Theory of multiple-cell response of redox electrodes

The theory is developed of the voltage of several cells connected in series that have an electrolyte bridge between each cell. The measured voltage increases as the ratio of the electrolyte resistance between cells to that within each cell is increased. Experiments with half cell compartments with platinum and silver electrodes in 0.001 mol dm^–3 potassium permanganate solution connected by thin tubes of different lengths showed a fit to theory if a small constant resistance was included.     

Layer-by-layer thin film-coated electrodes for electrocatalytic determination of ascorbic acid

Multilayer thin films composed of poly(allylamine hydrochloride) (PAH) and carboxymethyl cellulose (CMC) have been prepared on the surface of a gold (Au) disk electrode by a layer-by-layer deposition of PAH and CMC and ferricyanide ions ([Fe(CN)₆]³⁻) were confined in the film. [Fe(CN)₆]³⁻ ions can be successfully confined in the films from weakly acidic or neutral [Fe(CN)₆]³⁻ solutions, while, in basic solution, [Fe(CN)₆]³⁻ ion was not confined. The [Fe(CN)₆]³⁻ ion-confined Au electrode showed clear redox peaks in the cyclic voltammogram around 0.35 V versus Ag/AgCl. The amounts of [Fe(CN)₆]³⁻ ions confined in the films depended on the thickness of the films or the number of layers in the LbL films. The [Fe(CN)₆]³⁻ ion-confined Au electrode was used for electrocatalytic determination of ascorbic acid in the concentration range of 1-50 mM.     

Reduction of a simple ion at permeable film-coated stationary electrodes

Recently proposed chemically prepared electrodes are coated with a thin, permeable, insulating, inert film which does not react with the depolarizer, does not allow depolarization on its surface and does not change the standard constant of the depolarization rate. It only changes the diffusion coefficient of a certain ion near the surface of the electrode. In this article, the theory of a reversible reduction of a simple ion at a film-coated stationary planar electrode is developed. If the film thickness is comparable with a diffusion layer thickness, considerable changes on the i-t curves can occur, but the position of the half-wave potential will remain constant.     

Kinetics of film-coated electrodes: Effect of a finite mass transfer rate of substrate across the film—solution interface at steady state

Previous models for describing the mediation kinetics of film-coated electrodes quantitatively are extended to account for a finite mass transfer rate of the substrate across the film—solution interface. Experimental data from polymer-coated rotating disk electrode experiments, analyzed by the extended model, provide evidence for finite interfacial mass transfer rates. Substrate size and charge contribute to this interfacial rate. Interfacial mass transfer resistance is more pronounced for polymerized films such as poly(vinyl ferrocene) and poly[Ru(vbpy)₃]²⁺ than for highly swollen polymers which bind electroactive species, e.g., poly(lysine).     

聚苯胺薄膜电极上示差脉冲伏安法可逆波理论研究

本文提出了聚苯胺(PANI)薄膜电极上示差脉冲伏安法可逆波理论,经验证理论和实验结果相符合.     

Use of poly(ester-sulfonic acid) film-coated electrodes as amperometric detectors in flow injection analysis

Within the past several years significant advances have been made towards the development and incorporation of chemically modified electrodes as selective detectors for high performance liquid chromatography and flow injection analysis. In many cases the chemically modified electrode systems closely approach the “ideal” detector specifications of chemical and mechanical stability along with a significant linear response region. This paper will discuss the characterization and incorporation of ionomeric poly(ester-sulfonic acid) coated electrodes as nonaqueous electrochemical detectors. The orientation of the electrodes in the detector system as well as the increased sensitivity levels to 10⁻¹⁰ g ml⁻¹ for cationic species and 10⁻⁹ g ml⁻¹ for neutral species will be presented. Also the applicability of the ionomer coated electrodes as nonelectrolyte detectors achieved a reproducible response with detection limits to 10⁻⁶ g ml⁻¹. Overall this system performed as well as, or better than, more specialized and expensive thin layer electrochemical detectors.     

