Chronoamperometric Response Research Articles

Chronoamperometric response of ion-exchange membrane systems

The electrical response of an ion-exchange membrane system to a square shaped electric potential, has been investigated from both experimental and theoretical viewpoints. The chronoamperometric response of a cation-exchange membrane in contact with a NaCl solution was experimentally obtained for different values of the amplitude of the perturbing electric potential. From the theoretical viewpoint, the system under study is considered to be constituted by a cation-exchange membrane and two diffusion boundary layers on both sides of the membrane. The ionic transport processes are prescribed by the Nernst–Planck flux equations, the electrical neutrality condition, and the Donnan equilibrium relations at the membrane/solution interfaces. The theoretical results are numerically obtained by using the network simulation method. Some of our results confirm that the chonoamperometric techniques can be used to measure the thickness of the diffusion boundary layers. Others provide new insights in relation with the time evolution of the short circuit electric current supplied by the salinity gradient due to the concentration polarization in ion-exchange membrane systems, showing the role played by the concentration polarization in the field of the renewable energies.

Indirect electrochemical oxidation of pentachlorophenol in the presence of different halides: behavior and mechanism

Indirect electrochemical oxidation (EO) of pentachlorophenol (PCP) wastewater was carried out in the presence of different halides through the electrogeneration of active halide (AH). The EO effect and electrochemical behaviors of PCP under different conditions are present in this paper. The cyclic voltammetry (CV) curves indicated higher electrogeneration efficiency of active halogen in NaBr solution. Chronoamperometric response proved the formation of passivating polymer on anode surface. The conversion rate of PCP was distinctly different for different halides following the order Br− ##xgt; Cl− ##xgt; F− ##xgt; I−. The proper oxidation potential of Br− to active bromine led to the optimal electrooxidation effect of Br−. With the rise of temperature the reaction rate decreased at first from 30 to 45°C and then increased from 45 to 60 °C. The complicated variation of PCP conversion on rising temperature was depicted by the electrochemical measurements and a mathematic model.

Fabrication of High-Activity Hybrid Pt@ZnO Catalyst on Carbon Cloth by Atomic Layer Deposition for Photoassisted Electro-Oxidation of Methanol

ZnO nanorods with a diameter of 25 nm have been synthesized on carbon cloth (CC) by combining atomic layer deposition (ALD) and hydrothermal methods. Platinum nanoparticles were then deposited on photoinduced hydrophilic surface of ZnO nanorods by ALD. Electrochemical performance of the nanocomposite catalyst (Pt@ZnO@CC) for methanol oxidation with or without UV irradiation was evaluated. According to the X-ray photoelectron spectroscopic (XPS) analysis, the surface of ZnO nanorods rich in hydroxide species was more favorable for removal of CO via the so-called bifunctional mechanism. Additionally, the XPS study indicates that the charge transfer occurs between the ZnO nanorods and the Pt nanoparticles. UV light irradiation on the catalyst surface increases the chronoamperometric response by 62%, which is attributed to a synergistic effect of large surface area and strong light absorption in the UV region by the presence of ZnO nanorod arrays.

Enhanced Electrocatalytic Performance for Methanol Oxidation via Insertion of Ruthenium Oxide Particles into Pt and Polyaniline-Poly(Acrylic Acid-co-Maleic Acid) Composite Electrode

Polyaniline (PANI) is doped with poly(acrylic acid-co-maleic acid) (PAMA) containing HCl to obtain PANI-PAMA film. Platinum particles are deposited into the PANI-PAMA film via electrochemical deposition to obtain PANI-PAMA-Pt composite electrodes. Subsequently, ruthenium oxide (RuO2) particles are incorporated into the composite electrodes by cyclic voltammetry for 20 and 60 cycles to obtain PANI-PAMA-Pt-RuO220 and PANI-PAMA-Pt-RuO260 composite electrodes, respectively. X-ray diffraction analysis explains a decrease in the number of Pt crystalline facets for the incorporation of RuO2 into PANI-PAMA-Pt. Cyclic voltammetry results and chronoamperometric response measurements demonstrate that the PANI-PAMA-Pt-RuO220 electrode has the best activity and stability toward methanol oxidation among the three electrodes.

