Within the series tested, DETA induced a significant increase in CO2 selectivity to formate, reaching high FEHCOO-of 51%, while DEA had no significant effect on the catalyst's activity or selectivity (FEHCOO-= 25%). The most striking results were obtained by the addition of PMDETA, which strongly shifted the selectivity of Mn/CC towards formate, with a remarkable FEHCOO-of 66%. Noteworthy, while FEH2 of DETA, DEA and PMDETA are similar (12, 21 and 11%, respectively), FECO values of PMDETA is significantly lower (5%). The main difference between the three amines is that PMDETA presents three tertiary amine functionalities, which orients CO2 capture exclusively toward carbonation (eq.2, Scheme 1). For this reason, three other tertiary amines or guanidine were tested at the very same concentration: TEA, TMEDA and TBG. These species respectively present one, two and three tertiary amine functionalities, which are conjugated into a guanidine pattern in the latter. Surprisingly, these additives did not induce an increase in the production of formate compared to the aminefree reference system. In contrary, TMEDA displayed an NMR analyses performed on amine samples at different concentration in CD3OD but with a fixed 50 mM D2O provided some clues about the species that may be present in the cathodic compartment and on their relative abundance (supporting section 7). On average, amines can be loaded with around 0.3 -0.4 eq of CO2 per nitrogen site at 500 mM. This loading does not vary substantially upon dilution with CO2saturated CD3OD containing 50 mM D2O, as attested by measurement of the protonation state (from 1 H chemical shift and potentiometry) and by the absence of stripping. For amines bearing primary and secondary nucleophilic nitrogen binding sites such as DEA and DETA, dilution from 500 to 5 mM globally switches the CO2 fixation pathway, from carbamation to carbonation. At high alkalinity/amine concentration, methyl carbonate MeCO3 ─ is observed as a carbonation side product.