Recent results on the dynamic response of precipitate-based ion-selective electrodes

The e.m.f. vs. time curves of the precipitate-based ion-selective electrodes have been interpreted mathematically on the basis of the desolvation of ions at the electrode surface. A new method has been suggested for the characterization of ion-selective electrodes by the half-life time of the first-order desolvation reaction.     

High rate performances of hydrogen titanate nanowires electrodes

In this study, H₂Ti₃O₇ nanowires were successfully synthesized via a hydrothermal process and post-treatments. The diameter of the nanowires is found to be about 30 nm and the length up to several micrometers. A lithium battery using H₂Ti₃O₇ nanowires as the active material of the positive electrode exhibits a discharge capacity of 100 mA hg⁻¹ and still keeps stable after 200 cycles at a current density as high as 40 Ag⁻¹, demonstrating excellent high rate performance.     

How to understand the response mechanism of ion-selective electrodes

The present study breaks with the earlier mechanism of electrode potential on basis of experimental investigations and theoretical considerations. It rejects that the transport through the membrane produces the electrode potential and definitely proves that the electrode potential is created via surface chemisorption; i.e., the electrode potential is produced by a surface reaction. The reaction centres can be acid-base groups or complex formation groups (e.g., valinomycin or other alkaline earth metal complexing ligands.     

Electrocatalytic response of carbohydrates at copper-alloy electrodes

The voltammetric responses observed for carbohydrates and polyalcohols at 0.60 V in 0.10 M NaOH are significantly larger at preanodized CuMn (95:5) electrodes as compared to preanodized pure Cu electrodes. Apparent values for the number of electrons transferred (n_app) and the corresponding values of heterogeneous rate constants (k_app) are estimated for selected reactants from the slopes and intercepts, respectively, of Koutecký–Levich plots of background-corrected voltammetric currents obtained at CuMn and Cu rotated disk electrodes (RDEs). Values of n_app (and k_app) for sorbitol and glucose are 11.8 (9.2×10⁻³ cm s⁻¹) and 11.7 (8.0×10⁻³ cm s⁻¹), respectively, at a CuMn RDE. These are compared to the values 10.4 (1.8×10⁻³ cm s⁻¹) and 9.6 (2.0×10⁻³ cm s⁻¹) for sorbitol and glucose, respectively, at a Cu RDE. The larger sensitivities observed at the CuMn RDE in comparison to the Cu RDE are concluded to be the beneficial result of larger k_app values at the alloy electrode. Furthermore, the larger k_app values are speculated to result from enhanced preadsorption of the reactant species at Mn(IV) sites in the preanodized CuMn surface. In flow-injection measurements, the peak signals obtained for successive injections of glucose using a CuMn electrode (0.60 V vs. SCE) were quite stable with a standard deviation of 1.5%. However, large day-to-day variations (±15%) observed in the average peak signals are attributed to the temperature sensitivities of the k_app value and the diffusion coefficient for glucose.     

The mechanism of the potential response of bromide-selective electrodes based on mercury salts

Bromide-selective electrodes based on Hg₂Br₂—HgS—Ag₂S membranes are discussed. X-ray diffraction studies indicate the formation of HgBr₂ and mercury under certain conditions. Improved preparations are reported. Electrode response can be interpreted on the basis of the theory for second-kind electrodes. In very dilute nitric acid solutions (3 × 10^-4 mol dm^-3), the linear range extends almost to pBr 6 and the electrodes are useful at pBr> 7.     

Theory and practice of sensors with hot-wire electrodes

The possibilities and applicability of electrochemical sensors with heated electrodes are overviewed. A theory for such devices is developed, including the interactions between the heating alternating current and the electrochemical cell and the measuring circuit, as well as calculation of the temperature expansion. Experimental details on the circuitry and the electrode design are given, and results are presented for some analytical applications. Received: 1 December 1997 / Revised: 28 January 1998 / Accepted: 2 February 1998     

Theory and applications of ion-selective electrodes Part III

This review of ion-selective electrodes is arranged in the same way as Parts I and II. The continuous growth of the whole subject should be noted. Theory has particularly progressed through mechanistic studies. Among new types of electrodes, ISFET systems have become important. Among new applications of both solid and liquid membrane electrodes, the fluoride electrode still predominates, closely followed by potassium electrodes. In the field of biological and medical applications, the steady growth is significant. More than 800 papers published between mid-1976 and the end of 1978 are mentioned in the review.     

