Nitrogen Doping Level Research Articles

Nitrogen-Doped Carbon Materials for Persulfate Activation via Electron Transfer Pathways.

The incorporation of nitrogen into carbon materials is a strategy that effectively boosts their catalytic potency. Herein, a nitrogen-enriched carbon substance, designated as CN0.6, was synthesized from melamine, serving as a precursor. This substance has been established to act as an efficient catalyst devoid of metals for the activation of peroxymonosulfate (PMS). At a temperature of 25 °C, a concentration of 0.05 g/L CN0.6 along with 1 mM PMS suffices to achieve the complete degradation of concentrated tetracycline hydrochloride (TC) in a short period of 4 min. This enhanced catalytic performance is attributed to the optimal level of nitrogen doping, which elevates the pyrrolic nitrogen content and introduces additional defects characterized by an ID/IG ratio of 1.02. These factors collectively augment the adsorptive capacity for PMS and create a greater number of active sites to facilitate its activation. The dominance of a nonradical electron transfer mechanism in the CN0.6/PMS system has been confirmed through a series of analyses, including radical identification, quenching tests, and electrochemical assessments. Employing high-resolution liquid chromatography coupled with tandem mass spectrometry (LC-MS), the investigation identified three potential degradation routes for TC. Furthermore, the intermediates produced are determined to possess reduced toxicity in comparison to TC. The findings of this study offer a approach to the synthesis of highly efficient nitrogen-doped, metal-free catalysts, presenting a promising strategy for the degradation of environmental pollutants.

Low-grade lignite derived nitrogen doped hierarchical porous carbon for advanced lead-carbon batteries

The addition of carbon materials to the negative electrode would inhibit sulfation and prolong the cycle life of the lead-acid batteries. However, carbon materials contribute to the emergence of hydrogen evolution reaction (HER) and loss of water on the negative electrode. Accordingly, low-grade lignite raw material was one-step pyrolyzed to prepare nitrogen doped porous carbon (LNC) materials, which were further employed as negative additives to mitigate the above issues. The as-prepared LNC delivered large specific surface area (SSA) in the range of 1675.0–2503.3 m2 g−1, micro-mesoporous hierarchical structure, and high nitrogen doping level. Nitrogen doping considerably inhibited the HER and promoted the conversion kinetics between PbSO4/Pb in the negative electrode. Besides, the cycling life of lead-carbon battery containing LNC-1/3 at high-rate partial state of charge reached 9100 cycles, which reflected a 5.5-fold improvement over the blank. The improved performance could be attributed to the large SSA and plentiful functional groups, which offer active sites for the conversion of active substances, construct abundant ion channels, and refine the PbSO4 particles, thereby successfully minimizing irreversible sulfation. The short-route synthesis method provides a feasible approach to the reutilization of low-grade lignite, reflecting the circular economy.

Synergistic effects of nitrogen/oxygen co-doping in 3D mesoporous carbon nanospheres for enhanced microwave absorption

Mesoporous carbon nanospheres have attracted significant attention in the microwave absorption (MA) field due to the broad benefits provided by their mesoporous structure. This study presents a facile hard template strategy to construct distinctive 3D N/O co-doped mesoporous carbon nanospheres (NOCS). The high surface area, abundant mesopores, and high nitrogen (N) doping levels, with proper defects on the surface provide multiple sites to absorb electromagnetic waves (EMW). Mesoporous carbon nanospheres achieve significant reflection loss (RL) of −48.19 dB and extensive effective absorption bandwidth (EAB) up to 5.52 GHz. Moreover, computer simulation technology (CST) demonstrated that all simulated Radar cross-section (RCS) values were below 20 dB m2. Thus, this work holds significant promise for effective microwave absorbers using mesoporous carbon nanospheres.

