for my modified electrode oxidation of uric acid oxidation peak starts early but oxidation peak broader than bare GC electrode????
onset potential starts from 0.25 V and ends at 0.45V
Strictly speaking, the concept of "current onset potential, Eon" has very little meaning in quantitative analysis in comparison with the "current peak potential, Ep" and the "half-wave (or half-peak) potential, E1/2". Unfortunately, it has been reported in many publications (also in some of my own papers) when comparison is needed or it is difficult to determine the peak or half-wave potentials.
Nevertheless, the current onset potential is usually measured by linearly extrapolating the fast rising current portion of the current wave (or peak) to the linear extrapolation of the baseline (background) current, and the intercept potential is regarded as Eon. The attached drawing illustrates this method.
Because the current variation with potential is not really linear in the CV of an electrode reaction, the problem is obviously that the extrapolation results depend on how much the current-potential plot is expand. A simple thumb of rule is that you only apply the extrapolation on a CV that shows the full CV, or at least the whole current peak. Do not try to obtain a "more accurate" result by expanding the CV, which will only make the situation worse.
Strictly speaking, the concept of "current onset potential, Eon" has very little meaning in quantitative analysis in comparison with the "current peak potential, Ep" and the "half-wave (or half-peak) potential, E1/2". Unfortunately, it has been reported in many publications (also in some of my own papers) when comparison is needed or it is difficult to determine the peak or half-wave potentials.
Nevertheless, the current onset potential is usually measured by linearly extrapolating the fast rising current portion of the current wave (or peak) to the linear extrapolation of the baseline (background) current, and the intercept potential is regarded as Eon. The attached drawing illustrates this method.
Because the current variation with potential is not really linear in the CV of an electrode reaction, the problem is obviously that the extrapolation results depend on how much the current-potential plot is expand. A simple thumb of rule is that you only apply the extrapolation on a CV that shows the full CV, or at least the whole current peak. Do not try to obtain a "more accurate" result by expanding the CV, which will only make the situation worse.
Then how can i measured onset potential????
is it possible with LSV???
can you help me to learn how to run LSV???
Karhikeyan Rangasamy: The figure attached to my message illustrates how you measure the current onset potential, Eon. (It really should be current onset potential, whilst people use onset potential for convenience.)
The plot shown in the figure is an LSV which is a half of the CV. You can simply run the potential scan in one direction to obtain an LSV, or take half of the data of CV as an LSV.
The way to measure Eon is the same on both the LSV and CV as I have illustrated.
Could you give a reference to the picture of plot you posted? I am looking for a reference that mentions Ip=2I1/2
I drew it myself, but you can find the relevant information in most textbooks on electrochemistry. Please be informed that the plot I showed above is for you to use E1/2 and Ep as the more appropriate parameters from LSV and CV for electrochemical analysis and comparison. Eon is not really a good alternative unless your LSV or CV does not show a current peak properly.
if we want to calculate onset potential for Oxygen evolution reaction what should we do?
for example if we want to calculate it which one (black or green) should we consider?
The black line is for the current onset of oxygen adsorption, whilst the green line for that of oxygen gas evolution. Therefore, it is necessary to clarify which electrode process is concerned when you are describing the so called onset potential.
The term "oxygen evolution reaction" should refer to both the adsorption and evolution steps, and hence is too general in terms of cyclic voltammetry.
I guess your SWVs were recorded in an acidic or neutral electrolyte, and hence showed both steps. However, if recorded in an alkaline electrolyte, the two steps would occur at very close potentials, making it into an apparent single current rise, and hence only one onset potential.
@ George Zheng Chen
Prof. I want to calculate onset potential for Oxygen Reduction reaction (ORR), Can you provide me a graph as above I will be thankful.
@ Anand Parkash
There is no specific rules for onset potential. It is better and easy way to find potential at current density of 0.1 or 1 mA cm-2 and state as "onset potential of .........at current density of 0.1 or 1 mA cm-2 same as overpotential. you can follow the article below
http://dx.doi.org/10.1016/j.electacta.2015.09.147
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