Doping process effect of polyaniline doped with poly(styrenesulfonic acid) supported platinum for methanol oxidation

Polyaniline (PANI) is doped with poly(styrenesulfonic acid) (PSS) using doping time of 10, 60, 300, 900, and 1800s to obtain PANI–10PSS, PANI–60PSS, PANI–300PSS, PANI–900PSS, and PANI–1800PSS films, respectively. Fourier transform infrared spectroscopy (FT-IR) results confirm that PANI is doped with PSS. X-ray photoelectron spectroscopy (XPS) results indicate that a saturated doping state is achieved when PANI dope with PSS up to 300s. Scanning electron microscopy (SEM) images reveal that PANI doped with PSS films are composed of highly porous nanowires. Platinum (Pt) can be incorporated into PANI–10PSS, PANI–60PSS, PANI–300PSS, PANI–900PSS, and PANI–1800PSS via electrochemical deposition to obtain PANI–10PSS–Pt, PANI–60PSS–Pt, PANI–300PSS–Pt, PANI–900PSS–Pt, and PANI–1800PSS–Pt composite electrodes, respectively. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) results indicate that Pt particles disperse more uniformly into the spatial regions of PANI–300PSS than those of other films, and the PANI–300PSS–Pt electrode provides the most active surface area of Pt in these electrodes. Cyclic voltammetry results and chronoamperometric response measurements show that the activity and stability toward methanol oxidation of the PANI–300PSS–Pt electrode are the best in these electrodes, respectively.

The Long-Time Chronoamperometric Current at an Inlaid Microband (or Laminar) Electrode

In this article, we derive an approximate asymptotic analytical expression for the long-time chronoamperometric current response at an inlaid microband (or laminar) electrode. The expression is applicable when the length of the microband is much greater than the width, so that the diffusion of the electrochemical species can be regarded as two-dimensional. We extend the previously known result for the diffusion-limited current response (Aoki, K. et al. J. Electroanal. Chem. 1987, 225, 19–32 and Phillips, C.G. J. Electroanal. Chem. 1992, 333, 11–32) to accommodate quasi-reversible reactions and unequal diffusion coefficients of the oxidant and the reductant. Comparison with numerical calculations validates the analytical expression, and we demonstrate that unequal diffusion coefficients can substantially change the current response. Finally, we discuss the form of the long-time current response for a one-step, one-electron redox reaction if the rate constants are modelled in the Butler–Volmer framework, and indicate the importance of choosing the width of the microband appropriately to allow accurate experimental determination of the standard kinetic rate constant and the electron transfer coefficient.

Chronoamperometric response at nanoscale liquid–liquid interface arrays

In this work, potential step chronoamperometry (PSCA) was used to study the behaviour of arrays of nanoscale interfaces between two immiscible electrolyte solutions (nanoITIES). The nanoITIES arrays were formed at nanoporous silicon nitride membranes containing 400 nanopores in a hexagonal close-packed arrangement. Three membrane designs, with nanopore radii of 75, 50 and 17nm, were studied by ion-transfer of tetrapropylammonium cations across the nanopore array-supported water|1,6-dichlorohexane interface. The cell time constants and charging times were determined prior to experimental PSCA. The three membrane designs studied exhibited charging times in the range of 0.08–0.46s, with the smallest pore configuration (17nm radius) exhibiting the longest charging time. The experimental steady-state currents were 30–50% lower than of the calculated inlaid disc model currents, due to diffusion zone overlap at adjacent interfaces. The three nano-interface arrays studied also showed response times of 6±1s, being the time required to reach 95% of the steady-state current.

The Chronoamperometric and Voltammetric Behaviour of Glutathione at Screen-Printed Carbon Micro-Band Electrodes Modified with Cobalt Phthalocyanine

Screen-printed carbon electrodes (SPCEs) incorporating the electrocatalyst cobalt phthalocyanine (CoPC) have been successfully used for the manufacture of microband electrodes for the determination of reduced glutathione (GSH). Initially investigations were performed to explore the cyclic voltammetric behaviour of these electrodes with potassium ferrocyanide. It was shown that steady state behaviour occurred which is indicative of radial diffusion at a microelectrode. Current densities of 2173 μAcm-2 were obtained compared to 464.4 μAcm-2 for conventional sized (3 mm x 3 mm) screen-printed electrodes were obtained. At scan rates between 5 and 20 mV/s no significant increase in current response was observed. The application of these microband CoPC–SPCEs, to the measurement of GSH by both chronoamperometry and cyclic voltammetry was investigated. The chronoamperometric response was found to be linear between 50 µM and 8.0 mM with a detection limit of 7.3 µM using an applied potential of +0.25 V (vs. Ag/AgCl).

