Facile synthesis of molybdenum carbide nanoparticles in situ decorated on nitrogen-doped porous carbons for hydrogen evolution reaction

Molybdenum-based electrocatalysts are promising candidates of platinum (Pt)-based materials in electrocatalyzing hydrogen evolution reaction (HER), due to their cost-efficient and resembled electronic properties. Reported herein is the preparation of molybdenum carbide nanoparticles uniformly decorated on nitrogen-modified carbons (Mo2C/NC) through the carbonization of Mo-based polymers under hydrogen atmosphere by using poly(p-phenylenediamine) and ammonium heptamolybdate polymer analogue as precursors. And the molybdenum nitride nanoparticles loaded on porous N-doped carbons (Mo2N/NC) are also fabricated by calcination the polymer precursors in nitrogen gas. The Mo2C/NC shows more excellent electrocatalytic activity than Mo2N/NC in 0.5 M H2SO4, together with robust long-term durability. The well-crystalline nanoparticles and the increased electron conductivity are the main characters responded for the high catalytic efficiency of the fabricated electrocatalysts. This easily fabrication procedure may provide a facile route to prepare non-noble metal carbide/nitride catalysts featuring wellengineered structural and textural peculiarities for realistic energy conversion system.

Construction of 3D porous Cu_(1.81)S/nitrogen-doped carbon frameworks for ultrafast and long-cycle life sodium-ion storage

Transition metal sulfides have great potential as anode mterials for sodium-ion batteries(SIBs)due to their high theoretical specific capacities.However,the inferior intrinsic conductivity and large volume variation during sodiation-desodiation processes seriously affect its high-rate and long-cyde performance,unbeneficial for the application as fast-charging and long-cycling SIBs anode.Herein,the three-dimensional porous Cu_(1.81)S/nitrogen-doped carbon frameworks(Cu_(1.81)S/NC)are synthesized by the simple and facile sol-gel and annealing processes,which can accommodate the volumetric expansion of Cu_(1.81)S nanoparticles and accelerate the transmission of ions and electrons during Na^(+)insertion/extraction processes,exhibiting the excellent rate capability(250.6 mA·g^(-1)at 20.0 A·g^(-1))and outstanding cycling stability(70% capacity retention for 6000 cycles at 10.0 A·g^(-1))for SIBs.Moreover,the Na-ion full cells coupled with Na_(3)V_(2)(PO_(4))_(3)/C cathode also demonstrate the satisfactory reversible specific capacity of 330.5 mAh·g^(-1)at 5.0 A·g^(-1)and long-cycle performance with the 86.9% capacity retention at 2.0 A·g^(-1)after 750 cycles.This work proposes a promising way for the conversionbased metal sulfides for the applications as fast-charging sodium-ion battery anode.

Nitrogen-doped porous carbons from polyacrylonitrile fiber as effective CO_(2) adsorbents

In this report, nitrogen-doped porous carbons were synthesized from polyacrylonitrile fiber by a facile two-step synthesis process i.e. carbonization followed by KOH activation. Activation temperature and KOH/carbon ratio are two parameters to tune the porosity and surface chemical properties of sorbents. The as-obtained sorbents were carefully characterized.Special attention was paid concerning the change of sorbents’ morphology with respect to synthesis conditions. Under the activation temperatures of this study, the sorbents can still retain their fibrous structure when the KOH/carbon mass ratio is 1. Further increasing the KOH amount will destroy the original morphology of polyacrylonitrile fiber. CO_(2)adsorption performance tests show that a sorbent retaining the fibrous shape possesses the highest CO_(2)uptake of 3.95 mmol/g at 25℃and 1 bar. Comprehensive investigation found that the mutual effect of narrow microporosity and doped N content govern the CO_(2)adsorption capacity of these adsorbents. Furthermore, these polyacrylonitrile fiber-derived carbons present multiple outstanding CO_(2)capture properties such as excellent recyclability, high CO_(2)/N_(2)selectivity, fast adsorption kinetics, suitable heat of adsorption, and good dynamic adsorption capacity. Hence, nitrogen-doped porous carbons with fibrous structure are promising in CO_(2)capture.

