Carbon–polymer composite electrodes for redox cells

Conductive carbon–polymer composite electrodes for the vanadium redox flow battery were developed and their properties investigated. Conductive polymer composite materials were fabricated by mixing PVC, nylon 6, nylon 11, LDPE, and HDPE with conductive fillers. To overcome the deterioration in the mechanical properties of carbon–polymer composites with high carbon loading, a range of chemically resistant rubbers was blended into the composites. Electrical, mechanical, permeation, and electrochemical studies show that the HDPE composite is the best electrode matrix material for the vanadium redox battery. The performance of a vanadium redox flow cell employing the best composite electrode was also evaluated and voltage efficiencies as high as 88% were obtained with electrodes employing graphite felt active layers bonded to the carbon–polymer composite substrates. © 1995 John Wiley & Sons, Inc.     

Planar aqueous electrode technique for polymer impedance spectroscopy

In this article, we develop an aqueous electrode technique that can adapt to complex sample geometries while maintaining perfect contact between the electrodes and the measured sample. In contrast to surface deposited electrodes, the aqueous electrode technique measures the ionic conduction of the polymer sample instead of the inherent dielectric properties of the polymer. Polymer ionic conduction is often related to the polymer thermodynamic state, which itself is closely linked to many other polymer properties. As such, the aqueous electrode method provides an approach to conduct in situ monitoring of polymer samples subjected to degradation; changes in the impedance provide an indication of polymer sample degradation. This article presents the aqueous electrode setup and discusses experimental results obtained using it. Changes in the impedance response of PVC and polyimide films due to moisture absorption, ionic conduction, pinholes, chemical degradation, and temperature are presented. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

A unitized approach to regenerative solid polymer electrolyte fuel cells

In this work on regenerative fuel cells, the initial part deals with water electrolysis using a cell design that closely resembled that of a solid polymer fuel cell. The electrolytes were Nafion® 117 and the Dow experimental membrane. The electrodes were Pt-on-C and Pt/Ir-on-C gas diffusion electrodes on the oxygen side and Pt-on-C on the hydrogen side. Fuel cells were built with the above mentioned electrodes and membranes. These cells were run to obtain fuel cell and electrolysis data. Data for a maximum of five regenerative cycles were obtained. The current-potential data in the regenerative electrolysis were characterized by a gradual decay with time. The fuel cell data were very stable. The membrane-electrode assemblies were found in very good condition, and no visible corrosion of electrodes was evident.     

Influence of the structure in low-Pt loading electrodes for polymer electrolyte fuel cells

The influence of the structure and composition of the electrodes on a polymer electrolyte fuel cell (PEFC) performance has been investigated. Electrodes have been prepared by varying the composition of diffusion and/or catalyst layer. Improvements have been obtained by introducing a hydrophobic carbon layer between the carbon paper and the catalyst layer for the gas diffusion backing. High performance has been achieved with low Pt-loading electrodes (0.15 mg/cm²) by including the ionomer Nafion in the catalyst ink. Electrodes have been characterized by SEM-EDX analyses and electrochemical tests in a 50 cm² single cell.     

Electrochemical characterization of polymer precoated lithium electrodes

The electrochemical behaviour of lithium electrodes in contact with solutions of propylene carbonate is investigated as a function of different polymer precoating materials (poly-(2-vinylpyridine) and poly-(ethylene oxide)). Impedance and polarization measurements show that the electrochemical behaviour of the surface is influenced markedly by precoating due to a modification of the passivating layer. Such information is important for lithium electrodes in batteries with organic electrolytes.     

Electrodes covered with thin,permeable polymer films

Because of the recent interest in electrodes modified with thin polymer films the question of permeability of such films to electrolytes and electroactive species is discussed. Glow-discharge polymer films prepared on platinum electrodes from 4-vinylpyridine were used as model systems. They were investigated mainly with electrochemical techniques. ln particular, the analysis of the electrode impedance over a frequency range of 10–3000 Hz gave valuable information about the structure of the metal—polymer interface in presence of the electrolyte.The films prepared on the anode of the glow discharge were found to act as semi-permeable membranes. Hydrogen could be oxidized on the platinum—polymer interface of these polymer covered electrodes at rates comparable to uncovered platinum, while the films were impermeable to iron ions. The matrix prepared on the cathode was more rigid due to cross-links, and thus less permeable.The polymer matrix was more or less electroactive itself. This was probably due to quinone-type groups formed with oxygen and water after the glow-discharge polymerization process. The oxidation and reduction of these groups gave rise to a Warburg-type contribution to the electrode impedance.     

