Controllable‐Nitrogen Doped Carbon Layer Surrounding Carbon Nanotubes as Novel Carbon Support for Oxygen Reduction Reaction

Novel nitrogen‐doped carbon layer surrounding carbon nanotubes composite (NC‐CNT) (N/C ratio 3.3–14.3 wt.%) as catalyst support has been prepared using aniline as a dispersant to carbon nanotubes (CNTs) and as a source for both carbon and nitrogen coated on the surface of the CNTs, where the amount of doped nitrogen is controllable. The NC‐CNT so obtained were characterized with scanning electron microscopy (SEM), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and nitrogen adsorption and desorption isotherms. A uniform dispersion of Pt nanoparticles (ca. 1.5–2.0 nm) was then anchored on the surface of NC‐CNT by using aromatic amine as a stabilizer. For these Pt/NC‐CNTs, cyclic voltammogram measurements show a high electrochemical activity surface area (up to 103.7 m² g^–1) compared to the commercial E‐TEK catalyst (55.3 m² g^–1). In single cell test, Pt/NC‐CNT catalyst has greatly enhanced catalytic activity toward the oxygen reduction reaction, resulting in an enhancement of ca. 37% in mass activity compared with that of E‐TEK.     

Carbon nanotube/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composite for air electrode of lithium-air battery

A carbon nanotube [CNT]/Co₃O₄ composite is introduced as a catalyst for the air electrode of lithium-air [Li/air] batteries. Co₃O₄ nanoparticles are successfully attached to the sidewall of the CNT by a hydrothermal method. A high discharge capacity and a low overvoltage indicate that the CNT/Co₃O₄ composite is a very promising catalyst for the air electrode of Li/air batteries.     

Ethynedithiol‐based polyeneoligosulfides as active cathode materials for lithium‐sulfur batteries

Ethynedithiol‐based polyeneoligosulfides have been synthesized in 96% yield by the reaction of sodium acetylides (HC?CNa, NaC?CSNa) and elemental sulfur through the Na? C_sp bond in liquid ammonia with the following spontaneous polymerization of ethynedithiols (HSC?CSH) formed by the hydrolysis. The polyeneoligosulfides synthesized are brown powders (up to 77% sulfur content, mp 128–184°C), partially soluble in organic solvents. They are high‐resistance semiconductors (10^?13 to 10^?14 S cm^?1), possess paramagnetic (10¹⁷ to 10¹⁸ spin g^?1) and redox properties. The oligosulfides obtained, being redox systems capable of reversible redox processes, provide high values of discharge capacity (345–720 mA h g^?1) of rechargeable lithium‐sulfur batteries. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mass‐Production of Electrospun Carbon Nanofiber Containing SiOx for Lithium‐Ion Batteries with Enhanced Capacity

In this study, electrospun carbon nanofibers hybridized with silicon oxide (SiO_x) are prepared by using a syringeless electrospinning system of polyacrylonitrile (PAN) solution containing tetraethylorthosilicate (TEOS) via a sequential pyrolysis process. The syringeless electrospinning system provides a large number of composite nanofibers in a short time, and the obtained composite nanofibers exhibit uniform diameter and morphology. The composite nanofiber is converted into a carbon nanofiber containing SiO_x via a simple pyrolysis. The obtained SiO_x‐carbon nanofiber mat exhibits higher charge/discharge capacity than a general carbon nanofiber, and it provides more stable retention than single crystalline silicon materials. Thus, the mass‐production of a SiO_x‐carbon nanofiber from syringeless electrospinning is a promising method to produce anodic materials for Li‐ion batteries.     

Nonstoichiometry and Li‐ion transport in lithium zirconate: The role of oxygen vacancies

Understanding Li‐ion migration mechanisms and enhancing Li‐ion transport in Li₂ZrO₃ (LZO) is important to its role as solid absorbent for reversible CO₂ capture at elevated temperatures, as ceramic breeder in nuclear reactors, and as electrode coating in high‐voltage lithium‐ion batteries (LIBs). Although defect engineering is an effective way to tune the properties of ceramics, the defect structure of LZO is largely unknown. This study reports the defect structure and electrical properties of undoped LZO and a series of cation‐doped LZOs: (i) depending on their charge states, cation dopants can control the oxygen vacancy concentration in doped LZOs; (ii) the doped LZOs with higher oxygen vacancy concentrations exhibit better Li⁺ conductivity, and consequently faster high‐temperature CO₂ absorption. In fact, the Fe (II)‐doped LZO shows the highest Li‐ion conductivity reported for LZOs, reaching 3.3 mS/cm at ~300°C that is more than 1 order of magnitude higher than that of the undoped LZO.     