Systematic study of the N concentration effects on metal-free ORR electrocatalysts derived from corncob: Less is more

We report nitrogen-doped biomass-derived porous carbon materials with great performance for the Oxygen Reduction Reaction (ORR) in alkaline media. The level of nitrogen doping in a simple pyrolysis of corncob (CC) was varied systematically, a 1:1 CC:urea ratio (CC1U) gave the best performance in terms of onset potential (Eonset = 0.97 V vs. RHE), maximum current density (jmax = -3.22 mA cm−2), hydroperoxide ion yield (%HO2– = 1.18 % at 0.5 V), and electron transfer number (n = 3.86 at 0.5 V). Unexpectedly, for higher CC:urea ratios the doping decreases, instead of plateauing, with lower concentration of C-N sites and more sp2 sites as determined by XPS, as well as lower specific surface area (SSA), while increasing both porosity and carbon (002) interplanar distance (d(002)). These materials should be durable and robust, since their performance actually improved after accelerated degradation tests. This study proves that renewable “waste” can be upconverted into metal-free electrocatalysts for electrochemical energy conversion technologies and emphasizes the need for studying and controlling doping levels to enhance performance.

Reinforcing cementitious composites with nitrogen-doped graphene: insights into molecular interactions and interfacial behavior

Graphene materials are useful functional fillers in cementitious materials. They are essential in creating intelligent cementitious materials, enabling the construction of internal conductive networks and the addition of thermoelectric properties. The success of this process hinges on the functional filler's compatibility with the cement matrix, which must be excellent to ensure optimal results. In this study, we delved into the interactions between nitrogen-doped graphene and calcium silicate hydrate (C-S-H), which is the principal binding phase in cementitious materials, employing Density Functional Theory (DFT) calculations. In this study, we explored diverse nitrogen doping configurations and levels, while concurrently analyzing the influence of calcium cations at the C-S-H matrix interface. The findings indicate that nitrogen atoms in doped graphene interact considerably with nucleophilic oxygen atoms on silicate chains, forming covalent N-O bonds with high bonding energies (length 1.4 A, −107.81 kcal/mol) during graphitic nitrogen doping. The presence of calcium ions further strengthens the interaction energy between C-S-H and graphene, suggesting a synergistic effect between different types of nitrogen doping. The binding and total bond energies under the synergistic effect were −479.52 kcal/mol and −183.23 kcal/mol, respectively. These values were 1.5 times higher than those of single nitrogen doping. These findings offer significant insights into the molecular-level interaction between CSH and carbon nanoparticles.

Insight into the effect of N-doping level in N-doped carbons modified separator on improving the electrochemical performance of Li-S batteries

Carbon materials are widely applied in lithium-sulfur (Li-S) batteries due to their large specific surface area, high conductivity, and tunable properties. An appropriate heteroatom doping can enhance the adsorption ability and electrochemical activity toward lithium polysulfides, thus improving the overall performance of Li-S batteries. Herein, three nitrogen-doped carbons (NCs) with different nitrogen doping levels are firstly prepared and then used as the model materials to coat the common polypropylene (PP) separator, aiming to elaborate the effect of adsorption behavior from various N-doping level carbons surface toward lithium polysulfides on the subsequent catalytic conversion kinetics. The experimental data demonstrate that the NC800 with appropriate N-doped level shows the moderate adsorption of polysulfides as well as exhibits the best reaction kinetics on polysulfides conversion. In comparison, an assembled Li-S battery with NC800-PP separator delivers high capacity and good cycling stability, achieving an initial specific capacity of ∼ 1302.2 mAh g−1 at 0.2 C and a capacity fading rate of ∼ 0.061 % per cycle after 500 cycles at 1.0 C. Moreover, a Li-S battery using NC800-PP separator still delivers an initial specific capacity of ∼ 1147.6 mAh g−1 at 0.1 C and maintains a stable specific capacity of ∼ 833.5 mAh g−1 even with a sulfur loading of ∼ 3.9 mg cm−2. This study is believed to give better insight to reveal the internal correlation of adsorption and catalytic effect on polysulfides, as well as provide a guidance for rationally designing heteroatom doping carbon materials in Li-S batteries.

