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.

Cobalt Sulfide Confined in N-Doped Porous Branched Carbon Nanotubes for Lithium-Ion Batteries

Lithium-ion batteries(LIBs) are considered new generation of large-scale energy-storage devices.However,LIBs suffer from a lack of desirable anode materials with excellent specific capacity and cycling stability.In this work,we design a novel hierarchical structure constructed by encapsulating cobalt sulfide nanowires within nitrogen-doped porous branched carbon nanotubes(NBNTs)for LIBs.The unique hierarchical Co9S8@NBNT electrode displayed a reversible specific capacity of 1310 mAhg-1 at a current density of 0.1 Ag-1,and was able to maintain a stable reversible discharge capacity of 1109 mAhg-1 at a current density of 0.5 Ag-1 with coulombic efficiency reaching almost 100% for 200 cycles.The excellent rate and cycling capabilities can be ascribed to the hierarchical porosity of the one-dimensional Co9S8@NBNT internetworks,the incorporation of nitrogen doping,and the carbon nanotube confinement of the active cobalt sulfide nanowires offering a proximate electron pathway for the isolated nanoparticles and shielding of the cobalt sulfide nanowires from pulverization over long cycling periods.

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 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.

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.

Hierarchical N-Doped Porous Carbons for Zn–Air Batteries and Supercapacitors

Nitrogen-doped carbon materials with a large specific surface area,high conductivity,and adjustable microstructures have many prospects for energy-related applications.This is especially true for N-doped nanocarbons used in the electrocatalytic oxygen reduction reaction(ORR)and supercapacitors.Here,we report a low-cost,environmentally friendly,large-scale mechanochemical method of preparing N-doped porous carbons(NPCs)with hierarchical micro-mesopores and a large surface area via ball-milling polymerization followed by pyrolysis.The optimized NPC prepared at 1000°C(NPC-1000)offers excellent ORR activity with an onset potential(Eonset)and half-wave potential(E1/2)of 0.9 and 0.82 V,respectively(vs.a reversible hydrogen electrode),which are only approximately 30 mV lower than that of Pt/C.The rechargeable Zn–air battery assembled using NPC-1000 and the NiFe-layered double hydroxide as bifunctional ORR and oxygen evolution reaction electrodes offered superior cycling stability and comparable discharge performance to RuO2 and Pt/C.Moreover,the supercapacitor electrode equipped with NPC prepared at 800℃ exhibited a high specific capacity(431 F g^−1 at 10 mV s^−1),outstanding rate,performance,and excellent cycling stability in an aqueous 6-M KOH solution.This work demonstrates the potential of the mechanochemical preparation method of porous carbons,which are important for energy conversion and storage.

A Molecular Foaming and Activation Strategy to Porous N-Doped Carbon Foams for Supercapacitors and CO2 Capture

Hierarchically porous carbon materials are promising for energy storage,separation and catalysis.It is desirable but fairly challenging to simultaneously create ultrahigh surface areas,large pore volumes and high N contents in these materials.Herein,we demonstrate a facile acid-base enabled in situ molecular foaming and activation strategy for the synthesis of hierarchically macro-/meso-/microporous N-doped carbon foams(HPNCFs).The key design for the synthesis is the selection of histidine(His)and potassium bicarbonate(PBC)to allow the formation of 3D foam structures by in situ foaming,the PBC/His acid-base reaction to enable a molecular mixing and subsequent a uniform chemical activation,and the stable imidazole moiety in His to sustain high N contents after carbonization.The formation mechanism of the HPNCFs is studied in detail.The prepared HPNCFs possess 3D macroporous frameworks with thin well-graphitized carbon walls,ultrahigh surface areas(up to 3200 m^2 g^-1),large pore volumes(up to 2.0 cm^3 g^-1),high micropore volumes(up to 0.67 cm^3 g^-1),narrowly distributed micropores and mesopores and high N contents(up to 14.6 wt%)with pyrrolic N as the predominant N site.The HPNCFs are promising for supercapacitors with high specific capacitances(185-240 F g^-1),good rate capability and excellent stability.They are also excellent for CO2 capture with a high adsorption capacity(~4.13 mmol g^-1),a large isosteric heat of adsorption(26.5 kJ mol^-1)and an excellent CO2/N2 selectivity(~24).

