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.

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.

Nitrogen-doped cobalt nanoparticles/nitrogen-doped plate-like ordered mesoporous carbons composites as noble-metal free electrocatalysts for oxygen reduction reaction

In this work, nitrogen-doped cobalt nanoparticlesinitrogen-doped plate-like ordered mesoporous carbons (N/Co/OMCs) were used as noble-metal free electrocatalysts with high catalytic efficiency. Compared with OMCs with long channel length, due to more entrances for catalytic target accessibility and a short pathway for rapid diffusion, the utilization efficiency of cobalt nanoparticles inside the plate-like OMCs with short pore length is well improved, which can take full advantage of porous structure in electrocatalysis and increase the utilization of catalysts. The active sites in N/Co/OMCs for oxygen reduction reaction (ORR) are highly exposed to oxygen molecule, which results in a high activity for ORR. By combination of the catalytic properties of nitrogen dopant, incorporation of Co nanoparticles, and structural properties of OMCs, the N/Co/plate-like OMCs are highly active noble-metal free catalysts for ORR in alkaline solution. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Nitrogen-doped carbon nanotube encapsulating cobalt nanoparticles towards efficient oxygen reduction for zinc–air battery

Nitrogen-doped carbon materials encapsulating 3 d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction(ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube(N–CNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of N–CNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.

Stabilising Cobalt Sulphide Nanocapsules with Nitrogen-Doped Carbon for High-Performance Sodium-Ion Storage

Conversion-type anode materials with a high charge storage capability generally su er from large volume expansion, poor electron conductivity, and sluggish metal ion transport kinetics. The electrode material described in this paper, namely cobalt sulphide nanoparticles encapsulated in carbon cages(Co9S8@NC), can circumvent these problems. This electrode material exhibited a reversible sodium-ion storage capacity of 705 mAh g^-1 at 100 mA g^-1 with an extraordinary rate capability and good cycling stability. Mechanistic study using the in situ transmission electron microscope technique revealed that the volumetric expansion of the Co9S8 nanoparticles is bu ered by the carbon cages, enabling a stable electrode–electrolyte interface. In addition, the carbon shell with high-content doped nitrogen significantly enhances the electron conductivity of the Co9S8@NC electrode material and provides doping-induced active sites to accommodate sodium ions. By integrating the Co9S8@NC as negative electrode with a cellulose-derived porous hard carbon/graphene oxide composite as positive electrode and 1 M NaPF6 in diglyme as the electrolyte, the sodium-ion capacitor full cell can achieve energy densities of 101.4 and 45.8 Wh kg^-1 at power densities of 200 and 10,000 W kg^-1, respectively.

Enhancing anchoring and catalytic conversion of polysulfides by nitrogen deficient cobalt nitride for advanced lithium-sulfur batteries

While lithium-sulfur(Li-S)battery has attracted remarkable attention owing to the high theoretical capacity,its practical application is still hindered by the shuttle and sluggish conversion kinetics of intermediate lithium polysulfides(Li PSs).Defect engineering,which can regulate the electronic structure and in turn influence the surface adsorption and catalytic capability,has been regarded as a feasible strategy to deal with the above challenges.However,few studies on nitrogen vacancies and their mechanisms are reported.Herein,cobalt nitride with nitrogen vacancies grown on multi-walled carbon nanotube(CNTCo N-VN)is designed and applied as the separator modification material to investigate the enhancing mechanism of nitrogen vacancies on Li-S batteries.The experimental evidence and theoretical calculation indicate that the introduction of nitrogen vacancies into cobalt nitride can enhance the chemical affinity to Li PSs and effectively hamper the shuttle effect.Meanwhile the reduced band gap of the d-band center of Co and p-band center of N for CNT-Co N-VNand the promoted diffusion of Li^(+) can expedite the solid-liquid and liquid-liquid conversions of sulfur species.Due to these superiorities,the cell with CNT-Co NVNmodified separator delivers a favorable initial capacity of 901 m Ah g^(-1)and a capacity of 660 m Ah g^(-1)can be achieved after 250 cycles at 2 C.This work explores the application of metal nitride with nitrogen vacancies and sheds light on the development of functional separators for high-efficient Li-S batteries.

