聚合物发光电化学池的研究——中国科学院有机固体重点实验室导电聚合物电化学研究工作简介(Ⅱ)

简要介绍本研究组 1997年以来在聚合物发光电化学池 (LEC)研究中取得的一些成果,包括发光聚合物的电化学性质及其HOMO和LUMO能级的电化学测量,LECp i n结的交流阻抗分析,双功能嵌段共聚物LEC,以及咪唑盐离子液体掺杂的室温准冷冻p i n结LEC等.     

High resolution scanning optical imaging of a frozen planar polymer light-emitting electrochemical cell: an experimental and modelling study

Light-emitting electrochemical cells(LECs) are organic photonic devices based on a mixed electronic and ionic conductor.The active layer of a polymer-based LEC consists of a luminescent polymer,an ion-solvating/transport polymer,and a compatible salt.The LEC p-n or p-i-n junction is ultimately responsible for the LEC performance.The LEC junction,however,is still poorly understood due to the difficulties of characterizing a dynamic-junction LEC.In this paper,we present an experimental and modeling study of the LEC junction using scanning optical imaging techniques.Planar LECs with an interelectrode spacing of 560μm have been fabricated,activated,frozen and scanned using a focused laser beam.The optical-beam-induced-current(OBIC)and photoluminescence(PL) data have been recorded as a function of beam location.The OBIC profile has been simulated in COMSOL that allowed for the determination of the doping concentration and the depletion width of the LEC junction.     

Lithium-ion batteries based on vertically-aligned carbon nanotube electrodes and ionic liquid electrolytes

In conjunction with environmentally benign ionic liquid electrolytes, vertically-aligned carbon nanotubes (VA-CNTs) sheathed with and without a coaxial layer of vanadium oxide (V(2)O(5)) were used as both cathode and anode, respectively, to develop high-performance and high-safety lithium-ion batteries. The VA-CNT anode and V(2)O(5)-VA-CNT cathode showed a high capacity (600 mAh g(-1) and 368 mAh g(-1), respectively) with a high rate capability. This led to potential to achieve a high energy density (297 Wh kg(-1)) and power density (12 kW kg(-1)) for the prototype batteries to significantly outperform the current state-of-the-art Li-ion batteries.     

Ionic liquids for soft functional materials with carbon nanotubes

A serendipitous finding that ionic liquids gel with carbon nanotubes has opened a new possibility of ionic liquids as modifiers for carbon nanotubes. Upon being ground into ionic liquids, carbon nanotube bundles are untangled, and the resultant fine bundles form a network structure. This is due to the possible specific interaction between the imidazolium ion component and the pi-electronic nanotube surface. The resultant gelatinous materials, consisting of highly electroconductive nanowires and fluid electrolytes, can be utilized for a wide variety of electrochemical applications, such as sensors, capacitors, and actuators. Ionic liquids allow for noncovalent and covalent modifications of carbon nanotubes and fabrication of polymer composites with enhanced physical properties. The processing of carbon nanotubes with ionic liquids is not accompanied by the disruption of the pi-conjugated nanotube structure and does not require solvents; therefore it can readily be scaled up. This article focuses on new aspects of ionic liquids for designer soft materials based on carbon nanotubes.     

Identifying and alleviating electrochemical side-reactions in light-emitting electrochemical cells

We demonstrate that electrochemical side-reactions involving the electrolyte can be a significant and undesired feature in light-emitting electrochemical cells (LECs). By direct optical probing of planar LECs, comprising Au electrodes and an active material mixture of {poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) + poly(ethylene oxide) (PEO) + KCF3SO3}, we show that two direct consequences of such a side-reaction are the appearance of a "degradation layer" at the negative cathode and the formation of the light-emitting p-n junction in close proximity to the cathode. We further demonstrate that a high initial drive voltage and a high ionic conductivity of the active material strongly alleviate the extent of the side reaction, as evidenced by the formation of a relatively centered p-n junction, and also rationalize our findings in the framework of a general electrochemical model. Finally, we show that the doping concentrations in the doped regions at the time of the p-n junction formation are independent of the applied voltage and relatively balanced at approximately 0.11 dopants/MEH-PPV repeat unit in the p-type region and approximately 0.15 dopants/MEH-PPV repeat unit in the n-type region.     

