N-doped Carbon Layer Research Articles

Oxygen-defect-rich ZnV2O4/ZnO heterojunction as multifunctional separator to boost lithium polysulfide adsorption and conversion for superior lithium‑sulfur batteries

Lithium‑sulfur (Li-S) batteries have been recognized as one of the promising energy systems which can meet the large amounts of energy demanding. However, its practical application has been seriously hindered due to the instinct drawbacks such as low conductivity, large volume expansion and notorious “shuttle effect”. Herein, multi-structure lamellar flower-like zinc vanadate/zinc oxide heterojunction (CoNi@ZnV2O4/ZnO-N,C) with abundant oxygen vacancies, CoNi nanoalloys and N-doped carbon (C) layer has been successfully constructed. XPS and ex-situ XRD analysis reveal that the oxygen vacancies can replace lattice oxygen to adsorb lithium polysulfides (LPS), then stabilize the crystal structure. Additionally, with the synergistic catalysis of CoNi nanoalloys and N-doped C layer, the heterojunction can effectively accelerate the conversion of LPS and promote the precipitation of Li2S. When the lamellar flower-like heterojunction is applied as separator modifier, the “shuttle effect” of LPS can be effectively hindered, leading to synergistic enhancement of long cycle performance of Li-S batteries: the initial discharging capacities of 1468.9 and 1394.9 mAh g−1 can be obtained at 0.1 and 1C, respectively. After 1000 long-term cycles at 3C, the discharging capacity can be still maintained at 467.9 mAh g−1, with a capacity loss rate of 0.049 % per cycle, showing a stable high-rate performance.

Effect of polypyrrole-derived N-doped carbon coating on the sodium storage properties of NiCo2S4 synthesized by recycling discarded mobile phone batteries

NiCo2S4 with a spherical spinel structure was innovatively synthesized from discarded mobile phone batteries using a simple hydrothermal method, and the surface was coated with N-doped carbon to form NiCo2S4@NC. The products were used as anode materials of sodium-ion batteries to study the effect of the N-doped carbon layer on the electrochemical properties, structure and morphology. The results of XRD, FESEM and TEM revealed that the N-doped carbon layer derived by carbonizing polypyrrole had a minimal effect on the structure and morphology of NiCo2S4, but was coated on the surface of NiCo2S4 with different thicknesses to adjust the electrochemical performance. The presence of N-doped carbon in NiCo2S4@NC was confirmed by Raman spectroscopy. The mesoporous structure of NiCo2S4 and NiCo2S4@NC was corroborated by N2 adsorption-desorption isotherm analysis, and the optimal specific surface area and pore size were 23.14 cm2/g and 18.0 nm, respectively. X-ray photoelectron spectroscopy indicated that Co2+/Co3+ and Ni2+/Ni3+ coexist in the spinel NiCo2S4@NC50 synthesized upon adding 50 μL of pyrrole monomer. NiCo2S4@NC50 outperformed other products in terms of its electrochemical properties, where its initial discharge specific capacity under the current density of 0.1 A g−1 was 1099.6 mA h g−1 and the specific capacity following 100 cycles reached 327.5 mA h g−1. NiCo2S4@NC50 exhibited an optimal electrochemical performance and demonstrated a competent approach toward recycling discarded mobile phone batteries and building electrodes with high performance for use in energy equipment.

Active Sites of Mixed-Metal Core-Shell Oxygen Evolution Reaction Catalysts: FeO4 Sites on Ni Cores or NiN4 Sites in C Shells?