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.

Ultrafine VN nanodots induced generation of abundant cobalt single-atom active sites on nitrogen-doped carbon nanotube for efficient hydrogen evolution

Development of highly active and stable non-noble electrocatalysts with well-defined nanostructures is crucial for efficient hydrogen evolution reaction(HER). Herein, a novel three-dimensional(3D) selfsupported electrode consists of vanadium nitride(VN) nanodots and Co nanoparticles co-embedded and highly active single Co atoms anchored in N-doped carbon nanotubes supported on carbon cloth(VN-Co@CoSAs-NCNTs/CC) is fabricated via a one-step in situ nanoconfined pyrolysis strategy, which shows remarkable enhanced HER electrocatalytic activity in acidic medium. During pyrolysis, the formed VN nanodots induce the generation of atomic Co Nxsites in NCNTs, contributing to superior electrocatalytic activity. Experimental and density functional theory(DFT) calculation results reveal that the electrode has multiple accessible active sites, fast reaction kinetics, low charge/mass transfer resistances,high conductivity, as well as downshifted d-band center with a thermodynamically favorable hydrogen adsorption free energy(△G_(H·)), all of which greatly boost the HER performance. As a result, the VNCo@CoSAs-NCNTs/CC electrode displays superb catalytic performance toward HER with a low overpotential of 29 mV at 10 mA cm^(-2) in acidic medium, which could maintain for at least 60 h of stable performance. This work opens a facile avenue to explore low-cost, high performance, but inexpensive metals/nitrogen-doped carbon composite electrocatalysts for HER.

Paper-derived cobalt and nitrogen co-doped carbon nanotube@porous carbon as a nonprecious metal electrocatalyst for the oxygen reduction reaction

The oxygen reduction reaction(ORR)is a vitally important process in fuel cells.The development of high‐performance and low‐cost ORR electrocatalysts with outstanding stability is essential for the commercialization of the electrochemical energy technology.Herein,we report a facile synthesis of cobalt(Co)and nitrogen(N)co‐doped carbon nanotube@porous carbon(Co/N/CNT@PC‐800)electrocatalyst through a one‐step pyrolysis of waste paper,dicyandiamide,and cobalt(II)acetylacetonate.The surface of the hierarchical porous carbon supported a large number of carbon nanotubes(CNTs),which were derived from dicyandiamide through the catalysis of Co.The addition of Co resulted in the formation of a hierarchical micro/mesoporous structure,which was beneficial for the exposure of active sites and rapid transportation of ORR‐relevant species(O2,H+,OH?,and H2O).The doped N and Co formed more active sites to enhance the ORR activity of the electrocatalyst.The Co/N/CNT@PC‐800 material exhibited optimal ORR performance with an onset potential of 0.005 V vs.Ag/AgCl and a half‐wave potential of?0.173 V vs.Ag/AgCl.Meanwhile,the electrocatalyst showed an excellent methanol tolerance and a long‐term operational durability than that of Pt/C,as well as a quasi‐four‐electron reaction pathway.The low‐cost and simple synthesis approach makes the Co/N/CNT@PC‐800 a prospective electrocatalyst for the ORR.Furthermore,this work provides an alternative approach for exploring the use of biomass‐derived electrocatalysts for renewable energy applications.

Controllable active sites and facile synthesis of cobalt nanoparticle embedded in nitrogen and sulfur co-doped carbon nanotubes as efficient bifunctional electrocatalysts for oxygen reduction and evolution reactions

Development of efficient and promising bifunctional electrocatalysts for oxygen reduction and evolutionreactions is desirable. Herein, cobalt nanoparticles embedded in nitrogen and sulfur co-doped carbonnanotubes(Co@NSCNT) were prepared by a facile pyrolytic treatment. The cobalt nanoparticles and co-doping of nitrogen and sulfur can improve the electron donor-acceptor characteristics of the carbon nan-otubes and provide more active sites for catalytic oxygen reduction and evolution reactions. The preparedCo@NSCNT, annealed at 900℃, showed excellent electrocatalytic performance and better durability thancommercial platinum catalysts. Additionally, Co@NSCNT-900 catalysts exhibited comparable onset poten-tials and Tafel slopes to ruthenium oxide. Overall, Co@NSCNT showed high activity and improved dura-bility for both oxygen evolution and reduction reactions.