Efficient CO_(2) adsorption and mechanism on nitrogen-doped porous carbons

In this work,nitrogen-doped porous carbons(NACs)were fabricated as an adsorbent by urea modification and KOH activation.The CO_(2) adsorption mechanism for the NACs was then explored.The NACs are found to present a large specific surface area(1920.72-3078.99 m2·g^(-1))and high micropore percentage(61.60%-76.23%).Under a pressure of 1 bar,sample NAC-650-650 shows the highest CO_(2) adsorption capacity up to 5.96 and 3.92 mmol·g^(-1) at 0 and 25℃,respectively.In addition,the CO_(2)/N_(2) selectivity of NAC-650-650 is 79.93,much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650.The CO_(2) adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles.Analysis of the results show that the CO_(2) capacity of the NACs has a linear correlation(R^(2)=0.9633)with the cumulative pore volume for a pore size less than 1.02 nm.The presence of nitrogen and oxygen enhances the CO_(2)/N_(2) selectivity,and pyrrole-N and hydroxy groups contribute more to the CO_(2) adsorption.In situ Fourier transform infrared spectra analysis indicates that CO_(2) is adsorbed onto the NACs as a gas.Furthermore,the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat,and it is found to be controlled by CO_(2) diffusion.The CO_(2) adsorption kinetics for NACs at room temperature and in pure CO_(2) is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model.

Conversion of Lignin into Porous Carbons for High-Performance Supercapacitors via Spray Drying and KOH Activation: Structure-Properties Relationship and Reaction Mechanism

Lignin-derived porous carbons have emerged as promising electrode materials for supercapacitors.However,the challenge remains in designing and controlling their structure to achieve ideal electrochemical performance due to the complex molecular structure of lignin and its intricate chemical reactions during the activation process.In this study,three porous carbons were synthesized from lignin by spray drying and chemical activation with vary-ing KOH ratios.The specific surface area and structural order of the prepared porous carbon continued to increase with the increase of the KOH ratio.Thermogravimetric-mass spectrometry(TG-MS)was employed to track the molecular fragments generated during the pyrolysis of KOH-activated lignin,and the mechanism of the thermochemical conversion was investigated.During the thermochemical conversion of lignin,KOH facili-tated the removal of H2 and CO,leading to the formation of not only more micropores and mesopores,but also more ordered carbon structures.The pore structure exhibited a greater impact than the carbon structure on the electrochemical performance of porous carbon.The optimized porous carbon exhibited a capacitance of 256 F g-1 at a current density of 0.2 A g-1,making it an ideal electrode material for high-performance supercapacitors.

Controllable synthesis of nitrogen-doped porous carbon from metal-polluted miscanthus waste boosting for supercapacitors

High-value reclamation of metal-polluted plants involved in phytoremediation is a big challenge.In this study,nitrogen-doped nanoporous carbon with large specific area of 2359.1 m^(2)g^(-1) is facilely fabricated from metal-polluted miscanthus waste for efficient energy storage.The synergistic effect of KOH,urea and ammonia solution greatly improve the nitrogen quantity and surface area of the synthesized carbon.Electrodes fabricated with this carbon exhibit the excellent capacitance performance of 340.2 F g^(-1) at 0.5 A g^(-1) and a low combined resistance of 0.116Ω,which are competitive with most of previously reported carbon-based electrodes.In addition,the as-obtained carbon electrode shows a high specific capacitance retention of over 99.6%even after 5000 cycles.Furthermore,the symmetric supercapacitor fabricated using the synthesized carbon achieves a superior energy density of 25.3 Wh kg^(-1)(at 400 W kg^(-1))in 1 mol L^(-1) Na_(2)SO_(4)aqueous solution.This work provides an efficient route to upcycle metal-polluted plant waste for supercapacitor applications.