Water electrolysis for clean hydrogen production requires high-activity, high-stability, and low-cost catalysts for its particularly sluggish half-reaction, the oxygen evolution reaction (OER). Currently, the most promising of such catalysts working in alkaline conditions is a core-shell nanostructure, NiFe@NC, whose Fe-doped Ni (NiFe) nanoparticles are encapsulated and interconnected by N-doped graphitic carbon (NC) layers, but the exact OER mechanism of these catalysts is still unclear, and even the location of the OER active site, either on the core side or on the shell side, is still debated. Therefore, we herein derive a plausible active-site model for each side based on various experimental evidence and density functional theory calculations and then build OER free-energy diagrams on both sides to determine the active-site location. The core-side model is an FeO4-type (rather than NiO4-type) active site where an Fe atom sits on Ni oxide layers grown on top of the core surface during catalyst activation, whose facile dissolution provides an explanation for the activity loss of such catalysts directly exposed to the electrolyte. The shell-side model is a NiN4-type (rather than FeN4-type) active site where a Ni atom is intercalated into the porphyrin-like N4C site of the NC shell during catalyst synthesis. Their OER free-energy diagrams indicate that both sites require similar amounts of overpotentials, despite a complete shift in their potential-determining steps, i.e., the final O2 evolution from the oxophilic Fe on the core and the initial OH adsorption to the hydrophobic shell. We conclude that the major active sites are located on the core, but the NC shell not only protects the vulnerable FeO4 active sites on the core from the electrolyte but also provides independent active sites, owing to the N doping.

Ru nanoparticles embedded in Ru/SiO2@N-CS for boosting hydrogen production via ammonia decomposition with robust lifespan

Ammonia decomposition for onsite hydrogen production has been regarded as an important reaction which links to efficient hydrogen storage, transport and utilization. However, it still remains challenging to develop efficient catalysts with robust stability for ammonia decomposition. Herein, an integrated strategy was employed to synthesize Ru/SiO2@N-CS via wrapping a thin layer of N-doped carbon onto the SiO2 sphere, following the anchor of Ru nanoparticles (NPs) onto the support. The obtained Ru/SiO2@N-CS (Ru loading: 1 wt%) shows a promising performance for ammonia decomposition, reaching 94.5 % at 550 °C with a gas hourly space velocity (GHSV) of 30 000 mL gcat-1h−1. The combination of the SiO2 as the core prevents the degradation of N-doped carbon layers and then enhance the durability of the catalysts, remaining stable after 50 h at evaluated temperatures. Adequate characterizations were used to illustrate the effect of microchemical environment on ammonia decomposition activity of Ru/SiO2@N-CS catalyst under different calcination atmosphere and the correlation between structure and performance.

Dual-Step Redox Engineering of 2D CoNi-Alloy Embedded B, N-Doped Carbon Layers Toward Tunable Electromagnetic Wave Absorption and Light-Weight Infrared Stealth Heat Insulation Devices.

2D layered metallic graphite composites are promising electromagnetic wave absorption materials (EWAMs) for their combined properties of abundant interlayer free spaces, rich metallic polarized sites, and high conductivity, but the controllable synthesis remains rather challenging. Herein, a dual-step redox engineering strategy is developed by employing cobalt boron imidazolate framework (Co-BIF) to construct 2D CoNi-alloy embedded B, N-doped carbon layers (2D-CNC) as a promising EWAM. In the first step, a chemical etching oxidation process on Co-BIF is used to obtain an optimized 2D-CoNi-layered double hydroxide (2D-CoNi-LDH) intermediate and in the second, high-temperature calcination reduction is implemented to modify graphitization of the degree of the 2D-CNC. The obtained sample delivers superior reflection loss (RLmin) of -60.1dB and wide effective absorption bandwidth (EAB) of 6.24GHz. The synergy mechanisms of interfacial/dipole polarization and magnetic coupling are in-depth evidenced by the hologram and Lorentz electron microscopy, revealing its significant contribution on multireflection and impedance matching. Further theoretical evaluation by COMSOL simulation in different fields based on the dynamic loss process toward the test ring reveals the in situ EW attenuation process. This work presents a strategy to develop multifunctional light-weight infrared stealthy aerogel with superior pressure-resistant, anti-corrosion, and heat-insulating properties for future applications.

Hierarchical Ni3V2O8@N-Doped Carbon Hollow Double-Shell Microspheres for High-Performance Lithium-Ion Storage.

