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.

Elucidating the role of embedding dispersed cobalt sites in nitrogen-doped carbon frameworks in Si-based anodes for stable and superior storage

Unsatisfactory conductivity and volume effects have hindered the commercial application of siliconbased materials as advanced anode materials for high-performance lithium-ion batteries. Herein, nitrogen doped carbon silicon matrix composite with atomically dispersed Co sites(Si/Co-N-C) is obtained via the design of the frame structure loaded with nano-components and the multi-element hybrid strategy. Co atoms are uniformly fixed to the N-C frame and tightly packed with nanoscale silicon particles as an activation and protection building block. The mechanism of the N-C framework of loaded metal Co in the Si alloying process is revealed by electrochemical kinetic analysis and ex situ characterization tests.Impressively, the nitrogen-doped Co site activates the intercalation of the outer carbon matrix to supplement the additional capacity. The Co nanoparticles with high conductivity and support enhance the conductivity and structural stability of the composite, accelerating the Li^(+)/Na^(+) diffusion kinetics. Density functional theory(DFT) calculation confirms that the hetero-structure Si/Co-N-C adjusts the electronic structure to obtain good lithium-ion adsorption energy, reduces the Li^(+)/Na^(+) migration energy barrier.This work provides meaningful guidance for the development of high-performance metal/non-metal modified anode materials.

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.

Ultra-stable and High-rate Lithium Ion Batteries Based on Metal-organic Framework-derived ln2O3 Nanocrystals/Hierarchically Porous Nitrogen-doped Carbon Anode

Exploring electrode materials with attractive specific capacity and prominent cyclic durability is of the essence for promoting lithium ion batteries(LIBs).In2O3 has shown an extraordinary promise for LIBs with advantageous gravimetric capacity(theoretically 965 mA h g-1) and low working voltage.However,In2O3 still suffers from the inherent weaknesses of metal oxides in practical application,especially low conductivity and incorrigible volume expansion upon the cycling process.Here,we demonstrate the architecture of metal-organic framework(MOF)-derived In2O3 nanocrystals/hierarchically porous nitrogen-doped carbon composite(In2O3/HPNC) for ultra-stable LIBs anode.This hierarchically porous structure(micro/meso/macro-pores) with nitrogen doping not only ensures exceptional mechanical strength and accommodates the volume expansion of In2O3 nanocrystals,but also offers electrons and lithium ions efficient interpenetrating pathways to migrate rapidly during charge/discharge processes.Thus,In2O3/HPNC exhibits excellent cyclic stability with a high specific capacity of 623 mA h g-1 over2000 cycles at 1000 mA g-1,corresponding to an ultra-low specific capacity decay of 0.017% per cycle(the best among the ln203-based anode for LIBs),and outstanding rate performance,suggesting a critical step toward achieving long-life and high-rate LIBs in practical devices.

Pre-fixing defects in carbon framework for revealing the active sites of oxygen reduction reaction at nitrogen-doped carbon nanotubes

Nitrogen-doped carbon-based materials are promising non-platinum group metal electrocatalysts for the oxygen reduction reaction(ORR).Understanding their ORR active sites is vital for the rational design and development of nitrogen-doped carbon-based electrocatalysts with enhanced catalytic efficiency and selectivity.However,the conclusive analysis of the ORR mechanism of nitrogen-doped carbon-based electrocatalysts remains a grand challenge because the catalysts have a complex inhomogeneous structure.Here,we elucidate this problem using nitrogen-doped carbon nanotubes framework catalysts with fixed defect concentrations prepared by pre-thermal treatment at a low temperature.The generation of defects under high-temperature treatment was effectively suppressed to enable a simple model for ORR mechanism study.A correlation between ORR pathways and the different nitrogen species in the nitrogen-doped carbon catalysts was revealed through a combination of structural and electrochemical properties investigations.Besides,our results also demonstrate the importance of defects for ORR.We believe that the results will provide instructive guidance for designing and developing novel carbon nanomaterials for ORR.

