Voltammetry at porous electrodes: A theoretical study

Theory is presented to simulate both chronoamperometry and cyclic voltammetry at porous electrodes fabricated by means of electro-deposition around spherical templates. A theoretical method to extract heterogeneous rate constants for quasireversible and irreversible systems is proposed by the approximation of decoupling of the diffusion within the porous electrode and of bulk diffusion to the electrode surface

Double potential step chronoamperometry at a microband electrode: Theory and experiment

Numerical simulation is used to characterise double potential step chronoamperometry at a microband electrode for a simple redox process A + e- goes to B, under conditions of full support such that diffusion is the only active form of mass transport. The method is shown to be highly sensitive for the measurement of the diffusion coefficient of both A and B, and is applied to the one electron reduction of decamethylferrocene (DMFc), DMFc - e- goes to DMFc+, in the room temperature ionic liquid 1-propyl-3-methylimidazolium bistrifluoromethylsulfonylimide. Theory and experiment are seen to be in excellent agreement and the following values of the diffusion coefficients were measured at 298 K: D_(DMFc) = 2.50 x 10^(-7) cm^(2) s^(-1) and D_(DMFc+) = 9.50 x 10^(-8) cm^(2) s^(-1)

Dual Band Electrodes in Generator-Collector Mode: Simultaneous Measurement of Two Species

A computational model for the simulation of a double band collector-generator experiment is applied to the situation where two electrochemical reactions occur concurrently. It is shown that chronoamperometric measurements can be used to take advantage of differences in diffusion coefficients to measure the concentrations of both electroactive species simultaneously, by measuring the time at which the collection efficiency reaches a specific value. The separation of the electrodes is shown to not affect the sensitivity of the method (in terms of percentage changes in the measured time to reach the specified collection efficiency), but wider gaps can provide a greater range of (larger) absolute values of this characteristic time. It is also shown that measuring the time taken to reach smaller collection efficiencies can allow for the detection of smaller amounts of whichever species diffuses faster. The case of a system containing both ascorbic acid and opamine in water is used to exemplify the method, and it is shown that mole fractions of ascorbic acid between 0.055 and 0.96 can, in principle, be accurately measured.Comment: 34 pages, 8 figure

Double Electrode Experiments Reveal the Processes Occurring at PEDOT-Coated Neural Electrode Arrays

Neural electrodes have recently been developed with surface modifications of conductive polymers, in particular poly­(3,4-ethylenedioxythiophene) (PEDOT), and extensively studied for their roles in recording and stimulation, aiming to improve their biocompatibility. In this work, the implications for the design of practical neural sensors are clarified, and systematic procedures for their preparation are reported. In particular, this study introduces the use of in vitro double electrode experiments to mimic the responses of neural electrodes with a focus on signal-recording electrodes modified with PEDOT. Specifically, potential steps on one unmodified electrode in an array are used to identify the responses for PEDOT doped with different anions and compared with that of a bare platinum (Pt) electrode. The response is shown to be related to the rearrangement of ions in solution near the detector electrode resulting from the potential step, with a current transient seen at the detector electrode. A rapid response for PEDOT doped with chloride (ca. 0.04 s) ions was observed and attributed to the fast movement of chloride ions in and out of the polymer film. In contrast, PEDOT doped with poly­(styrenesulfonate) (PSS) responds much slower (ca. 2.2 s), and the essential immobility of polyanion constrains the direction of current flow

Electrochemical and nanostructural characterization of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films as coatings for neural electrodes

Poly(3,4-ethylenedioxythiophene) (PEDOT), a well-characterized conducting polymer, has been applied for coating metal neural electrodes to improve their stimulating or recording performance. The coated electrodes possess advantages in better neuron attachment, lower impedance, and larger capacitance compared to the bare metal substrate due to the biocompatibility and porous surface of the polymer. However, the PEDOT-coated electrodes have frequently reported issues associated with mechanical instability, such as cracking and delamination. Solving this problem is crucial for stimulating electrodes, whereas a massive film is unnecessary for recording purposes. Moreover, the thickness control for the latter has rarely been investigated. In this work, we systematically studied and characterized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with cyclic voltammetry and atomic force microscopy (AFM) to evaluate the electropolymerization of PEDOT:PSS from the basis and analyze the surface morphology for a range of deposition times. The polymerization potential was obtained, and the deposition charge density was optimized for recording neural electrodes. In addition, high-resolution AFM height and phase images reveal the heterogeneity of the polymer surface. The modified electrode was also tested for its electrochemical performance in a small potential window with both a standard electrochemical cell setup and stainless steel microscrews. The results showed that despite a shift of potential (0.42 V) due to the change of setup, the electrode functions well in the capacitive region without triggering redox reactions