Decoding intrinsic features of carbons from their capacitive performance

Carbon-based materials, prized for their diverse applications, are at the forefront of scientific exploration. Performance of these materials relies on their basic properties, yet traditional characterization methods are often laborious. In our study, we introduce a machine learning (ML) based approach that leverages electrochemical performance data to elucidate the intrinsic properties of carbon materials. We highlight a technique, Cap2SSA, that expeditiously and precisely determines the specific surface area (SSA) of carbon materials through capacitive responses gathered during electrochemical tests. The efficacy of Cap2SSA is substantiated using the commercial carbon material across diverse current densities in both aqueous and organic electrolytes. Our findings reveal that the SSA values derived from capacitance measurements align closely with actual measurements, with discrepancies under 14 %. Significantly, this evaluation method extends beyond the SSA estimation, offering a versatile tool for inferring additional carbon material features, such as nitrogen and oxygen doping levels. Overall, combining electrochemical measurements with ML enables rapid assessment of material composition and structure, driving forward material science analysis.

Synthesis of N-doped graphene film with tunable graphitic and pyridinic doping content

Nitrogen-doped (N-doped) graphene films with up to a 17.39 at.% doping level were synthesized with the chemical vapor deposition growth method. An extensive range of tunable nitrogen doping levels was achieved by selecting organic molecules as precursors grown at a wide temperature range of 300 to 1000 °C. The benzene rings in the precursor significantly reduced the energy requirements of N-doped graphene. The incorporation of bridgehead nitrogen and amino groups ensured a high nitrogen doping level and offered the tunable modulation of nitrogen dopant concentrations. The influence of temperature on the nitrogen content was investigated, distinguishing the graphitic and pyridinic dopant types, each demonstrating unique trends considering the dopant stability and growth mechanism. Specifically, the proportion of graphitic doping could be modulated from 40 % to 100 %. Notably, the pyrrolic type was absent at lower temperatures and was nearly negligible at elevated temperatures. Therefore, we developed a synthesis method for N-doped graphene growth that allowed for the selective and prioritized tuning of nitrogen dopant types. This method is particularly favorable when specific nitrogen dopants at certain doping levels are required for electrical and chemical catalytic applications.

Metal‐to‐insulator transition in oxide semimetals by anion doping

AbstractOxide semimetals exhibiting both nontrivial topological characteristics stand as exemplary parent compounds and multiple degrees of freedom, offering a promise for the realization of novel electronic states. In this work, we report the structural and transport phase transition in an oxide semimetal, SrNbO3, achieved through effective anion doping. Notably, the resistivity increased by more than three orders of magnitude at room temperature upon nitrogen‐doping. The extent of electronic modulation in SrNbO3 is strongly correlated with misfit strain, underscoring its phase instability to both chemical doping and crystallographic symmetry variations. Using first‐principles calculations, we discern that elevating the level of nitrogen doping induces an upward shift in the conductive bands of SrNbO3−δNδ. Consequently, a transition from a metallic state to an insulating state becomes apparent as the nitrogen concentration reaches a threshold of 1/3. This investigation shows effective anion engineering in oxide semimetals, offering pathways for manipulating their physical properties.

NH2-MIL-125-Derived N-Doped TiO2@C Visible Light Catalyst for Wastewater Treatment.

The utilization of titanium dioxide (TiO2) as a photocatalyst for the treatment of wastewater has attracted significant attention in the environmental field. Herein, we prepared an NH2-MIL-125-derived N-doped TiO2@C Visible Light Catalyst through an in situ calcination method. The nitrogen element in the organic connector was released through calcination, simultaneously doping into the sample, thereby enhancing its spectral response to cover the visible region. The as-prepared N-doped TiO2@C catalyst exhibited a preserved cage structure even after calcination, thereby alleviating the optical shielding effect and further augmenting its photocatalytic performance by increasing the reaction sites between the catalyst and pollutants. The calcination time of the N-doped TiO2@C-450 °C catalyst was optimized to achieve a balance between the TiO2 content and nitrogen doping level, ensuring efficient degradation rates for basic fuchsin (99.7%), Rhodamine B (89.9%) and tetracycline hydrochloride (93%) within 90 min. Thus, this study presents a feasible strategy for the efficient degradation of pollutants under visible light.