High-performance Pt catalysts supported on hierarchical nitrogen-doped carbon nanocages for methanol electrooxidation

Hierarchical nitrogen-doped carbon nanocages （hNCNC） with large specific surface areas were used as a catalyst support to immobilize Pt nanoparticles by a microwave-assisted polyol method. The Pt/hNCNC catalyst with 20 wt% loading has a homogeneous dispersion of Pt nanoparticles with the average size of 3.3 nm, which is smaller than 4.3 and 4.9 nm for the control catalysts with the same loading supported on hierarchical carbon nanocages （hCNC） and commercial Vulcan XC-72, respec- tively. Accordingly, Pt/hNCNC has a larger electrochemical surface area than Pt/hCNC and Pt/XC-72. The Pt/hNCNC catalyst exhibited excellent electrocatalytic activity and stability for methanol oxidation, which was better than the control catalysts. This was attributed to the en- hanced interaction between Pt and hNCNC due to nitrogen participation in the anchoring function. By making use of the unique advantages of the hNCNC support, a heavy Pt loading up to 60 wt% was prepared without serious agglomeration, which gave a high peak-current density per unit mass of catalyst of 95.6 mA/mg for achieving a high power density. These results showed the potential of the Pt/hNCNC catalyst for methanol oxidation and of the new hNCNC support for wide applications.

Preparation of nitrogen-doped carbon nanoblocks with high electrocatalytic activity for oxygen reduction reaction in alkaline solution

The oxygen reduction reaction （ORR） is traditionally performed using noble‐metals catalysts, e.g. Pt. However, these metal‐based catalysts have the drawbacks of high costs, low selectivity, poor stabili‐ties, and detrimental environmental effects. Here, we describe metal‐free nitrogen‐doped carbon nanoblocks （NCNBs） with high nitrogen contents （4.11%）, which have good electrocatalytic proper‐ties for ORRs. This material was fabricated using a scalable, one‐step process involving the pyrolysis of tris（hydroxymethyl）aminomethane （Tris） at 800℃. Rotating ring disk electrode measurements show that the NCNBs give a high electrocatalytic performance and have good stability in ORRs. The onset potential of the catalyst for the ORR is-0.05 V （vs Ag/AgCl）, the ORR reduction peak potential is-0.20 V （vs Ag/AgCl）, and the electron transfer number is 3.4. The NCNBs showed pronounced electrocatalytic activity, improved long‐term stability, and better tolerance of the methanol crosso‐ver effect compared with a commercial 20 wt%Pt/C catalyst. The composition and structure of, and nitrogen species in, the NCNBs were investigated using Fourier‐transform infrared spectroscopy, scanning electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction. The pyroly‐sis of Tris at high temperature increases the number of active nitrogen sites, especially pyridinic nitrogen, which creates a net positive charge on adjacent carbon atoms, and the high positive charge promotes oxygen adsorption and reduction. The results show that NCNBs prepared by pyrolysis of Tris as nitrogen and carbon sources are a promising ORR catalyst for fuel cells.

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.

Hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets as an efficient bifunctional catalyst for Zn–air battery

Rational design of low-cost, highly electrocatalytic activity, and stable bifunctional electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) has been a great significant for metal–air batteries. Herein, an efficient bifunctional electrocatalyst based on hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets(Co/N-Pg) is fabricated for Zn–air batteries. A lowcost biomass peach gum, consisting of carbon, oxygen, and hydrogen without other heteroatoms, was used as carbon source to form carbon matrix hosting hollow cobalt oxide nanoparticles. Meanwhile, the melamine was applied as nitrogen source and template precursor, which can convert to carbon-based template graphitic carbon nitride by polycondensation process. Owing to the unique structure and synergistic effect between hollow cobalt oxide nanoparticles and Co-N-C species, the proposal Co/N-Pg catalyst displays not only prominent bifunctional electrocatalytic activities for ORR and OER, but also excellent durability. Remarkably, the assembled Zn–air battery with Co/N-Pg air electrode exhibited a low discharge-charge voltage gap(0.81 V at 50 mA cm^-2) and high peak power density(119 mW cm^-2) with long-term cycling stability. This work presents an effective approach for engineering transition metal oxides and nitrogen modified carbon nanosheets to boost the performance of bifunctional electrocatalysts for Zn–air battery.

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Developing robust oxygen electrocatalyst with high-performance is very significant for practical rechargeable Zn-air battery.We report herein the preparation of three-dimensional continuous nanocarbon network composed of interconnected nitrogen-doped carbon nanotubes and its application as oxygen electrocatalysis in rechargeable Zn-air battery.Except the excellent electrochemical bifunctionality,this carbon nanotube matrix also delivers an impressive battery performance.Specifically,an opencircuit voltage of 1.50 V as well as a high power density of 220 m W cm^(-2) with remarkable cycling stability for 1600 h is achieved in the rechargeable Zn-air battery.The study not only provides an efficient bifunctional oxygen electrocatalyst but more importantly may pave significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies.