Simple and fast fluorimetric determination of the critical gel concentration of soft nanomaterials

Soft materials or gels are new interesting materials resulting from the combination of carbon nanotubes with ionic liquids. However, it should be noted that not all ionic liquid/carbon nanotubes combinations lead to the formation of gels. In fact, this requires using an optimum concentration of CNTs known as “critical gel concentration” (CGC) in the mixture. Up to now, this critical concentration has been determined by means of rheological measurements or by observing a change of a physical property in the new material such as density. On the basis of the high stability of gels in solvents, owing to the presence of carbon nanotubes, this paper reports for the first time a simple and fast method to determine the critical gel concentration for the formation of soft materials by means of fluorescence measurements. We have determined the critical gel concentration of four gels obtained by the combination of three different types of multi walled carbon nanotubes and one single walled carbon nanotubes with the ionic liquid 1-hexyl 3-methylimidazolium hexafluorophosphate. The main characteristics of carbon nanotubes and gels resulting of them were established by Raman spectroscopy. The proposed methodology is presented as an alternative to traditional complex rheological measurements.     

Preparation of a polyacetylene composite with single-walled carbon nanotubes and study of its electrochemical properties

A composite consisting of single-walled carbon nanotubes (2.4 wt %) covered by polyacetylene has been prepared. Polyacetylene synthesized directly on single-walled carbon nanotubes is a defectless long-chain polymer composed of trans and cis units with a sufficient length (60% trans and 40% cis isomers). An appreciable acceleration of the lithium ion intercalation-deintercalation corresponds to an increase in the conductivity of the composite material near the percolation threshold. The polyacetylene layer on single-walled carbon nanotubes plays the role of an electrochemically active ion-conductive membrane suitable for the transport of Li⁺ cations to the surface of nanotubes.     

Quasi-solid-state dye-sensitized solar cell based on a polymer gel electrolyte with in situ synthesized ionic conductors

A polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors was prepared for fabricating a quasi-solid-state dye-sensitized solar cell (QS-DSSC). The in situ synthesized Acac-Py-I₂ ionic conductors show weaker influence on the liquid electrolyte absorbency of the polymer gel electrolyte than that of Acac-Py-I₂ ionic conductors dissolved in liquid electrolyte. Owing to the higher liquid electrolyte absorbency, the polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors shows higher ionic conductivity than that of polymer gel electrolyte with Acac-Py-I₂ ionic conductors absorbed from liquid electrolyte. QS-DSSC containing the polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors shows 3.815% energy conversion efficiency, which is 21.6% higher than that of QS-DSSC containing polymer gel electrolyte with Acac-Py-I₂ ionic conductors absorbed from liquid electrolyte.     

The use of methylcellulose for the synthesis of Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>/C composites

The key parameters related to cathode materials for commercial use are a high specific capacity, good cycling stability, capacity retention at high current rates, as well as the simplicity of the synthesis process. This study presents a facile synthesis of a composite cathode material, Li₂FeSiO₄ with carbon, under extreme conditions: rapid heating, short dwell at 750 °C and subsequent quenching. The water-soluble polymer methylcellulose was used both as an excellent dispersing agent and a carbon source that pyrolytically degrades to carbon, thereby enabling the homogeneous deployment of the precursor compounds and the control of the Li₂FeSiO₄ particle growth from the earliest stage of processing. X-ray powder diffraction reveals the formation of Li₂FeSiO₄ nanocrystallites with a monoclinic structure in the P2₁/n space group (#14). The composite’s electrochemical performance as a cathode material in Li-ion batteries was examined. The influence of the amount of methylcellulose on the microstructural, morphological, conductive, and electrochemical properties of the obtained powders has been discussed. It has been shown that the overall electrochemical performance is improved with an increase of carbon content, through both the decrease of the mean particle diameter and the increase of electrical conductivity.     

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.     

