Electrostatic synthesis and electrochemical properties of a composition comprising ultrathin layers of silicododecamolybdate anions and poly(allyl ammonium) cations

A layer-by-layer (LbL) composition comprising ultrathin anionic layers of silicododecamolybdate and cationic layers of poly(allyl ammonium) is synthesized. The synthesis is realized by means of successive immersion of a glassy-carbon rod into aqueous sulfuric acid solutions of silicododecamolybdic acid and poly(allyl ammonium) hydrochloride. Cyclic voltammetry shows that the silicododecamolybdate anion in the composition undergoes three steps of reversible reduction with formal potentials of 0.34, 0.22, and 0.02 V (SCE). It is established that in the course of synthesis one can obtain a sixfold increase in the currents of redox conversions as compared with currents of a monolayer of the anion chemisorbed on glassy carbon. The LbL composition exhibits catalytic activity during electrochemical reduction of NO ₂ ^? : the cathodic current of the third redox transition considerably increases and the peak in the reverse run of a cyclic voltammogram disappears. The calculated Michaelis constant of 5 × 10^?2 M speaks of a high catalytic activity of the electrode.     

Anion-Dependent Redox Chemistry of p-Type Poly(vinyldimethylphenazine) Cathode Materials

Metal-free organic electrode materials have attracted vast research attention owing to their designable structures and tunable electrochemical properties. Although n-type cathode materials could be used in various metal-ion batteries, p-type ones with high potential can deliver high energy density. Herein, we report a new p-type polymeric cathode material, poly(2-vinyl-5,10-dimethyl-dihydrophenazine) (PVDMP), with a theoretical capacity of 227 mAh g⁻¹. PVDMP featuring two-step redox reaction will be doped by two anions to maintain electroneutrality during oxidation, which resulted in an anion-dependent electrochemical behavior of PVDMP-based cathode. The suitable dopant anion for PVDMP was selected and the doping mechanism was confirmed. Under the optimized condition, PVDMP cathode can deliver a high initial capacity of 220 mAh g⁻¹ at 5 C and even remains 150 mAh g⁻¹ after 3900 cycles. This work not only provides a new kind of p-type organic cathode materials but also deepens the understanding of its anion-dependent redox chemistry.     

A combined electrochemical quartz-crystal microbalance probe beam deflection (EQCM-PBD) study of solvent and ion transfers at a poly

The oxidative polymerisation of the complex2,3-dimethyl-N,N'-bis-(salicylidene)butane-2,3-diaminatonick-el(II), [Ni(saltMe)], was monitored by the electrochemical quartz microbalance (EQCM) and crystal impedance techniques. Polymerisation efficiency was maintained throughout deposition of a film, which behaved rigidly, on the electrode. A combined EQCM-PBD (probe beam deflection) study of the redox process of the film exposed to a monomer-free solution of 0.1 M tetraethylammonium perchlorate (TEAP) in acetonitrile showed an electroneutrality mechanism dominated by anion movement accompanied by co-transfer of solvent above 0.8 V. The individual contributions of all the mobile species involved in the redox switching of the poly[Ni(saltMe)] film were determined quantitatively by temporal convolution analysis; the estimated solution-phase diffusion coefficient of the exchanged species was 1.24 x 10(-5) cm2s-1.     

Electrochemistry and electrochromic properties of phenanthroline-iron(II/III) complex films

New films of the iron complexes with bis((2-hydroxyphenyl)methylaminosulfonyl)bathophenanthroline(HPBP) and bis((2-aminophenyl)methylaminosulfonyl)bathophenanthroline(APBP) ligands are prepared on the electrode surfaces by electrochemical polymerization. The resulting film-coated electrode shows a well-defined reversible voltammogram corresponding to the redox reaction of the Fe(II/III) complexes and an electrochromic change from red(absorption maximum: 540 nm) to colorless. The response rate of the color change to a potential step was found to be correlated to the apparent diffusion coefficient(Dapp) for the homogeneous charge-transport process within the film. The Dapp values estimated are (3-4) × 10⁻⁹cm²s⁻¹ for the [Fe(APBP)₃] film and(1-2) × 10⁻⁸cm²s⁻² for the [Fe(HPBP)₃] film, respectively, by potential-step chronoamperometric and chronocoulometric methods. The result of electrochemical quartz crystal microbalance(EQCM) measurements⁴) and dependence of the formal potential of the metal complex of the Fe(II/III) redox couple with activity of the supporting electrolyte anion in NaClO₄ aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement⁴⁾ of the poly[Fe(APBP)₃] coated quartz crystal electrode showed that the viscosity of the film is affected by the oxidation state of iron.     

