Continuum modeling of solid oxide fuel cell electrodes: introducing the minimum dissipation principle

A simple continuum one-dimensional model of porous mixed-conducting electrode applied onto solid oxide electrolyte is proposed and discussed. Assuming linear relationships between the reaction overpotential and current, the model makes it possible to derive analytical solutions for the electrode thickness dependence of the overall electrode resistance. The least dissipation principle is used to determine the distribution of the ionic and electronic currents throughout the mixed-conducting layer. The area-specific resistance is expressed in terms of the electron and ion resistivities of the electrode material, its “reaction resistivity” as a slope of current–overpotential dependence, and geometric parameters. The solution is expanded to describe the electrode impedance and gas transport resistance under DC conditions.     

Determination of lead ions using an diantipyrylmethane-based electrode

The possibility of using diantipyrylmethane as an ionophore component of a lead-selective electrode membrane was assessed. Membrane composition (wt %) was optimized: polyvinyl chloride (31.89), dioctyl sebacate (63.81), diantipyrylmethane (2.50), and oleic acid (1.80). The proposed model of the electrode works in the concentration range of 1 × 10^–5–0.1 M with a detection limit of 2 mg/L. A slope of the electrode function of the diantipyrylmethane-based electrode is 29.4 ± 0.5 mV/pPb. Concentration of Pb(II) ions in various samples was determined.     

TiO<Subscript>2</Subscript> nanotube arrays based DSA electrode and application in treating dye wastewater

Dimensionally stable anode (DSA) of antimony-doped tin dioxide electrode based on TiO₂-nanotube arrays (NTs) has been successfully fabricated through thermal decomposition. The surface morphology and composition of the electrodes were characterized by using scanning electron microscopy and X-ray diffraction. Methyl orange (MO) was used as a model pollutant to investigate the electrochemical properties of these two electrodes. The optimized anodic oxidation voltage and time for TiO₂-nanotubes array based DSA electrode is 60 V and 10 min, respectively. The results show that Ti/TiO₂–NTs/Sb–SnO2 electrode has an increase of 100 mV in oxygen evolution overpotential and the service life is 56% longer than that of the traditional DSA electrode. Under the optimum conditions, MO solution decolorization rate and TOC removal rate reached approximately 100 and 80%, respectively. Study suggested that the as-prepared Ti/TiO₂–NTs/Sb–SnO2 DSA electrode exhibits high activity for degradation of organic pollutant with high concentration.     

Characterization and electric field dependence of N,N′‐bis(9H‐fluoren‐9‐ylidene)benzene‐1, 4‐diamine thin film/substrate interface

N,N′‐bis(9H‐fluoren‐9‐ylidene)benzene‐1,4‐diamine deposited onto highly oriented pyrolytic graphite (HOPG) was investigated by contact angle measurement(CAM), Raman spectroscopy and tunneling spectroscopy. The results of CAM and Raman spectra have confirmed that organic layers had deposited on substrate. Tunneling spectra obtained in the scanning tunneling microscopy measurement system were reported as a function of electrode potential. The tunneling current data were acquired at different electrode–electrode separations and depicted significant trend under the action of electric field. Under weak electric fields, the electrode–electrode separation has little effect on the potential of conductance peak. However, with the shrinkage of electrode–electrode separation, the electron transport model obeys the Ohmic law. Copyright © 2010 John Wiley & Sons, Ltd.     

Impedance of metal hydride electrodes. Rate of phase transformation limited by nucleation and growth mechanisms

A mathematical model for the electrochemical impedance spectroscopy of a metal hydride electrode was developed. Ac impedance data of phase transformation were derived by considering a nucleation and growth mechanism based on the theory developed by Johnson–Mehl–Avramy. Different mechanisms such as grain edge and grain boundary preferential nucleation sites are discussed. Global Nyquist plots of the metal hydride electrode are obtained by adding a surface charge transfer reaction and a double-layer capacitance to the model.     

