High N-doping Research Articles

Nitrogen-doped porous carbon derived from bimetallic zeolitic imidazolate frameworks for electrochemical Li+/Na+ storage

Porous carbon is regarded as one of the most promising anode candidates for Li-ion battery and Na-ion battery, and the specific porous structure and heteroatom doping within porous carbon play a key role in the electrochemical performance. We herein demonstrate a series of nitrogen-doped porous carbon (NPC) by simply carbonizing bimetallic ZnCo-containing zeolitic imidazolate frameworks (ZnCo-ZIFs). The nitrogen content, specific surface area, and microstructure of prepared NPCs are balanced by adjusting the Zn2+/Co2+ molar ratio of ZnCo-ZIFs and carbonization process parameters. The optimized NPC derived from ZnCo-ZIFs delivers high specific capacity of 876.5 and 352.6 mA h g−1 for Li+ storage at 0.1 and 5 A g−1, respectively. After repeating 500 cycles at a high current density of 1 A g−1, it almost has no capacity loss. In addition, the electrode also shows a great promise for Na+ storage. The excellent electrochemical Li+/Na+ storage performances could be attributed to the hierarchical porous structure, large specific surface area, and relatively high N-doping content.

Tailoring atomically dispersed cobalt–nitrogen active sites in wrinkled carbon nanosheets via “fence” isolation for highly sensitive detection of hydrogen peroxide

Wrinkled CNSs with abundant mesopores, high N-doping, and atomically dispersed Co–Nx active sites through “fence” isolation enable efficient H2O2 detection.

Optimized nano-metal particles filled into carbon nanohorns to achieve high N-doping amount and high porosity for enhanced oxygen evolution reaction.

Nano-metal-filled N-doped carbon materials have been actively verified as promising alternatives for precious-metal catalysts in the oxygen evolution reaction (OER). Herein, Ni/Fe/Cu-filled N-doped carbon nanohorns (CNHs) are synthesized via a positive pressure assisted arc discharge method using a Ni/Fe/Cu rod charged in an anode hole in a N2 and Ar mixture. We first found that the amount of N atom doping can be controlled by the types of nano-metal particles encapsulated by CNHs. The content of N atoms on CNHs uniquely depended on the initial Ni wires inserted into the anode graphite; increasing the number of Ni wires induced the enrichment of N atoms until 3.56 at%, whereas the content of N atoms for Cu- and Fe-filled CNHs is against the results; loading Cu and Fe nanoparticles decreases the N-doping amount. And the morphologies and N-configurations can be changed by the types of metal nanoparticles. Furthermore, the OER performance of Ni-filled CNHs is much superior to that of Cu- and Fe-filled CNHs, which can be significantly enhanced by the tip opening structure, and the increase in Ni loading amount and the N atom content.

Highly dispersed Ru anchored on nanosheet N-doped carbon for efficient and chemoselective hydrogenation of nitroaromatics to aromatic amines under mild conditions

An efficient catalyst for chemoselective hydrogenation of nitroaromatics to produce aromatic amines under mild conditions is highly desirable. In this work, a series of N-doped carbon (NC-x) with high nitrogen contents were firstly synthesized by pyrolysis of 1-butyl-3-vinylimidazolium bromide-co-acrylonitrile with a template of g-C3N4. Furthermore, Ru/NC-x catalysts were successfully prepared by ultrasonic-assisted impregnation method. The catalysts were characterized by various methods in detail, e.g.X-ray diffraction, N2 physical adsorption-desorption, Transmission electron microscopy, Raman spectra, Scanning electron microscopy and H2 temperature programmed reduction. Characterization results revealed that N-doping on carbon contributed to the high dispersion of Ru nanoparticles and resulted in the forming of the electron-deficient of Ru species. Nanosheet Ru/NC-2 with high N-doping content of 28 wt% exhibited superior performance under room temperature, i.e., nitrobenzene conversion >99.0% and aniline selectivity 98.4%. Kinetic study indicated that the hydrogenation of nitrobenzene over Ru/NC-2 was the first-order kinetics with an intrinsic activation energy of 43.7 kJ/mol. Density functional theory calculation results suggested that Ru-Nx species, especially, Ru-pyrrolic-N facilitated nitrobenzene adsorption and H2 dissociation, resulting in enhanced catalytic performance. In addition, the excellent stability of Ru/NC-2 made it essentially reserved for 410 h in the fixed-bed reactor. Moreover, Ru/NC-2 exhibited superior performance for the hydrogenation of various nitroaromatics to corresponding aromatic amines. This work could provide meaningful guidance on designing effective and stable catalyst for chemoselective hydrogenation of nitroaromatics to aromatic amines under mild conditions.