Transition metal oxides (TMOs) are highly dense in energy and considered as promising anode materials for a new generation of alkaline ion batteries. However, their electrode structure is disrupted due to significant volume changes during charging and discharging, resulting in the short cycle life of batteries. In this paper, the hierarchical Ni3V2O8@N-doped carbon (Ni3V2O8@NC) hollow double-shell microspheres were prepared and used as electrode materials for lithium-ion batteries (LIBs). The utilization efficiency and ion transfer rate of Ni3V2O8 were improved by the hollow microsphere structure formed through nanoparticle self-assembly. Furthermore, the uniform N-doped carbon layer not only enhanced the structural stability of Ni3V2O8, but also improved the overall electrical conductivity of the composite. The Ni3V2O8@NC electrode has an initial discharge capacity of up to 1167.3 mAh g-1 at a current density of 0.3 A g-1, a reversible capacity of up to 726.5 mAh g-1 after 200 cycles, and still has a capacity of 567.6 mAh g-1 after 500 cycles at a current density of 1 A g-1, indicating that the material has good cycle stability and high-rate capability. This work presents new findings on the design and fabrication of complex porous double-shell nanostructures.

A simple, controllable, and scalable synthetic strategy for highly uniform N-doped carbon coating on nanoparticles

The carbon coating enables nanoparticles to withstand harsh environments, but achieving uniformity and scalability for their industrial use remains a challenge. In this work, we present a simple, controllable, and scalable strategy for one-pot coating with an N-doped carbon layer on the surface of various nanoparticles, including semiconductors, oxides, transition metals, and noble metals. Uniform coverage of the N-doped carbon layer was achieved through an autogenic pressure reaction of gaseous species derived from starting precursors in a closed reactor. The thickness of the coating layer could be precisely controlled by adjusting the amount of precursor, even down to the 1 nm level, because the precursor is completely consumed in the reactor without any loss. The crystallinity of the N-doped carbon layer could be modified by altering the coating temperature. Moreover, the results demonstrate that this coating process can be applied to different types of nanoparticles. Tests confirmed that nanoparticles retain their inherent nature while exhibiting more stable and enhanced properties after the N-doped carbon coating. We believe this approach offers a straightforward synthetic route for the design and application of nanoparticle coatings.

Polyoxometalate coupled polymers induced molybdenum phosphide with large surface area for efficient hydrogen evolution

Developing highly active hydrogen evolution reaction (HER) electrocatalysts possesses great significance for the green renewable energy conversion and storage. Here, through the electrostatic attraction between polyoxometalate (PMo12) and ammonium polyphosphate (APP) and the coordination with polyallylamine hydrochloride (PAH), the precursor was constructed, and then nitrogen-doped graphite carbon layer-coated MoP active particles (MoP@NC) were successfully prepared by high temperature carbonization. For HER, the overpotential of η10 for MoP@NC is 119 and 126 mV in acidic and alkaline electrolyte. Furthermore, in alkaline solution, when the current density reaches a certain degree (≥110 mA cm−2), the hydrogen production activity of the catalysts are the same as that of the industrial Pt/C catalysts, or even have a slight advantage. The synergistic interaction of active particles (MoP) and graphitic carbon layers and high specific surface area ensure the excellent activity of HER. N-doped porous carbon layers also protect MoP@NC working for 24 h. Moreover, the catalysts prepared in the same experimental environment with ammonium molybdate as metal source also showed good HER performance in acidic and alkaline environments. This study opens a general way to develop earth-rich Mo-based phosphide electrocatalysts with high activity for hydrolysis applications.

In-situ fabrication of MoO2/MoxC heterojunction on rodlike carbon-coated zirconia for enhanced oxidative desulfurization of fuel oils

