Electrochemical Polymerization of Aniline at Low Supporting-Electrolyte Concentrations and Characterization of Obtained Films

Conductive polymers of aniline were synthesized in aqueous acidic media such as perchloric, sulfuric, hydrochloric, phosphoric, and trifluoroacetic acids and the effect of supporting electrolyte was investigated. The conductivity of each polyaniline (PAn) sample was determined by the four-probe technique. PAn (H₂SO₄) sample was shown to have the highest conductivity, specifically, 3.55 S cm^–1. The effect of concentrations of monomers and acids on the conductivity of PAn's was studied. It was observed that the conductivity decreased with increasing aniline concentration and increased with increasing sulfuric acid concentration. The conductivities of PAn (CF₃COOH) were also investigated in different supporting electrolytes and highly good increments of its conductivities were obtained. Magnetic properties of the PAn salts were analyzed by Gouy balance measurements and it was found that their conducting mechanisms are of bipolaron nature. From the FTIR analysis it was found that polymerization occurs via the –NH₂ group in a head-to-tail mechanism. The thermal analyses revealed that PAn (HCl) among the PAn salts studied shows the highest thermal stability. Surface analyses of polymers were clarified by scanning electron microscopy. From elemental analysis results, PAn salts were concluded to be in emeraldine structure.     

电化学联用表面等离子体共振光谱法对苯胺电化学聚合过程的研究

采用双光电池传感器作为检测器件,设计并构建了新型表面等离子体共振( SPR)光谱仪,在一定范围内实现了SPR角度的快速测量。将此SPR光谱仪与电化学工作站联用,构建了电化学联用-时间分辨SPR ( EC-TR-SPR)光谱仪,以聚苯胺电化学制备过程为研究体系,验证了此EC-TR-SPR光谱仪的特性。同时通过对聚苯胺膜的暂态电化学方法测试(计时电流法和差分脉冲法),考察了仪器的时间分辨能力及其响应速度,验证了此仪器系统在小分子反应动力学以及稳态和暂态电化学联用方法研究中的应用价值。实验结果表明,此SPR光谱仪具有高的时间分辨能力,其时间分辨率可达0.1 ms;对聚苯胺膜的暂态电化学测试结果表明,此联用技术可实时监测SO2-4在聚苯胺膜中的掺杂和去掺杂过程,而单纯的电化学电流-时间曲线无法区分。     

Preparation and Electrochemical Properties of Tin–Iron–Carbon Nanocomposite as the Anode of Lithium‐Ion Batteries

Tin–iron–carbon nanocomposite is successfully prepared by a sol–gel method followed by a chemical vapor deposition (CVD) process with acetylene gas as the carbon source. The structural properties, morphology, and electrochemical performances of the nanocomposite are comprehensively studied in comparison with those properties of tin–carbon and iron–carbon nanocomposites. Sheet‐like carbon architecture and different carbon contents are induced thanks to the catalytic effect of iron during CVD. Among three nanocomposites, tin–iron–carbon demonstrates the highest reversible capacity of 800 mA h g^?1 with 96.9 % capacity retention after 50 cycles. It also exhibits the best rate capability with a discharge capacity of 420 mA h g^?1 at a current density of 1000 mA g^?1. This enhanced performance is strongly related to the carbon morphology and content, which can not only accommodate the large volume change, but also improve the electronic conductivity of the nanocomposite. Hence, the tin–iron–carbon nanocomposite is expected to be a promising anode for lithium‐ion batteries.     

Temperature‐Responsive Polymer/Carbon Nanotube Hybrids: Smart Conductive Nanocomposite Films for Modulating the Bioelectrocatalysis of NADH

A temperature‐sensitive polymer/carbon nanotube interface with switchable bioelectrocatalytic capability was fabricated by self‐assembly of poly(N‐isopropylacrylamide)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PNIPAm) onto the PNIPAm‐modified substrate. Electron microscopy and electrochemical measurements revealed that these fairly thick (>6 μm) and highly porous nanocomposite films exhibited high conductivity and electrocatalytic activity. The morphological transitions in both the tethered PNIPAm chains on a substrate and those polymers wrapping around the MWNT surface resulted in the opening, closing, or tuning of its permeability, and simultaneously an electron‐transfer process took place through the channels formed in the nanostructure in response to temperature change. By combining the good electron‐transfer and electrochemical catalysis capabilities, the large surface area, and good biocompatibility of MWNTs with the responsive features of PNIPAm, reversible temperature‐controlled bioelectrocatalysis of 1,4‐dihydro‐β‐nicotinamide adenine dinucleotide with improved sensitivity has been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The mechanism behind this approach was studied by Raman spectroscopy, in situ attenuated total reflection FTIR spectroscopy, and contact angle measurements. The results also suggested that the synergetic or cooperative interactions of PNIPAm with MWNTs gave rise not only to an increase in surface wettability, but also to the enhancement of the interfacial thermoresponsive behavior. This bioelectrocatalytic “smart” system has potential applications in the design of biosensors and biofuel cells with externally controlled activity. Furthermore, this concept might be proposed for biomimetics, interfacial engineering, bioelectronic devices, and so forth.     