Novel Ag@Nitrogen-doped Porous Carbon Composite with High Electrochemical Performance as Anode Materials for Lithium-ion Batteries

A novel Ag@nitrogen-doped porous carbon(Ag-NPC) composite was synthesized via a facile hydrothermal method and applied as an anode material in lithium-ion batteries(LIBs). Using this method, Ag nanoparticles(Ag NPs) were embedded in NPC through thermal decomposition of Ag NO_3 in the pores of NPC. The reversible capacity of Ag-NPC remained at 852 m Ah g^(-1)after 200 cycles at a current density of 0.1 A g^(-1), showing its remarkable cycling stability. The enhancement of the electrochemical properties such as cycling performance,reversible capacity and rate performance of Ag-NPC compared to the NPC contributed to the synergistic effects between Ag NPs and NPC.

Hierarchically porous nitrogen-doped carbon as cathode for lithium–sulfur batteries

Porous nitrogen-doped carbon is an especially promising material energy storage due to its excellentconductivity, stable physicochemical properties, easy processability, controllable porosity and low price.Herein, we reported a novel well-designed hierarchically porous nitrogen-doped carbon （HPNC） via acombination of salt template （ZnC12） and hard template （SiO2） as sulfur host for lithium-sulfur batter-ies. The low-melting ZnC12 is boiled off and leaves behind micropores and small size mesopores duringpyrolysis process, while the silica spheres are removed by acid leaching to generate interconnected 3Dnetwork of macropores. The HPNC-S electrode exhibits an initial specific capacity of 1355 mAh g^-l at 0.IC （IC= 1675 mAh g^-1 ）, a high-rate capability of 623 mAh g-l at 2 C, and a small decay of 0.13% per cycleover 300 cycles at 0.2 C. This excellent rate capability and remarkable long-term cyclability of the HPNC-Selectrode are attributed to its hierarchical porous structures for confining the soluble lithium polysulfideas well as the nitrogen doping for high absorbability of lithium polysulfide.

Biomass-derived nitrogen-doped hierarchical porous carbon as efficient sulfur host for lithium–sulfur batteries

Lithium-sulfur(Li-S) battery is a potential energy storage technology with high energy density and low cost. However, the gap between theoretical expectation and practical performance limits its wide implementation. Herein, we report a nitrogen-doped porous carbon derived from biomass pomelo peel as sulfur host material for Li-S batteries. The hierarchical porous architecture and the polar surface introduced by N-doping render a favorable combination of physical and chemical sulfur confinements as well as an expedite electron/ion transfer, thus contributing to a facilitated and stabilized sulfur electrochemistry. As a result, the corresponding sulfur composite electrodes exhibit an ultrahigh initial capacity of 1534.6 mAh g^-1, high coulombic efficiency over 98% upon 300 cycles, and decent rate capability up to 2 C. This work provides an economical and effective strategy for the fabrication of advanced carbonaceous sulfur host material as well as the significant improvement of Li-S battery performance.

Nitrogen-doped hierarchical porous carbon from polyaniline/silica self-aggregates for supercapacitor

In this paper, nitrogen-doped hierarchical porous carbon(N-HPC) was prepared from polyaniline(PANI)/silica self-aggregates. H-bonding between N\\H groups in aniline/PANI and \\OH groups in nano silica template led to a self-assembly type, which enabled the formation of uniform N-HPC nanoparticles. Silica self-aggregates provided macroporous channels resulted in a decreased diffusion distance. After removing the hard template,the N-HPC had a high surface area(899 m^2·g^(-1)). Owing to two co-existed synergetic energy-storage mechanisms and the hierarchical porous structure, the obtained N-HPC exhibited a high specific capacitance of 218.75 F·g^(-1) at 0.5 A·g^(-1), compared with the nonporous nitrogen-doped carbon(N-C) derived from pure PANI. Moreover, the N-HPC electrode demonstrated excellent cycle life, retaining 99% of its initial specific capacitance after 1000 cycles.