凝胶聚合物电解质的电化学性能

用化学交联法制备了凝胶聚合物电解质.聚烯烃多孔膜支撑的凝胶聚合物电解质具有优良的电化学性能, 室温电导率为1.01×10^-3S•cm^-1,锂离子迁移数为0.41,在Al电极上的氧化起始电位达到4.2 V以上.采用聚烯烃多孔膜支撑的凝胶聚合物电解质制备了聚合物锂离子电池,并研究了工艺条件对聚合物锂离子电池电化学性能的影响.研究的工艺条件包括：单体添加量和电极组合方式.优化后的聚合物锂离子电池具有良好的电化学性能,1 C放电容量为0.2 C放电容量的93.2%,经100次1 C循环后的剩余容量仍在80%以上.     

Properties of electrochemically synthesized polymer electrodes Part VII: Kinetics of poly-3-methylthiophene in lithium cells

The electrochemical behaviour of poly-3-methylthiophene is discussed in comparison with that of other parent polymer electrodes, such as polythiophene and polydithiophene, on the basis of voltammetric and impedance response analysis. The results indicate that the kinetics of the redox processes of the three electrodes are controlled by ion diffusion into the polymer structure and that poly-3-methylthiophene is the most suitable material for the use as cathode in lithium, rechargeable batteries.     

Dye-sensitized solar cells with quasi-solid-state cross-linked polymer electrolytes containing aluminum oxide

Cross-linked gel polymer electrolytes containing aluminum oxide nanoparticles are prepared by in situ chemical cross-linking after injection of the gel precursor into the dye-sensitized solar cell (DSSC). This makes it possible to directly solidify the electrolyte in the cell and maintain good interfacial contacts between the electrolyte and the electrodes without suffering loss of performance in the DSSC. These gel polymer electrolytes exhibit high ionic conductivity and favorable charge transfer reaction at the interfaces of electrodes and electrolyte. The quasi-solid-state DSSC assembled with optimized gel polymer electrolyte exhibited remarkably high conversion efficiency, 6.34% at 100 mW cm⁻², and better long-term stability, as compared to the DSSC with liquid electrolyte.     

Optimization of inverted bulk heterojunction polymer solar cells

We have successively fabricated inverted bulk heterojunction polymer solar cells employing ZnO and MoO₃ as electron and hole selective layers, respectively. The device structure is ITO/ZnO/P3HT: PCBM/MoO₃/Al. Differently from conventional polymer solar cells, ITO and Al work as electron and hole collecting electrodes in this inverted structure, respectively. We have found the optimal thickness of ZnO and MoO₃ to be 100 nm and 5 nm, respectively. The highest PCE was obtained to be 3.32% under AM 1.5 illumination at 1,000W/m², which is the highest PCE of inverted solar cells reported previously in the literature.     

A multi-walled carbon nanotube/polymer actuator that surpasses the performance of a single-walled carbon nanotube/polymer actuator

Actuators were developed using activated and non-activated multi-walled carbon nanotube (MWCNT)–ionic liquid (IL) gel electrodes and compared to a single-walled carbon nanotube (SWCNT)-based actuator with respect to the electrochemical and electromechanical properties. The activated MWCNT–COOH/polymer actuator surpassed the SWCNT/polymer actuator in terms of the generated strain.     