Asymmetric double-layer composite electrolyte with enhanced ionic conductivity and interface stability for all-solid-state lithium metal batteries

All-solid-state Li metal battery has been regarded as a promising battery technology due to its high energy density based on the high capacity of lithium metal anode and high safety based on the all solid state electrolyte without inflammable solvent.However,challenges still exist mainly in the poor contact and unstable interface between electrolyte and electrodes.Herein,we demonstrate an asymmetric design of the composite polymer electrolyte with two different layers to overcome the interface issues at both the cathode and the anode side simultaneously.At the cathode side,the polypropylene carbonate layer has enough viscosity and flexibility to reduce the inter-facial resistance,while at the Li anode side,the polyethylene oxide layer modified with hexagonal boron nitride has high mechanical strength to suppress the Li dendrite growth.Owing to the synergetic effect between different components,the asprepared double layer composite polymer electrolyte demonstrates a large electrochemical window of5.17 V,a high ionic conductivity of 6.1×10~(-4) S/cm,and a transfe rence number of 0.56,featuring excellent ion transport kinetics and good chemical stability.All-solid-state Li metal battery assembled with LiFePO_4 cathode and Li anode delivers a high capacity of 150.9 mAh/g at 25℃ and 0.1 C-rate,showing great potential for practical applications.     

Active layer of fuel cell electrode with polymer electrolyte: Modeling of support grains, calculation of overall cathode characteristics

The active layer of the cathode of a fuel cell with polymer electrolyte (Nafion) is considered. The optimum carbon support structure is constructed using computer simulation: its carbon “skeleton” possesses the maximum outer surface area and provides electronic conductivity of the grains, support cubes, along the three coordinate axes. Nafion is absent in the support grain, so that the grain is capable of participating only in the transport of oxygen molecules, it possesses no proton conductivity. An estimate of all parameters of an optimum support grain is provided; in particular, the value of the effective Knudsen diffusion coefficient of oxygen is established. After this, effective proton conductivity and effective Knudsen diffusion coefficient are calculated already on the whole active layer scale, according to the model of equally sized cube grains of three types. In conclusion, the overall current in the active layer of a cathode with a polymer electrolyte was calculated for the percolation cluster consisting only of Nafion grains and the Knudsen diffusion of oxygen created only by a combined gas percolation cluster consisting of void grains and all support grains. The overall current value for t = 80°C and pressure of p* = 101 kPa proved to be low, hundreds of mA/cm². The current value can apparently be increased to several A/cm² if the support grains are developed that would simultaneously possess both proton conductivity and ability to sustain oxygen diffusion.     

A Nitrogen‐Rich 2D sp2‐Carbon‐Linked Conjugated Polymer Framework as a High‐Performance Cathode for Lithium‐Ion Batteries

A two‐dimensional (2D) sp²‐carbon‐linked conjugated polymer framework (2D CCP‐HATN) has a nitrogen‐doped skeleton, a periodical dual‐pore structure and high chemical stability. The polymer backbone consists of hexaazatrinaphthalene (HATN) and cyanovinylene units linked entirely by carbon–carbon double bonds. Profiting from the shape‐persistent framework of 2D CCP‐HATN integrated with the electrochemical redox‐active HATN and the robust sp² carbon‐carbon linkage, 2D CCP‐HATN hybridized with carbon nanotubes shows a high capacity of 116 mA h g^?1, with high utilization of its redox‐active sites and superb cycling stability (91 % after 1000 cycles) and rate capability (82 %, 1.0 A g^?1 vs. 0.1 A g^?1) as an organic cathode material for lithium‐ion batteries.     

Catalytic fire retardant nanocomposites

In this paper the chemical activity of carbon nanotubes and polyhedral oligomeric silsesquioxane during thermal degradation and combustion of polymer nanocomposites is addressed. Indeed, polymer-nanofiller systems may exhibit chemical effects capable of thermal stabilisation of polymers as well as reduction of combustion rate and heat released, owing to catalytic effects induced by the nanofillers at high temperature.Carbon nanotubes in the presence of oxygen are shown to promote oxidative dehydrogenation in polyethylene with production of a stable surface layer of carbon char that provides an effective oxygen barrier effect. A similar action is performed by metal-containing polysilsesquioxanes dispersed in polypropylene.With either carbon nanotubes or metal POSS, partial carbonisation of the polymer matrix occurs during combustion, subtracting part of the organic polymer from combustion, targeting one of the major fire retardancy aim.     

