneficial to CO2 adsorption, abundant mesopores for CO2 transport improvement, a high content of pyridinic and graphitic nitrogen that is favorable for a CO2 reduction reaction and a low interfacial charge transfer resistance leading to a rapid electron transfer rate from the catalyst to CO2. This study shows the feasibility of N self-doped biomass-derived catalysts for CO2RR with the potential for large-scale industrial applications.

Bottom-up synthesis of pyridinic nitrogen-containing carbon materials with C–H groups next to pyridinic nitrogen from two-ring aromatics

Carbon materials containing pyridinic nitrogen are expected to be effective for electrodes and catalysts. However, it is challenging to selectively and simultaneously introduce both pyridinic nitrogen and C–H groups next to the pyridinic nitrogen at a high content, which has been reported to work as an active site for oxygen reduction reaction, in the absence of catalysts. In this work, among six relatively inexpensive precursors with pyridinic N and two-fused rings, 1,5-naphthyridine showed the highest percentage of pyridinic nitrogen (80%) and the highest pyridinic-nitrogen content (12.4 at%) after carbonization in an ampoule at 873 K. Unlike carbon materials prepared from precursors with three- or more-fused rings, C–H groups next to pyridinic nitrogen remained in carbonized 1,5-naphthyridine with two-fused rings. Carbonization mechanisms of precursors with two-fused rings were quite different from those of precursors with three- or more-fused rings because of the low thermal stability of the precursors with two-fused rings as results of energy calculation and ReaxFF. The highest percentage and content of pyridinic nitrogen were attained using 1,5-naphthyridine because 1,5-naphthyridine had the highest thermal stability of C–N bonds and the low probability to form tertiary nitrogen among precursors with two-fused rings.

Metal-organic framework derived inverse opal type 3D graphitic carbon for highly stable lithium-ion batteries.

Graphitic carbon-based anodes for lithium-ion batteries have seen remarkable development and commercial acceptance during the past three decades. Still, the performance of these materials is limited due to the low surface area, stacking of layers, poor porosity, and meager conductivity. To overcome these limitations, we propose using polystyrene as a core and small-sized zeolitic imidazolate framework-67 (ZIF-67) particles as decorators to develop a highly porous three-dimensional graphitic carbon material. The developed material is optimized with the carbonization temperature for the best anodic performance of LIBs. The pyridinic nitrogen content in the material carbonized at 700 °C makes it high performing and more stable than the samples treated at 600, 800, and 900 °C. The packed coin cell exhibited an initial discharge capacity of 775 mA h g-1 at a current density of 50 mA g-1, which increases to 806 mA h g-1 after testing the material at different current densities for 55 cycles. The packed half-cell exhibited a highly stable performance of about 96% even after testing for 2000 cycles at 1 A g-1.

Pyridinic nitrogen dominated doping on Pd/carbon catalysts for enhanced hydrogenation performance.

The hydrogenation of 4-carboxylbenzaldehyde over Pd catalysts is a crucial process during the production of pure terephthalic acid. Herein, ZIF-8 derived carbon materials (NC) with adjustable N types were synthesized and used as the supports of Pd catalysts. Pd supported on NC with 50.5% of pyridinic N exhibited best hydrogenation activity with a TOF value of 4.1min-1. The microstructures of NC support and electronic structures of Pd in Pd/NC were investigated by techniques such as XRD, N2 physisorption, XPS, H2-O2 titration and TEM. The nitrogen species in CN surface not only can adjust chemical state and dispersion of Pd nanoparticles (NPs), but also promote the adsorption and activation capability of H2 molecular. Besides, the ratio of Pd0/Pd2+ and Pd dispersion were closely correlated with pyridinic nitrogen content. The improvement in hydrogenation activity and stability of Pd/CN catalyst in relative to Pd/C were ascribed to the synergistic effect of pyridinic nitrogen and active site Pd0.