A host-guest approach to fabricate metallic cobalt nanoparticles embedded in silk-derived N-doped carbon fibers for efficient hydrogen evolution

Hydrogen evolution reaction(HER) plays a key role in generating clean and renewable energy. As the most effective HER electrocatalysts, Pt group catalysts suffer from severe problems such as high price and scarcity. It is highly desirable to design and synthesize sustainable HER electrocatalysts to replace the Pt group catalysts. Due to their low cost, high abundance and high activities, cobalt-incorporated N-doped nanocarbon hybrids are promising candidate electrocatalysts for HER. In this report, we demonstrated a robust and eco-friendly host-guest approach to fabricate metallic cobalt nanoparticles embedded in N-doped carbon fibers derived from natural silk fibers. Benefiting from the onedimensional nanostructure, the well-dispersed metallic cobalt nanoparticles and the N-doped thin graphitized carbon layer coating, the best Cobased electrocatalyst manifests low overpotential(61 mV@10 mA/cm^2) HER activity that is comparable with commercial 20% Pt/C, and good stability in acid. Our findings provide a novel and unique route to explore high-performance noble-metal-free HER electrocatalysts.

An integrated strategy towards the facile synthesis of core-shell SiC-derived carbon@N-doped carbon for high-performance supercapacitors

Porous active core-shell carbon material with excellent synergistic effect has been regarded as a prospective material for supercapacitors.Herein,we report an integrated method for the facile synthesis of carbide-derived carbon(CDC)encapsulated with porous N-doped carbon(CDC@NC)towards highperformance supercapacitors.Polydopamine(PDA)as nitrogen and carbon sources was simply coated on SiC nanospheres to form SiC@PDA,which was then directly transformed into CDC@NC via a onestep molten salt electro-etching/in-situ doping process.The synthesized CDC@NC with hierarchically porous structure has a high specific surface area of 1191 m^(2) g^(-1).The CDC core and NC shell are typical amorphous carbon and more ordered N-doped carbon,respectively.Benefitting from its unique dual porous structures,the CDC@NC demonstrates high specific capacitances of 255 and 193 F g^(-1) at 0.5 and20 A g^(-1),respectively.The reaction mechanism of the electro-etching/in-situ doping process has also been investigated through experimental characterizations and theoretical density functional theory calculations.It is suggested that the molten salt electro-etching/in-situ doping strategy is promising for the synthesis of active core-shell porous carbon materials with synergistic properties for supercapacitors without the need for additional doping/activation processes.

Pyridinic nitrogen enriched porous carbon derived from bimetal organic frameworks for high capacity zinc ion hybrid capacitors with remarkable rate capability

Aqueous zinc ion hybrid capacitors(ZIHCs)hold great potential for large-scale energy storage applications owing to their high safety and low cost,but suffer from low capacity and energy density.Herein,pyridinic nitrogen enriched porous carbon(nPC)was successfully synthesized via the growth,subsequent annealing and acid etching of bimetal organic frameworks for high capacity and safe ZIHCs with exceptional rate capability.Benefiting from the mesopores for easy ion diffusion,high electrical conductivity enabled by in-situ grown carbon nanotubes matrix and residual metal Co nanoparticles for fast electron transfer,sufficient micropores and high N content(8.9 at%)with dominated pyridinic N(54%)for enhanced zinc ion storage,the resulting nPC cathodes for ZIHCs achieved high capacities of 302 and137 m Ah g^(-1) at 1 and 18 A g^(-1),outperforming most reported carbon based cathodes.Theoretical results further disclosed that pyridinic N possessed larger binding energy of-4.99 eV to chemically coordinate with Zn2+than other N species.Moreover,quasi-solid-state ZIHCs with gelatin based gel electrolytes exhibited high energy density of 157.6 Wh kg^(-1) at 0.69 kW kg^(-1),high safety and mechanical flexibility to withstand mechanical deformation and drilling.This strategy of developing pyridinic nitrogen enriched porous carbon will pave a new avenue to construct safe ZIHCs with high energy densities.