Conducting poly(aniline) nanotubes and nanofibers: controlled synthesis and application in lithium/poly(aniline) rechargeable batteries

The primary aim of this work was to synthesize aligned perchloric-acid-doped poly(aniline) (HClO(4)-doped PANI) nanotubes by a simple alumina template method and to investigate their application in lithium/poly(aniline) rechargeable batteries. Powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) analysis were used to characterize the nanostructures obtained. The second aim addressed the preparation of HClO(4)-doped PANI microspheres and nanofibers on a large scale through a modified spraying technique, since the template synthesis has limitations in mass production. The present synthesis methods are simple and can be extended to the preparation of a broad range of one-dimensional conductive polymers. Furthermore, electrochemical measurements showed that the as-prepared HClO(4)-doped PANI nanotubes exhibit better electrode performances than their commercial counterparts because they possess more active sites, higher conductivity, and relative flexibility. This indicates that HClO(4)-doped poly(aniline) nanomaterials are promising in the application of lithium/polymer rechargeable batteries.     

Composite PET Membrane with Nanostructured Ag/AgTCNQ Schottky Junctions: Electrochemical Nanofabrication and Charge‐Transfer Properties

Large‐area nanostructured Ag/Ag‐tetracyanoquinodimethane (TCNQ) Schottky junctions are fabricated electrochemically on a mesoporous polyethylene terephthalate (PET) membrane‐supported water/1, 2‐dichloroethane (DCE) interface. When the interface is polarized, Ag⁺ ions transfer across the PET membrane from the aqueous phase and are reduced to form metallic Ag on the PET membrane, which reacts further with tetracyanoquinodimethane (TCNQ) in the DCE phase to form nanostructured Ag/AgTCNQ Schottky junctions. Once the mesoporous membrane is blocked by metallic Ag, a bipolar mechanism is proposed to explain the successive growth of AgTCNQ nanorods and Ag film on each side of the PET membrane. Due to the well‐formed nanostructure of Ag/AgTCNQ Schottky junctions, the direct electrochemical behavior is observed, which is essential to explain the physicochemical mechanism of its electric performance. Moreover, the composite PET membrane with nanostructured Ag/AgTCNQ Schottky junctions is tailorable and can be assembled directly into electric devices without any pretreatment.     

Facile Fabrication of Nanoparticles Confined in Graphene Films and Their Electrochemical Properties

The development of novel nanostructured electrode materials with high performance and based on abundant elements is a key element in the societal pursuit of sustainable energy. Graphene‐based structures with rich macroporosity and high conductive networks are promising components to develop novel electrode materials. Herein, we described a facile procedure to confine Ni(OH)₂ particles in a graphene film, leading to a new sandwich‐like hybrid structure. The hybrid film offers simultaneously ordered ion diffusion channels and high electrical conductivity, which facilitate the improvement of both electrode kinetics and electrochemical stability, thus leading to high capacitance, fast rate capability, and stable cycle life as supercapacitor materials. This work provides a facile pathway for optimized structures for electrode materials, and represents a benefit for the global issues of energy shortage and environmental pollution.     

Ionic Ingress and Charge‐Neutralization Phenomena of Conducting‐Polymer Films

Ionic ingress and diffusion through a conducting‐polymer (CP) film containing embedded charges under potential and concentration gradients is studied. Electroneutrality, a common assumption in modeling of similar systems, is not justified in this case or similar diffusion‐limited processes, as the timescale of ionic diffusion in the solid matrix is quite large. Counter ions therefore cannot move instantaneously for effective neutralization of excess charges. Poisson–Nernst–Planck (PNP) equations have to be solved for such cases without any simplifying assumption. Analytical solution shows the existence of a charge boundary layer, which limits and strongly influences the ionic flux. A general numerical method for solution is also developed for the dynamic modeling, analysis, and design of these types of systems. The numerical results are validated by comparison with analytical solutions as well as with some experimental results available in the literature. With this modeling framework, the basic features of controlled release of molecules across a CP film under an applied electrical potential can be explained quantitatively.     

