I have a chromium-hexacyanoferrate on graphene symmetric cell in an aqueous sodium electrolyte.
I expect a capacity of around 23microAh in the charge-discharge test of the symmetric cell. But at a rate of 1C (23microA current) i get around 0.8microAh!!!
At a current of 0.8microA the charging had been running for 25h+ and the cell voltage was stuck at 0.6V. The charge was >21microAh so I discharged the cell and tried higher current rates. It was never going to reach the 0.9V.
At 10 microA current I get 0.97microAh capacity.
Does anyone know what is going on?
A quick yet a little destructive way for a trouble-shoot is to apply an even larger current density, say, 1 A to see if the cell potential can surmount the 0.6 V plateau. Based on the CV you provided, the charge-discharge profiles expect to experience a plateau at around 0.6 V when charging and a plateau at ~0.4 V when discharging. So if you choose a small current density to run, the cell potential may need an extra long time to go through the plateau.
What is the initial state of your "symmetric cell" (particular) electrodes ?
If you could measure, also, the potential VC of the (acknowledged as the) Counter electrode (vs. Ag/AgCl) in your symmetric cell, it (VC) might illustrate the answer.
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