Rotating minidisk–disk electrodes

Rotating minidisk–disk electrode (RMDDE) was developed by replacing ring electrode of rotating ring–disk electrode (RRDE) with a minidisk electrode. Its applications were demonstrated by studying electrochemical reactions of ferricyanide and divalent copper. The replacement of ring electrode by minidisk electrode results in following advantages. First, the fabrication of RMDDE is easier than that of RRDE with the same electrode material. Second, there is more freedom in choosing electrode materials and sizes, since it is difficult to make thin ring electrodes of RRDE with fragile materials. Third, the replacement of ring electrode by minidisk electrode saves electrode materials, especially rare materials. Finally, the substitution of minidisk electrode for ring electrode allows using multiple minidisks for simultaneous monitoring of multiple components. Therefore, RMDDE is a promising generator–collector system, especially when special generator–collector systems are not commercially available, such as corrosion study and electrocatalysis study of new electrode materials.     

A bio-selective membrane electrode prepared with living bacterial cells.

A novel potentiometric sensor has been devised by coupling intact microorganisms (Streptococcus faecium) with an ammonia gas-sensing membrane electrode. The resulting electrode provides a linear response to arginine over the concentration range 5.0 × lO^-5–1. 0 × 10^-3 M in phosphate buffer pH 7.4, with selectivity over other amino acids. The slope of the calibration graph is -40 to -45 mV/decade during the period 2–20 days after preparation. This membrane electrode with living bacterial cells may serve as a model for the development of other new sensing systems.     

Differential capacitance of the electric double layer: mean-field modeling approaches

Electrolytes screen the charges carried by an electrode through the formation of a diffuse double layer. The corresponding differential capacitance reflects the change of the surface charge density with the applied surface potential. Mean-field modeling of the differential capacitance is an attempt to qualitatively explain experimental findings such as the camel-to-bell shape transition in terms of physical factors including the ion size and concentration, nonelectrostatic ion–ion interactions, electrostatic ion–ion correlations, and the influence of the electrode curvature. We highlight the central role of the lattice gas model as a conceptual tool to describe concentrated electrolytes and ionic liquids, and we briefly summarize how extensions and generalizations of this model give rise to concepts known as ‘overscreening’ and ‘underscreening’.     

Flow-injection determination of iodide with a silver electrode

A procedure is developed for the flow-injection determination of iodide using a modified silver electrode; it extends the analytical range of iodide by an order of magnitude as compared to potentiometric determination using an iodide-selective electrode with a polycrystalline membrane. The detection limit is 7 μg/L. The procedure was used to determine iodide in natural mineral waters and model solutions. The throughput was 20–25 samples/h.     

Studying the process of oxygen ionization on a porous metal hydride electrode

Problems that are connected with utilization of oxygen evolving during overcharge of the nickel oxide electrode in sealed nickel metal hydride batteries are considered. It is established experimentally that the rate of the process of oxygen reduction in conditions of forced gas supply into pores of a metal hydride electrode increases by two orders of magnitude as compared with the intensity of this process during natural convection. Up to 80% of evolved oxygen undergo ionization on a metal hydride electrode in these conditions even in a regime of forced (hour-long) charge of a model sealed nickel-metal hydride battery. The dependence of the current density of oxygen reduction at a metal hydride electrode on the filling of the electrode’s porous space by oxygen is estimated with the aid of manometric and potentiostatic methods. It is shown that practically all the oxygen ionization current is generated at the walls of gas-filled electrode pores, under thin electrolyte films, with a local current intensity of 1–3 mA cm^?2.     

Multi-enzyme anode composed of FAD-dependent and NAD-dependent enzymes with a single ruthenium polymer mediator for biofuel cells

A multi-enzyme electrode composed of FAD-dependent and NAD-dependent enzymes was fabricated using a poly-ruthenium complex (PAHA–Ru), which has two 1,10-phenanthroline-5,6-dione molecules as ligands. PAHA–Ru was used to immobilize FAD-dependent glucose dehydrogenase (FAD–GDH) onto an electrode and to examine PAHA–Ru containing the quinone moieties as an electron mediator. In cyclic voltammetry measurements of the FAD–GDH modified electrode in the presence of D-glucose, a catalytic current was obtained, which indicated electron transfer from FAD–GDH to PAHA–Ru. Our previous study has reported that PAHA–Ru with the quinone ligands also works as a mediator for NADH oxidation on an NAD-dependent alcohol dehydrogenase (NAD–ADH) modified electrode. Hence, FAD–GDH and NAD–ADH were co-immobilized with PAHA–Ru to make a multi-enzyme electrode. Using this multi-enzyme electrode as an anode, catalytic currents were observed in D-glucose solution, ethanol solution, and a mixed D-glucose and ethanol solution. The catalytic current in the mixed solution was greater than the currents obtained in the single substrate solutions, indicating bioelectrocatalysis reactions by the two enzymes and the single mediator in the mixed solution. Thus, we demonstrated that PAHA–Ru modified electrode enables selection of enzymes and their substrates from a wider range for enzymatic biofuel cells.     

