DigiElch8 Help

The Property Page: Chemical Reactions works as previously described for the CV-Simulation Document.

The Property Page: Surface Reactions works as previously described for the CV-Simulation Document.

A value of Cdl (F) written in magenta indicates that a time/potential dependent double layer capacity has been entered by the user. The polynomial coefficients describing the dependence of the double layer capacity as function of the electrode potential can be edited by clicking with the right mouse button while the cursor is localized over the input field associated with Cdl (F).

The following parameter groups
 

•Geometry

•Diffusion

•Pre-Equilibrium

•Simulation Name

 
as  well as the Simulation Parameters headlined
 

•Experimental Conditions

•Model Parameters

•2D-Simulation

•FEM-Simulation

work exactly in the same way as already described for cyclic voltammetry. The meaning and functionality of the Scan Parameters is as follows:
 

1. Scan Parameters:

•Scan segment, Estart (V), Eend (V), f(Hz)
DigiElch provides a highly flexible way for defining the potential scan used in the square wave experiment. The overall scan can be composed of any number of scan segments characterized by starting potential, Estart (V), end-potential, Eend (V) and the square wave frequency, f (Hz).
 
Examples 1: (classical SW-experiment, 1 scan segment is executed)

   Examples 3: (3 scan segments are executed )

Estart - values plotted on a grey background are automatically filled in. They are "read only" and cannot be edited/modified. This ensures a "smooth scan" where the starting potential of a scan is always equal to the end potential of the previous scan.
 

•Check Box: use the same value of f(Hz) in each scan segment
If this check box is ticked any modification of f (Hz) will be taken over for all other scan segments.

•Check Box: apply background correction
This check box is visible only if both Ru (Ohm) and Cd (F) are different from zero. The need for this option is similarly as demonstrated in the CV-example.
This check box is visible only if Cdl (F) > 0 and Ru(Ohm) > 0.

•Esw (V), dEs (V)
Square wave amplitude and potential steps. The definition of the square-wave signal by Estart (V) = Ei, Esw (V) , dEs (V) and f(Hz) = τ-1 becomes clear from the following picture:
 

Figure 1

•Time steps/SW-halfcylce
Indicates the number of time steps used for simulating the current referring to the end points of the t/2 - cycles.
 
τ (and consequently f(Hz)) must be equal within a scan segment (characterized by starting and end potential) but may differ from scan segment to scan segment. Esw and dEs must be equal in all scan segments.
 
 

Removing scan segments:
A scan segment (and all subsequent scan segments) can be removed by entering an empty string into the associated Eend - input filed. For instance, if a user wants that only the first scan segment is executed in Example 2, an empty string must be entered into the input field "Eend (V)" associated with the scan index 2.

Relationship to OSWV (Osteryoung Square Wave Voltammetry)

In the case of OSWV the height of the difference peak current for a reversible charge-transfer can be expressed by the following equation

where ψp has been tabulated in a paper by Osteryoung and O’Dea (J. Electroanal. Chem. 14, 209 (1986)) as function of the OSWV parameters ΔEs  and ΔEp, respectively. The relation between these parameters and those used by DigiElch is as follows:

ΔEs  = dEs

ΔEp = ½ Esw

tp = 1/(2*f)