Electronic structure of catalysts is of great importance in redox reactions. Virtually, fabricating Mo-based heterojunction nanocomposites and elucidating their role in the nature of synergic effect between Mo compounds hold the key to promoting the electron transfer and eventually improving oxidative desulfurization (ODS) performances. Herein, the molybdenum dioxide/molybdenum carbides (MoO2/MoxC) heterojunction was in situ dispersedly immobilized on a rodlike N-doped carbon (NC)-coated zirconia (ZrO2) via a facile annealing route employing phosphomolybdic acid (PMo12)-loaded Zr(IV) porphyrinic metal–organic framework (MOF-545) (i.e. PMo12@MOF-545) as a precursor. The optimized catalyst (MoO2/MoxC@NC@ZrO2) exhibits outstanding oxidative desulfurization (ODS) activities for fuel oil with sulfur content in a wide range of 200～4000 ppm. It is indicated that the extraordinary ODS activity of MoO2/MoxC@NC@ZrO2 significantly stems from the accelerated electron transfer by the MoO2/MoxC heterojunction, the strong electron-donating effect of NC layer, and abundant active sites from the extremely dispersed Mo compounds realized by both NC and ZrO2. The ODS reaction is elucidated by the •OH radical mechanism. Moreover, MoO2/MoxC@NC@ZrO2 shows excellent stability, and the sulfur removal could remain over 96.5 % after thirteen cycles. This work not only opens up a new avenue for in situ integrating Mo-based heterojunctions, but also manifests a promising potential for practical ODS process.

Unconventional thick cobalt telluride electrodes enable homogeneous ion flow for high capacity, fast and safe potassium storage

The demand for high-energy density, fast-charging, and safe potassium-ion batteries (PIBs) is crucial for large-scale applications in electric vehicles and grid systems. Despite the potential of thick electrode designs by a conventional technique (CTEs) to boost energy density, they often encounter challenges such as reduced capacity, limited cycling lifespan, and localized short circuits. Here, we present a novel cobalt telluride composite anode by a simple tellurization and subsequent heat reduction, featuring Co1.67Te2 nanoparticles uniformly embedded within an N-doped carbon layer on a trace amount of reduced graphene oxide (CT@NC/rGO). By constructing low tortuosity electrodes (LTEs), a homogeneous distribution of potassium ions and current density is achieved, resulting in enhanced potassium storage performance. The CT@NC/rGO LTEs demonstrate excellent discharge capacities: 311.7, 276.5, and 243.7 mA h g−1 after 500 cycles at 0.25 A g−1 for mass loadings of 1.4, 1.9, and 2.8 mg cm−2, respectively. At a higher current density of 0.5 A g−1, discharge capacities after 650 cycles are 245.3, 175.6, and 159.2 mA h g−1 for mass loadings at 1.6, 2.4, and 3.0 mg cm−2, respectively. These improvements are attributed to enhanced pseudocapacitive behavior, reduced charge resistance, and accelerated ion diffusion kinetics, as evidenced by experimental and simulation studies. The proposed strategy for synthesizing high-density electrodes holds promise for developing high-performance metallic compound electrodes for PIBs and potentially extending to other types of energy storage systems.

One-step constructing advanced N-doped carbon@metal nitride as ultra-stable electrocatalysts via urea plasma under room temperature

Highly active transition metal nitrides are desirable for electrocatalytic reactions, but their long-term stability is still unsatisfactory and thus limiting commercial applications. Herein, for the first time, we report a unique and universal room-temperature urea plasma method for controllable synthesis of N-doped carbon coated metal (Fe, Co, Ni, etc.) nitrides arrays electrocatalysts. The preformed metal oxides arrays can be successfully converted into metal nitrides arrays with preserved nanostructures and a thin layer of N-doped carbon (NC) via one-step urea plasma. Typically, as a representative case, NC@CoN nanowire arrays are illustrated and corresponding formation mechanism by plasma is proposed. Notably, the designed NC@CoN catalysts deliver excellent electrocatalytic activity and long-term stability both in oxygen evolution reaction (OER) and urea oxidation reaction (UOR). For OER, a low overpotential (264 mV at 10 mA/cm2) and high stability (>50 h at 20 mA/cm2) are acquired. For UOR, a current density of 100 mA/cm2 is achieved at only 1.39 V and maintain over 100 h. Theoretical calculations reveal that the synergetic coupling effect of CoN and NC can significantly facilitate the charge-transfer process, optimize adsorbed intermediates binding strength and further greatly decrease the energy barrier. This strategy provides a novel method for fabrication of NC@ metal nitrides as highly active and stable catalysts.