Monte Carlo simulations of heterogeneous electron transfer: New challenges

We report results of MC simulations of electron transfer across a metal electrode/electrolyte solution interface. The model presumes the Landau–Zener theory and a random walk on a two-dimensional lattice formed by crossing parabolic reaction free energy surfaces along the solvent coordinate. Emphasis is put on investigating the activationless discharge regime; the bridge-assisted electron transfer is also partially addressed. We have calculated effective electronic transmission coefficient as a function of the electrode overpotential and temperature in a wide range of orbital overlap. The dependence of the transmission coefficient on the electronic density of states is analyzed as well.     

Fabrication of Sn–C composite electrodes by electrodeposition and their cycle performance for Li-ion batteries

To improve the cycle performance of the thick Sn electrode of 10 μm thickness, the Sn–C composite electrodes were fabricated by co-electrodeposition with two kinds of carbon particles which were the graphite and the acetylene black. The acetylene black particles were well dispersed in the Sn matrix more than the graphite particles. The carbon content in the Sn–C composite electrodes was measured about 12% of the graphite and 16% of the acetylene black particles. Even though carbon content of the Sn–acetylene black electrode was not significantly higher than that of the Sn–graphite electrode, the cycle performance of the Sn–acetylene black electrode was much higher than that of the Sn–graphite electrode. This demonstrates that the ‘buffering effects’ of well dispersed acetylene black particles was larger than that of the graphite particles. The cycle performance of the Sn–acetylene black electrode was significantly improved by the aging treatment.     

Electrochemical Behavior and Determination of Rutin at the Copper Nanoparticles-Doped Zeolite A/Graphene Oxide-Modified Electrode

In this work, a novel Cu?zeolite A/graphene modified glassy carbon electrode was applied for the determination of rutin. The Cu?zeolite A/graphene composites were prepared using copper doped zeolite A and graphene oxide as the precursor, subsequently reduced by chemical agents. Based on the Cu?zeolite A/graphene modified electrode, the overpotential of the rutin oxidation was lowered by ~300 mV. Also the proposed Cu?zeolite A/graphene modified electrode showed higher electrocatalytic performance than zeolite A/graphene electrode or graphene modified electrode. The electrochemical behavior of copper incorporated in the zeolite A modified electrode illustrated the adsorption-controlled reaction at the modified electrode. The behavior of electrocatalytic oxidation of rutin at the modified electrode was investigated. The diffusion coefficient of rutin was equal to 4.2 × 10^–7 cm²/s. A linear calibration graph was obtained for rutin over the concentration range of 2.3 × 10^–7–2.5 × 10^–3 M. The detection limit for rutin was 1.2 × 10^–7 M. The RSDs of 10 replicate measurements performed on a single electrode at rutin concentrations between 2.3 × 10^–7–2.5 × 10^–3 M were between 1.1 and 2.1%. Study of the influence of potentially interfering substances on the peak current of rutin showed that the method was highly selective. The proposed electrode was used for the determination of rutin in real samples with satisfactory results.     

Heat transport in a PEFC: Exact solutions and a novel method for measuring thermal conductivities of the catalyst layers and membrane

We develop a model of heat transport in the membrane–electrode assembly of a polymer electrolyte fuel cell. The exact analytical solutions to model equations are derived. Rather cumbersome solutions lead to remarkably simple formulas for the temperature of the anode and the cathode sides of the membrane. Based on these formulas a novel method for measuring thermal conductivities of the catalyst layers and membrane in a working fuel cell environment is proposed.     