Mechanochemistry-driven prelinking enables ultrahigh nitrogen-doping in carbon materials for triiodide reduction

Nitrogen (N)-doping in graphene is now known to effectively modulate the charge density of carbon atoms, rendering the carbon materials catalytic activity. Often, the activity improves with increasing the N content. Although, as early as 2015 (Zhang et al., 2015) theoretical investigation has anticipated that it is possible to realize a high N-doping level through improving pyridinic N, by which there is still a lack of experimental verification what a doping level can be reached up to now. Herein, as a proof-of-concept study, we demonstrate, through mechanochemistry-driven prelinking to enhance the interaction between graphitic carbon nitride and graphitic lattice to preferably form pyridinic N (the maximum proportion thus obtained is 47.7%), that an ultrahigh N up to 12.4 at% is doped in the as-prepared carbon materials at a carbonization temperature up to 1000 °C. As an example, the higher N-doping can induce more carbon atoms, especially those adjacent to the pyridinic N, to be active for triiodide reduction, resulting in a wonderful power conversion efficiency of 8.86%.

Hollow N-doped carbon nanoflowers with nanosheets subunits for electrocatalytic oxygen reduction

The synthesis of economic carbon-based metal-free catalysts with high electroactivity for the oxygen reduction reaction (ORR) is still a huge challenge for energy storage and conversion devices. Herein, the hollow N-doped carbon nanoflowers (h-N-CFs) with nanosheets subunits were synthesized by using 3,5-diaminobenzoic acid-1,3,5-benzenetricarboxaldehyde (DABA-BTCO) complex nanoflowers as the self-template and nitrogen resource. Various physical characterizations show that h-N-CFs with hollow and porous architecture have a high surface area (1390.3 m2g−1) and abundant activated N atoms (i.e., graphitic N and pyridinic N). Electrochemical measurements demonstrate that h-N-CFs synthesized at 800 °C can be used as an efficient metal-free ORR catalyst with prominent electroactivity and stability due to hollow architecture, abundant pores, and high N-doping content. Meanwhile, h-N-CFs also show eminent ORR selectivity (i.e., methanol tolerance) in alkaline media, which markedly surpasses benchmark Pt/C catalyst in the presence of methanol.

Hydrogen-Bonded Biohybrid Framework-Derived Highly Specific Nanozymes for Biomarker Sensing.

Nanozymes are of particular interest due to their enzyme-mimicking activity and high stability that are favorable in biomedical sensing and immunoassays. In this work, we report a highly specific N-doped nanozyme through pyrolysis of framework-confined bovine serum albumin (BSA). This strategy allows one to translate the low-cost and featureless BSA into a highly active enzyme mimic. The obtained carbon nanozyme (denoted as HBF-1-C800) displays 3- to 7-fold enhancement on peroxidase (POD) activity compared with the conventional carbon nanozymes and also shows ca. 5-fold activity enhancement compared to the reported N-doping graphene. Such excellent POD activity originates from high N-doping efficiency, protein-induced defective sites, and the intrinsic porous structure of HBF-1-C800, which provides abundantly accessible active sites and accelerates substrate diffusion simultaneously. Importantly, the HBF-1-C800 nanozyme has highly specific POD activity and also enables resistance to several harsh conditions that should denature natural enzymes. These features allow it with high accuracy, stability, and sensitivity for biosensing applications. Moreover, HBF-1-C800 has been designed as a promising platform for colorimetric biosensing of several biomarkers including H2O2, glutathione, and glucose, with wide linear ranges and low limits of detection that are satisfied with the disease diagnosis.