Nitrogen-doped porous carbon nanosheets as both anode and cathode for advanced potassium-ion hybrid capacitors

Potassium-ion hybrid capacitors(PIHCs)as a burgeoning research hotspot are an ideal replacement for lithium-ion hybrid capacitors(LIHCs).Here,we report nitrogen-doped porous carbon nanosheets(NPCNs)with enlarged interlayer spacing,abundant defects,and favorable mesoporous structures.The structural changes of NPCNs in potassiation and depotassiation processes are analyzed by using Raman spectroscopy and transmission electron microscopy.Due to the unique structure of NPCNs,the PIHC device assembled using NPCNs as both the anode and cathode material(double-functional self-matching material)exhibits a superior energy density of 128 Wh kg^(-1)with a capacity retention of 90.8%after 9000 cycles.This research can promote the development of double-functional self-matching materials for hybrid energy storage devices with ultra-high performance.

Nitrogen-doped hierarchical few-layered porous carbon for efficient electrochemical energy storage

Large surface area,high conductivity,and rich active site of carbon electrode materials are necessary characteristics for energy storage devices.However,high conductivity and high nitrogen doping of carbon electrode materials are difficult to coordinate.Here,a facile method via the carbonization of nitrogen-containing Schiff base polymer has been developed to prepare high conductivity and high nitrogen-doped hierarchical porous carbon.The organic components with a benzene ring structure in the polymer promote the formation of more sp^(2)-graphitized carbon,which is beneficial for the improvement of electrical conductivity.Nitrogen-doped hierarchical porous carbon calcined at 900℃ under the NH3 atmosphere possesses high nitrogen content of 7.48 at%,a large specific surface area of 1613.2m2/g,and high electrical conductivity of 2.7 S/cm.As electrode materials in an aqueous-based supercapacitor,nitrogen-doped hierarchical porous carbon exhibits superior specific capacitance of 385 F/g at 1 A/g as well as excellent rate performance(242 and 215 F/g at a current density of 100 and 200 A/g,respectively).In addition,the specific capacitance of electrode measured in a two-electrode system is 335 F/g at 1 A/g,and the long-term cycling stability can be achieved with more than 94%initial capacitance after 10000 cycles.The constructed symmetric supercapacitor delivers high energy density and high power density.The outstanding electrochemical performances combined with the novel and scalable synthetic approach make the nitrogen‐doped hierarchical porous carbon potential electrode material for electrochemical devices.

Nitrogen-doped hierarchically porous carbon spheres for low concentration CO_(2) capture

Synthesis of spherical carbon beads with effective CO_2 capture capability is highly desirable for large scale application of CO2 sorption, but remains challenging. Herein, a facile and efficient strategy to prepare nitrogen-doped hierarchically porous carbon spheres was developed via co-pyrolyzation of poly(vinylidene chloride) and melamine in alginate gel beads. In this approach, melamine not only serves as the nitrogen precursor, but also acts as a template for the macropores structures. The nitrogen contents in the hierarchically porous carbon spheres reach a high level, ranging from 11.8 wt% to 14.7 wt%, as the melamine amount increases. Owing to the enriched nitrogen functionalities and the special hierarchical porous structure, the carbon spheres exhibit an outstanding CO_2 capture performance, with the dynamic capacity of as much as about 7 wt% and a separation factor about 49 at 25 °C in a gas mixture of CO_2/N_2(0.5:99.5, v/v).

Nitrogen-doped ordered mesoporous carbon:Effect of carbon precursor on oxygen reduction reactions

Aniline,pyrrole and phenanthroline,which have different nitrogen compositions,are used as carbon precursors to synthesize nitrogen-doped ordered mesoporous carbons（NOMCs） by the nanocasting method.The effect of the precursor on the resultant NOMC is extensively investigated by nitrogen adsorption-desorption measurements,scanning electron microscopy,X-ray photoelectron spectroscopy（XPS）,cyclic voltammetry and rotating ring-disk electrode measurements.Salient findings are as follows.First,the precursor has a significant influence on the specific surface area and textural properties.The NOMC materials derived from pyrrole（C-PY-900：765 m^2/） and phenanthroline（C-Phen-900：746 m^2/） exhibit higher specific surface areas than the aniline analog（C-PA-900：569 m^2/）.Second,the XPS results indicate that the total nitrogen content（ca.3.1–3.3 at%） is similar for the three carbon sources,except for a slight difference in the nitrogen configuration.Furthermore,the content of the nitrogen-activated carbon atoms is found to closely depend on the precursor,which is the highest for the phenanthroline-derived carbon.Third,the electrochemical results reveal that the electrocatalytic activity follows in the order C-PA-900 C-PY-900 C-Phen-900,confirming that the nitrogen-activated carbon atoms are the active sites for the oxygen reduction reaction（ORR）.In summary,the precursor has considerable influence on the composition and textural properties of the NOMC materials,of which the ORR electrocatalytic activity can be enhanced through optimization of the NOMCs.

