Chronoamperometry single potential step

The simplest chronoamperometric technique is that defined as single potential step chronoamperometry. It consists of applying an appropriate potential to an electrode (under stationary conditions similar to those of cyclic voltammetry), which allows the electron transfer process under study (for instance Ox + ne — Red) to run instantaneously to completion (i.e. COx(0,0 —1 0). At the same time the decay of the generated current is monitored.20... 

The simplest and most useful case that one can study by single potential step chronoamperometry is that in which " /2> 0/i (z.e. AEor = E2 - E 5 180 mV). This means that the primarily electrogenerated species Red converts to a new species Ox, which is more easily reducible than the initial species Ox. As seen in Section 1.4.3, in cyclic voltammetry such a system exhibits a single reversible process in the forward scan. 

Fig. 3.14 Single potential step chronoamperometry at large overpotentials, (a) Variation of the limiting current with time (b) concentration profiles at the end of the pulse. Planar electrode. / jrn (/)//ii , (t p) /d o"e (/)//d>1c"e ( p) f°r the two kinetic models considered. k° = 10-4 cm/s. Reproduced with permission of reference [30]. In this Figure X = A.

Finally, the physicochemical role of alkali-metal cation size in electron transfer from BPH2 to M l ion pairs (eq 3) is established by correlation of kinedc data (changes in kobs values as a function of [M ]) with data obtained by paramagnetic Li NMR spectroscopy, cyclic voltammetry and single-potential step chronoamperometry. ... 

Single-potential step chronoamperometry The reduction of protons catalyzed by hydrogenase in the presence of a mediator (viologen) was used as a model of EC at mechanism not only in CV experiments [87], but also for chronoamperometric studies [88]. During the cathodic potential step, the current was sampled in 10 ms intervals. In this way I-t curves were obtained for blank solutions, for solutions with mediator and for solutions with mediator and with increasing amounts of hydrogenase, respectively. The current-time curves are schematically drawn in Fig. 22. Important is the characteristic shape for the catalytic reaction the trend to achieve the steady-state in the presence of both the mediator and the enzyme is evident. 

The potential step methods are called chronoamperometry and like LSV and CV can deal with only the forward process (single step) or with the reverse process, involving the primary intermediate, as well. The latter is called double potential step chronoamperometry (DPSC) and is by far the most useful in kinetic studies. The applied potential-time wave form as well as the currenttime response for a reversible electrode process are illustrated in Fig. 3. The potential is stepped from a rest value where no current flows, usually 200-300 mV from the potential where the process of interest takes place, to one... 

Macpherson JV, Unwin PR (1997) Determination of the diffusion coefficient of hydrogen in aqueous solution using single and double potential step chronoamperometry at a disk ulttamicroelectrode. Anal Chem 69 2063—2069... 

Chronopotentiometry closely resembles chronoamperometry with the exception that the role of current and potential are reversed. In chronopotentiometry the current is controlled and is the variable and the electrode potential is the observable. A single step of the current or a double step can be employed. The double step method called current reversal chronopotentiometry is more information-rich as in previous comparisons. Both the applied currenttime wave form and the potential-time response for a reversible electrode process are illustrated in Fig. 4. The current step from 0 to a predetermined value depending upon the experimental conditions is maintained until time... 

In single- and double-step chronoamperometries, one or two constant potential pulses are applied and the signal corresponds to the variation of the... 

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