Cyclic Polarization Setup Parameters
Here is a Cyclic Polarization Setup dialog box complete with its default parameters.
Starting point for the initial sweep during data-acquisition. The allowed range is ±10 V with a resolution of 1/8 mV. Its accuracy depends on the setting.
Scan Rate for the potential sweep during the initial scan.The Scan Rate is entered in units of mV/s. A practical bound on the Scan Rate is 1 mV/s. Higher Scan Rates may run, but yield unreliable data because the potentiostat’s compensation and filtering are set for long time constants.A lower bound on the Scan Rate is given by the minimum Step Size divided by the longest Sample Period. For scans shorter than 2 V, the slowest Scan Rate is 52.1 nV/s or 0.1875 mV/hour. Multiply these limits by four for scans longer than 2 V.
One of the two conditions to reverse the potential sweep. The sweep reverses when it reaches the Apex E if the Apex I (current) is not reached first.The allowed range for Apex E is ±10 V with a resolution of 1/8 mV. Its accuracy depends on the setting.
Scan Rate for the potential sweep following a scan reversal.The Scan Rate is entered in units of mV/s. A practical upper bound on the Scan Rate is 1 mV/s. Higher Scan Rates may run, but yield unreliable data because the potentiostat’s compensation and filtering are set for long time constants.A lower bound on the Scan Rate is given by the minimum Step Size divided by the longest Sample Period. For scans shorter than 2 V, the slowest Scan Rate is 52.1 nV/s or 0.1875 mV/hour. Multiply these limits by four for scans longer than 2 V.
Ending point for the potential sweep following scan reversal. The allowed range is ±10 V with a resolution of 1/8 mV. Its accuracy depends on the setting.The Scan Range, defined as the most anodic voltage in the scan minus the most cathodic voltage, must be less than 8 V.
Sets one of the conditions to cause a reversal of the initial ramp. The scan reverses as soon as the absolute value of the current exceeds the Apex I. If you always want to reverse at a potential rather than at a current, enter a value larger than your potentiostat’s maximum current for the Apex I.The units of Apex I are milliamperes (mA). The allowed range for Apex I is zero to the potentiostat’s maximum rated current. Negative values for Apex I are not allowed, because of the absolute value in the comparison.
Spacing between data points. It also helps determine the Step Size of the staircase ramp and the Number of Points in the data curve.The Sample Period sets the length of a step. The height of a step depends on both the Scan Rate and the Sample Period. Calculate the Step Size and the Number of Points in the scan from:
Step Size = Scan Rate × Sample Period
Number of Points = Scan Range / Step Size
The Step Size is rounded to the resolution of the D/A converter making the steps. The resolution of the D/A converter is dependent on the type of potentiostat you are using. Consult your potentiostat manual for more information. A typical Step Size for a Cyclic Polarization scan is between 0.2 and 1 mV/step. If the Step Size has to be rounded to fit the resolution of the D/A converter, the Sample Period is also adjusted so that the scan rate is correct. The Number of Points must be less than 262 143. If you have more points, the experiment aborts just before the scan phase of the sequence.The units used for the Sample Period are seconds. The shortest Sample Period we recommend is 0.25 second. The longest Sample Period allowed is 715 seconds.
Comments are closed.