Cyclic voltammetry with or without ohmic drop compensation

Files:
Ohmic Drop Compensation.EXP
No ODC 035.CRV
Dynamic ODC 045.CRV
No ODC (Bis) 055.CRV
Static ODC 075.CRV

Different modes of ohmic drop compensation are compared: No, Dynamic and Static auto using cyclic voltammetries performed with Pt in H2S04 [1] [3]. The cell resistance is determined (±2.5 Ohms) and the cyclic voltammetries obtained with Dynamic and Static auto ODC exhibit a peak shift versus the cyclic voltammetry obtained with No ODC as expected from theory. (Peak shift = 25 mV = 10 mA * 2.5 Ohm). The cell resistance is measured and the potential Set value = Potential + Ohmic drop is recorded with the A/D IN additional channel.

Solution H2SO4 0.5 M
WORK Platinised platinum
Plate ± 5X5 mm
(CDC641T conductivity cell) [2]
REF Calomel electrode (XR100)
AUX Platinum wire (XM100)
A/D IN E OUT (Potential output)

CP06 cell, temperature: ambient ( 22 °C), without nitrogen bubbling. The initial Chrono coulometry performed at -300 mV /REF stabilises the WORK and saturates the solution with H2 in the vicinity of the WORK. The cyclic voltammetries were stabilised since the second cycle within every run. The experimental curves are "extract" of one cycle for each ODC mode. Scan rate 50 mV/s (5 mV potential steps).

Display: Type = Normal X = Potential Y1 = Current Y2 = No

Overlay No ODC 035.CRV with Dynamic ODC 045.CRV, No ODC (Bis) 055.CRV and Static ODC 075.CRV and use the graphic data to distinguish between the curves with (blue) and without (red) ohmic drop compensation.
For instance, select these representations:
No ODC 035.CRV (red triangles) No ODC (Bis) 055.CRV (red line)
Dynamic ODC 045.CRV (blue squares) Static ODC 075.CRV (blue line)

The different modes of ohmic drop compensation can be run within the same experiment and compared. The cell resistance determined either by Dynamic or Static auto is of the same value and is compensated so that the cyclic voltammetries obtained with Dynamic and/or Static auto ODC exhibit a peak shift versus the cyclic voltammetry obtained with No ODC, as expected from theory. (Peak shift at 8 mA = 20 mV = 8 mA * 2.5 Ohm). The cell resistance is measured point per point with the Dynamic ODC and the Set value = Potential + Ohmic drop recorded with the A/D IN additional channel can be compared to the potential value. These two values are equal whenever there is No ODC or no current. The Dynamic ODC does not modify the look of the cyclic voltammetry obtained with Static auto and this proves that the determination of the cell resistance by impedance which is performed point per point in Dynamic mode does not modify the interface studied.

[1] P.A. Christensen and A. Hamnett "Techniques and Mechanisms in Electrochemistry" p228 - Blackie A&P (Imprint of Chapman&Hall, Glasgow, 1994
[2] Platinised platinum amplifies the catalytic effect of Pt.
[3] Ronald Woods "Chemisorption at Electrodes" In "Electroanalytical Chemistry" Vol 9 pp 1-162 - M Dekker, 1976.