Boosting the Performance of on-Chip Vertically-Aligned Carbon Nanotube Supercapacitors Via Solvent-Free Radiofrequency Nitrogen Plasma Treatment

Supercapacitors are essential components for energy storage devices in many fields, including renewable energy systems, electric vehicles, and portable electronics [1]. Carbon nanotube arrays have shown great promise for use in supercapacitors due to their high surface area and excellent electrical conductivity. However, the specific capacitance of these arrays needs to be increased to improve the overall energy storage capacitance of the supercapacitor.This study presents an innovative approach to enhance the specific capacitance of on-chip vertically-aligned carbon nanotube (VACNT) structures for the development of high-performance supercapacitors. The proposed technique involves employing a solvent-free radiofrequency (RF) nitrogen plasma treatment to dope nitrogen onto VACNT surfaces. The plasma doping process utilizes reactive ion etching-induced coupled plasma (RIE-ICP) to optimize the parameters for nitrogen incorporation [2]. The nitrogen plasma treatment introduces nitrogen-containing functional groups, thereby improving their specific capacitance. The dry process is compatible with semiconductor fabrication and can be integrated into existing manufacturing techniques [1]. This study provides a promising avenue for tailoring the nitrogen doping process to achieve desired performance enhancements for on-chip VACNT supercapacitors.The plasma doping process involves the generation of reactive nitrogen species in the plasma, which subsequently interact with the VACNT surfaces. Under the influence of the RF electric field, nitrogen gas molecules are ionized and can react with the carbon atoms of the VACNTs, resulting in the formation of nitrogen-containing functional groups and the substitution of carbon atoms with nitrogen atoms within the carbon lattice [3].The improved capacitance can be attributed to the incorporation of nitrogen functional groups and to the modification of the electronic properties of the carbon nanotubes, including additional charge carriers, leading to an increase in electrical conductivity [4] and introduction of the pseudocapacitance effect [5]. There are various types of nitrogen species in the carbon lattice, such as pyridinic, pyrrolic, and graphitic nitrogen. Among these, pyridinic and pyrrolic nitrogen are known to be more electrochemically active [5], contributing to the enhanced specific capacitance. The increased electrical conductivity stems from the introduction of nitrogen dopants, which alter the electronic structure of the VACNTs, creating localized states near the Fermi level and thus facilitating charge transport [4].The level of nitrogen doping depends on several process factors, including the plasma power, gas pressure, and treatment duration. Higher plasma power generates a larger number of reactive nitrogen, while lower gas pressure results in a higher ionization efficiency. Furthermore, a longer treatment duration increases the chance of nitrogen incorporation into the VACNT structures [3]. By carefully controlling these parameters during the nitrogen plasma treatment, it is possible to tailor the nitrogen doping process to achieve the desired performance enhancement for on-chip VACNT supercapacitors.The treatment is performed in a chamber with a pressure of 10 Pa, a nitrogen gas flow rate of 10 sccm, an ICP power of 200W, and a bias voltage of -120 V. We report a specific capacitance of modified VACNTs of 18 mF/cm2(Figure 1), nearly twice that of pristine samples (Figure1(B)), for dense arrays of 1012 CNTs/ cm2. XPS result confirms 11.76% nitrogen content and 13% oxygen content in treated samples (N-VACNTs), aligning with previous studies on wet process nitrogen-doped carbon nanotubes [5]. Oxygen content also plays a crucial role in VACNT-based supercapacitor performance, improving surface wettability which will reduce the resistance between electrode and electrolyte [6, 7]. However, excessive oxygen content can negatively affect VACNT supercapacitor lifetime. By finding the trade-off between nitrogen and oxygen content, we optimized the doping process, enhancing specific capacitance, stability (Figure 2), and lifetime for on-chip VACNT structures.In conclusion, our study demonstrates that the solvent-free RF nitrogen plasma treatment can effectively enhance the specific capacitance of on-chip VACNT structures by up to 100%, making them suitable for integration into high-performance on-chip supercapacitor.