Highly efficient removal of bulky tannic acid by millimeter‐sized nitrogen‐doped mesoporous carbon beads

Millimeter‐sized nitrogen‐doped mesoporous carbon beads (NMCBs) with a controllable nitrogen content are synthesized for the first time via a suspension‐polymerization assisted hard templating method. In contrast to conventional activated carbons, NMCBs exhibit outstanding structural advantages, including macroscopic morphology, a developed mesoporous structure and enriched surface chemistry. When used as adsorbents for the removal of the bulky organic pollutant tannic acid, these NMCBs demonstrated fast adsorption kinetics and very high adsorption capacity. The adsorption capacity strongly depends on the nitrogen content doped into the carbon framework. At a nitrogen content of 4.1 wt %, the adsorption capacity reaches 318 mg g^?1. The molecular mechanics simulation and zeta potential measurements suggest that the enhanced adsorption by nitrogen doping may be due to the electrostatic attraction between the nitrogen functional groups and the phenol groups of tannic acid. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3016–3025, 2017     

Electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) fiber‐based polymer electrolytes for lithium‐ion batteries

Novel single‐ion conducting polymer electrolytes based on electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) (PAMPSLi) membranes were prepared for lithium‐ion batteries. The preparation started with the synthesis of polymeric lithium salt PAMPSLi by free‐radical polymerization of 2‐acrylamido‐2‐methylpropanesulfonic acid, followed by ion‐exchange of H⁺ with Li⁺. Then, the electrospun PAMPSLi membranes were prepared by electrospinning technology, and the resultant PAMPSLi fiber‐based polymer electrolytes were fabricated by immersing the electrospun membranes into a plasticizer composed of ethylene carbonate and dimethyl carbonate. PAMPSLi exhibited high thermal stability and its decomposition did not occur until 304°C. The specific surface area of the electrospun PAMPSLi membranes was raised from 9.9 m²/g to 19.5 m²/g by varying the solvent composition of polymer solutions. The ionic conductivity of the resultant PAMPSLi fiber‐based polymer electrolytes at 20°C increased from 0.815 × 10^?5 S/cm to 2.12 × 10^?5 S/cm with the increase of the specific surface area. The polymer electrolytes exhibited good dimensional stability and electrochemical stability up to 4.4 V vs. Li⁺/Li. These results show that the PAMPSLi fiber‐based polymer electrolytes are promising materials for lithium‐ion batteries. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High Active Hollow Nitrogen‐Doped Carbon Microspheres for Oxygen Reduction in Alkaline Media

Dopamine, a sustainable and cheap raw material, was selected as the carbon and nitrogen sources to synthesize hollow nitrogen‐doped carbon microspheres (HNCMS). The obtained HNCMS were used as a non‐noble‐metal electrocatalyst for oxygen reduction in alkaline solution and show high electrocatalytic activity, excellent long‐term stability, and tolerance to crossover effect of methanol.     

Improved specific capacity of sulfur/starch‐based activated carbon spheres composites by polyaniline‐based carbon encapsulation strategy

Lithium‐sulfur battery is one of the most promising electrochemical energy storage systems because of its high theoretical specific capacity and energy density. When carbon materials are used for immobilizing sulfur, the technical challenge is designing their framework to relieve the shuttle effect of polysulfides intermediates and the volume change of sulfur, and to improve the conductivity of sulfur. Herein, polyaniline‐based carbon (PANI‐C) coated corn starch‐based activated carbon spheres (ACS@PANI‐C) was prepared and used as hosts of sulfur, which can effectively combine the advantages of physical entrapment and chemical binding interactions of sulfur species. The results of electrochemical performance test indicate that S/ACS@PANI‐C composites exhibit much better electrochemical performance than S/ACS composites. Its reversible capacities at 320, 480, 800 and 1600 mA g^?1 are 687, 582, 504 and 393 mAh g^?1, respectively. The improved electrochemical performance can be attributed to the PANI‐C which can also act as a flexible cushion to accommodate volume changes of sulfur cathode as well as a barrier to trap soluble polysulfide intermediates during the charge–discharge process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46544.     

