Chrono amperometry

Other Techniques - Other electrochemical techniques that could be employed in sensor technology would include potential-step methods (or chrono-amperometry, as current is recorded with time), current-step methods (or chronopotentiometry, as potential is recorded with time) and AC impedance. None of these techniques appear to have yet been applied to catalyst sensing in a systematic way. 

The simplest controlled potential experiment is the potential step [34] illustrated in Fig. 15. Such experiments are sometimes termed chrono-amperometry , signifying that the current (-ampero-) is measured (-metry) as a function of time (chrono-). Sometimes, two steps, as in a double-step experiment [34] [Fig. 16(a)], or a sequence of small steps, as in staircase voltammetry [35—37] [Fig. 16(b)], are applied. When the potential of the working electrode is changed by a step for only a brief period of time before being returned to its original (or near to its original) value, we speak of a pulse . There are many varieties of pulse voltammetry [38—41], some of which are discussed in Chap. 4. 

Potential step perturbation chrono-amperometry, pulse polaro-graphy, and d.c. polarography... 

Detection launch the detection in Immusoft in order to follow the enzymatic reaction by chrono-amperometry at 250 mV versus Ag/AgCl (sequential detections of 2 s of potential application performed in each channel one after the other). 

The enzymatic reaction occurring in the various micro-channels during the detection step is followed by chrono-amperometry as presented in Fig. 50.2A. The measured currents result from the oxidation of the p-aminophenol produced by the enzymes, and it is thus increasing with the reaction time. Finally, the values of the slopes of these current versus time curves (in A/s) are reported as a function of the known concentrations of the IL-1B standards, thereby providing a calibration curve as shown in Fig. 50.2B. 

Pt Si Au electrodes) 15). Vielstich P-Delahay, JACS 79, 1874-76 (1957) (Chrono-amperometry at const potential) 16)Y. Takemori et al, JPhysChem 61, 968-69... 

G.Chariot, J.Badoz-Lambling B- Tre-millon, "Electrochemical Reactions. The Electrochemical Methods of Analysis , Elsevier Amsterdam (196 2), 309 10 (Chrono-amperometry at const potential) 3IO-I3 (Chronoamperometry with varying potential) 314-18 (Chronopotentiometry) 318-24 (Oscillographic polarography) 32)D.N.Hume, Anal Chem 34, I78R-I79R (April 1962) (Chronopotentiometry a review)... 

A series of tip feedback current-distance curves for a range of PhOH concentrations is shown in Figure 29. This shows that a PhOH increases, the current decreases due to the consumption of AC - in the gap, causing a diminution in the extent of positive feedback for the AC/AC - couple. Analysis of all data sets allowed values for the effective first-order rate constants to be determined, from which the second-order rate constant, k2 = C/[PhOH] = (4.4 0.4) X 103 M 1 s, was deduced. This value was found to be in good agreement with that measured earlier by double potential step chrono-amperometry (40), confirming the applicability of SECM in the study of ECE/D1SP1 processes. 

M. Tupin, C. Bataillon, J.P. Gozlan, P. Bossis, High temperature corrosion of Zircaloy-4 followed by in-situ impedance spectroscopy and chrono- amperometry. Effect of an anodic polarization, in Electrochemistry in Light Water Reactors Reference Electrodes, Measurement, Corrosion and Tribocorro- sion Issues (European Federation of Corrosion Publ. No. 49), ed. by R.-W. Bosch, D. Feron, J.-P. Celis (CRC Press, Boca RatonAVood- head/ Cambridge, UK, 2007), pp. 134-155... 

In this method, [37] an electrode at equilibrium is polarized by a small shift of potential, thus keeping a constant concentration of inserted atoms on the surface of the electrode. The DC can be calculated from the registered current-versus-time curve called chronoamperogram. The method is also called single-step chrono-amperometry (SSCAM). In this method, the condition D const is under better control than in the GSPM. 

Normalized chrono amperometry at disk UME Measure current as a function of time and normalize by steady-state current. Plot normalized current vs. D =... 

Using electrochemistry to probe the transport of Ox/Red within polymer brushes grafted onto substrates, (a) Direct electrochemical measurement at a grafted electrode by chrono-amperometry (CA), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) represented by their respective waveform, (b) Indirect measurement by SECM. The overall process is decomposed in (a) into the subsequent steps (from top to bottom) solution diffusion, partition at the solution-polymer brush interface, diffusion in the brush, and electron transfer at the electrode. (Adapted from Matrab, T., et al., ChemPhysChem, 11,670-682,2010.)... 

Before applying power to the SPE, the ME A was moisturized for 30-60min at 25 °C or in some cases several days, and the water flow rate was set at between 3 and 5.0 mL/s. Chrono-amperometry was performed by stepping the potential to the desired value (between —1.3 and -2.0 V) and after a dwell time of 300 seconds, recording the current. 

It is not necessary to complete a CV, when one needs to measure just erossover or capacitance. For example, crossover measurements can be made by chrono-amperometry technique, where the potential of the cathode side is elevated to 0.4 V from a rest potential of 0.08 V. During the chrono-amperometry experiment, inducing backpressure on the anode chamber elevates the partial pressure of the hydrogen. If there are pinholes, more hydrogen permeates increasing the background current substantially beyond the step changes as indicated in Fig. 19. 

Potential Step, Reversible Case (Chrono-amperometry)... 

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