Boosting zinc-ion storage capability by engineering hierarchically porous nitrogen-doped carbon nanocage framework

In virtue of combining superb power of supercapacitors and high energy of batteries, zinc-ion hybrid supercapacitors become a competitive candidate in current energy storage systems. However, the cell chemistry related to carbon cathode still suffers from the obstacles of reaction kinetics and charge storage efficiency. Herein, a three-dimensional framework of N-doped carbon nanocages is constructed through pyrolyzing and activating polypyrrole on the platform of ZIF-8, synchronously achieving hierarchical porosity and high N-doping content. Thanks to the comprehensive modulation of the morphology, pore structure, and surface chemistry, the obtained carbon shows the significant enhancement in active site exposure and diffusion kinetics. Therefore, the zinc-ion hybrid supercapacitor using this carbon cathode achieves the remarkably improved Zn-ion storage capability (124 mAh g−1 at 0.25 A g−1 with a 65.9% capacity retention at 20 A g−1, and nearly no capacity decay after 10000 cycles at 10 A g−1). Moreover, this device exhibits superior energy/power densities of 107.3 Wh kg−1/16647.7 W kg−1, together with a low self-discharge rate of 3 mV h−1. Our work presents a good design strategy to develop advanced carbon-based cathodes to accelerate the development of Zn-based devices.

Bio-Derived Lithium-Ion Battery Anode Material for Fast Charging and Long-Cycle Life

Currently graphite is the most commercially used anode material for lithium-ion batteries (LIB), however its limited theoretical capacity of 372 mAhg-1 and slow kinetics cannot satisfy the requirements for EVs. Hence, alternative high energy density anode materials with fast kinetics are the need of the hour. The most recent development involves Mitsubishi Outlander PHEV which takes around 40 minutes for empty to full charging. Extreme fast charging, with a goal of 15 minutes fast charging, is poised to accelerate mass market production of electric vehicles. Extensive research is now directed towards carbonaceous materials that can fulfill the requirements for EV application. Key strategies involved in improving the rate capability of carbonaceous materials are (a) heteroatom doping, especially nitrogen doping and (b) increasing the d-spacing for accessing more active sites. Using conventional methods of heteroatom doping like pyrolysis of graphene oxide with urea or melamine as nitrogen source led to inclusion of up to 12 at% of nitrogen in general. Inclusion of nitrogen showed improvement in rate capability and capacity. Further search to increase nitrogen content led to the application of graphitic carbon nitride with nearly 55 at% nitrogen. Nevertheless, due to less electronic conductivity and change of crystallinity upon lithiation curbed its application in lithium-ion battery. So, currently our objective is to use nitrogen rich polymer as a single source of nitrogen and carbon to prepare heavily nitrogen doped carbon with nearly 20 at% of nitrogen with increased d-spacing and understand its effect on Li ion storage. Poly (2, 5-benzimidazole) (PBI) was synthesized by homo-polycondensation method using a bio derivable starting material 3, 4-diaminobenzoic, as earlier reported by Kaneko et.al1. The as prepared PBI was ground into fine powder before pyrolyzing at 800 ℃ in nitrogen atmosphere. Obtained carbon material was washed with HCl and water repeatedly and dried at 80 ℃ under vacuum before grinding into fine powder using mortar and pestle. Obtained material was systematically characterized before preparation of anodes for Li ion battery application. The SEM-EDX data revealed the content of nitrogen was as high as 18 at%. Using XPS studies, different types of nitrogen moieties were identified. Deconvolution of N1s peak revealed the presence of nitrogen in four different forms, graphitic nitrogen (10.3%), pyridinic nitrogen (6%), pyrrolic nitrogen (0.6%) and oxidized nitrogen (0.6%). The presence of pyridinic and graphitic nitrogen improve the electrical conductivity. The presence of high pyridinic nitrogen results in improved electrochemical activity. The contribution of pyridinic nitrogen in lithium storage is known to be maximum. XRD technique was utilized to understand the d-spacing of the material. Reflection corresponding to C (002) was used to calculate d-spacing. The results revealed that the d-spacing was found to be 3.5 Å which is nearly 0.2 Å higher than conventional graphite. The increased d-spacing can promote in faster diffusion of Li ion during intercalation and de-intercalation. TEM micrographs revealed the presence of macropores and mesopores. Using Cyclic Voltammograms at different scan rates and Randles Sevcik equation, the diffusion coefficient was calculated. Diffusion coefficient of PY PBI 800 was found to be several times higher than the conventional graphite anode, attributed to the increased d-spacing along with porous nature. Upon galvanostatic charge-discharge studies at different current rates, anode showed reversible capacity with nearly 99% coulombic efficiency upto 5C (1.8 Ag-1) rate. Further, long cycling studies were performed for >1000 cycles at 0.4, 0.8 and 1.8Ag-1 rates. Results indicated that PY PBI 800 can deliver highest de-lithiation capacity of ̴ 260 mAhg-1 at specific capacity of 0.4 Ag-1 rate (Fig) with nearly 88% capacity retention after 1000 cycles. At higher current rate of 0.8Ag-1, and 1.8 Ag-1 it showed highest discharge capacity of 165 mAhg-1 and 135 mAhg-1 with 90% and 75% capacity retention after 1000 cycles respectively. At 5C current rate, the battery can be charged and discharged in just 9 mins. Further, full cell was studied with LiCoO2 as cathode and PY PBI 800 as anode. Full cell studies also revealed the promising nature of PY PBI 800. Thus, carbonization is found to be a single method to enable high N-doping and increased d-spacing. The battery’s performance of charge discharge in just 9 min at 5C, with good capacity retention of nearly 75% after 1000 cycles demonstrated its promising potential for EV application.