Electrochemical impedance studies of the undoping process of platinum phthalocyanine charge transfer microcrystals

Platinum phthalocyanine (PtPc) microcrystal films undergo three successive electrochemical oxidations. Each of these processes is associated with anion insertion or doping. The reverse process of anion insertion, undoping, has been investigated using electrochemical impedance spectroscopy and in-situ UV–vis spectroscopy. The impedance theory of conductive polymer films developed by Vorotyntsev et al. is applicable to this process. The kinetics of the undoping process depend upon the previous oxidative treatment, and thus the doping level. Three different states of the film can be demarcated, depending on the degree of oxidation (and thus the degree of doping) of the PtPc film. These are called the lightly doped, the conductive and the over-doped state, respectively. For lightly doped films, the film conductivity, the redox capacitance, the diffusion coefficient for charge transport and the rate of electrochemical reaction all decrease with decreasing potential. The film conductivity depends upon the concentration of free charge carriers. For the more highly doped conductive film, all of the above parameters are greatly enhanced, and the electrochemical reaction is accelerated and proceeds at a very high rate. The potential dependence of the redox capacitance and the diffusion coefficient depends on the type of anion. During undoping at 0 V, unusually high diffusion coefficients with a magnitude of order 10⁻² cm² s⁻¹ are observed and are attributed to the strong interactions between the electronic and ionic carriers during the phase transformation. For the over-doped film, undoping leads to an increase in the film conductivity and electrochemical reaction rate. The potential dependence of the redox capacitance and diffusion coefficients for charge transport implies strong interactions within the film. Hypsochromic shifts in UV–vis spectra with decreasing potential indicate conformational relaxation during the undoping process. SEM investigation confirms that the doped film swells during the de-doping process.     

PREPARATION, CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES OF POLYPYRROLE-POLYSTYRENE SULFONIC ACID COMPOSITE FILM

Polypyrrole-polystyrene sulfonic acid (PPy-PSSA) composite films have been electrosynthesized in an aqueous solution of PSSA. The electro-active films exhibit cation exchange during the redox process. Infrared, Raman and energy-dispersive spectroscopic results demonstrated that the polyanion of PSS^- is co-deposited into the PPy matrix and couldn‘t be stripped from the film extensively by dedoping. The doping level together with dipolaron content of the PPy-PSSA composite film increases during electrochemical polymerization process. SEM images revealed that the composite film has smooth and compact morphology and AFM pictures suggested that PPy chains are possibly grown perpendicular to the electrode surface. TGA tests indicated that the composite films has much better thermal stability than that of pure PPy.Furthermore, electrochemical studies showed that the relaxation process at certain holding potential has great effect on the shape of the cyclic voltammetric curves of PPy-PSSA composite film. The composite film exhibits cation and anion exchange during the redox process after undergoing the relaxation step. It is more difficult for divalent anion to enter the polymer matrix than a univalent ion, and a large cation such as (CH3CH2CH2CH2)4N^ cannot be involved in the ion exchange process.     

Polymer-based bilayer interfaces for electrochemical rectification

In this paper, the electrochemical current rectification phenomenon exhibited at an electrochemical interface constituted by a glassy carbon electrode covered with a bilayer of polymer films is discussed. The authors have shown that Methylene Blue (MB) redox species can be confined to a very thin insulating polymer film formed from orthophenylene diamine. The poly(opd) film exhibited excellent blocking properties to redox molecules in solution. On the other hand, the insulating poly(opd) film trapped with MB could mediate electron transfer between the redox molecules in solution and the electrode. Further, a second polymeric layer (Nafion film) trapped with ferrocene redox species was formed as the outer layer over the inner poly (opd) film containing MB. This bilayer-modified electrode, due to the significant difference in the redox potentials of the MB and ferrocene species immobilized in the inner and outer layers, respectively, exhibits unidirectional current flow and the results of the voltammetric investigations on the modified electrodes are described in this communication.     

