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I am working for PEM fuel cell cathode material. I am confused regarding the onset potential determination for my catalyst (CV attached, fig 1 is complete CV while fig 2 is its zoom image for clear understanding of change in reduction curve direction) and also why the reduction starts from 0.8e-4 A instead of 0 A. I performed this CV in calomel electrode under oxygen in 0.5M H2SO4.

i) If I use Argon and overlap both the graphs then probably the curves start to separate at around 0.58V.

ii) I have read in some discussions to consider the onset potential at which current density approaches 0.1mA/cm2 while in other discussion, I have read to consider 20microA/cm2 as onset potential. If I plot current density instead of current only, then in first case (0.1mA/cm2), it would be 0.785V while in second case (20microA/cm2), it would be 0.775V

iii) If I only consider the point from where curve starts to change the direction of reduction peak, it would be 0.64V or 0.56V iv) if I draw tangents then this would be around 0.5V. So please help me in i) analyzing onset potential ii) guide me why there is positive current in the reduction peak iii) i also don't know what does the background correction mean and should I need to do it for my CV? All potentials are measured in SCE.

enter image description here

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The reason the current starts at 0.8x10^-4 A is probably because you have an equilibration time built in to your procedure (say of a few seconds),or even if you do not,there are parasitic currents always occurring, especially if you are starting at 0.8 V (vs SCE). Given that I don't know much more about your system or how you arrived at the onset potential calculations, I cannot comment. Could you please provide more details?

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  • $\begingroup$ Thanks for your response. I dont know what information do you require so i am mentioning all the details: the compound is C/N/S/transition metal, medium: 0.5 M H2SO4, 3mm glassy carbon electrode, scan rate = 0.01V/s, quiet time = 2sec, sensitivity=1e-4A/V. $\endgroup$ – m.s87 Oct 18 '18 at 10:32

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