Facile preparation of N-doped porous carbon nanosheets derived from potassium citrate/melamine for high-performance supercapacitors

Nitrogen (N)-doped porous carbon nanosheets have attracted research attention owing to their effective structure for fast ion diffusion and pseudocapacitive properties in supercapacitors. However, to synthesize N-doped porous carbon nanosheets while maintaining their original shape requires complicated multistep processes such as plasma and arc-discharge methods. Herein, we propose a facile and effective method for N-doping into interconnected porous carbon nanosheets that preserves their original structure with a stepwise thermal annealing using melamine as N-doping source. The stepwise thermal annealing is advantageous to improve N-doping efficiency into the carbon matrix compared to direct thermal annealing method owing to the condensation of melamine. As-synthesized N-doped carbon nanosheets with interconnected and porous structure exhibits high specific surface area and N-doping contents, which favorable for the fast ion movement, adsorption, and increasing the wettability of the electrolyte. The electrochemical performance shows a maximum specific capacitance of 350F g−1 at 1 A g−1 in a three-electrode test. Moreover, a fabricated symmetric full-cell device using an optimized N-doped carbon electrode demonstrates a long-term durability over 10,000 cycles and a maximum energy density of 16.1 Wh kg−1.

One-step ultrafast deflagration synthesis of N-doped WO2.9 nanorods for solar water evaporation

Up to now, the seawater desalination utilizing solar water evaporation has been considered as the most promising solution to solve water-shortage problems. Thus, preparing efficient photo-thermal conversion materials for water evaporation with an ultrafast and cheap method is a big challenge. Herein, the N-WO2.9 photo-thermal materials with the oxygen vacancy and N co-doping are synthesized by an ultrafast one-step NaN3 deflagration method. The deflagration produces Na clusters and N radicals, subsequently the former acts as a reductant capturing partial O from WO3, and the latter is partly doped in crystal lattice, which causes the phase transition from WO3 to N-WO2.9 and leads to a narrowed band gap. The modified materials significantly increase solar absorption and photo-thermal conversion, especially in visible and near infrared light. Hence, the N-doped WO2.9/cellulose paper photo-thermal membranes possess the superb water evaporation rate of 1.45 kg m-2h−1, stable efficiency of 83.1%, and the excellent desalination capability under 1 solar illumination. In addition, the deflagration method simultaneously achieving oxygen vacancy and high N-doping have opened up a new route for the design and synthesis of photo-thermal semiconductor materials.