Wormhole-like mesoporous magnesium oxide fabricated by surfactant templating method to enhance cycling performance of lithium-sulfur batteries

Lithium-sulfur (Li–S) batteries are considered to have the best development prospect for electric vehicles. But enhancing the cycling performance of Li–S batteries is necessary and urgent. Mesoporous MgO particles (MMgO) are prepared by surfactant templating method and used to prepare cathode materials for the first time. The prepared MMgO has a hexagonal flake-like structure with a thickness of 50–80 nm, a transverse length of 150–350 nm, a processing area of 181.56 m²/g, an average pore diameter of 3.11 nm and a pore volume of 0.26 cc/g. MMgO shows low intensity and slightly broader diffraction peaks in the XRD pattern, indicating the presence of lattice distortion, defects, dislocations or unsaturated valence bonds. MMgO particles are uniformly distributed on the sulfur surface to provide high surface area, many active sites and interconnected channel structure, which makes more sulfur contact with MMgO to be adsorbed, activated and participated in charge and discharge reaction. The Li–S battery containing sulfur/MMgO composite at weight ratio 90:10 shows the best cyclic stability with capacity retention rate 84.7% after 100 cycles at 0.2 C. The initial specific capacity of a Li–S battery with sulfur/MMgO composite at weight ratio 70:30 can reach 1062 mAh/g at 0.2 C, which is much higher than sulfur/commercial MgO at the same weight ratio.     

Gradually anchoring sulfur into in-situ doped carbon substrate as cathode for Li–S batteries with excellent wide-temperature performance

Carbon spheres, prepared by hydrothermally treating fresh potato starch, is employed as the sulfur host to configure a high-performance cathode substrate candidate for Li–S batteries. As confirmed by experimental results, both the improved the rate and cycle performances of Li–S batteries cathode with gradient sulfur immobilization, are mainly attributed to the confining, adsorption and conduction multi-functions of as-prepared carbon spheres toward polysulfides. Specifically, on starting the discharging/charging cycles, the active material α-S₈ is irreversibly converted to polysulfides and then transformed between β-S₈ and polysulfides during the next charge/discharge cycles. After initialization at 0.1C for 3 cycles, the initial reversible discharge capacities of the Li–S batteries cathode with optimized sulfur amount are 1072.5, 831.3, 780.4, 726.8, 714.3, 702.7 mAh g^?1_sulfur at 0.1, 0.5, 1, 2, 3 and 4 C, which is superior to those of the most previously reported reports. Besides that, as-designed potato-derived carbon based composite cathodes exhibits remarkable rate performance and cycling stability even at wide temperature ranging from ?40 to 60 °C, which evidently supports the dominant role of as-prepared 3D carbon spheres in boosting the cathode performance for Li–S batteries.     

Carbon nanotube array anodes for high-rate Li-ion batteries

The electrochemical performance of carbon nanotube array (CNTA) and entangled carbon nanotube (ECNT) electrodes are studied as anodes for Li-ion batteries. CNTA anodes display higher capacity (373 mAh g⁻¹) and much better rate and cycle performances than ECNT anodes. The performance of CNTA electrode shows length dependencies, i.e., shorter CNTA electrodes present higher specific capacity and better rate performance. The energy storage characteristics of CNTA electrodes are discussed on the basis of experimental results of SEM, TEM, and Raman spectra. The inner graphene layers of CNTs in CNTA electrode, which can form electron conductive paths and ensure a high conductivity, are retained during Li-ion insertion/extraction. These mechanically robust inner graphene layers can avoid the loss of outer active materials during Li-ion insertion/extraction, which, in turn, results in a good cycle performance.     

Sulfonated poly(sulfone‐pyridine‐amide)/sulfonated polystyrene/multiwalled carbon nanotube‐based fuel cell membranes