Influence of carbonization temperature on cobalt-based nitrogendoped carbon nanopolyhedra derived from ZIF-67 for nonoxidative propane dehydrogenation

Propylene is a significant basic material for petrochemicals such as polypropylene,propylene oxide,etc.With abundant propane supply from shale gas,propane dehydrogenation(PDH)becomes extensively attractive as an on-purpose propylene production route in recent years.Nitrogen-doped carbon(NC)nanopolyhedra supported cobalt catalysts were synthesized in one-step of ZIF-67 pyrolysis and investigated further in PDH.XPS,TEM and N_(2) adsorption-desorption were used to study the influence of carbonization temperature on as-prepared NC supported cobalt catalysts.The temperature is found to affect the cobalt phase and nitrogen species of the catalysts.And the positive correlation was established between Co0 proportion and space time yield of propylene,indicating that the modulation of carbonization temperature could be important for catalytic performance.

Electrocatalytic water splitting at nitrogen-doped carbon layers-encapsulated nickel cobalt selenide

Generally,the catalytic overpotentials of hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)are unavoidable because of the low charge transfer.In this work,two strategies of alloying of Co with Ni and enclosing of electrocatalysts with carbonaceous materials were both used to accelerate the catalytic efficiency of cobalt selenide for water splitting.The nitrogen-doped carbon(NC)layer improves the reaction kinetics by efficient charge transfer.The alloying of metal into composited electrocatalysts can modify the electronic properties of host materials,thereby tuning the adsorption behavior of intermediate and improving the electrocatalytic activity.As expected,Nyquist plots reveal that the charge-transfer resistance(Rct)of nickel cobalt selenide encapsulated into nitrogen-doped carbon layer(CoNiSe/NC-3,Co:Ni=1:1)are just 5 and 9 for HER and OER,respectively,which are much lower than those of CoSe/NC-1(Co:Ni=1:0)(81 and 138)and CoNiSe/NC-3 without NC(CoNiSe-3)(54 and 25).With the high charge transfer and porous structure,CoNiSe/NC-3 shows good performance for both HER and OER.When current density reaches 10 m A cm-2,only 100 and 270 mV overpotentials are required for HER and OER,respectively.With the potential of 1.65 V,full water splitting also can be catalyzed by Co Ni Se/NC-3 with current density of 20 m A cm-2,suggesting that CoNiSe/NC-3 could be used as replacement for noble metal electrocatalysts.

Regulating local charges of atomically dispersed Moδ+ sites by nitrogen coordination on cobalt nanosheets to trigger water dissociation for boosted hydrogen evolution in alkaline media

Now,Pt-based materials are still the best catalysts for hydrogen evolution reaction(HER).Nevertheless,the scarcity of Pt makes it impossible for the large-scale applications in industry.Although cobalt is taken as an excellent HER catalyst due to its suitable H*binding,its alkali HER catalytic property need to be improved because of the sluggish water dissociation kinetics.In this work,nitrogen with small atomic radius and metallophilicity is employed to adjust local charges of atomically dispersed Mo^(δ+)sites on Co nanosheets to trigger water dissociation.Theoretical calculations suggest that the energy barrier of water dissociation can be effectively reduced by introducing nitrogen coordinated Mo^(δ+)sites.To realize this speculation,atomically dispersed Mo^(δ+)sites with nitrogen coordination of Mo(N)/Co were prepared via reconstruction of CoMoO_(4).High angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)and X-ray absorption spectroscopy(XAS)demonstrate the coordination of N atoms with atomically dispersed Mo atoms,leading to the local charges of atomically dispersed Mo^(δ+)sites in Mo(N)/Co.The measurement from ambient pressure X-ray photoelectron spectroscopy(AP-XPS)reveals that the Mo^(δ+)sites promote the adsorption and activation of water molecule.Therefore,the Mo(N)/Co exhibits an excellent activity,which need only an overpotential of 39 mV to reach the current density of 10 mA cm^(-2).The proposed strategy provides an advance pathway to design and boost alkaline HER activity at the atomic-level.