EQCM studies on polypyrrole in aqueous solutions

Electrochemical quartz crystal microbalance (EQCM) studies revealed that the electrochemical properties of polypyrrole (PPY) in aqueous solutions are greatly dependent on the solution pH. A PPY film immersed in an aqueous KCl solution shows redox processes which involve not only anion transport but also cation transport if the solution pH is greater than 3–4, whereas at lower pH values only anion transport prevails as has been widely recognized. It has been found from comparative studies using poly(N-methylpyrrole) that protonation and deprotonation at nitrogen atoms of PPY play a key role in the observed pH-dependent electrochemical behavior. Deprotonated PPY allows transient incorporation of hydrated cations upon reduction in weak alkaline aqueous solutions, followed by slow ejection of the incorporated cations when conventional electrolytes such as KCl and NaClO₄ are used, but not in NH₄Cl solution. Discussion on the cation transport in PPY is made in terms of deprotonation and protonation of nitrogen atoms of pyrrole subunits in PPY.     

Electrochemical behavior of polypyrrole/ kodak aq composite polymeric films

The anodic polymerization of pyrrole (P) onto glassy carbon in an aqueous solution of the Kodak-AQ poly(ester sulfonic acid) polyelectrolyte gives a PP/AQ composite film. While incorporated as charge compensators during the anodic growth of PP, the entangled AQ⁻ chains cannot easily diffuse out upon reduction. The composite layer, resulting from such unique use of AQ ionomers (as electrolyte and dopant) possesses the features of both its conducting polymer and cation exchanger components. These include effective loading of hydrophobic cations, potential switch effect or permselective response. For example, the uptake of Ru(bpy)²⁺₃ by the AQ anion, residing in the conducting polymer, is facilitated by an electrochemical event (reduction of the film to PP⁰/AQ⁻). Similarly, the redox switchable PP component offers electrochemical control of the release of loaded cations. These and other attractive properties of PP/AQ composite layers are explored by cyclic voltammetry, chronocoulometry, potentiometry and flow injection amperometry.     

Redox monomer ionic liquid based on quaternary ammonium: From electrochemistry to polymer brushes

Bifunctional quaternary ammonium ionic liquid bearing redox and polymerisable units was synthesized. The electrochemical investigations of the ferrocene monomer ionic liquid were performed. Following that, surface-initiated atom transfer radical polymerization (SI-ATRP) was used to build polymer brushes onto the electrode surface. The presence of the Poly(ferrocenyl quaternary ammonium) was evidenced by surface and electrochemical analysis. The latter exhibits high electron transfer rate and the presence of ions within the polymer framework leads to record the attached ferrocenyl redox signal in solution without adding supporting electrolyte. Finally, the wettability of the surface was modulated by electrochemical switch and by anion exchange within the polymer.     

Electrostatic layer-by-layer deposition and electrochemical characterization of thin films composed of MnO2 nanoparticles in a room-temperature ionic liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.     

电化学石英晶体微天平研究六氰亚铁铜膜修饰电极及其离子效应

利用电化学石英晶体微天平（EQCM）手段，结合循环伏安法．计时电流法对六氰亚铁铜（CuHCF)膜修饰电极及其在不同水溶液中的离子交换机制进行了研究。结果表明；通过循环伏安法，在Pt电极上可以牢固地形成CuHCF膜．在氧化还原过程中，不仅是阳离子，阴离子也参与了在CuHCF膜中的传输。     

Azulene-substituted aromatic amines. synthesis and amphoteric redox behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine and their derivatives

[reaction: see text] N,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine (2a) and their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b) were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic amines for multistage amphoteric redox materials. The redox behavior of each compound was characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene ring including the central nitrogen atoms. UV-vis spectral analysis of amines 1a,b and diamines 2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption bands of the neutral species along with an increase of the new absorption maxima at 625, 605, 640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562, 478, and 545 nm, respectively. As indicated by a combined ESR and UV-vis spectral study, the species giving rise to the new absorption maxima are concluded to be the generation of anion radicals and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.     

