Uncovering the active species in amine-mediated CO2 reduction to CO on Ag

Electrochemical reactive capture of CO2, which integrates CO2 capture with its conversion directly from amine and other capture solutions, is of growing interest but introduces considerable complexity to the electrochemical process due to the wide range of possible reactant participants. In this work, we reveal the governing parameters and basic mechanism behind amine-mediated CO2 conversion as an essential first step towards improving these processes. We first demonstrate the critical influence of CO2 partial pressure of the capture stream on the resulting solution pH, which directly affects amine speciation and the Faradaic efficiency (FE) of CO production on Ag. Moreover, by considering amines of different pKa and with different propensities to form the amine-CO2 adduct carbamate, we show that CO2R FE is governed primarily by dissolved CO2, enabling some amine-containing solutions to have comparable CO2R selectivity and kinetics to amine-free bicarbonate solutions. Finally, descriptors of high selectivity CO production are identified.