A three-step process to produce biochar with good magnetism, high specific surface area, and high levels of nitrogen doping for the efficient removal of sulfamethoxazole

Efficient sorbents that have high sorption capacity and suitable separability are promising and are urgently needed to remove diverse contaminants from water environments. In this study, nitrogen-doped magnetic porous biochars (NMPBs) were synthesized from marine algae by a three-step process consisting of prepyrolysis, copyrolysis and coprecipitation. For NMPBs, the surface area was up to 1531 m2/g, the magnetization strength was up to 31 emu/g, and the surface nitrogen content was up to 3 %. The NMPBs showed the expected sorption capability for sulfamethoxazole, with the removal quantity reaching 502 mg g−1 based on the sorption isotherm model. NMPBs also showed excellent separability and reusability, and the removal rate remained at 87 % after seven cycles. Partitioning and adsorption, including pore filling, hydrogen bonding, π-π stacking, partitioning and electrostatic interactions, were the sorption processes in removing sulfamethoxazole. In this work, marine algae were converted into an engineered biochar that is promising for environmental remediation.

Dissolution of alkali lignin in ionic liquid to fabricate nitrogen-doped carbon microspheres for electrochemical supercapacitors

Ionic liquids (ILs) have been extensively sought after for green solvents, catalysts, adsorbents, and carbon precursors. Herein, 1-ethyl-3-methylimidazolium acetate ([Emim][Ac])–lignin nitrogen-doped carbon microspheres (ECLMs) were easily synthesized through pre-oxidation and carbonization processes using a solution containing [Emim][Ac] and alkali lignin. The pre-oxidation process is analogous to the ionothermal carbonization method, wherein [Emim][Ac] serves as a reaction medium for preparing the ELCMs precursor. During the carbonization process, [Emim][Ac] served as a templating agent and heteroatom source to facilitate nitrogen doping and formation of micropores and mesopores. The as-synthesized ELCMs exhibits a considerably high specific surface area of 1267.2 m2/g and an optimal nitrogen-doping level of 2.21 %. This reveals its potential as a promising candidate for electrode materials in supercapacitor. The ELCMs demonstrate a remarkable specific capacitance of 262.5 F/g at 0.5 A/g and excellent rate capability in a three-electrode system. Additionally, the symmetric supercapacitor fabricated with electrode materials of ELCMs and a cellulose separator exhibits excellent cycling stability, with an impressive capacitance retention rate of 91.0 % after undergoing 5000 cycles at 5 A/g. Moreover, it achieves an ideal energy density of 4.17 Wh/kg at power density of 126 W/kg. This study investigates an effective strategy for designing and synthesizing different heteroatom-doped carbon materials from IL-biomass resources to enhance their applicability in energy storage devices.

Atomic-scale carbon framework reconstruction enables nitrogen-doping up to 33.8 at% in graphene nanoribbon

Nitrogen-doping is well-known to be an effective and promising strategy to tune the electronic states and configurations of carbon materials for catalysis, energy conversion and storage. Since 2009, numerous investigations have demonstrated that the catalytic activity of the nitrogen-doped carbon materials can be improved with an increased doping concentration, yet, how to realize a high doping level remains a great challenge, and to what level remains an open and elusive question. Herein, we report an “in situ framework reconstruction of g-C3N4” that can provide a suitable and simple approach for Nitrogen-superdoping, where nitrogen vacancy formed at C-N = C site in the g-C3N4 framework help to activate adjacent C atoms that are endowed with unpaired electrons dwelling, thus, to be more active. Importantly, both density functional theory analyses and experiments reveal that they are energetically favorable to bond with an ethene molecule, reconstructing a π-bonded dual nitrogen-doped hexagonal-C ring that further acts as building block of the as-formed graphene nanoribbons. Finally, the nitrogen-doping level and the configuration can be finely tuned in a wide range, and up to 33.8 at% of nitrogen is homogenously doped. With the Nitrogen-superdoped graphene nanoribbons as counter electrodes in dye-sensitized solar cells, which have attracted wide attention due to their easy fabrication and relative high power conversion efficiency (PCE), a PCE of 8.60% is achieved. This present work represents a breakthrough in high-efficiency nitrogen-doping of carbon materials, and will fastly promote the chemistry, chemical engeering and material industry involved in carbon.

