Cation effect on dual-function amine-based electrolytes for CO2 capture and electroreduction

Dual-function amine-based electrolytes provide both carbon dioxide (CO 2 ) capture and electrocatalytic CO 2 reduction capabilities, combining the capture and conversion steps of conventional separations in a single system, increasing efficiency and reducing energy consumption. Cations serve as critical constituents within bifunctional amine-based electrolytes, integral to both CO 2 absorption mechanisms and the electrochemical reduction of carbamates, but this issue has not been comprehensive studied. In this study, we investigated the effect of five different cations (M + = Li + 、Na + 、K + 、Rb + 、Cs + ) on the CO 2 capture and electroreduction properties of dual-function amine-based electrolyte. Electrochemical comparative analyses reveal that the presence of larger cations (Cs + ) significantly reduces series resistance and charge-transfer resistance, while augmenting electric double-layer capacitance and electrochemical surface area. These synergistic effects culminate in elevated current densities and accelerated reaction rates during carbamate reduction processes. Density functional theory (DFT) simulations elucidate that expanding cationic radii strengthen both adsorption trends and charge transfer of carbamate (R 1 R 2 NCOO - ) at electrode–electrolyte interface. Comparative analysis of the HOMO-LUMO orbitals shows that R 1 R 2 NCOO - Cs + is more easily reduced and electronic excited. These computational validate the observed enhancements in current density from experimental electrochemical. Higher electrolyte concentrations (≥1 M) enhance the selectivity of carbamate reduction but impede mass transfer due to increased viscosity following CO 2 absorption. Conversely, lower electrolyte concentrations (<1 M) improve the current density of carbamate reduction but reducing CO 2 capture rates. Moreover, an equimolar cation-to-amine optimizes the enhancement of CO 2 absorption capacity and electroreduction efficiency. This work provides a comprehensive understanding of how cations influence the electrocatalytic reduction of captured CO 2 in amine-rich solutions, offering valuable insights for the design of electrolytes for CO 2 capture and electroreduction.