N-Doped Carbon Nanofibrous Film with Unique Wettability, Enhanced Supercapacitive Property, and Facile Capacity to Demulsify Surfactant Free Oil-in-water Emulsions

Electrospinning and calcination technique have been combined to fabricate N-doped carbon nanofibers(N-CNFs) by introducing amino grafted few-layered hexagonal boron nitride (amino@BN) into polyacrylonitrile(PAN) matrix as filler followed by carbonization. For the high N-doping level(10.7%, atomic fraction) with the final product, the as-prepared N-CNFs exhibit interesting surface wettability(superamphiphilicity in air and underwater oleophilicity). Moreover, compared with pristine PAN derived carbon nanofibers(marked as CNFs), N-CNFs exhibit higher graphic structure under fixed carbonizing temperature as well. Taking these advantages aforementioned, the as-prepared N-CNFs exhibit good specific capacitance(ca. 200.1 F/g) without activation treatment at the current density of 0.5 A/g in three-electrode configuration, which is about 149% that of CNFs(ca. 134 F/g). What’s more, our N-CNFs also display the unexpected capacity to demulsify diverse surfactant free oil-in-water emulsions by simple filtration in large scale with the high water flux ca.(23578±150) L·m−2·h−1

Magnesium-intercalated graphene on SiC: Highly n-doped air-stable bilayer graphene at extreme displacement fields

We use angle-resolved photoemission spectroscopy to investigate the electronic structure of bilayer graphene at high n-doping and extreme displacement fields, created by intercalating epitaxial monolayer graphene on silicon carbide with magnesium to form quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide. Angle-resolved photoemission spectroscopy reveals that upon magnesium intercalation, the single massless Dirac band of epitaxial monolayer graphene is transformed into the characteristic massive double-band Dirac spectrum of quasi-freestanding bilayer graphene. Analysis of the spectrum using a simple tight binding model indicates that magnesium intercalation results in an n-type doping of 2.1 × 1014 cm−2 and creates an extremely high displacement field of 2.6 V/nm, thus opening a considerable gap of 0.36 eV at the Dirac point. This is further confirmed by density-functional theory calculations for quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide, which show a similar doping level, displacement field and bandgap. Finally, magnesium-intercalated samples are surprisingly robust to ambient conditions; no significant changes in the electronic structure are observed after 30 min exposure to air.

Preparation of hollow mesoporous carbon spheres by pyrolysis-deposition using surfactant as carbon precursor

Hollow mesoporous carbon spheres (HCS) are widely used in many fields, such as supercapacitors, adsorption, separation, batteries, etc., due to their large specific surface area, large cavity, thin mesoporous shell and good chemical stability. Herein, N-doped HCS was prepared using the pyrolysis-deposition method, with cetyltrimethylammonium bromide (CTAB) micelles derived from a hard template of solid silica core coated with mesoporous silica (SiO2@mSiO2), as the carbon and nitrogen precursor. This method realizes direct carbon formation from the decomposable surfactant CTAB, which avoids the need for other carbon precursors and simplifies the preparation process. The mesopores on the SiO2@mSiO2 template shell provide limited space and the transition metals provide active sites, which promotes the deposition of carbon derived from surfactants.The shell thickness of HCS can be adjusted by the thickness of the SiO2@mSiO2 template shell, which leads to a change in the morphology, i.e. from imperfect (macropore) hollow spheres to complete hollow spheres and transformation of the surface from rough to smooth. Ultimately, the resultant HCS completely replicates the morphology of the template and shows a uniform spherical shape with a mesoporous shell, a cavity, a high specific surface area and suitable N-doping content, which ensures good electrochemical performance as an active electrode material in supercapacitors.

Vertically Aligned N-doped Carbon Nanotubes Arrays as Efficient Binder-free Catalysts for Flexible Li-CO2 Batteries

The Li-CO2 battery is a newly-emerging energy storage and conversion system, making CO2 renewable utilization and capture in a green way. However, the unsatisfactory electrochemical performances such as high polarization, short cyclic life and poor rate capability caused by the sluggish decomposition the product Li2CO3 and the lacking of mechanical flexibility due to the rigid cathode, greatly hinder its real application, especially for the compliant and wearable devices. Herein, the vertically aligned N-doped carbon nanotube (VA-NCNT) arrays on Ti wire are prepared as freestanding, binder-free cathodes for flexible quasi-solid-state Li-CO2 battery. The VA-NCNT arrays have thousands of vertical CNT with high N-doping percentage, rich defects and void space, which facilitate the CO2 diffusion and electrolyte permeation, provide exposed active sites and more space for the formation and accommodation of Li2CO3 and help the oxidation of Li2CO3 and amorphous carbon in charge process. As a result, the fabricated battery shows ultralong cycle life, small potential gap, outstanding rate capability and high flexibility. Our work provides an alternative option towards CO2 conversion and utilization as high performance energy sources.