N-doped carbon decorated Na3V2(PO4)3@NC composite derived from melamine as cathode material for high-rate and ultralong-life sodium-ion batteries

Sodium superionic conductor (NASICON) Na3V2(PO4)3 (NVP) is one of the most promising cathode materials for Sodium ion batteries (SIBs). However, its low electronic conductivity makes the cycle and rate performance less ideal. Increasing the electronic conductivity of NVP by carbon coating has been more and more confirmed, especially for N-doped carbon. Here, in-situ melamine-derived N-doped carbon-coated Na3V2(PO4)3@NC (NVP@NC) by hydrothermal-assisted sol-gel method is prepared. The introduction of N has no effect on the original NASICON structure of NVP@C, but the melamine addition amount affected the intensity of the diffraction peak from different NVP@NC samples. The NVP@NC shows superior cycling and rate performance. In the NVP@NC-2 sample with nC3N6H6/nNVP = 2, its discharge capacity maintains 106.82 mAh·g−1 at the 500th cycle at 0.2 C. The reversible capacities at 10 and 20 C are 90.5 and 85.0 mAh·g−1 with capacity retention of 81.2% and 76.3%, respectively. The zero-band gap of NVP@NC-2 through first-principles calculations means the ionic conductivity of NVP@C is greatly enhanced after N doping. The addition of the N element to the carbon layer contributes a pair of lone pairs of electrons to the matrix carbon and introduces certain active sites and defects. The reason for the improved electrochemical performance is that the N-doped carbon layer (NC) enables the expansion and deformation of the crystal structure to be controlled, increasing the Na+ diffusion coefficient and the electrical conductivity of NVP.

Hexavalent Chromium Reduction Mediated by Interfacial Electron Transfer over the Co@NC Nanosheet-Assembled Microflowers.

The reductive transformation of Cr(VI) into Cr(III) mediated by formic acid with efficient, stable, and cost-effective catalysts is a promising strategy for remediating Cr(VI) contamination. Herein, we report the facile construction of uniform Co@NC nanosheet-assembled microflowers for the reduction of Cr(VI). Both experimental results and density functional theory (DFT) calculations reveal the vital role of the intensive interfacial electronic interaction between Co nanoparticles and the N-doped carbon layer in facilitating the anchoring and dispersion of Co nanoparticles within the carbon framework. The interfacial electron transfer from Co to NC contributes to the interaction with Cr2O72- ions, promoting the subsequent H-transfer reaction. A Langmuir-Hinshelwood kinetic model has been established for the Cr(VI) reduction catalyzed by the CNCF2 (pyrolyzed at 700 °C), which shows a superior reaction performance. This study provides a facile strategy to delicately design well-assembled heterostructures with rich interfaces and strong interfacial interactions for a series of applications in environmental/thermal catalysis.

Co-synthesis and Electrochemical Investigation of the Nitrogen-Doped Carbon Layer with Metallic Nano Beads on the SiOx Anode for Lithium Secondary Batteries.

The high theoretical capacity (∼2000 mAh g-1) of silicon suboxide (SiOx, with 1 < x < 2) can solve the energy density issue of the graphite anode in Li-ion batteries. In addition, it has an advantage in terms of volume expansion or side reactions compared to pure Si or Li metals, which are considered as next-generation anode materials. However, the loading content of SiOx is limited in commercial anodes because of its low cycle stability and initial coulombic efficiency. In this study, a nitrogen-doped carbon layer with Cu beads (N-C/Cu) derived from copper phthalocyanine (CuPc) is applied to a SiOx electrode to improve its electrochemical performance. The SiOx electrode is simultaneously coated with a Cu- and N-doped carbon layer using CuPc. N-C/Cu synergistically enhances the electric conductivity of the electrode, thus improving its electrochemical performance. The SiOx/N-C/Cu composite has better cyclability and higher capacity (1095.5 mAh g-1) than the uncoated electrode, even after 200 cycles in the 0.5 C condition. In full-cell cycling with NCM811 cathodes, the SiOx (60 wt % of SiOx, with a n/p ratio of 1.1) and graphite-mixed (7.8 wt % of SiOx, with a n/p ratio of 1.1) anodes also show improved electrochemical performances in the same conditions.