In this study, aromatic sulfonated poly(sulfone‐pyridine‐amide) (S‐PSPA) has been prepared via polycondensation of sulfonated monomer 1‐(4‐thiocarbamoylaminophenyl‐sulfonylphenyl)thiourea and 2,6‐pyridinedicarboxylic acid at high temperature. Mechanically robust and thermally stable hybrid membranes were prepared using non‐functional and functional multiwalled carbon nanotube (MWCNT) i.e., S‐PS/S‐PSPA/MWCNT‐NF and S‐PS/S‐PSPA/MWCNT via solution blending. Field emission scanning electron microscopy exhibited porous membrane structure for 0.1–0.5 wt% nanotube loading, whereas well‐aligned functional MWCNT were observed in 1 wt% loaded sample. Increasing the functional nanotube content from 0.1 to 1 wt% increased tensile strength of functional S‐PS/S‐PSPA/MWCNT hybrids from 62.19 to 65.29 MPa compared with non‐functional hybrid (53.34 MPa) and neat S‐PS/S‐PSPA. 10% decomposition temperature of S‐PS/S‐PSPA/MWCNT 0.1–1 was in the range 491–502°C, while S‐PS/S‐PSPA/MWCNT‐NF showed relatively lower thermal stability (T₁₀ 489°C). Glass transition temperature of functional S‐PS/S‐PSPA/MWCNT was also higher (201–243°C) relative to S‐PS/S‐PSPA/MWCNT‐NF (194°C). Furthermore, functional MWCNT‐based membranes had higher ion exchange capacity (IEC) 3.2–3.6 mmol/g and lower activation energies (95–36 kJ/mol). Novel functional membranes also revealed high proton conductivity 1.68–2.55 S/cm in a wide range of humidity at 80°C higher than that of perfluorinated Nafion® membrane (1.1 ×10^?1 S/cm) at 80°C (94% RH). POLYM. ENG. SCI., 55:1776–1786, 2015. © 2014 Society of Plastics Engineers     

纳米管壁数对氮掺杂碳纳米管氧还原反应活性的影响

通过预氧化和氨水水热法在含有不同壁数的碳纳米管表面成功引入含氮基团，从而获得了氮掺杂碳纳米管（NCNT），并研究了纳米管壁数对不同NCNT氧还原反应活性的影响。研究表明，各NCNT中氮元素的含量和含氮基团的种类相似，但不同含氮基团的比例则相差较大，其中平均壁数为2.5的NCNT样品含有最低的吡啶氮和石墨氮比例，而该样品却展现出最高的电子转移数和最大的氧还原反应极限扩散电流。分析表明，NCNT的氧还原反应活性决定于纳米管壁数，而不是吡啶氮和石墨氮活性基团的比例，即NCNT的内壁为反应电荷的转移提供了有效导电途径，并通过隧穿效应将电子转移到外壁，而外壁的含氮基团活性位点得到电子从而将O₂转变为OH^-。随着NCNT壁数的增加，NCNT中电子隧穿效应减弱，NCNT的氧还原反应（ORR）活性也随之降低。     

Construction of hierarchical yolk-shell structured Mn3O4@NC as efficient sulfur hosts for Li–S batteries

The high theoretical capacity and abundant reserves of sulfur makes Li–S batteries a promising candidate for future energy-storage devices. However, the low electrical conductivity of sulfur and severe polysulfides dissolution and migration hinder it practical application. To address the problems, we design a hierarchical yolk-shell structure with polar metal oxide Mn₃O₄ yolks and N-doped carbon shells as sulfur host. The N-doped carbon shell enhances the conductivity and provide physical confinement to polysulfides while the Mn₃O₄ yolks have strong chemical bonding effect with polysulfides. Besides, the sufficient void space in yolk-shell structure can ensure a high sulfur loading content (80%) as well as accommodate severe volume change of sulfur during lithiation. Benefiting from these merits, the yolk-shell Mn₃O₄@NC/S electrode exhibit a high capacity of 581 mAh g^-1 at 1 C and enhanced cycling stability with a capacity retain of 84% over 300 cycles at 0.5 C, which is superior to yolk-shell Mn₃O₄@NC/S with more Mn₃O₄ residual and N-doped carbon shells/S without Mn₃O₄ inside.     

Hollow C/Co9S8 hybrid polyhedra-modified carbon nanofibers as sulfur hosts for promising Li–S batteries