Influence of Polymer Electronics on Selective Dispersion of Single‐Walled Carbon Nanotubes

The separation and isolation of semiconducting and metallic single‐walled carbon nanotubes (SWNTs) on a large scale remains a barrier to many commercial applications. Selective extraction of semiconducting SWNTs by wrapping and dispersion with conjugated polymers has been demonstrated to be effective, but the structural parameters of conjugated polymers that dictate selectivity are poorly understood. Here, we report nanotube dispersions with a poly(fluorene‐co‐pyridine) copolymer and its cationic methylated derivative, and show that electron‐deficient conjugated π‐systems bias the dispersion selectivity toward metallic SWNTs. Differentiation of semiconducting and metallic SWNT populations was carried out by a combination of UV/Vis‐NIR absorption spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and electrical conductivity measurements. These results provide new insight into the rational design of conjugated polymers for the selective dispersion of metallic SWNTs.     

Electrochemical Synthesis of Perfluorinated Ion Doped Conducting Polyaniline Films Consisting of Helical Fibers and their Reversible Switching between Superhydrophobicity and Superhydrophilicity

Superhydrophobic conducting polyaniline (PAni) films were electrochemically deposited in acetonitrile‐H₂O electrolyte containing aniline monomer and perfluorooctanesulfonic (PFOS) acid. The films exhibited an extended network structure composed of helical PAni sub‐micron fibers. The helical fibrous structure is thought to form through a supermolecular templating process. The surface of the PFOS‐doped PAni films showed a water contact angle of 153°. Reducing the PFOS‐doped PAni (in emeraldine salt form) by negative potential led to de‐doped PAni films (in leucoemeraldine base form) which were superhydrophilic (water contact angle close to 0°). By controlling the electrical potential, PAni films were changed between the doped state and de‐doped state, resulting in reversibly switchable superhydrophobic and superhydrophilic surfaces.

     

Relationship between Carbon Nanotube Structure and Electrochemical Behavior: Heterogeneous Electron Transfer at Electrochemically Activated Carbon Nanotubes

The electrochemical activation of multiwalled carbon nanotubes (MWCNTs) (at potentials of 1.5–2.0 V vs Ag/AgCl for 60–360 s) results in significantly increased rate constants ( ) for heterogeneous electron‐transfer with [Fe(CN)₆]^3?/4? (from 8.34×10^?5 cm s^?1 for as‐received MWCNTs to 3.67×10^?3 cm s^?1 for MWCNTs that were electrochemically activated at 2.0 V for 180 s). The increase in the value of arises from the introduction of wall defects exposing edge planes of the MWCNTs, as observed by high‐resolution TEM. The density of the edge plane defects increases from almost zero (for as‐received MWCNTs) to 3.7 % (for MWCNTs electrochemically activated at 2.0 V for 180 s). High‐resolution X‐ray photoelectron spectroscopy (HR‐XPS), Raman spectroscopy, and electrochemical impedance spectroscopy were used to gain a better understanding of the phenomena. HR‐XPS revealed that the increase in electrochemical activation potential increases the number of oxygen‐containing groups on the surface of carbon nanotubes.     

Chemical Solution Deposition of Epitaxial Metal‐Oxide Nanocomposite Thin Films

Epitaixial metal‐oxide nanocomposite films, which possess interesting multifunctionality, have found applications in a wide range of devices. However, such films are typically produced by using high‐vacuum equipment, like pulse‐laser deposition, molecular‐beam epitaxy, and chemical vapor deposition. As an alternative approach, chemical solution methods are not only cost‐effective but also offer several advantages, including large surface coating, good control over stoichiometry, and the possible use of dopants. Therefore, in this Personal Account, we review the chemistry behind several of the main solution‐based approaches, that is, sol‐gel techniques, metal‐organic decomposition, chelation, polymer‐assisted deposition, and hydrothermal methods, including the seminal works that have been reported so far, to demonstrate the advantages and disadvantages of these different routes.     

Preparation of Polymer‐Metal Composites via In Situ Decomposition of Metal Salts by Frontal Polymerization

Composites containing powdered zinc, and zinc/lead acetate were prepared via frontal polymerization. In the case of the acetates, elemental metal was formed in an in situ decomposition process. The local area function was used to demonstrate the distribution of fillers, and the uniformity of the area fraction for the quantitative characterization of the distribution. With the use of metal acetates, composites of uniform metal distribution can be produced, unlike in systems with metal powder, where the metal particles are enriched at the margin of the sample. It can be established that the specific direct‐current resistance significantly decreases in AA‐TGDMA composites by the addition of zinc acetate, compared to that of the initial monomer mixture. On heating, the unreacted zinc acetate decomposes further, which results in the further decrease in electrical resistance.