Dimerization of Propylene by Nickel (Ⅱ) and Cobalt (Ⅱ) Catalysts Based on Bidentate Nitrogen-phosphino Chelating Ligands

The catalytic property of propylene dimerization by several nickel (Ⅱ), cobalt (Ⅱ) complexes containing N-P bidentate ligands was studied in combination with organoaluminum co-catalysts. The effects of the type of aluminum co-catalysts and its relative amount, the nature of precursors in terms of ligand backbone and metal center were investigated. The results indicated that precursor I (N,N-dimethyl-2-(diphenylphosphino)aniline nickel (Ⅱ) dichloride) exhibited high activity in propylene dimerization in the presence of the strong Lewis acid Et3Al2Cl3, whereas low productivity by its cobalt analogues was observed under identical reaction conditions.

Cobalt nanoparticles encapsulated in nitrogen-doped carbon for room-temperature selective hydrogenation of nitroarenes

Here,we report cobalt nanoparticles encapsulated in nitrogen‐doped carbon(Co@NC)that exhibit excellent catalytic activity and chemoselectivity for room‐temperature hydrogenation of nitroarenes.Co@NC was synthesized by pyrolyzing a mixture of a cobalt salt,an inexpensive organic molecule,and carbon nitride.Using the Co@NC catalyst,a turnover frequency of^12.3 h?1 and selectivity for 4‐aminophenol of>99.9%were achieved for hydrogenation of 4‐nitrophenol at room temperature and 10 bar H2 pressure.The excellent catalytic performance can be attributed to the cooperative effect of hydrogen activation by electron‐deficient Co nanoparticles and energetically preferred adsorption of the nitro group of nitroarenes to electron‐rich N‐doped carbon.In addition,there is electron transfer from the Co nanoparticles to N‐doped carbon,which further enhances the functionality of the metal center and carbon support.The catalyst also exhibits stable recycling performance and high activity for nitroaromatics with various substituents.

Studies on the Displacement Reaction of Trialkylaluminum with Ethylene Catalyzed by Nitrogen Chelate Cobalt Complexes

The catalytic properties of a series of cobalt complexes containing bidenated nitrogen ligand for displacement reaction of trialkylaluminum with ethylene is reported. Effect of different reaction time, temperature and cobalt complexes containing different ligand on catalyst performance has been investigated.

Integration of morphology and electronic structure modulation on cobalt phosphide nanosheets to boost photocatalytic hydrogen evolution from ammonia borane hydrolysis

The controllable and safe hydrogen storage technologies are widely recognized as the main bottleneck for the accomplishment of sustainable hydrogen energy.Ammonia borane(AB)has regarded as a competitive candidate for chemical hydrogen storage.However,developing efficient yet high-performance catalysts towards hydrogen evolution from AB hydrolysis remains an enormous challenge.Herein,cobalt phosphide nanosheets are synthesized by a facile salt-assisted along with low-temperature phosphidation strategy for simultaneously modulating its morphology and electronic structure,and function as hydrogen evolution photocatalysts.Impressively,the Co_(2)P nanosheets display extraordinary performance with a record high turnover frequency of 44.9 min^(-1),outperforming most of the noble-metal-free catalysts reported to date.This remarkable performance is attributed to its desired nanosheets structure,featuring with high specific surface area,abundant exposed active sites,and short charge diffusion paths.Our findings provide a novel strategy for regulating metal phosphides with desired phase structure and morphology for energy-related applications and beyond.