Time-dependent chronoamperometric response of dual inlaid disk electrodes

Dual-disk electrodes allow for novel electrochemical investigations, particularly when used in generator–collector mode. However analytical understanding of how the current response of each individual electrode is affected by the presence of the neighbouring electrode is limited. In this article, we derive an approximate analytical solution for the time-dependent chronoamperometric current response of a pair of electrodes, each subjected to a different initial potential step. The solution is valid when the centre-to-centre distance between the disks is much larger than the disk radii, and for times such that the diffusion layers generated at each electrode have started to interact. It accommodates quasi-reversible reactions and unequal diffusion coefficients of the oxidant and the reductant. The generator–collector system is a specific case, and we deduce simple expressions for the time-dependent current and steady-state collection efficiencies at each electrode. The analytical solution facilitates analysis of shielding and feedback effects, and shows the explicit dependence of the currents on the underlying electrochemical parameters.

How low does the oxygen concentration go within a sandwich-type amperometric biosensor?

Software for the automatic non-linear least squares fit of chronoamperometric responses corresponding to sandwich-type amperometric biosensors has been developed. The so-called Simplex algorithm computes a minimum value for the difference between experimental and theoretical data. The latter consider a numerical model based on a ping-pong reaction mechanism corresponding to an oxidase enzyme that has been immobilized between diffusion membranes. The results obtained from the simulation of a first-generation lactate biosensor in presence of 0.1 mM substrate indicate that the concentration of O2 would decrease only 0.1% with regards to its bulk value. Besides, the concentration of this natural mediator would remain practically unchanged during a typical calibration curve. This is because the rather high diffusion coefficient of O2 and its regeneration at the electrode surface minimize the concentration changes of this species. In addition, it was found that the thicknesses of polycarbonate membranes and the enzymatic matrix have average values of 13 μm and 20 μm, respectively. However, these membranes might exhibit smaller thickness depending on the time provided for the crosslinking reaction. In this regard, if this reaction is slow enough, the enzymatic matrix would be able to diffuse through the pores of polycarbonate membranes and they will appear to be thinner than expected. This effect may compromise the response-time and the reproducibility of this kind of biosensors.

Polyaniline Doped with Various Inorganic Acids and Polymeric Acids as Platinum Catalyst Support for Methanol Electro‐oxidation

AbstractPolyaniline (PANI) is doped with H2SO4, HCl, poly(acrylic acid) (PAA), poly(acrylic acid‐co‐maleic acid) (PAMA), PAA+HCl, and poly(styrenesulfonic acid) (PSS) to obtain PANI‐H2SO4, PANI‐HCl, PANI‐PAA, PANI‐PAMA, PANI‐(PAA+HCl), and PANI‐PSS films, respectively. Ultraviolet‐visible (UV‐Vis) and Fourier transform infrared (FT‐IR) spectroscopy result confirm that PANI is doped with PSS. X‐ray photoelectron spectroscopy (XPS) results indicate that the nitrogen atoms of PANI‐PSS are the most positively charged in these films. Scanning electron microscopy (SEM) images reveal that these films are composed of highly porous nanowires. Platinum (Pt) can be incorporated into PANI‐H2SO4, PANI‐HCl, PANI‐PAA, PANI‐PAMA, PANI‐(PAA+HCl), and PANI‐PSS films via electrochemical deposition to obtain PANI‐H2SO4‐Pt, PANI‐HCl‐Pt, PANI‐PAA‐Pt, PANI‐PAMA‐Pt, PANI‐(PAA+HCl)‐Pt, and PANI‐PSS‐Pt composite electrodes, respectively. Auger electron spectroscopy (AES) results indicate that Pt particles disperse more uniformly into the spatial regions of PANI‐PSS and PANI‐(PAA+HCl) than those of other films. The PANI‐PSS‐Pt electrode provides the most active surface area of Pt in these electrodes. Cyclic voltammetry results and chronoamperometric response measurements show that the activity and stability toward methanol oxidation of the PANI‐PSS‐Pt electrode are the best in these electrodes.