Pioneering Piezoelectric-Driven Atomic Hydrogen for Efficient Dehalogenation of Halogenated Organic Pollutants.

The electrocatalytic hydrodehalogenation (EHDH) process mediated by atomic hydrogen (H*) is recognized as an efficient method for degrading halogenated organic pollutants (HOPs). However, a significant challenge is the excessive energy consumption resulting from the recombination of H* to H2 production in the EHDH process. In this study, a promising strategy was proposed to generate piezo-induced atomic H*, without external energy input or chemical consumption, for the degradation and dehalogenation of HOPs. Specifically, sub-5 nm Ni nanoparticles were subtly dotted on an N-doped carbon layer coating on BaTiO3 cube, and the resulted hybrid nanocomposite (Ni-NC@BTO) can effectively break C-X (X = Cl and F) bonds under ultrasonic vibration or mechanical stirring, demonstrating high piezoelectric driven dehalogenation efficiencies toward various HOPs. Mechanistic studies revealed that the dotted Ni nanoparticles can efficiently capture H* to form Ni-H* (Habs) and drive the dehalogenation process to lower the toxicity of intermediates. COMSOL simulations confirmed a "chimney effect" on the interface of Ni nanoparticle, which facilitated the accumulation of H+ and enhanced electron transfer for H* formation by improving the surface charge of the piezocatalyst and strengthening the interfacial electric field. Our work introduces an environmentally friendly dehalogenation method for HOPs using the piezoelectric process independent of the external energy input and chemical consumption.

Ni and VN Nanoparticles Supported on N-Doped Carbon Layer Containing Ni Single Atoms as Electrocatalyst for the Hydrogen Evolution Reaction

Ni and VN Nanoparticles Supported on N-Doped Carbon Layer Containing Ni Single Atoms as Electrocatalyst for the Hydrogen Evolution Reaction

The N-doped carbon coated Na3V2(PO4)3 with different N sources as cathode material for sodium-ion batteries: Experimental and theoretical study

NASICON (super ion conductor)-type Na3V2(PO4)3 (NVP) is considered to be one of the most promising cathode materials for sodium-ion batteries (SIBs) due to its good structural stability, fast Na+ diffusion coefficient, and excellent electrochemical properties. However, the poor intrinsic conductivity and electronic conductivity and severe volume shrinkage of NVP, resulting in serious limitations in the practical application of NVP materials. Carbon, especially N-doped carbon modification, is the most effective method and strategy to improve the conductivity of NVP. The study of N source and N content in carbon plays a very important role in improving the electronic properties. Herein, N-doped carbon coated NVP composites was synthesized via the classical sol-gel method using common, green and inexpensive urea and polyvinylpyrrolidone (PVP) as N sources, respectively. According to EIS tests and GITT tests, N-doped carbon layers with urea as the N source significantly improved the conductivity of the carbon layers and the Na+ diffusion kinetics. The effects of N-doped carbon layers on the electrode kinetics and electrochemical properties of NVP materials were investigated in detail. The optimized U-NC15@NVP composite exhibited a maximum discharge capacity of 114.2 mAh g−1 at 0.2C and 92.1% capacity retention after 400 cycles at 1C. When the optimal U-NC15@NVP electrode was selected to assemble a symmetric full cell, the reversible discharge capacity was 75.0 mAh g−1 after 100 cycles at 1C. The density functional theory (DFT) calculations establish that N-doped carbon can generate lots of active sites and external defects, which is beneficial to reduce the energy bandwidth of the carbon layer and thus improve the conductivity of the carbon layer. Additionally, it can also reduce the Na+ diffusion barrier and improve the adsorption energy for Na+. Experimental tests and theoretical calculations show that N-doped carbon can significantly increase the conductivity of the carbon layer and improve the electrochemical properties of NVP.