Supermolecule-regulated synthesis strategy of general biomass-derived highly nitrogen-doped carbons toward potassium-ion hybrid capacitors with enhanced performances

Biomass-derived carbons are promising anodes in potassium-ion hybrid capacitors owing to their tunable structure and competitive cost-effectiveness. The intercalation of K+ ions into carbonaceous anode is a sluggish reaction due to the turbostratic structure and large radius of K+ ions, resulting in the inability to exploit its high capacity and high-rate capability. Nitrogen-doping strategy could enhance the K-ion storage performance by surface capacitive adsorption mechanism. Nevertheless, conventional nitrogen-doping strategies could only endow biomass-derived carbons with low nitrogen-doping levels (<10 at.%), owing to the general agglomeration issue of biomass molecules and the easy release of nitrogen dopant during carbonization. Herein, we proposed a supermolecule-regulated strategy, which enables the breakage of the agglomeration of lignin molecule and disperses lignin in Lewis alkali-acid coupled supermolecule through inter-molecule interactions between lignin and the supermolecule. The co-decomposition of supermolecule/lignin composite precursor could form a covalent-bonded graphitic carbon nitride/carbon intermediate, ensuring the high nitrogen doping level (17.0 at.%) in lignin-derived carbon. The obtained carbon anode delivered high reversible capacities and high-rate capability. All-carbon potassium-ion hybrid capacitors constructed by this carbon as both anode and cathode exhibited a high energy density and power density. This work proposes a general method for constructing highly nitrogen-doped carbon anodes with superior performances.

Boron- and Nitrogen-Codoped Diamond Electrodes for the Improved Reactivity of Electrochemical CO2 Reduction Reaction

We investigated the electrochemical CO2 reduction reaction (CO2RR) properties of boron- and nitrogen-codoped diamond (BNDD) electrodes. The BNDD electrodes exhibited higher CO2RR performance than boron-doped diamond (BDD) electrodes, indicating that the nitrogen doping can promote CO2RR reactivity. In particular, the faradaic efficiencies of the CO2RR products, obtained at a relatively low negative potential (−2.0 V vs Ag/AgCl) in this study, were significantly higher using BNDD electrodes with high nitrogen-doping levels. At this potential, it should be difficult to generate CO2•– as an initial intermediate of CO2RR; therefore, nitrogen doping promoted the generation of the intermediate through another reaction pathway. Linear sweep voltammetry revealed that nitrogen doping could promote the generation of adsorbed hydrogen atoms on the electrode surface by proton reduction. Thus, we concluded that nitrogen doping promoted the initial step of CO2RR through the adsorption of hydrogen atoms on the electrode surface. In addition, electrolysis using various electrolyte solutions confirmed that the influence of dopants on the BNDD electrode surface was significant for CO2RR, particularly at low overpotentials.

Catalytic degradation of dimethomorph by nitrogen-doped rice husk biochar

N-doped biochar is widely used for activating persulfate to degrade organic pollutants. Which type of N atom is the key factor for activation is still unclear and needs to be further explored and analyzed. In this study, four kinds of biochar were prepared using urea and rice husk as precursors, and tested for the catalytic degradation of dimethomorph. Increasing the nitrogen doping level caused the catalytic removal efficiency of dimethomorph in the presence of peroxymonosulfate increased from 16.6% to 86.8%. A correlation analysis showed that the ability of N-doped biochar to activate PMS is mainly related to the content of pyrrole N, graphite N and carbonyl and the degree of defects. In experiments on electron paramagnetic resonance and free radical suppression, the reactive species of SO4•-, 1O2,·OH and O2.− were detected, among which 1O2 was found to be the main agent in the nonradical pathway. The degradation pathways for dimethomorph were analyzed based on a total of 8 degradation products identified by high-performance liquid chromatography-time of flight mass spectrometry (HPLC-Q-TOFMS). The results of this study provide a fundamental basis for using agricultural waste to produce inexpensive and efficient nonmetal catalysts that are highly effective in reducing dimethomorph levels in agricultural lands.