An Ionic Molecular Glass as Electron Injection Layer for Efficient Polymer Light‐Emitting Diode

An ionic molecular glass based on a dendronized monoammonium salt has been facilely synthesized and utilized as an interfacial electron‐injection layer in a light‐emitting diode (LED). The characterization of a yellow‐green LED that involves an Al cathode and a thin layer of the new compound spin cast from a methanol solution has shown device performances comparable to those obtained with a Ba/Al cathode. Photovoltaic measurements under white light irradiation reveal that a thin layer of the new compound can significantly increase the built‐in potential and thus facilitate electron injection from an Al cathode. Furthermore, it is interesting to observe that the new ionic salt could undergo reorganization on the emissive conjugated polymer layer, which leads to the formation of nearly uniform nanoaggregates.

     

Synthesis of Multishell Carbon Nanotube Composites via Template Method

Multishell nanotubes of polyaniline and carbon were synthesized via a template approach. A thin layer of MnO₂ coated on carbon nanotubes acts as a reactive template for the consequent formation of the polyaniline coating. The polyaniline-carbon nanotubes show enhanced dispersibility in water and can be possibly used as a functional material of electrochemical capacitors with improved performance. The general method operates by coating carbon nanotubes on functional materials such as poly (3,4-ethylenedioxythiophene), polypyrrole, silica, and carbon.     

Surface initiated ring-opening polymerization of l-proline N-carboxy anhydride from single and multi walled carbon nanotubes

Ring-opening surface initiated polymerization of l-proline N-carboxyanhydride was performed from amine functionalized single (SWNTs) and multi walled carbon nanotubes (MWNTs). The primary amines were grafted on the surfaces via a well-studied Diels–Alder cycloaddition. The initiator attachment helped the debundling of carbon nanotubes as shown by atomic force microscopy (AFM) studies where only small aggregates were observed. Thermogravimetric analysis revealed high wt% of grafted polyproline on the carbon nanotubes surface after the ring-opening polymerization. AFM studies showed a rather uniform layer of grafted polyproline from both MWNTs and SWNTs. The grafting of PLP on the surface was also verified by FTIR and Raman spectroscopy as well as ¹H NMR in CDCl₃/d-TFA. The polyproline grafted carbon nanotubes (CNTs) were readily dissolved in organic solvents in contrast to the insoluble pristine and amine-functionalized CNTs.     

EFFECT OF DISPERSED PHASE PARTICLES ON ELECTRICAL CONDUCTION OF PEO-NaSCN

Fast ionic conductors are one kind of solid state material with ionic conductivity as high as that of melten salts or liquid electrolytes.Ionic conductivity is one of the important parameters for characterizing a fast ionic conductor.For a long time materialists and chemists have made great efforts in search of new fast ionic conductors with high ionic conductivity.In view of structure,they have synthesised silver and copper fast ionic conductors with so called open structures.But it is not so successful for searching more applicable alkaline fast ionic conductors.Since polymer has flexibility for making thin film,it concentrates attention on the polymer-alkaline salt complex.Fenton et al.have first reported poly(ethylene oxide) (PEO)-alkaline salt complex.Later on Armard et al.have investigated the electrical property of PEO-NaSCN.     

纳米碳材料在可穿戴柔性导电材料中的应用研究进展

可穿戴设备的兴起使得对柔性器件的需求日益提高,柔性导电材料作为可穿戴器件的重要组成部分而成为研究的热点。传统的电极材料主要是金属,因金属材料本身不具有柔性,一般通过降低金属层厚度以及设计波纹结构等策略实现其在柔性器件中的应用,其加工程序复杂,成本较高。以碳纳米管和石墨烯为代表的纳米碳材料兼具良好的柔性和优异的导电性,且具有化学稳定、热稳定、光学透明性等优点,在柔性导电材料领域展现了极大的应用潜力。本文简要综述了近年来纳米碳材料在柔性导电材料领域的研究进展,首先介绍了碳纳米管基柔性导电材料,分别包括基于碳纳米管水平阵列、碳纳米管垂直阵列、碳纳米管薄膜、碳纳米管纤维的柔性导电材料;继而介绍了石墨烯基柔性导电材料,包括基于剥离法制备的石墨烯和化学气相沉积法制备的石墨烯以及石墨烯纤维基柔性导电材料;并简述了碳纳米管/石墨烯复合柔性导电材料;最后论述了纳米碳材料基柔性导电材料所面临的挑战并展望了其未来发展方向。