Preparation of cyclodextrin membrane-modified electrodes as sensor materials

Cyclodextrin membrane-modified electrodes as sensor materials have been prepared by dipping platinum electrodes in the water suspensions of an oriented cyclodextrin polymer, followed by drying the polymer layers on the electrodes. The polymer is obtained by the solid-liquid reaction between the crystal of cyclodextrin inclusion complex and hexamethylene diisocyanate in anisole. The thickness (2 ? 80 μm) of the cyclodextrin membrane is satisfactorily controlled by changing the concentration of the water suspension of the polymer. The cyclodextrin membranemodified electrodes show a significant response to p-nitrophenolate in water which is highly in contrast with no measurable response to o- and m-nitrophenolates.     

Investigation of vapour-grown conductive polymer/heteropolyacid electrodes

Heteropolyacid-doped conductive polymer coatings were grown by vapour transport of monomer (pyrrole or N-methylpyrrole) onto carbon paper coated with aqueous oxidant solutions (heteropolyacids or iron(III) chloride). Coated electrodes were studied by scanning electron microscopy and cyclic voltammetry. Polymer/heteropolyanion coatings had smooth morphologies giving pseudocapacitance of up to 422 F g⁻¹ (with respect to active polymer material) and 0.45 F cm⁻² (geometric area of the electrode).     

Functionalized carbon support with sulfonated polymer for direct methanol fuel cells

Recently electrodes for direct methanol fuel cell (DMFC) have been developed for getting high fuel cell performances by controlling composition of catalysts and sulfonated polymers, developing catalyst particles, modifying carbon supports, etc. The electrodes in DMFCs are porous layers, which are composed of catalyst, which is black or carbon supported, and sulfonated polymers in a blended form. In the present study, carbon support for catalysts was functionalized to play dual roles of a mass transport and a catalyst support. The functionalized carbon support was characterized and compared with pristine one by thermal and spectroscopic analysis, and loading of platinum (Pt) catalysts on modified support was performed by gas reduction. The electrodes with Pt on functionalized carbon support were fabricated, though the conventional electrodes were prepared with sulfonated polymer and Pt catalysts. Membrane electrode assembly with Pt catalyst on functionalized support showed a higher DMFC performance of 30 mW cm⁻² at 50 °C without using additional sulfonated polymer. Integration of electrode components in one body has another advantage of easier and simpler process in preparing electrodes for DMFCs. Improved DMFC performance of the electrode containing functionalized carbon was be attributed to a better mass transport which maximize the catalytic activities.     

Ion-selective electrodes with superhydrophobic polymer/carbon nanocomposites as solid contact

Possibility of using superhydrophobic polymer/carbon nanocomposites as a new type of solid-contact material for solid-state ion-selective electrodes has been presented for example potassium-sensitive electrodes. The solid contact layers were prepared with the highly porous graphene/carbon black – fluorinated acrylic copolymer. Potassium-selective electrodes were exhibited a good Nernstian response with a slope of 59.10 mV/dec in the range from 10^−6.5 to 10⁻¹ M KCl. The stability of the electrical potential of the new solid-contact electrodes was tested by performing current-reversal chronopotentiometry, and the electrodes capacitance is 1471 μF. Due to the large capacitance and super hydrophobic character of the solid contact the developed electrodes exhibit excellent a long-term potential stability.     

Effect of diffusion-layer porosity on the performance of polymer electrolyte fuel cells

The gas-diffusion layer (GDL) influences the performance of electrodes employed with polymer electrolyte fuel cells (PEFCs). A simple and effective method for incorporating a porous structure in the electrode GDL using sucrose as the pore former is reported. Optimal (50 w/o) incorporation of a pore former in the electrode GDL facilitates the access of the gaseous reactants to the catalyst sites and improves the fuel cell performance. Data obtained from permeability and porosity measurements, single-cell performance, and impedance spectroscopy suggest that an optimal porosity helps mitigating mass-polarization losses in the fuel cell resulting in a substantially enhanced performance.     

Metallic-lithium, LiFePO4-based polymer battery using PEO—ZrO2 nanocomposite polymer electrolyte

A study of the electrochemical properties of a PEO-based polymer electrolyte with nanometric ZrO₂ as ceramic filler has been carried out in order to confirm an earlier reported model dealing with the role of ceramic fillers within PEO-based polymer electrolytes as components that enhance such properties as conductivity, lithium transference number, compatibility with lithium metal electrodes and cyclability. A prototype of a lithium polymer battery, based on a membrane made from a nanocomposite polymer electrolyte doped with ZrO₂, utilizing LiFePO₄ + 1%Ag as cathode, has been assembled and galvanostatically cycled, resulting in excellent performance at temperatures ranging from 100 °C to 60 °C (close to the crystallization temperature of PEO).     