Electrochemical Detection of Ammonia in Aqueous Solution using Fluorescamine: A Comparison of Fluorometric Versus Voltammetric Analysis

荧光胺是一种非荧光剂，其易与伯胺反应形成荧光产物，被普遍用于伯胺的荧光光谱定量分析. 本文利用荧光胺与伯胺反应发展了一种新型灵敏的伏安法用于检测水溶液中的伯胺. 首先，在有、无伯胺的0.1 mol L-1 PBS (pH 9.0)缓冲液中，研究了玻碳电极表面荧光胺的循环伏安电化学行为. 荧光胺的不可逆氧化峰出现在0.70 V (vs. SCE)，当加入伯胺时，在0.46 V (vs. SCE)出现另一不可逆的氧化峰，为荧光胺与伯胺反应的产物. 继续加入氨水，荧光胺的氧化峰变弱，反应产物的氧化峰则由于荧光胺按反应化学计量比随氨消耗增多而随之增大. 上述两个阳极峰分别对应于荧光胺及其反应产物，采用方波伏安和荧光光谱技术可实现水溶液中伯胺的定量检测. 在0 ~ 60 μmol L-1氨浓度范围内，该反应产物方波伏安检测成线性响应. S/N = 3或3σ时检测下限分别为0.71 μmol L-1和3.17 μmol L-1，与荧光法检测的结果相近.Fluorescamine is a non-fluorescent reagent widely used for the quantitative determination of primary amines by fluorescence spectroscopy as it reacts readily with primary amines to form a fluorescent product. In this work, a new sensitive voltammetric method for the detection of ammonia in aqueous solution by the reaction with fluorescamine has been developed. First, the electrochemical behaviour of fluorescamine in the absence and presence of ammonia was investigated in 0.1 mol L-1 borate buffer solution (pH 9.0) by cyclic voltammetry using a glassy carbon (GC) electrode. As for fluorescamine itself, a well-defined irreversible oxidation peak could be observed at ca. 0.70 V vs. SCE. When ammonia was added to the fluorescamine solution, another irreversible oxditaion peak corresponding to the oxidation of the reaction product formed between fluorescamine and ammonia could be observed at ca. 0.46 V vs. SCE. Upon the addition of ammonia, the oxidation peak of fluorescamine became smaller while the oxidation peak of the reaction product formed increased in height, due to the stoichiometric chemical consumption of fluorescamine by ammonia and the formation of the product during the reaction, respectively. These two anodic peaks corresponding to the oxidation of fluorescamine and its fluorescent product formed were then used for the quantitative detection of ammonia, explored by square wave voltammetry and by fluorescence spectroscopy. The square wave voltammetric response of the reaction product formed showed a linear response over ammonia concentration range of 0 to 60 μmol L-1. The limits of detection (LOD) was found to be 0.71 μmol L-1 and 3.17 μmol L-1 determined based upon Signal/Noise (S/N) = 3 and 3σ, respectively. These limits of detection are similar to those obtained with the fluorometric method.Syngenta are acknowledged for partial funding of this work.Syngenta are acknowledged for partial funding of this work.作者联系地址：牛津大学化学系，物理化学与理论化学实验室，英国 牛津OX1 3QZAuthor's Address: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom通讯作者E-mail：[email protected]

Distinguishing Heterogeneous and Homogeneous CE Mechanisms: Theoretical Insights into Square-Wave Voltammetry

A theoretical study of an electrode mechanism where the electrode reaction (E) is preceded by a chemical reaction that takes place solely at the electrode surface (Chet) is presented under conditions of square-wave voltammetry (SWV). Rigorous mathematical solutions in the form of integral equations derived by means of Laplace transforms are presented for the surface concentration of all species involved in the electrode mechanism, yielding explicit recurrent formulas for the simulation of the voltammetric response. The theory approximately predicts that the chemical reaction starts at the beginning of the voltammetric experiment, disregarding its occurrence in the short time period between inserting the electrode in the solution until starting the voltammetric experiment. It is demonstrated that SWV can differentiate between the common CE mechanism, where C is a homogeneous chemical reaction taking place in the vicinity of the electrode, and the current ChetE mechanism, which is relevant for plethora of electrocatalytic processes at electrodes modified with catalytically active enzymes and/or noble-metal nanoparticles, as well as for electrocatalytic processes of fundamental importance such as CO2, N2, O2, and H+ reduction