Cobalt and nitrogen codoped porous carbon as superior bifunctional electrocatalyst for oxygen reduction and hydrogen evolution reaction in alkaline medium

Cobalt and nitrogen codoped carbon materials(Co-N-C) were fabricated by pyrolysis of the mixture of poly(4-vinylpyridine) and cobalt chloride using SiO_2 nanoparticles as hard template, which were the first transition metal/nitrogen-codoped carbon bifunctional electrocatalyst derived from noncarbonizable polymer for ORR and HER. The as-made Co-N-C possessed hierarchical pore structure and high specific surface area, achieving excellent electrocatalytic performances for ORR and HER. Its ORR catalytic performances were comparable to those of Pt/C catalyst and its HER catalytic performances were superior to those of most doped carbon catalysts in KOH electrolyte. Moreover, its bifunctional electrocatalytic performances for ORR and HER were better than those of most bifunctional doped carbon catalysts in alkaline electrolyte.

Porous nitrogen-doped carbon/MnO coaxial nanotubes as an efficient sulfur host for lithium sulfur batteries

As a promising candidate for next generation energy storage devices, lithium sulfur (Li-S) batteries still confrant rapid capacity degradation and low rate capability. Herein, we report a well-architected porous nitrogen-doped carbon/MnO coaxial nanotubes (MnO@PNC) as an efficient sulfur host material. The host shows excellent electron conductivity, sufficient ion transport channels and strong adsorption capability for the polysulfides, resulting from the abundant nitrogen-doped sites and pores as well as MnO in the carbon shell of MnO@PNC. The MnO@PNC-S composite electrode with a sulfur content of 75 wt.% deliveries a specific capacity of 802 mAh·g^-1 at a high rate of 5.0C and outstanding cycling stability with a capacity retention of 82% after 520 cycles at 1.0C.

S-enriched porous polymer derived N-doped porous carbons for electrochemical energy storage and conversion

Porous polymers have been recently recog- nized as one of the most important precursors for fabrication of heteroatom-doped porous carbons due to the intrinsic porous structure, easy available heteroatom- containing monomers and versatile polymerization meth- ods. However, the heteroatom elements in as-produced porous carbons are quite relied on monomers. So far, the manipulating of heteroatom in porous polymer derived porous carbons are still very rare and challenge. In this work, a sulfur-enriched porous polymer, which was prepared from a diacetylene-linked porous polymer, was used as precursor to prepare S-doped and/or N-doped porous carbons under nitrogen and/or ammonia atmo- spheres. Remarkably, S content can sharply decrease from 36.3% to 0.05% after ammonia treatment. The N content and specific surface area of as-fabricated porous carbons can reach up to 1.32% and 1508 m^2·g^-1, respectively. As the electrode materials for electrical double-layer capacitors, as-fabricated porous carbons exhibit high specific capacitance of up to 431.6 F·g^-1 at 5 mW·s^-1 and excellent cycling stability of 99.74% capacitance retention after 3000 cycles at 100 mV·s^-1. Furthermore, as the electro- chemical catalysts for oxygen reduction reaction, as- fabricated porous carbons presented ultralow half-wave- potential of 0.78 V versus RHE. This work not only offers a new strategy for manipulating S and N doping features for the porous carbons derived from S-containing porous polymers, but also paves the way for the structure- performance interrelationship study of heteroatoms co- doped porous carbon for energy applications.

Preparation of nitrogen doped clews-like carbon materials and their application as the electrode in supercapacitor

In this work, nitrogen doped clews-like carbon materials were successfully fabricated through hydrothermal polymerization method, followed by post treatment that integrated the carbonization,activation and post-nitrogen doping into one process. This preparation method can form particular hierarchical porous structure without using any sacrificial templates. The experimental results show that the nitrogen doped clews-like hierarchical porous carbon materials possess a relatively high specific surface area of 815 m^2/g with the nitrogen content of 10.58 at%. The electrochemical properties show that the resulting sample delivers 258 F/g at a 0.5 A/g and excellent capacity retention of 79% at 20 A/g. After conducting 10,000 charge-discharge cycles at 10 A/g, the capacitance retention of 98.3% is achieved.These intriguing results demonstrate that the obtained nitrogen doped clews-like carbon materials will be promising electrode materials for supercapacitor and other energy storage devices.