Electrocatalytic hydrogen peroxide formation on mesoporous non-metal nitrogen-doped carbon catalyst

Direct electrochemical formation of hydrogen peroxide（H2O2） from pure O2 and H2on cheap metal-free earth abundant catalysts has emerged as the highest atom-efficient and environmentally friendly reaction pathway and is therefore of great interest from an academic and industrial point of view. Very recently,novel metal-free mesoporous nitrogen-doped carbon catalysts have attracted large attention due to the unique reactivity and selectivity for the electrochemical hydrogen peroxide formation [1–3]. In this work,we provide deeper insights into the electrocatalytic activity, selectivity and durability of novel metal-free mesoporous nitrogen-doped carbon catalyst for the peroxide formation with a particular emphasis on the influence of experimental reaction parameters such as p H value and electrode potential for three different electrolytes. We used two independent approaches for the investigation of electrochemical hydrogen peroxide formation, namely rotating ring-disk electrode（RRDE） technique and photometric UV–VIS technique. Our electrochemical and photometric results clearly revealed a considerable peroxide formation activity as well as high catalyst durability for the metal-free nitrogen-doped carbon catalyst material in both acidic as well as neutral medium at the same electrode potential under ambient temperature and pressure. In addition, the obtained electrochemical reactivity and selectivity indicate that the mechanisms for the electrochemical formation and decomposition of peroxide are strongly dependent on the p H value and electrode potential.

Red-blood-cell-like nitrogen-doped porous carbon as an efficient metal-free catalyst for oxygen reduction reaction

A red-blood-cell-like nitrogen-doped porous carbon catalyst with a high nitrogen content(9.81%)and specific surface area(631.46 m^2/g)was prepared by using melamine cyanuric acid and glucose as sacrificial template and carbon source,respectively.This catalyst has a comparable onset potential and a higher diffusion-limiting current density than the commercial 20 wt%Pt/C catalyst in alkaline electrolyte.The oxygen reduction reaction mechanism catalyzed by this catalyst is mainly through a 4e pathway process.The excellent catalytic activity could origin from the synergistic effect of the in-situ doped nitrogen(up to 9.81%)and three-dimensional(3D)porous network structure with high specific surface area,which is conducive to the exposure of more active sites.It is interesting to note that the catalytic activity of oxygen reduction strongly depends on the proportion of graphic N rather than the total N content.

Nitrogen-doped carbon encapsulated in mesoporous TiO2 nanotubes for fast capacitive sodium storage

Controllable synthesis of insertion-type anode materials with beneficial micro-and nanostructures is a promising approach for the synthesis of sodium-ion storage devices with high-reactivity and excellent electrochemical performance.In this study,we developed a sacrificial-templating route to synthesize TiO_(2)@N-doped carbon nanotubes(TiO_(2)@NC-NTs)with excellent electrochemical performance.The asprepared mesoporous TiO_(2)@NC-NTs with tiny nanocrystals of anatase TiO_(2) wrapped in N-doped carbon layers showed a well-defined tube structure with a large specific surface area of 198 m^(2) g^(-1) and a large pore size of~5 nm.The TiO_(2)@NC-NTs delivered high reversible capacities of 158 m A h g^(-1) at 2 C(1 C=335 m A g^(-1))for 2200 cycles and 146 m A h g^(-1) at 5 C for 4000 cycles,as well as an ultrahigh rate capability of up to 40 C with a capacity of 98 m A h g^(-1).Even at a high current density of 10 C,a capacity of 138 m A h g^(-1) could be delivered over 10,000 cycles.Thus,the synthesis of mesoporous TiO_(2)@NC-NTs was demonstrated to be an efficient approach for developing electrode materials with high sodium storage and long cycle life.