Increased dependence on nitrogen-fixation of a native legume in competition with an invasive plant

Suppression of roots and/or their symbiotic microorganisms,such as mycorrhizal fungi and rhizobia,is an effective way for alien plants to outcompete native plants.However,little is known about how invasive and native plants interact with the quantity and activity of nutrient-acquisition agents.Here a pot experiment was conducted with monoculture and mixed plantings of an invasive plant,Xanthium strumarium,and a common native legume,Glycine max.We measured traits related to root and nodule quantity and activity and mycorrhizal colonization.Compared to the monoculture,fine root quantity(biomass,surface area)and activity(root nitrogen(N)concentration,acid phosphatase activity)of G.max decreased in mixed plantings;nodule quantity(biomass)decreased by 45%,while nodule activity in Nfixing via rhizobium increased by 106%;mycorrhizal colonization was unaffected.Contribution of N fixation to leaf N content in G.max increased in the mixed plantings,and this increase was attributed to a decrease in the rhizosphere soil N of G.max in the mixed plantings.Increased root quantity and activity,along with a higher mycorrhizal association was observed in X.strumarium in the mixed compared to monoculture.Together,the invasive plant did not directly scavenge N from nodule-fixed N,but rather depleted the rhizosphere soil N of the legume,thereby stimulating the activity of N-fixation and increasing the dependence of the native legume on this N source.The quantity-activity framework holds promise for future studies on how native legumes respond to alien plant invasions.

ZmbZIP27 regulates nitrogen-mediated leaf angle by modulating lignin deposition in maize

In grain crops such as maize(Zea mays),leaf angle(LA)is a key agronomic trait affecting light interception and thus planting density and yield.Nitrogen(N)affects LA in plants,but we lack a good understanding of how N regulates LA.Here,we report that N deficiency enhanced lignin deposition in the ligular region of maize seedlings.In situ hybridization showed that the bZIP transcription factor gene ZmbZIP27 is mainly expressed in the phloem of maize vascular bundles.Under N-sufficient conditions,transgenic maize overexpressing ZmbZIP27 showed significantly smaller LA compared with wild type(WT).By contrast,zmbzip27_(ems)mutant showed larger LA under both N-deficient and N-sufficient conditions compared with WT.Overexpression of ZmbZIP27 enhanced lignin deposition in the ligular region of maize in the field.We further demonstrated that ZmbZIP27 could directly bind the promoters of the microRNA genes ZmMIR528a and ZmMIR528b and negatively regulate the expression levels of ZmmiR528.ZmmiR528 knockdown transgenic maize displayed erect architecture in the field by increasing lignin content in the ligular region of maize.Taken together,these results indicate that ZmbZIP27 regulates N-mediated LA size by regulating the expression of ZmmiR528 and modulating lignin deposition in maize.

Microfluidic-oriented synthesis of enriched iridium nanodots/carbon architecture for robust electrocatalytic nitrogen fixation

Electrocatalytic nitrogen reduction reaction(NRR)is considered as a promising candidate to achieve ammonia synthesis because of clean electric energy,moderate reaction condition,safe operating process and harmless by-products.However,the chemical inertness of nitrogen and poor activated capacity on catalyst surface usually produce low ammonia yield and faradic efficiency.Herein,the microfluidic technology is proposed to efficiently fabricate enriched iridium nanodots/carbon architecture.Owing to in-situ co-precipitation reaction and microfluidic manipulation,the iridium nanodots/carbon nanomaterials possess small average size,uniform dispersion,high conductivity and abundant active sites,producing good proton activation and rapid electrons transmission and moderate adsorption/desorption capacity.As a result,the as-prepared iridium nanodots/carbon nanomaterials realize large ammonia yield of 28.73 μg h^(-1) cm^(-2) and faradic efficiency of 9.14%in KOH solution.Moreover,the high ammonia yield of 11.21 μg h^(-1) cm^(-2) and faradic efficiency of 24.30%are also achieved in H_(2)SO_(4) solution.The microfluidic method provides a reference for large-scale fabrication of nano-sized catalyst materials,which may accelerate the progress of electrocatalytic NRR in industrialization field.