Electrochemical determination of unithiol and lipoic acid at electrodes modified with carbon nanotubes

Conditions are found for the voltammetric determination of lipoic acid and unithiol at a glassy-carbon electrode modified with multiwalled carbon nanotubes. Possible mechanisms for the oxidation of lipoic acid and unithiol are proposed. As compared to an unmodified electrode, the use of the modified electrode allows the analyst to reduce overvoltage (ΔE = 0.1 V) and increase the oxidation current of lipoic acid. Unithiol is oxidized in the accessible range of potentials only at an electrode modified with carbon nanotubes. The determination limits for unithiol and lipoic acid are 4.1 × 10^?5 and 1.9 × 10^?5 M, respectively. Milligram amounts of these substances are determined in model solutions with RSD = 1–5%. Procedures for determining the active substances (lipoic acid and unithiol) in pharmaceuticals are proposed.     

Silver/graphene–polypyrrole composite for levosimendan detection

This study used a facile method to develop a novel silver/Graphene–polypyrrole (Ag/G–PPy)-modified electrode that can be used as an electrochemical sensor for levosimendan detection. The properties of the synthesized Ag/G–PPy-modified electrode were examined through field-emission scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. The Ag/G–PPy-modified electrode exhibited satisfactory current signals toward levosimendan concentrations ranging from 0.21 to 6.88 μM and exhibited a low detection limit (0.12 μM). Accordingly, the proposed electrode can serve as a simple and inexpensive electrochemical sensor for levosimendan detection.     

Scientific Importance of Water‐Processable PEDOT–PSS and Preparation,Challenge and New Application in Sensors of Its Film Electrode: A Review

In this review, PEDOT–PSS is mainly a commercially available PEDOT–PSS, which is a water‐dispersible form of the intrinsically conducting PEDOT doped with the water‐soluble PSS, including its derivatives, copolymers, analogs (PEDOT:PSSs), even their composites via the chemical or physical modification toward the structure of PEDOT and/or PSS. First, we will focus on discussing the scientific importance of PEDOT–PSS in conjunction with its extraordinary properties and broad multidisciplinary applications in organic/polymeric electronics and optoelectronics from the viewpoint of the historical development and the promising application of representative ECPs. Subsequently, versatile film‐forming techniques for the preparation of PEDOT–PSS film electrode were described in details, including common coating approaches and printing techniques, and many emerging preparative methods were mentioned. Then challenges (e.g., conductivity, stability in Water, adhesion to substrate electrode) of PEDOT–PSS film electrode for devices under the high humidity/watery circumstances, especially electrochemical devices are discussed. Fourth, we take PEDOT–PSS film electrode for a relatively new application in sensors as an example, mainly summarized advances in the development of various sensors based on PEDOT–PSSs and their composites in combination with its preparative methods and extraordinary properties. Finally, we give the outlook of PEDOT–PSS for possible applications with the emphasis on PEDOT–PSS film electrode for electrochemical devices, including sensors. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1121–1150     

Numerical Modeling of an RF Argon–Silane Plasma with Dust Particle Nucleation and Growth

A one-dimensional numerical model and simulation results are presented for a capacitively-coupled radio frequency parallel-plate argon–silane dusty plasma. The model includes self-consistently coupled numerical modules, including a plasma fluid model, a sectional aerosol model, and a simple chemistry model to predict rates of particle nucleation and surface growth. Operating conditions considered include 13.56 MHz frequency, 100 mTorr pressure, a 4-cm electrode gap, gas flow through the top electrode with a 30:1 ratio of argon to silane, and applied radio frequency voltage amplitude of either 100 or 250 V. In the higher voltage case two lobes of relatively large particles are formed by ion drag, while fresh nucleation occurs in the void between these lobes. It is shown that the reason that fresh nucleation occurs in the void involves an interplay among several coupled phenomena, including nanoparticle transport, the plasma potential profile, and trapping of silicon hydride anions that drive nucleation in this system.     

Modelling of Amperometric Biosensors with Rough Surface of the Enzyme Membrane

A two-dimensional-in-space mathematical model of amperometric biosensors has been developed. The model is based on the diffusion equations containing a nonlinear term related to the Michaelis–Menten kinetic of the enzymatic reaction. The model takes into consideration two types of roughness of the upper surface (bulk solution/membrane interface) of the enzyme membrane, immobilised onto an electrode. Using digital simulation, the influence of the geometry of the roughness on the biosensor response was investigated. Digital simulation was carried out using the finite-difference technique.