Toward strategical bottom-up synthesis of carbon materials with exceptionally high pyridinic-nitrogen content: Development of screening techniques

Selective doping of nitrogen-containing functional groups of carbon materials is the most essential technique for enhancing properties significantly for various applications such as catalysts and electrodes. Reported carbon materials with controlled pyridinic nitrogen are generally synthesized on substrates, leading to low productivity and high cost. Thus, simple preparation methods for selective doping of nitrogen in carbon materials without substrates are indispensable for mass production. This work discovered that simple heat treatment of 1,7-phenanthroline at 973 K formed carbon material with exceptionally high pyridinic nitrogen content (92%). The selective doping of pyridinic nitrogen was attained by the protection of pyridinic nitrogen due to the steric hindrance by the neighboring C–H group on armchair edges to avoid the formation of N–H bonding on pyridinic nitrogen on armchair edges. Screening techniques of precursors for preparing carbon materials with high pyridinic nitrogen content are also essential to minimize research costs. Screening by 1) formation energy of hydrogenation on pyridinic nitrogen, 2) molecular dynamic simulation with reactive force field, and 3) comparison of structures of precursors revealed that 1,7-phenanthroline was the best precursor to maintain the high percentage of pyridinic nitrogen after carbonization. Thus, strategic synthesis is now possible using screening techniques.

Boosting Activity and Stability of Metal Single-Atom Catalysts via Regulation of Coordination Number and Local Composition.

Controlling the chemical environments of the active metal atom including both coordination number (CN) and local composition (LC) is vital to achieve active and stable single-atom catalysts (SACs), but remains challenging. Here we synthesized a series of supported Pt1 SACs by depositing Pt atoms onto the pretuned anchoring sites on nitrogen-doped carbon using atomic layer deposition. In hydrogenation of para-chloronitrobenzene, the Pt1 SAC with a higher CN about four but less pyridinic nitrogen (Npyri) content exhibits a remarkably high activity along with superior recyclability compared to those with lower CNs and more Npyri. Theoretical calculations reveal that the four-coordinated Pt1 atoms with about 1 eV lower formation energy are more resistant to agglomerations than the three-coordinated ones. Composition-wise decrease of the Pt-Npyri bond upshifts gradually the Pt-5d center, and minimal one Pt-Npyri bond features a high-lying Pt-5d state that largely facilitates H2 dissociation, boosting hydrogenation activity remarkably.

Performance evaluation of functionalized carbon aerogel as oxygen reduction reaction electrocatalyst in zinc-air cell

The comparable catalytic activities of non-noble metal electrocatalysts are the prime to enable their breakthrough performances for oxygen reduction reaction (ORR). In this work, the nitrogen-doped carbon aerogels are strategically functionalized with Ce/Fe elements. The increased content of pyridinic nitrogen from 16.71% to 20.28% coupled with a macro-porous structure result in an enhanced ORR catalytic performance. The performance evaluation shows that the ORR onset potential of the functionalized sample shifts from 0.893 V to 0.968 V comparing to the unfunctionalized sample. The open cell voltage reaches 1.450 V when the optimal catalyst is assembled into a zinc-air cell as the cathode, and such performance is comparable to the commercial Pt/C catalyst.

Metal organic framework derived iron-nitrogen doped porous carbon support decorated with cobalt and iron as efficient nanocatalyst toward oxygen reduction reaction

Two porous carbon supports as N-doped carbon (NC) and Fe/N-co-doped carbon (Fe-NC), are obtained from ZIF-8 (zeolitic imidazolate framework) and Fe@ZIF-8, respectively, through the pyrolysis process. They are then decorated with transition metals using a modified polyol method to precipitate Fe, Co, and Fe–Co nanoparticles. The as-prepared catalysts are characterized by different physicochemical, morphological, and electrochemical characterization methods. Field emission scanning electron microscopy images show well-defined preserved polyhedron morphology for all prepared catalysts. Transmission electron microscopy images confirm a uniform distribution of metal nanoparticles through the surface of the supports. X-ray photoelectron spectroscopy results illustrate the existence of high content of graphitic and pyridinic nitrogen. Oxygen reduction reaction (ORR) results show the prepared support, which is in-situ doped with iron (Fe-NC), has better ORR performance than NC support. The results also display Co and Fe nanoparticles' coincident precipitation on the supports can improve ORR. This finding indicates both in-situ and ex-situ metal doping can be beneficial for good ORR performance. The optimum catalyst (Fe–Co/Fe-NC) illustrates enhanced ORR activity and stability with onset potential ~0.9VRHE in 0.1 M HClO4. Superior performance is associated with a synergistic effect between small and uniform dispersion of Co and Fe nanoparticles and appropriate nitrogen content.

Carbon Nitride Anchored on a Nitrogen-Doped Carbon Nanotube Surface for Enhanced Oxygen Reduction Reaction.

