= Solution
Peak \b[I] is the cathodic reduction shifted positive of the unbound AQ$^{\bullet-}$/AQ$^{2-}$ event, consistent with reduction of the CO$_2$-bound semiquinone to mono-carbonate dianion. Peak \b[II] is the corresponding relatively negative-potential return oxidation of mono-carbonate dianion. Peak \b[III], appearing farther positive on the faster return scan, is consistent with direct oxidation of the more strongly protected bis-carbonate dianion, followed by CO$_2$ release.
This assignment is consistent with binding making the reduced species harder to oxidize. At slow scan, chemical interconversion and CO$_2$ dissociation can feed the easier mono-carbonate oxidation pathway; at fast scan a larger fraction of kinetically retained bis-adduct survives to its direct oxidation potential. The two separated reductions also show that initial capture and its associated potential shift are not sufficient to make every ECEC step a single equilibrated two-electron wave.
These traces support coupled electron-transfer/binding chemistry but do not determine every microscopic rate constant or exclude EECC pathways. The peak assignments are species-family assignments within the stated mechanism, rather than proof of a unique elementary sequence from voltammetry alone.
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