Electrochemical determination of methyl parathion using poly(malachite green)/graphene nanosheets–nafion composite film-modified glassy carbon electrode

A novel poly(malachite green)/graphene nanosheets–nafion (PMG/GNs–NF) composite film-modified glassy carbon electrode was developed to indirectly detect methyl parathion (MP). p-nitrophenol, the alkaline hydrolysis product of MP, was successfully determined at a relatively lower potential using this modified electrode due to the excellent electrocatalytic activity of PMG/GNs–NF composite film. The presence of GNs in the composite film enhanced the stability of PMG and increased the electron transfer rate. The kinetic parameters of modified electrodes were studied. What is more, the optimum experimental parameters affecting response were selected in terms of pH, accumulation potential, accumulation time, scanning cycles during polymerization of malachite green, and alkaline hydrolysis conditions. Under optimum conditions, the chronoamperometric response current was proportional to MP concentration over the range from 0.02 to 1.5 μM with a low-detection limit of 2.0 nM. Finally, the sensor was applied for the determination of MP in real samples, and the results were satisfactory with recoveries from 97.20 to 104.53 %. Due to its simple preparation, good reproducibility, and stability, this developed modified electrode provides a new platform for the detection of organophosphate pesticides.

A comparative study of poly(acrylic acid) and poly(styrenesulfonic acid) doped into polyaniline as platinum catalyst support for methanol electro-oxidation

Polyaniline (PANI) is doped with poly(acrylic acid) (PAA) and poly(styrenesulfonic acid) (PSS) via a doping–dedoping–redoping process. Fourier transform infrared (FT-IR) spectroscopy results confirm that PANI is doped with PSS (or PAA). X-ray photoelectron spectroscopy (XPS) results indicate that the nitrogen atoms of PANI–PSS are more positively charged than those of PANI–PAA. Scanning electron microscopy (SEM) images reveal that PANI–PSS is composed of highly porous nanowires. Platinum (Pt) can be deposited onto PANI–PAA and PANI–PSS films using the potentiostatic mode to obtain PANI–PAA–Pt and PANI–PSS–Pt composite electrodes, respectively. Auger electron spectroscopy (AES) results indicate that Pt particles disperse more uniformly into the spatial regions of PANI–PSS than those of PANI–PAA. The SO3H group in PANI–PSS may facilitate the electrodeposition of Pt better than the CO2H group in PANI–PAA. Cyclic voltammetry results and chronoamperometric response measurements show that the activity and stability toward methanol oxidation of the PANI–PSS–Pt electrode are better than those of the PANI–PAA–Pt electrode.

Study of Drug Metabolism by Xanthine Oxidase

In this work, we report the studies of drug metabolism by xanthine oxidase (XOD) with electrochemical techniques. Firstly, a pair of stable, well-defined and quasi-reversible oxidation/reduction peaks is obtained with the formal potential at −413.1 mV (vs. SCE) after embedding XOD in salmon sperm DNA membrane on the surface of pyrolytic graphite electrode. Then, a new steady peak can be observed at −730 mV (vs. SCE) upon the addition of 6-mercaptopurine (6-MP) to the electrochemical system, indicating the metabolism of 6-MP by XOD. Furthermore, the chronoamperometric response shows that the current of the catalytic peak located at −730 mV increases with addition of 6-MP in a concentration-dependent manner, and the increase of the chronoamperometric current can be inhibited by an XOD inhibitor, quercetin. Therefore, our results prove that XOD/DNA modified electrode can be efficiently used to study the metabolism of 6-MP, which may provide a convenient approach for in vitro studies on enzyme-catalyzed drug metabolism.

The long-time chronoamperometric current at an inlaid disk electrode

Existing analytical solutions for the long-time chronoamperometric current response at an inlaid disk electrode are restricted to diffusion-limited currents due to extreme polarisation or reversible kinetics at the electrode surface. In this article, we derive an approximate analytical solution for the long-time-dependent current when the kinetics of the redox reaction at the electrode surface are quasi-reversible and the diffusion coefficients of the oxidant and reductant are different. We also detail a novel method for calculating the steady-state current. We show that our new method encapsulates and extends the existing solutions, and agrees with numerically simulated currents.

