Difference between 2-electrode and 3-electrode cell

[Ricardo QR]

Hi! I'm currently starting to work with supercapacitors performing cyclic voltammetry of carbon electrodes in 2 and 3 electrodes cell.
Since the electrolyte is H2SO4 1M, the scan range is 0.0V to 0.8V. When using the 3-electrodes cell (RE: Ag/AgCl, CE: Pt) I can clearly observe a broad redox signal around 0.4V but when using the 2-electrodes cell (2 carbon electrodes) the redox signal is almost not visible but there seems to be something around 0.0V.
I believe that in the 2 electrodes cell, the potential is divided between the two electrodes so individual electrode potentials will range from -0.4V to 0.4V. Is my reasoning correct?
Will the electrolyte locally decompose when the electrode reaches -0.4V? Thanks!

 

[gtoguy97]

Yes, your reasoning is correct. When the electrode potential reaches -0.4V, the electrolyte may start to decompose. This can be prevented by adjusting the scan rate or changing the scan range to prevent the potential from reaching a too low value.