Lithium-sulfur (Li–S) batteries hold great expectations as next-generation advanced capacity storage devices due to their higher theoretical energy density and low cost. Even so, polysulfide shuttles, insulation, and volume expansion of sulfur impede its commercial progress. To suppress these problems, we used electrospinning and self-templating to construct C/Co₉S₈ hybrid polyhedra-modified carbon nanofibers (denoted as C/Co₉S₈–C@S fibers) as sulfur hosts. The quasi-metallic polar Co₉S₈ strongly bonds and locks polysulfides, and the hollow polyhedra provide sulfur storage space. Moreover, the overall nanofiber forms an interconnected conductive network to assist the transmission of Li⁺/e⁻ and restrain the escape of the sulfur phase to a certain extent. Compared with C/Co₉S₈ polyhedra and carbon nanofibers, the C/Co₉S₈–C@S fiber delivers excellent adsorption characteristics for polysulfides. As a Li–S battery cathode, the C/Co₉S₈–C@S fiber (sulfur content: 87.20 wt%) exhibits an initial specific capacity of 1013.7 mAh g⁻¹ at 0.1 C, displaying a stable capacity of 694.9 mAh g⁻¹ after 150 cycles. Additionally, it shows a high specific capacity of 894.7 mAh g⁻¹ at 1C with a capacity decay of ~0.116% per cycle over 500 cycles.     

The Complexation between Amide Groups of Polyamide‐6 and Polysulfides in the Lithium–Sulfur Battery

Lithium–sulfur batteries have attracted considerable attention due to its high theoretical specific capacity, low cost, environmental friendliness, etc. However, the dissolution of polysulfide intermediate in the electrolyte leads to rapid capacity decay in the charge–discharge process. A sulfur‐based cathode with the specific discharge capacity of 630 mAh g⁻¹ and ultrahigh capacity retention ratio of 0.11% per cycle after 400 cycles at 0.5 C that simply blend the sublimed sulfur and acetylene black in the mortar with the polyamide‐6 (PA6) as binder is reported. The intense complexation between the lithium polysulfide and amide groups ( CO NH ) in PA6 can effectively inhibit the “shuttling effect” and reduce the loss of active materials during the charge–discharge process. The discovery provides a handy and practicable strategy for developing the excellent cycling stability lithium–sulfur batteries.

     

Continuous amino-functionalized University of Oslo 66 membranes as efficacious polysulfide barriers for lithium−sulfur batteries

The shuttle effect of soluble polysulfides is a serious problem impeding the development of lithium−sulfur batteries. Herein, continuous amino-functionalized University of Oslo 66 membranes supported on carbon nanotube films are proposed as ion-permselective interlayers that overcome these issues and show outstanding suppression of the polysulfide shuttle effect. The proposed membrane material has appropriately sized pores, and can act as ionic sieves and serve as barriers to polysulfides transport while allowing the passage of lithium ions during electrochemical cycles, thereby validly preventing the shuttling of polysulfides. Moreover, a fast catalytic conversion of polysulfides is also achieved with the as-developed interlayer. Therefore, lithium−sulfur batteries with this interlayer show a desirable initial capacity of 999.21 mAh·g^–1 at 1 C and a durable cyclic stability with a decay rate of only 0.04% per cycle over 300 cycles. Moreover, a high area capacity of 4.82 mAh·cm^–2 is also obtained even under increased sulfur loading (5.12 mg·cm^–2) and a lean-electrolyte condition (E/S = 4.8 μL·mg^–1).     

Identifying the Catalytic Active Sites in Heteroatom‐Doped Graphene for the Oxygen Reduction Reaction

Density functional theory (DFT) calculations can be used to help elucidate the structures of active sites on the surface of fuel cell cathode catalysts, which are exceptionally difficult to identify by experimental techniques. The cathode catalysts were modeled in nitrogen‐, boron‐, sulfur‐, and phosphorus‐doped graphene basal planes. Dually‐doped graphene structures combining nitrogen with phosphorus or sulfur are also studied. Potential energy profiles were obtained, and the energies and activation barriers of molecular oxygen binding to the doped graphene model structures were estimated in order to identify potentially active sites for the oxygen reduction reaction in fuel cells. Among the investigated doped graphene structures, the active sites for molecular oxygen chemisorption are identified in graphene doped with either two nitrogen, or two phosphorus, or one sulfur and one phosphorus atoms. Further, the analysis of atomic spin densities and charges in the model structures enables the correlation of the catalytic activity with electron density distribution.     

Lithium–sulfur batteries with activated carbons derived from olive stones

A lithium–sulfur battery, using activated carbon obtained from olive stones as the sulfur host, is reported. The microporous texture allows large amounts of sulfur to be infiltrated into the host (sulfur loading 80%). The resulting composite material possesses a high capacity, about 670 mA h g⁻¹, excellent capacity retention on cycling and good rate capability. We believe that activated carbons derived from biomass could be an alternative source for the preparation of the cathode for Li–S batteries.