Cation Effects on CO2 Delivery to Cu Electrode in Reactive Capture of CO2.

Abstract

The direct electrochemical conversion of captured CO₂, known as reactive capture of CO₂ (RCC), remains a formidable challenge in heterogeneous catalysis. Given that amines are one of the most widely used capture agents for CO₂, it would be desirable to electrochemically reduce the resultant adducts, such as carbamate, directly in RCC. However, current understanding suggests that the primary species undergoing reduction in RCC with amines is the CO₂ dissociated from the sorbent. Herein, we employ ab initio molecular dynamics (AIMD) with DFT to analyze how the nature of alkali metal cations in the electrolyte affects carbamate at the Cu surface, thereby assessing the possibility of promoting RCC by cation effects. The simulations show that the carbamate's orientation with respect to the electrode is governed by the optimal distance between the carbamate and the cation, specifically how this distance aligns with the cation's hydration spheres. Moreover, the slow-growth AIMD results indicate that the CO₂ dissociation barrier correlates with the orientation of carbamate at the interface. When the carbamate resides beyond the cation's first hydration sphere, it adopts a flat orientation with respect to the surface that promotes the release of CO₂ from the capture agent. In contrast, when the carbamate disrupts the first hydration sphere and exhibits a strong cation-π interaction, it adopts an upright orientation that is less conducive to CO₂ release. These findings reveal a nontrivial cation effect in RCC, suggesting that it should be possible to optimize RCC via the choice of the electrolyte.