Template-free fabrication of MoP nanoparticles encapsulated in N-doped hollow carbon spheres for efficient alkaline hydrogen evolution

Based on the synergy between MoP and N-doped carbon, MoP nanoparticles encapsulated in N-doped carbon hollow spheres were synthesized using inorganic-organic hybrids as precursors, which shows an excellent stability and activity with an overpotential 96 mV at 10 mA cm −2 and a small Tafel slope of 53 mV dec −1 in alkaline solution. • A template-free approach was developed to fabricate MoP@NC hollow microsphere. • Inorganic-organic hybrids were used as precursors. • Remarkable electrocatalytic hydrogen evolution performance could be achieved. • The synergy between MoP and the pyridinic N could optimize the electronic structure. Encapsulating transition metal phosphides into nitrogen-doped carbon (NC) materials is an effective strategy to enhance the electrocatalytic performance. Herein, we develop a novel template-free approach to rationally fabricate molybdenum phosphide (MoP) nanoparticles encapsulated in N-doped carbon (MoP@NC) hollow microspheres for alkaline hydrogen evolution reaction (HER) by employing inorganic-organic hybrids as precursors, in which phosphorus source of the MoP@NC derives from tetra (hydroxymethyl) phosphorus chloride for the first time. The optimized MoP@NC sample shows a low overpotential of 96 mV at 10 mA cm −2 , a small Tafel slope of 53 mV dec −1 , and excellent stability. The enhanced HER performance is mainly attributed to the integrated effects of a distinctive hollow structure, high pyridinic N-doping level, and the extremely intimate synergy between MoP and NC. Theoretical calculations indicate that the active sites of the catalyst are mainly located at Mo atoms adjacent to the pyridinic N-doped carbon layer (pyridinic-N-MoP); the synergistic interaction between MoP and pyridinic N (rather than pyrrolic or graphitic N) atoms can lower the d band center of Mo, weaken the Mo-H ads bond and thereby enhance HER performance. In addition, the pyridinic N atoms at the interactive sites play a key role in adsorbing H 2 O and preventing the adsorption of OH*, resulting in accelerating the water splitting. This work provides a new method to rationally synthesize high-efficient and stable MoP-based hollow sphere electrocatalysts for alkaline HER through designing inorganic-organic hybrid precursors.

MOFs derived 3D sea urchin-like carbon frameworks loaded on PVDF membranes as PMS activator for highly efficient bisphenol A degradation

Catalytic membrane integrated with advanced oxidation processes (AOPs) was provided a promising prospect to overcome the obstacles of powder catalyst large-scale practical applications. Herein, we utilized a facile strategy to construct novel 3D sea urchin-like nitrogen doped carbon nanotube (CNT) frameworks encapsulated Co nanoparticles (ZIF-67/CNTs) through N-molecule assisted pyrolysis of ZIF-67, and then immobilized on poly(vinylidene fluoride) (PVDF) membrane to obtain the catalytic membranes (ZIF-67/CNTs-II@PVDF). As expected, benefiting from the strongly synergistic effect of high N-doping level, encapsulated 0D Co NPs, 1D N-CNTs and abundant Co@Co-Nx/pyridinic-N active sites and 3D porous structures, ZIF-67/CNTs-II achieved the best catalytic activity towards degrading bisphenol A (96.8%, 40 min and 0.0956 min−1), which was over 3 times higher than that of ZIF-67-derived ZIF-67/Cs (67.8%, 40 min and 0.0306 min−1). Furthermore, ZIF-67/CNTs-II@PVDF catalytic membrane not only exhibited the excellent catalytic ability in different pollutants/PMS system, but also maintained the desirable reusability and stability even after five runs. Notably, ZIF-67/CNTs-II as pore forming centers promoted the active sites exposure for oxidants and target pollutants. Scavenger experiments and EPR analysis verified that SO4−, OH and 1O2 participated the degradation process, while SO4− was the major active species. More significantly, this work provides a feasible pathway to fabricate novel catalytic membrane for environmental remediation.