Bifunctional electrodes for an integrated water-electrolysis and hydrogen-oxygen fuel cell with a solid polymer electrolyte

An alternative concept of an integrated water electrolysis/hydrogen-hydrogen fuel cell using metal electrocatalysts and a solid polymer electrolyte is described. Instead of operating both electrodes as hydrogen and oxygen electrodes respectively the electrodes are used as oxidation and reduction electrodes in both modes of operation. A more suitable selection of electrocatalysts and an improved cell design are possible; both can increase the efficiency of the cell considerably. New results on the electrocatalytic activity of various noble-metal containing catalysts with respect to both oxygen evolution and hydrogen oxidation in a proton exchange membrane-cell at 80°C are reported. Kinetic data derived from Tafel plots of the oxygen evolution polarization curves agree closely with those of experiments with aqueous sulphuric acid electrodes. This agreement allows the determination of kinetic parameters for electrocatalysts difficult to prepare in solid smooth electrodes but easy to be made into porous deposits. Polarization curves of the hydrogen oxidation reaction clearly indicate a relative activity rating of the studied catalysts. In cycling tests the lifetime stability of the new bifunctional oxidation electrode was determined. Polarization data obtained under these conditions agree with those obtained in earlier experiments where electrodes were exposed to only one type of oxidation reaction. During a test of 10 cycles (30 min of electrolyser and 30 min of fuel cell mode each) no changes in the electrode potential were observed. With the conventional cell design employing a hydrogen and an oxygen electrode both catalyzed with platinum and a current density of 100 mA cm^–2 a storage efficiency of 50% was calculated; with the alternative concept of oxidation and reduction electrodes and selected oxidation catalysts this was improved to 57%. With further improvements these efficiencies seem possible even at current densities of 500 mA cm^–2.     

All‐polymer electromechanical systems consisting of electrostrictive poly(vinylidene fluoride‐trifluoroethylene) and conductive polyaniline

The low elastic modulus and the ability to withstand high strain without failure make the conducting polymer attractive for a wide range of acoustic applications based on high‐strain electroactive polymers. In this article, we examine the electric and electromechanical performance of all‐polymer electromechanical systems, fabricated by painting conductive polyaniline (PANI) doped with camphor sulfonic acid (HCSA) on both sides of electrostrictive Poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) copolymer films, and compare them with those from the same copolymers with gold electrodes. The all‐polymer composite films are flexible, with strong coherent interfaces between the electrostrictive polymer layer and the conductive polymer layer. The electric performance such as dielectric properties and polarization hysteresis loops from P(VDF‐TrFE)/PANI film is nearly identical to those of P(VDF‐TrFE)/gold films in a wide temperature (from −50 to 120°C), and frequency range (from 1 Hz to 1 MHz). The all‐polymer systems also show a similar or even larger electric field induced strain response than that of films with electrodes under identical measurement conditions. The results demonstrate that the polyaniline/HCSA is good candidate material as the electrodes for electroactive polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 945–951, 2000     

Distribution of polymer deposition in glow discharge polymerization in a capacitively coupled system

The manner by which polymers created by plasma uniformly deposit onto substrates was sought. By rotating the substrate placed midway between electrodes, completely uniform distribution of polymer deposition was accomplished, and the deviation of the polymer deposition in a radius direction of the rotating substrate was within experimental errors. Materials of the substrate on which the polymer deposited had no influence on uiniformity of polymer deposition, but the electrical circuit of power source, i.e., grounding an electrode, markedly disturbed the uniformity. Thickness of polymers deposited on the substrate was linearly proportional to reaction time. Surface energies of deposited polymers prepared from methane, ethylene, and acetylene by plasma were independent of reaction time and were rather higher than those for conventionally polymerized polyolefines.