Hydrogel-involved portable colorimetric sensor based on oxidase mimic Fe/Co-NC for acetylcholinesterase detection and pesticides inhibition assessment

Herein, we synthesized a novel N-doped carbon layer encapsulated Fe/Co bimetallic nanoparticles (Fe/Co-NC), which exhibited superior oxidase-like activity due to the facilitation of electron penetration and the formation of metal-nitrogen active sites. Fe/Co-NC could catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) to blue oxTMB. Acetylcholinesterase (AChE) could catalyze the hydrolysis of thioacetylcholine to produce reducing thiocholine, which prevented TMB from oxidation. Thus, a portable hydrogel colorimetric sensor was developed for on-site and visual monitoring of AChE with the detection limit of 0.36 U L−1, and successfully applied to detect AChE in human erythrocyte samples. Furthermore, this platform was used to investigate the inhibition of triazophos on AChE activity.

Amorphous MoOx loaded on N-doped carbon-modified SiO2 for strongly enhanced oxidative desulfurization activity

Transition-metal oxides (TMOs) are good catalyst candidates for oxidation desulfurization (ODS) reaction, and its excellent dispersion in carriers could exert great influence on its catalytic performance. However, improving its catalytic activity still remains challenging. Herein, the amorphous molybdenum oxide (MoOx) was synthesized as the active sites for ODS reaction. Via a facile adsorption-pyrolysis approach, the amorphous MoOx was dispersedly immobilized onto N-doped carbon layer (NC)-encapsulated SiO2 using zinc pyridine porphyrin (ZnTPyP) and phosphomolybdic acid (PMo12)-modified SiO2 nanocomposites as precursor, obtaining the MoOx@NC@SiO2 catalyst. Owing to the wonderful pre-dispersion of Mo sources on the precursor leaded by the electrostatic interaction and spacial effect, the confinement effect of the derived carbon matrix, and the strong Mo-N bonds, the growth of MoOx crystal could be inhibited in pyrolysis procedure, ensuring the amorphous structure and good dispersion of MoOx species on SiO2. The as-prepared MoOx@NC@SiO2 exhibits excellent oxidation desulfurization (ODS) performances, and could promote the complete oxidation of DBT in model fuel into DBTO2 at the theoretical O/S molar ratio of 2, due to the perfect activation of all oxygen atoms of H2O2 by the amorphous MoOx. In addition, a plausible ODS mechanism over MoOx@NC@SiO2 is depicted to be the •OH radicals. Moreover, MoOx@NC@SiO2 still displays an outstanding reusability over at least 10 cycles owing to the encapsulation of NC layers and the strong Mo-N bonds. Therefore, this work provides a promising catalyst for industrial ODS application, and opens up a new avenue for developing the amorphous TMOs catalysts.

Well-Dispersed Bi nanoparticles for promoting the lithium storage performance of Si Anode: Effect of the bridging Bi nanoparticles

Silicon (Si) is considered a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity of up to 4200 mAh/g. However, the poor cycling and rate performances of Si induced by the low intrinsic electronic conductivity and large volume expansion during the lithiation/delithiation process limit its practical application. Herein, a novel silicon/bismuth@nitrogen-doped carbon (Si/Bi@NC) composite with nanovoids was synthesized and investigated as an advanced anode material for LIBs. In such a structure, ultrafine bismuth nanoparticles coupled with an N-doped carbon layer were introduced to modify the surface of Si nanoparticles. Subsequently, the lithiated LixBi has excellent high ionic conductivity and acts as a fast transport bridge for lithium ions. The introduced carbon coating layer and nanovoids can buffer the volume expansion of Si during the lithiation/delithiation process, thus maintaining structural stability during the cycling process. As a result, the Si/Bi@NC composite exhibits excellent electrochemical performance, providing a relatively high capacity of 955.8 mAh/g at 0.5 A/g after 450 cycles and excellent rate performance with a high capacity of 477.8 mAh/g even at 10.0 A/g. Furthermore, the assembled full cell with LiFePO4 as cathode and pre-lithium Si/Bi@NC as anode can provide a high capacity of 138.8 mAh/g at 1C after 90 cycles, exhibiting outstanding cycling performance.