Replacement of noble-metal-based electrocatalysts with inexpensive alternatives that have similar high performance will benefit the development of fuel cell technology. A metal-free composite of carbon nitride (CN) with nitrogen-doped carbon nanotubes (NCNTs) and its application as an electrocatalyst for the oxygen reduction reaction are reported for the first time in this study. The fabricated material (CN/NCNTs) formed a close interface between the two components and showed a comparable electrocatalytic activity in an alkaline medium to that of a conventional platinum-loaded carbon, superior tolerance to crossover effects, and excellent stability. The electrocatalytic efficiency of the CN/NCNT composite was nearly 100% of the four-electron (4 e-) pathway. The high performance of the current electrocatalyst was derived from its features, such as a relatively large surface area, high content of pyridinic nitrogen, and superior conductivity.

Porous graphitic carbon from mangosteen peel as efficient electrocatalyst in microbial fuel cells

In this study, a low-cost and efficient strategy to synthesize nitrogen self-doped porous graphitic carbon was proposed by using mangosteen peel as both the carbon and nitrogen source, combined with molten KOH activation and Co2+ catalytic graphitization. The mangosteen peel carbon catalyst prepared at 800 °C (referred to as MPC-800) possessed a large specific surface area (1168 m2/g), appropriate porous structure, high graphitization degree, and high pyridinic and graphitic nitrogen content. Further, electrochemical measurements indicated that the MPC-800 catalyst showed good oxygen reduction reaction activity. Moreover, MPC-800 as cathode catalyst displays an onset potential of 0.150 V (vs. Ag/AgCl) and half-wave potential of −0.091 V (vs. Ag/AgCl) in neutral medium, which is more positive than commercial Pt/C (0.121 V and −0.113 V, respectively). The maximum power density of microbial fuel cells using MPC-800 was 240 mW/m2, which was slightly superior to that of the Pt/C cathode (220 mW/m2). This work proposed a novel method, based on the low cost and wide availability of waste mangosteen peel, to synthesize an excellent oxygen reduction reaction catalyst for microbial fuel cells.

Effect of different itaconic acid contents of poly(acrylonitrile-co-itaconic acid)s on their carbonization behaviors at elevated temperatures

The carbonization procedure is a crucial step for polyacrylonitrile (PAN)-based precursors to be transformed into carbon materials. In this study, PAN and poly(acrylonitrile-co-itaconic acid)s (PAIs) with different contents of itaconic acid (IA) were prepared through free radical polymerization, and their carbonization behaviors were investigated at different thermal treatment temperatures. As confirmed by Fourier transform infrared spectroscopy analyses, functional groups containing heteroatoms practically disappeared above 600 °C, due to crosslinking, condensation, dehydrogenation, and gas-evolution reactions of the carbonization processes. Deconvolution of the carbon, oxygen and nitrogen peaks from X-ray photoelectron spectroscopy analyses revealed the development of ordered and doped graphitic carbons at elevated thermal treatment temperatures. The total yields of PAIs with excess amounts of IA (3 ~ 6 mol%) demonstrated a large carbon loss during the carbonization procedures. PAI with 1 ~ 2 mol% IA afforded carbon materials with a relatively high graphitic carbon content at 1200 °C, which is potentially important for electrical conductivity. Meanwhile, carbon materials prepared from PAI with 2 mol% IA at 1200 °C exhibited a relatively high content of pyridinic nitrogen, suggesting potentially superior catalytic activity. This study afforded technical guidelines on the structural elements of PAN-based precursors to prepare carbon materials with predesigned characteristics.

Reconstruction of pH-universal atomic Fe[sbnd]N[sbnd]C catalysts towards oxygen reduction reaction

Constructing of single atom catalysts that can stably exist in various energy conversion and storage devices is still in its infancy. Herein, a geometrically optimized three-dimensional hierarchically architectural single atomic FeNC catalyst with fast mass transport and electron transfer is rationally developed by post-molecule pyrolysis assisted with silicon template and reconstructs by ammonia treating. The ammonia-assisted secondary pyrolysis not only compensates for the volatilization of nitrogen species contained in organic precursors but also optimizes the surface structure of FeNC catalyst, thus increasing the content of pyridinic nitrogen and boosting the density of active sites (FeNx) in FeNC samples. In addition, the pyridinic nitrogen adjusts the electronic distribution in Fe 3d active center and promotes the catalytic performances. Therefore, this hollow spherical atomically dispersed FeNC catalyst delivers outstanding oxygen reduction reaction (ORR) activity in pH-universal electrolyte and surpasses the most reported values.

