Current decay

K. T. Hartwig, "An Eddy-Current Decay Technique for Low Temperature Resistivity Measurements," in G. Birnbaum and G. Eree, eds.,ASTM STP 722, American Society for Testing and Materials, Philadelphia, Pa., 1981, pp. 157—172. 

Coulometry. If it can be assumed that kinetic nuances in the solution are unimportant and that destmction of the sample is not a problem, then the simplest action may be to apply a potential to a working electrode having a surface area of several cm and wait until the current decays to zero. The potential should be sufficiently removed from the EP of the analyte, ie, about 200 mV, that the electrolysis of an interferent is avoided. The integral under the current vs time curve is a charge equal to nFCl, where n is the number of electrons needed to electrolyze the molecule, C is the concentration of the analyte, 1 is the volume of the solution, and F is the Faraday constant. 

Figure 12-23 shows simulation of time-of-flighl photocurrenl transients at variable temperature for a system containing 0.25 eV traps at a concentration c=3xl0. This translates into orjj= 0.080 eV. The current decays monotonously by several orders of magnitude to finally merge into a plateau followed by a rapid fall-off that reflects discharge of the carriers at the exit contact. This is in accord with experiment [74],... 

Cyclic voltammetry can also be useful for quantitative purposes, based on measurements of the peak current (equation 2-1). Such quantitative applications require the establishment of the proper baseline. For neighboring peaks (of a mixture), the baseline for the second peak is obtained by extrapolating the current decay of the... 

When a polymer relaxes at a constant anodic potential, the relaxation and partial opening of the polymeric structure involve a partial oxidation of the polymer. Once relaxed, the oxidation and swelling of the relaxed polymer goes on until total oxidation is reached this is controlled by the diffusion of the counter-ions through the film from the solution. This hypothesis seems to be confirmed by the current decay after the chronoam-perometric maximum is reached. We will focus now on the diffusion control. 

We can see when analyzing this equation that the right-hand side is smaller than unity and increases with increasing X. For A, > 5 it tends toward unity (i.e., the reaction is practically reversible under the given conditions). Therefore, the kinetic reaction parameters (X, and hence h) can be determined from the current decay curve only when X<5 (i.e., when Parameters of reactions for which... 

In later measurements, Tewari and Freeman (1968,1969) measured the ion mobilities from drift-time measurement and obtained k/u values from the current decay following a pulse of X-rays of 1 ms duration. The purpose was to find the dependence of Gfl on molecular structure. It was found that Gf. increased with the sphericity of the molecule. In liquid argon Gf. 5 was measured, which indicated that all ionized electrons in argon are free. However, this... 

This is known as the Cottrell equation. It shows that the faradaic transient current, it, decays t 1/2. In contrast, the capacitance current decays exponentially and much faster. According to Eq. (18b.16) a plot of it vs. t 1/2 is a straight line, the slope of which can be used to calculate the D of the analyte if the area of the electrode is known. Eq. (18b. 16) is also used to measure the active area of an electrode by using species with known D. At a spherical electrode (such as HMDE) of radius, r, the Cottrell equation has an added spherical term... 

The current decay rate of the 14C in a sample is 4.82 disintegrations per minute per gram (d/min-g). The14 C activity of living organisms is 15.3 d/min-g. The half-life of14C is 5730 years. How many years old is the sample ... 

The effects of the concentration of the add were investigated using 0.1 -10 M sulfuric add. The current decay curves are shown in Fig. 3-22. Although the initial current is higher in the less concentrated electrolytes, the sustained current after 2 min, is largest in 3 M sulfuric add. The less concentrated media suffered faster decay of the current. This trend was observed at any potentials from 400 to 700 mV. 

Medium concentrations (1—5 M) of acids showed the highest sustained current. Adds with higher or lower concentration showed faster current decay and faster COad coverage growth. 

A similar polymer, composed of osmium complexed with bis-dichlorobipyridine, chloride, and PVI in a PVI—poly(acrylamide) copolymer (Table 2, compound 3), demonstrated a lower redox potential, 0.57 V vs SHE, at 37.5 °C in a nitrogen-saturated buffer, pH 5 109,156 adduct of this polymer with bilirubin oxidase, an oxygen-reducing enzyme, was immobilized on a carbon paper RDE and generated a current density exceeding 9 mA/cm at 4000 rpm in an O2-saturated PBS buffer, pH 7, 37.5 °C. Current decayed at a rate of 10% per day for 6 days on an RDE at 300 rpm. The performance characteristics of electrodes made with this polymer are compared to other reported results in Table 2. 

This electrode is unique in that the bilirubin oxidase is active at neutral pH, whereas the laccase cited above is not, even though the redox potential of laccase is somewhat higher. Additionally, the bilirubin oxidase is much less sensitive to high concentrations of other anions such as chloride and bromide, which deactivate laccase. It was shown that mutations of the coordination sphere of bilirubin oxidase led to an increased redox potential of the enzyme, which increased current density and reduced current decay to 5%/day over 6 days at 300 rpm. The latter improvement was attributed to improved electrostatic attraction between the enzyme and the redox polymer. An electrode made with high-purity bilirubin oxidase and this redox polymer has recently been shown to outperform a planar platinum electrode in terms of activation potential and current density of oxygen reduction. ... 

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