Advanced non-precious electrocatalyst of the mixed valence CoO_x nanocrystals supported on N-doped carbon nanocages for oxygen reduction

Taking advantage of the nitrogen(N)-participation and large surface area of N-doped carbon nanocages(NCNCs),the Co Ox nanocrystals are conveniently immobilized onto the NCNCs with high dispersion.The Co Ox/NCNCs hybrid exists in the mixed valence with predominant Co O over Co3O4 and demonstrates superb oxygen reduction reaction activity and stability remaining^94%current density even after operation over 100 h.These results suggest a promising strategy to develop advanced electrocatalysts with the novel NCNCs or even beyond.

钴掺杂氮碳材料的制备及其在氧还原反应方面的应用

将三聚氰胺和Co的硝酸盐均质化混合后在N2氛围下热处理,使用H_(2)O_(2)对材料刻蚀后制得一种钴掺杂氮碳材料。经过扫描电镜、X射线衍射分析、X射线光电子能谱分析等测试显示材料为一种碳纳米管结构。电化学性能测试显示催化剂氧还原反应主要依靠四电子反应。线性扫描伏安测试显示半坡电位为832 mV,但是其功率密度为6.0 m A·cm^(-2),显示出该催化剂的氧还原能力,其抗甲醇能力和稳定性也优于商业化的Pt/C催化剂。

一锅法合成高性能N掺杂的Co(PO_(3))_(2)@C负极材料及其在超级电容器中的应用

以植酸(PA)、三聚氰胺(MA)、四水合乙酸钴(Co(OAc)_(2)·4H_(2)O)和聚偏氟乙烯(PVDF)中空纤维膜为原料,采用一锅法合成了偏磷酸钴和氮(N)掺杂碳(C)的复合材料(Co(PO_(3))2@C).其中,PA属于六齿配体,拥有6个磷酸基,每个磷酸基中的氧原子(O)都可作为配位原子和钴离子发生络合反应,形成化学性质稳定的络合物,可以作为绿色磷(P)源.MA含有丰富的N元素,PVDF中空纤维膜中含有氟(F)元素,同时还可以提供框架结构,N和F元素的掺杂可以使多孔碳材料具有更好的润湿性,有利于电解液中电子的传输,从而极大提高了材料的电化学电容性能.所制备的最佳活性负极材料在1 A·g^(-1)时的比电容为1 067.42 F·g^(-1).即使在10 A·g^(-1)的电流密度下,20 000次循环后,仍可以达到85.79%的保留率.

钴掺杂氮化碳传感器电化学检测牛奶中双酚A

电化学检测具有简便、快速、准确、灵敏度高等诸多优势,而其高效电极材料的研发则是关键。本文以三聚氰胺和CoCl2·6H2O为原料,通过煅烧法制备了钴掺杂氮化碳(Co-C3N4)复合材料,并将其作为电极传感器以用于不同牛奶样品中双酚A的检测。结果表明,所合成的Co-C3N4复合材料呈现多孔的层状堆叠结构,比表面积较大,而金属Co的引入有效抑制了C3N4的热聚合,且产物晶体结构没有发生显著变化,基本框架保持良好;Co-C3N4电极传感器在纯牛奶样品(巴氏杀菌奶和超高温瞬时灭菌奶)中均未检测到双酚A(BPA),其加标回收率达到81.86%~98.75%,RSDs为3.34%~3.57%,与常规高效液相色谱检测法相比,本文方法在低浓度范围内(0.0μmol/L~15.0μmol/L)具有更高的回收率和灵敏度,且BPA检出限可达3.7nmol/L。研究表明所合成的电极传感器抗干扰性强,适用于牛奶样品的BPA检测。

氮磷共掺杂碳点的合成及其对Co^(2+)的检测

以葡萄糖为碳源,通过乙二胺与浓磷酸中和放热碳化法合成氮磷共掺杂的荧光碳点,采用元素分析、TEM、FTIR、XPS、UV-vis和PL等分析测试技术对氮磷共掺杂碳点的形貌、结构、组成和光学性质进行了表征。实验结果表明,通过氮磷共掺杂得到的碳点不仅能增强其水溶性和光学稳定性,而且能有效提高碳点的量子产率。研究发现,Co2+能强烈猝灭氮磷共掺杂碳点的荧光,且Co2+浓度在0. 005～0. 250mmol·L-1范围内时与氮磷共掺杂碳点荧光的猝灭程度呈良好的线性关系,检出限为0. 6μmol·L-1。因此,建立了一种检测Co2+的荧光传感方法,该方法具有简单、快速、选择性高等优点。