Versatile bifunctional nitrogen-doped porous carbon derived from biomass in catalytic reduction of 4-nitrophenol and oxidation of styrene

The scarcity and weak durability of metal,especially precious metal catalysts are big obstacles for their large-scale application in many reactions.The state-of-the-art of the catalytic science prefers such type of catalysts,which can replace metal-based catalysts to alleviate energy and environmental crises and exhibit catalytic performance comparable to or even exceeding these metal catalysts.Herein,we report that N-doped porous carbon(NKC)derived from cheap and abundant radish can be employed as versatile and efficient bifunctional catalysts in both the catalytic reduction of 4-nitrophenol(NRR)and oxidation of styrene(SOR).The series of NKC catalysts were prepared with a simple and facile one-pot strategy by coupling the N-doping,carbonization and KOH activation processes.These catalysts show hierarchical porosity,with the specific surface area,total pore volume and N-doping content ranging from 918.9-3062.7 m^2 g^-1,1.01-2.04 cm^3 g^-1 and 1.29-15.3 at%,respectively.Interestingly,our finding suggests that the catalytic performance is not directly related to these parameters but correlates positively with the content of graphitic N dopants,which is the dominant contributor for impelling both the NRR and SOR.Another intriguing finding is that for both reactions,the optimal catalyst was found to be the NKC-3-800 which possesses the highest graphitic N content of 3.13 at%.In addition,to gain insight into the catalytic behavior,analyses of kinetics and thermodynamics were performed,and the catalytic mechanisms were postulated.This work paves the way for the construction of biomass-derived N-doped carbon catalysts for bi-or even multi-functional applications in various organic reactions.

Metal-organic Frameworks Derived Cobalt Encapsulated in Nitrogen-doped Porous Carbon Nanosheets for Oxygen Reduction Reaction and Rechargeable Zinc-air Batteries

Nitrogen(N)-doped carbon nanosheets(TCM-900)were prepared by pyrolyzing the cobalt metal organic framework(MOF)and acid treatment.The TCM-900 showed outstanding ORR performance with half-potential of 0.805 V.The density function theory(DFT)reveals the nitrogen activates the carbon atoms in the framework.The homemade ZAB with TCM-900 as ORR electrocatalyst exhibits high-power density of 45 mW·cm^(-2) and excellent long recharge cycling stability compared to Pt/C at 10 mA·cm^(-2).This work illustrates an attractive future of the rechargeable ZAB.

Nitrogen-doped hierarchical porous carbon derived from metal–organic aerogel for high performance lithium–sulfur batteries

Nitrogen-doped three-dimensional(3 D) porous carbon materials have numerous applications due to their highly porous structures, abundant structural nitrogen heteroatom decoration and low densities. Herein,nitrogen doped hierarchical 3 D porous carbons(NHPC) were prepared via a novel metal–organic aerogel(MOA), using hexamethylenetetramine(HMT), 1,3,5-benzenetricarboxylic acid and copper(II) as starting materials. The morphology, porous structure of the building blocks in the NHPC can be tuned readily using different amount of HMT, which makes elongation of the pristine octahedron of HKUST-1 to give rise to different aspect ratio rod-like structures. The as-prepared NHPC with rod-like carbons exhibit high performance in lithium sulfur battery due to the rational ion transfer pathways, high N-doped doping and hierarchical porous structures. As a result, the initial specific capacity of 1341 m A h/g at rate of 0.5 C(1 C = 1675 m A h/g) and high-rate capability of 354 m A h/g at 5 C was achieved. The decay over 500 cycles is 0.08% per cycle at 1 C, highlighting the long-cycle Li–S batteries.