Theory and applications of ion-selective electrodes part 4

This review of ion-selective electrodes is arranged in the same way as earlier reviews in this series. The growth of the whole subject approaches a steady state. Some mechanistic studies have deepened theoretical understanding. Better insight into the mechanism of liquid-membrane systems has been gained by electrolysis at the interface of two immiscible electrolyte solutions. In this field some interesting analytical applications are noted. A steady growth is shown by publications on ion-selective field-effect transistors. Otherwise the same proportion is preserved among well-established electrode types. About 800 papers published between the end of 1978 and the beginning of 1981 are mentioned.     

Theory and practice of sensors with hot-wire electrodes

The possibilities and applicability of electrochemical sensors with heated electrodes are overviewed. A theory for such devices is developed, including the interactions between the heating alternating current and the electrochemical cell and the measuring circuit, as well as calculation of the temperature expansion. Experimental details on the circuitry and the electrode design are given, and results are presented for some analytical applications. Received: 1 December 1997 / Revised: 28 January 1998 / Accepted: 2 February 1998     

Self-assembly and sensor response of photosynthetic reaction centers on screen-printed electrodes

Photosynthetic reaction centers were immobilized onto gold screen-printed electrodes (Au-SPEs) using a self-assembled monolayer (SAM) of mercaptopropionic acid (MPA) which was deliberately defective in order to achieve effective mediator transfer to the electrodes. The pure Photosystem II (PS II) cores from spinach immobilize onto the electrodes very efficiently but fair badly in terms of photocurrent response (measured using duroquinone as the redox mediator). The cruder preparation of PS II known as BBY particles performs significantly better under the same experimental conditions and shows a photocurrent response of 20-35 nA (depending on preparation) per screen-printed electrode surface (12.5mm(2)). The data was corroborated using AFM, showing that in the case of BBY particles a defective biolayer is indeed formed, with grooves spanning the whole thickness of the layer enhancing the possibility of mass transfer to the electrodes and enabling biosensing. In comparison, the PS II core layer showed ultra-dense organization, with additional formation of aggregates on top of the single protein layer, thus blocking mediator access to the electrodes and/or binding sites. The defective monolayer biosensor with BBY particles was successfully applied for the detection of photosynthesis inhibitors, demonstrating that the inhibitor binding site remained accessible to both the inhibitor and the external redox mediator. Biosensing was demonstrated using picric acid and atrazine. The detection limits were 1.15 nM for atrazine and 157 nM for picric acid.     

Effect of metal ion exchange on the photocurrent response from bacteriorhodopsin on tin oxide electrodes

The transient photocurrent response from bacteriorhodopsin (bR) on tin oxide electrodes was strongly influenced by metal ions bound to bR molecules. The photocurrent polarity reversal pH, which corresponded to the pH value for the reversal of the proton release/uptake sequence in the bR photocycle, of cation-substituted purple membrane (PM) was shifted to lower pH with the increase in the cation affinities to carboxyl groups and a close correlation was noted between the two values. This suggests that the metal ion present in the extracellular region of a bR molecule modulates the pK(a) of proton release groups of bR by stabilizing the ionized state of the proton-releasing glutamic acids. The behavior of photocurrents at light-off in alkaline media, reflecting the proton uptake by bR, was unchanged by binding monovalent (Na(+) and K(+)) or divalent cations (Mg(2+) and Ca(2+)), but was drastically changed by binding La(3+) ions. This can be explained by invoking a substantial slowing of the proton uptake process in the presence of La(3+).