Highly Dispersed Cobalt Nanoparticles Embedded in Nitrogen-Doped Graphitized Carbon for Fast and Durable Potassium Storage

Potassium-ion batteries(KIBs)have great potential for applications in large-scale energy storage devices.However,the larger radius of K+leads to sluggish kinetics and inferior cycling performance,severely restricting its practical applicability.Herein,we propose a rational strategy involving a Prussian blue analogue-derived graphitized carbon anode with fast and durable potassium storage capability,which is constructed by encapsulating cobalt nanoparticles in nitrogen-doped graphitized carbon(Co-NC).Both experimental and theoretical results show that N-doping effectively promotes the uniform dispersion of cobalt nanoparticles in the carbon matrix through Co-N bonds.Moreover,the cobalt nanoparticles and strong Co-N bonds synergistically form a threedimensional conductive network,increase the number of adsorption sites,and reduce the diffusion energy barrier,thereby facilitating the adsorption and the diffusion kinetics.These multiple effects lead to enhanced reversible capacities of 305 and 208.6 mAh g^−1 after 100 and 300 cycles at 0.05 and 0.1 A g^−1,respectively,demonstrating the applicability of the Co-NC anode for KIBs.

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.

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.

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.

Effects of Potassium and Manganese Promoters on Nitrogen-Doped Carbon Nanotube-Supported Iron Catalysts for CO_2 Hydrogenation

Nitrogen-doped carbon nanotubes （NCNTs） were used as a support for iron （Fe） nanoparticles applied in car- bon dioxide （CO_2） hydrogenation at 633 K and 25 bar （1 bar = 10-5 Pa）. The Fe/NCNT catalyst promoted with both potassium （K） and manganese （Mn） showed high performance in CO_2 hydrogenation, reaching 34.9% conversion with a gas hourly space velocity （GHSV） of 3.1 L-（g·h）-1. Product selectivities were high for olefin products and low for short-chain alkanes for the K-promoted catalysts. When Fe/NCNT catalyst was promot- ed with both K and Mn, the catalytic activity was stable for 60 h of reaction time. The structural effect of the Mn promoter was demonstrated by X-ray diffraction （XRD）, temperature-programmed reduction （TPR） with molecular hydrogen （H2）, and in situ X-ray absorption near-edge structure （XANES） analysis. The Mn pro- moter stabilized wtistite （FeO） as an intermediate and lowered the TPR onset temperature. Catalytic ammo- nia （NH_3） decomposition was used as an additional probe reaction for characterizing the promoter effects. The Fe/NCNT catalyst promoted with both K and Mn had the highest catalytic activity, and the Mn-promoted Fe/NCNT catalysts had the highest thermal stability under reducing conditions.

Low-Temperature Carbonized Nitrogen-Doped Hard Carbon Nanofiber Toward High-Performance Sodium-Ion Capacitors

Carbon nanofiber(CNF)was widely utilized in the field of electrochemical energy storage due to its superiority of conductivity and mechanics.However,CNF was generally prepared at relatively high temperature.Herein,nitrogen-doped hard carbon nanofibers(NHCNFs)were prepared by a lowtemperature carbonization treatment assisted with electrospinning technology.Density functional theory analysis elucidates the incorporation of nitrogen heteroatoms with various chemical states into carbon matrix would significantly alter the total electronic configurations,leading to the robust adsorption and efficient diffusion of Na atoms on electrode interface.The obtained material carbonized at 600°C(NHCNF-600)presented a reversible specific capacity of 191.0 mAh g^(−1)and no capacity decay after 200 cycles at 1 A g^(−1).It was found that the sodium-intercalated degree had a correlation with the electrochemical impedance.A sodium-intercalated potential of 0.2 V was adopted to lower the electrochemical impedance.The constructed sodium-ion capacitor with activated carbon cathode and presodiated NHCNF-600 anode can present an energy power density of 82.1 Wh kg^(−1)and a power density of 7.0 kW kg^(−1).

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 Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

In this study, hydrothermal carbonization(HTC)was applied for surface functionalization of carbon nanotubes(CNTs) in the presence of glucose and urea. The HTC process allowed the deposition of thin nitrogen-doped carbon layers on the surface of the CNTs. By controlling the ratio of glucose to urea, nitrogen contents of up to 1.7 wt%were achieved. The nitrogen-doped carbon nanotube-supported Pd catalysts exhibited superior electrochemical activity for ethanol oxidation relative to the pristine CNTs.Importantly, a 1.5-fold increase in the specific activity was observed for the Pd/HTC-N1.67%CNTs relative to the catalyst without nitrogen doping(Pd/HTC-CNTs). Furtherexperiments indicated that the introduction of nitrogen species on the surface of the CNTs improved the Pd(0)loading and increased the binding energy.