Electrochemical and electrocatalytic stability of Prussian blue/Berlin green redox transformation in Prussian blue-polypyrrole composite films

Redox transformation of Prussian blue to Berlin green (PB/BG) in Prussian blue-polypyrrole (PB-PPy) composites synthesized via original one-step method has been studied. It was shown that the nature of anion and composition of background electrolyte play an important role for both the stability and the shape of electrochemical response of composite film during redox transfer of Prussian blue to Berlin green. Nitric acid, phosphoric acid, malic acid and citric acid 0.05 N (eq/L) solutions and the same acids partially neutralized with 0.01 N KOH were used as electrolyte to study the role of potassium ions presence in solution. The most stable electrochemical response of PB/BG redox transfer was obtained for the nitrate anions containing solutions in the presence of potassium ions. Nevertheless, the stability of the electrochemical transformation PB/BG in composite films in other media is enough to detect the sulphite ions content in wine samples via electrocatalytic reaction at the potentials of PB/BG redox transformation.

     

Halogen-Bonding Strapped Porphyrin BODIPY Rotaxanes for Dual Optical and Electrochemical Anion Sensing

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. ¹H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P^+. redox couple.     

Monitoring formation of poly(neutral red) film by EQCM

An electrochemical quartz crystal microbalance (EQCM) is employed for monitoring the growth of poly(neutral red) films on platinum in the electrolytic solution containing 5.0 mmol dm⁻³ neutral red, 0.3 mol dm⁻³ H₂SO₄, and 0.5 mol dm⁻³ Na₂SO₄. The in situ measurement of the frequency changes of the EQCM reveals that both the adsorption/desorption of neutral red and the formation of poly(neutral red) film can be observed together with anion sorption/desorption during the redox transformation of the polymer, and that the polymerization rate of neutral red increases slowly before the 11th cycle and then increases quickly with increasing number of potential cycles. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 284–289. The text was submitted by the authors in English.     

阴离子硫氧化还原与Li1-xNiO2-ySy的结构稳定性:第一性原理研究

Ni-rich layered oxides are the preferred cathode materials for high-energy-density lithium-ion batteries currently used in electric vehicles. In this paper, we present a systematic first-principles evaluation of the deintercalation process in the Li_1-xNiO_2-yS_y. The partial density of states (PDOS) characters of the electrons near the Fermi level, redox behaviors, and thermal stability have been investigated within the GGA+U scheme. The results show that the introduction of sulfur alleviates the lattice distortion during charging, suppresses nickel migration, and enhances the stability of oxygen according to the contribution of sulfur anion redox to the charge compensation for the overcharged Li_1-xNiO_2-yS_y. This study provides a new insight on improving the stability of Ni-rich cathode materials by tuning of the electrochemical behaviors based on sulfur anion redox.     

Organic redox couples and organic counter electrode for efficient organic dye-sensitized solar cells

A series of organic thiolate/disulfide redox couples have been synthesized and have been studied systematically in dye-sensitized solar cells (DSCs) on the basis of an organic dye (TH305). Photophysical, photoelectrochemical, and photovoltaic measurements were performed in order to get insights into the effects of different redox couples on the performance of DSCs. The polymeric, organic poly(3,4-ethylenedioxythiophene) (PEDOT) material has also been introduced as counter electrode in this kind of noniodine-containing DSCs showing a promising conversion efficiency of 6.0% under AM 1.5G, 100 mW·cm(-2) light illumination. Detailed studies using electrochemical impedance spectroscopy and linear-sweep voltammetry reveal that the reduction of disulfide species is more efficient on the PEDOT counter electrode surface than on the commonly used platinized conducting glass electrode. Both pure and solvated ionic-liquid electrolytes based on a thiolate anion have been studied in the DSCs. The pure and solvated ionic-liquid-based electrolytes containing an organic redox couple render efficiencies of 3.4% and 1.2% under 10 mW·cm(-2) light illumination, respectively.     

Poly(neutral red): Electrosynthesis,Characterization, and Application as a Redox Mediator

The synthesis by electropolymerization, the characterization, and applications of poly(neutral red) (PNR), including as a redox mediator, are reviewed. PNR's high electrical conductivity and its redox characteristics have led to special applications of the polymer, and it has been used for the development of electrochemical and optical sensors. Moreover, the attractive properties of PNR allow it to be applied in the development of electrochemical biosensors. Future perspectives are indicated.