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes (CNTs), as one-dimensional nanomaterials, show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer. However, the security risks, time-consuming and high cost of the preparation process hinder its further application. Here, we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs (Co/N-CNTs) by using cobalt zeolitic imidazolate framework (ZIF-67) as a precursor, in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs. Importantly, the obtained Co/N-CNTs, with high content of pyridinic nitrogen and abundant graphitized structure, exhibit superior catalytic activity for oxygen reduction reaction (ORR) with half-wave potential (E1/2) of 0.85 V and durability in terms of the minimum current loss (2%) after the 30,000 s test. Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.

Facile synthesis of nitrogen-doped carbon coated Fe3O4/Pd nanoparticles as a high-performance catalyst for Cr (VI) reduction

A novel facile and cost-effective approach was developed to fabricate Fe3O4/Pd nanoparticles encapsulated in a nitrogen-doped carbon (NC) shell (Fe3O4/Pd@N–C) through a layer-by-layer assembly method coupled with high-temperature annealing. The Fe3O4/Pd@N–C nanocomposites acted as a high-performance catalyst for the catalytic reduction of Cr (VI) to Cr (III) using formic acid (HCOOH) as the reducing agent. Due to conductive and protective functions of the NC shell, the catalyst had a high stability and catalytic activity, and only needed 3 min were required to convert Cr(VI) to Cr(III). Furthermore, catalytic conditions such as annealing temperature, reaction temperature and Pd loading were optimized. The excellent catalytic performance of Fe3O4/Pd@N–C can be attributed to the following reasons: the thin NC shell, the high disperse of Pd NPs loaded on the Fe3O4, the high content of pyridinic nitrogen and graphitic nitrogen, as well as high surface area up to 110.77 m2 g−1.

Peroxymonosulfate activation by nitrogen-doped biochar from sawdust for the efficient degradation of organic pollutants

The fabrication of low-cost, high-performance and environmentally friendly carbon-based catalysts capable of activating peroxymonosulfate (PMS) for wastewater treatment applications is still a challenge. In this work, a novel nitrogen-doped biochar (N-biochar) was prepared through a facile one-step calcination method using sawdust and different organic nitrogen-containing compounds as starting materials. It was found that the catalytic activity of the N-biochar relies heavily on the type of nitrogen precursor, the relative amount of sawdust to nitrogen precursor, and the calcination temperature. Different types and amounts of the nitrogen precursor mainly affect the content of total nitrogen and pyridinic nitrogen, and the calcination temperature mainly affects the content of graphitic nitrogen in the N-biochar. Based on a systematic comparison, an optimized N-biochar (N-C-d-4-800) with a higher content of graphitic and pyridinic N, rich defects, larger SSA and porous structure was obtained, and exhibited a superior catalytic activity for activating PMS to oxidize various organic pollutants, such as bisphenol A (BPA), phenol, acetaminophen (AAP) and sulfamethoxazole (SMX). Moreover, the N-C-d-4-800/PMS system can work effectively at a wide pH range and high salinity conditions, despite the background of the real water matrix. The present study highlights the enormous potential of the novel N-biochar prepared from sawdust for wastewater remediation applications.

Effects of the Carbon Support Doping with Nitrogen for the Hydrogen Production from Formic Acid over Ni Catalysts

Porous nitrogen-doped and nitrogen-free carbon materials possessing high specific surface areas (400–1000 m2 g−1) were used for deposition of Ni by impregnation with nickel acetate followed by reduction. The nitrogen-doped materials synthesized by decomposition of acetonitrile at 973, 1073, and 1173 K did not differ much in the total content of incorporated nitrogen (4–5 at%), but differed in the ratio of the chemical forms of nitrogen. An X-ray photoelectron spectroscopy study showed that the rise in the synthesis temperature led to a strong growth of the content of graphitic nitrogen on the support accompanied by a reduction of the content of pyrrolic nitrogen. The content of pyridinic nitrogen did not change significantly. The prepared nickel catalysts supported on nitrogen-doped carbons showed by a factor of up to two higher conversion of formic acid as compared to that of the nickel catalyst supported on the nitrogen-free carbon. This was related to stabilization of Ni in the state of single Ni2+ cations or a few atoms clusters by the pyridinic nitrogen sites. The nitrogen-doped nickel catalysts possessed a high stability in the reaction at least within 5 h and a high selectivity to hydrogen (97%).