Can anyone explain why the current density during a potentiodynamic scan increases with the scan rate?
It depends on what type of reactions you are studying and what portion of the cyclic voltammetry curves you are interested in. For example if you are dealing with the diffusion-control reaction which in most of cases means the concentration of active species at the electrode-solution interface is time dependent, so increasing the scan rate will result in limiting current density increase. Also the capacitive current response of the cell is direct proportional to the potential change in time or in this case the scan rate.
It depends on what type of reactions you are studying and what portion of the cyclic voltammetry curves you are interested in. For example if you are dealing with the diffusion-control reaction which in most of cases means the concentration of active species at the electrode-solution interface is time dependent, so increasing the scan rate will result in limiting current density increase. Also the capacitive current response of the cell is direct proportional to the potential change in time or in this case the scan rate.
Thank you, Anatolie. I am interested in the anodic reactions in the active regime of a polarized carbon steel in a deoxygenated bicarbonate solution. Can you please comment on the effect of the scan rate on the measured currents (charges) in that region? many thanks.
More information would help, like a CV curve, how far you go in anodic region (potential range), concentration of bicarbonate
Actually the range is between -0.8 to -0.6 V vs. SCE, and the bicarbonate concentration is between 0.1 to 1 M. I am currently doing CV studies. Thank you, Anatolie.
.For an electrochemical reaction that is under the control of diffusion limitation the peak current density during potentiodynamic scan increases with scan rate. For diffusion control process the peak current density is related to the square root of the scan rate via the following Randles-Sevcik equation:
Peak current density = (scan rate)**0.5 + constant
Constant = 0. This means the line must pass through the origin. See
J.E.B. Randles, Trans. Faraday Soc. 44 (1948) 327.
A. Sevcik, Collect Czech Chem. Commun. 13 (1948) 349.
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