Synergistic effect of nitrogen and oxygen dopants in 3D hierarchical porous carbon cathodes for ultra-fast zinc ion hybrid supercapacitors

Zinc-ion hybrid supercapacitor is one of the most promising electrochemical energy storage devices for the applications needing both high energy densities and power densities. Nitrogen doping is an effective way to enhance the capacitive performance of porous carbon cathodes in zinc-ion hybrid supercapacitor. However, accurate evidence is yet needed to demonstrate how nitrogen dopants influence the charge storage of Zn2+ and H+ cations. Herein, we prepared 3D interconnected hierarchical porous carbon nanosheets by a one-step explosion method. The effect of nitrogen dopants on pseudocapacitance was analyzed by the electrochemical behaviors of as-prepared porous carbon samples with similar morphology and pore structure but different nitrogen and oxygen doping levels. Ex–situ XPS and DFT calculation demonstrate that nitrogen dopants promote the pseudocapacitive reactions by lowering the energy barrier for the change of oxidation states of carbonyl moieties. Owing to the improved pseudocapacitance by nitrogen/oxygen dopants and fast diffusion of Zn2+ ions in 3D interconnected hierarchical porous carbon matrix, the as-constructed ZIHCs show both high gravimetric capacitance (301 F g−1 at 0.1 A g−1) and excellent rate capability (a capacitance retention of 30% at 200 A g−1).

Porous graphitic carbon nitride nanosheets with three-dimensional interconnected network as electrode for supercapacitors

Graphitic carbon nitride material with hierarchical porous structure and high doping level has been reported to exhibit superior capacitive properties due to the facilitated electrolyte migration and redox process. In this work, porous graphitic carbon nitride layers (UMCN-A1.25) with typical three-dimensional (3D) network were prepared through a facile calcination process. For its preparation, NH4HCO3 was used as the pore generator and glucose was used as the carbon precursor. Urea and melamine, which worked as the binary precursors for sacrificial template, played important roles in the formation of the final 3D interconnected structure. The hierarchical pore structure and high nitrogen-doping level endow UMCN-A1.25 with high specific capacitances (520 F g−1 at 0.1 A g−1 and 219.4 F g−1 at 20 A g−1) and stable charge-discharge behavior with no capacitance declination after 10,000 cyclic tests. This work proposed an efficient route for the construction of inter-connected carbon nitride layers, and also revealed the importance of both lamellar morphology and interwoven structure for the acquisition of high capacitive properties.

Nitrogen-doped Ti3C2Tx MXene prepared by thermal decomposition of ammonium salts and its application in flexible quasi-solid-state supercapacitor

Two-dimensional (2D) Ti3C2Tx MXenes show great potential for application in flexible supercapacitors, due to their good hydrophilicity, metallic conductivity and excellent flexibility. Surface modification of the MXenes by heteroatom doping is a good strategy for adjusting the layer spacing and alleviateing various shortcomings. Herein, the ammonium salt decomposition method is shown to allow rapid nitrogen doping into Ti3C2Tx nanosheets at a low temperature of 350 °C. Compared to the raw Ti3C2Tx, the nitrogen-doped Ti3C2Tx (designated N-Ti3C2Tx) shows an increased layer spacing of 1.451 nm, nitrogen doping levels of 1.42 at% and a low number of residual fluorine functional groups. For the application as an electrode of supercapacitors, the N-Ti3C2Tx electrode shows an outstanding pseudocapacitance performance and mechanical flexibility, with a high specific capacitance of up to 449 F g−1 at 2 mV s−1, which is 1.4 times that of the raw Ti3C2Tx MXene (i.e., 321 F g−1). Furthermore, a quasi-solid-state symmetric supercapacitor assembled with a H2SO4-PVA gel electrolyte is shown to deliver an energy density of 9.57 Wh kg−1 at 250 W kg−1. The outstanding pseudocapacitance of the N-Ti3C2Tx is attributed to the positive effect of nitrogen doping on MXene, such as larger layer spacing and the increased number of surface active sites. The strategy presented herein also opens up a convenient and versatile approach for preparing high performance MXene Materials for energy conversion and storage.