Electrodeposition of Sb(III) in alkaline solutions containing xylitol

The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique. Initial stages of antimony electrocrystallization were determined by chronoamperometry. Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from −1.20 V to +0.60 V (vs Hg/HgO). There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of −1.75 V to 1.25 V (vs Hg/HgO) while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than −1.70 V (vs Hg/HgO). Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol, 0.64 and 4.40×10−6 A/m2, respectively. The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation. The average diffusion coefficient of antimony was calculated to be 1.53×10−6 cm2/s.

Electrochemistry of Carbon Nanotubes: Reactive Processes, Dual Sensing–Actuating Properties and Devices

Single-walled carbon nanotubes (SWCNT) embedded in a non-electroactive polymer are electrochemically characterized. The increasing voltammetric maximums obtained with rising temperature or electrolyte concentration point to a chemical nature of the processes. The chemical kinetic control of the processes is corroborated by its empirical chemical kinetics: the initial reaction rates are obtained from the chronoamperometric responses to potential steps. The activation energy of the reaction includes information about the structural state of the SWCNT before the potential step. Under constant current the potential evolution (chronopotentiometric response) and consumed electrical energy at any time change as a function of (are sensors of) the experimental temperature or the electrolyte concentration. The reactive material, or any device based on this material, senses these working variables, and shows dual and simultaneous actuating-sensing properties.

Kinetic Effects of the Complexation Reaction in the Facilitated Ion Transfer at Liquid Membrane Systems of One and Two Polarized Interfaces. Theoretical Insights

An in-depth study of the ion transfer facilitated by complexation in the organic phase (TOC mechanism) in liquid membrane systems of one and two polarized interfaces is carried out by taking into account the kinetic effects associated with the complexation reaction. Explicit analytical equations for the normal pulse voltammetric (I/E) and chronoamperometric (I/t) responses with an explicit dependence on the kinetic parameters of the chemical complexation are presented for both kinds of membrane system, which could be useful for modeling artificial and biological membranes. The equations are compared with those obtained by using the widely used approximation of total equilibrium conditions that leads to the transfer by interfacial complexation mechanism (TIC), which only depends on thermodynamic parameters. Simple methods are proposed that allow quantitative determination of the equilibrium and kinetic constants of the complexation reaction in the organic phase for both kinds of membrane system.

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbon monoxide (COad) and hydroxyl (OHad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species (θCO and θOH) and the CO and CO2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure of CO and CO2. Thus, it was demonstrated that the Gilman’s mechanism accurately describes the experimental results on steady state of the COOR on these metals.

Capacitive and faradic charge components in high-speed carbon nanotube actuator

When submitted to square-wave potentials of ±2 V, single-walled carbon nanotube films with an ionic liquid, taking part of an actuator, show high-frequency electromechanical responses (up to 100 Hz), with anodic current evolutions showing two maxima. Similar anodic chronoamperometric responses have been obtained from films of conducting polymers exchanging balancing anions with the electrolyte during reaction, being described by two stretched exponential functions deduced on physico-chemical bases: oxidation under nucleation–relaxation structural control and oxidation/swelling completion under diffusion control. Now by adding a third stretched function, describing a greater contribution now of the charge of the electrical double layer, a good mathematical fit of the chronoamperometric response of the carbon nanotube films was carried out. By recovering the original physico-chemical meaning of the electrochemical stretched functions, capacitive and structural faradic components of the chronoamperometric charge were quantified as a function of the applied frequency (1–10 Hz). The capacitive component of the charge ranges with frequency between 8.6% and 12.2% of the involved charge. The faradic (reactive) component ranges between 91.4% and 87.8%, being the main contributor to the volume variations in the actuating films. The order of magnitude of the diffusion coefficients was 10 −6 cm 2 s −1, in good agreement with the fast response of the reactive actuators constructed with those materials. A good separation of capacitive and faradic components will allow a better design of electrochemical applications of single-walled carbon nanotube films.