Anchoring MoSe2 nanosheets on N-doped carbon nanotubes as high performance anodes for potassium-ion batteries

Transition metal dichalcogenides (TMDs) such as MoSe2 have received extensive attention as anodes for Potassium-ion batteries (KIBs) due to their high energy density and unique layered structure. However, the low conductivity and structural collapse during the insertion and extraction of K+ can lead to fast capacity decay and poor rate performance. Herein, a sheet-on-tube structure of MoSe2 nanosheets@N-doped carbon nanotubes (MoSe2@NCT) is rationally designed and prepared by hydrothermal and subsequent annealing process. The NCT can increase the electrical conductivity and stabilize the MoSe2 nanosheets during repeated charging and discharging processes, thus improving the electrochemical performance of MoSe2@NCT. In addition, the high level N-doping in NCT can create paramount defects serving as the active sites to facilitate K+ storage. Electrochemical tests reveal that the MoSe2@NCT demonstrates a high reversible capacity (247 mA h g − 1 after 100 cycles at 0.1 A g − 1), cycling stability and superior rate performance. A series of physic-chemical tests indicate the very good electrochemical performances are resulting from the nanosheet structure of MoSe2, high conductivity of carbon and functional N-doping. The proposed strategy in structure engineering and the excellent electrochemical properties delivered in this work may provide a new idea to develop high performance anodes in KIBs.

Acetone dissolution to prepare N-doped hierarchical porous carbon for supercapacitor

The hierarchical porous carbon (HPC) materials have rich porous structure, high specific surface area and reasonable porosity for a wide range of applications in many fields, such as catalysis, adsorption, and energy storage, etc. Although some synthetic strategies have been developed, efficient preparing HPC materials remains challenging. In this work, we propose a method to prepare N-doped hierarchical porous carbon (NHPC) by acetone dissolution following co-assembly process. 1-Alkyl-3-methyl imidazole bromide ([C18Mim]Br), tetraethyl orthosilicate (TEOS) and resorcinol-formaldehyde were co-assembled to form a pleated sheet composite material, where [C18Mim]Br induced formation of the sheet structure and also led to nitrogen doping in the carbon skeleton. TEOS created a mesoporous structure and increased specific surface area, while acetone dissolved the oligomer of the resin, creating a macroporous structure, but destroying the morphology of the sheet. At an appropriate amount of acetone, the resulting NHPC exhibits the hierarchical porous structure, high specific surface area and N-doping characteristics. When used as a supercapacitor material, NHPC exhibits the specific capacitance is as high as 241 F g−1 at 1 A g−1. Furthermore, the symmetric supercapacitor manufactured with NHPC has a power density of 4.1 kW kg−1, an energy density of 2.56 Wh kg−1, and demonstrates excellent cycle stability of up to 92.82%, exhibiting the potential as good supercapacitor materials.

Understanding of the effect of nitrogen-doping level and micropore volume ratio on the capacitive performance of N,S-codoped hierarchically porous carbon

Four new N,S-codoped hierarchically porous carbons (NSHPCs) with similar sulfur content while obviously different nitrogen content and ratio of micropore volume to total pore volume (Vmicro/Vtot) are synthesized. It is found that the nitrogen content and the Vmicro/Vtot ratio of NSHPCs increase with the increasing of the mass ratio of thiourea to CaCl2. Electrochemical results indicate that reasonable N-doping level is favorable to enhancing the intrinsic capacitance, but excessive high N-doping level leads to many defect sites and then increases the charge transfer resistance; furthermore, the Vmicro/Vtot ratio displays an important effect on determining the rate performance of NSHPCs. Thus the NS-132 sample, obtained from the pyrolysis of the a mixed precursor containing of sugar bagasse, CaCl2 and thiourea in a mass ratio of 1:3:2 at 800 °C for 2 h, possesses nitrogen content of 8.67 atm% and Vmicopore/Vtotal ratio of 46.6% and displays the best capacitive performance. It exhibits high specific capacitances of 357.8, 376.4 and 237.8 F g−1 in 6 M KOH, 1 M H2SO4 and 2 M Li2SO4 at 1.0 A g−1, respectively. A symmetric capacitor prepared from the NS-132-based electrodes displays high energy, good power densities (18.0 Wh⋅kg−1 at 16.9 kW kg−1) and 95.4% capacitance retention capability after 10 000 cycles at 10.0 A g−1 in 2.0 M Li2SO4 electrolyte. These results provide a guidance for the structure design and an easy synthesis route for the NSHPCs with high electrochemical performance.