(131d) Electrolyte Design for Reactive Capture and Conversion of CO2: Interfacial Understanding of Functionalized Ionic Liquids, Hydrogen Bond Donors, and Alkali Cations

The electrochemical CO₂ reduction (ECO₂R) into value-added products presents a promising strategy for mitigating climate change. A critical factor in improving the efficiency and selectivity of this process is the design of electrolytes that can effectively capture CO₂ and convert it into valuable products without the need for energy-intensive CO₂ desorption and concentration steps. In recent years, functionalized ionic liquid (IL)-based electrolytes have gained attention as promising media for integrated CO₂ capture and conversion due to their high thermal and electrochemical stability, as well as their high CO₂ solubility.¹ Specifically, imidazolium-based ILs have been shown to stabilize CO₂ reduction products through electric field modulation, benefiting from their aromaticity, hydrogen bond-donating ability, and capacity for structural reorganization.^2-4

In this presentation, I will discuss our recent efforts to understand the role of IL ions at the electrode-electrolyte interface. Specifically, we focus on functionalized ILs, such as 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]),² and the unfunctionalized IL, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]),^{4, 5} in combination with various hydrogen bond donors (HBDs), including water, short-chain alcohols, and alkali metal cations with different atomic radii, on silver electrodes. Using a combination of voltammetry techniques, in-situ surface-enhanced Raman spectroscopy (SERS), and density functional theory (DFT) calculations, we demonstrate that the confinement of CO₂ between the [EMIM]⁺ ring and the Ag electrode stabilizes the CO₂ molecule at the interface, lowering the overpotential for electron transfer and facilitating CO formation with more than 94% Faradaic efficiency.^{2, 6} Our results further indicate that adding hydrogen bond donors with controlled hydrogen bonding modifies the local environment and improves the thermodynamics of ECO₂R. Additionally, we explore the relatively underexamined influence of alkali cations in aqueous [EMIM][BF₄]-based electrolytes. While both [EMIM]⁺ and alkali cations independently promote CO₂-to-CO conversion on Ag, their coexistence leads to negative effects. Specifically, Li⁺ significantly suppresses imidazolium-mediated CO₂RR, shifting selectivity toward hydrogen evolution due to stronger surface adsorption, which inhibits access to Ag active sites.⁵ These findings provide valuable insights into electrolyte design strategies for controlling selectivity during CO₂ reduction and suggest pathways for minimizing ECO₂R energy requirements while mitigating competing reactions.

References:

1. Dongare, S.; Zeeshan, M.; Aydogdu, A. S.; Dikki, R.; Kurtoğlu-Öztulum, S. F.; Coskun, O. K.; Muñoz, M.; Banerjee, A.; Gautam, M.; Ross, R. D.; Stanley, J. S.; Brower, R. S.; Muchharla, B.; Sacci, R. L.; Velázquez, J. M.; Kumar, B.; Yang, J. Y.; Hahn, C.; Keskin, S.; Morales-Guio, C. G.; Uzun, A.; Spurgeon, J. M.; Gurkan, B., "Reactive capture and electrochemical conversion of CO₂ with ionic liquids and deep eutectic solvents." Chemical Society Reviews 2024, 53, 8563-8631

2. Dongare, S.; Coskun, O. K.; Cagli, E.; Lee, K. Y. C.; Rao, G.; Britt, R. D.; Berben, L. A.; Gurkan, B., "A Bifunctional Ionic Liquid for Capture and Electrochemical Conversion of CO₂ to CO over Silver." ACS Catalysis 2023, 13 (12), 7812-7821.

3. Coskun, O. K.; Dongare, S.; Doherty, B.; Klemm, A.; Tuckerman, M.; Gurkan, B., "Tailoring Electrochemical CO₂ Reduction on Copper by Reactive Ionic Liquid and Native Hydrogen Bond Donors." Angewandte Chemie International Edition 2024, 63 (1), e202312163.

4. Coskun, O. K.; Bagbudar, Z.; Khokhar, V.; Dongare, S.; Warburton, R. E.; Gurkan, B., "Synergistic Effects of the Electric Field Induced by Imidazolium Rotation and Hydrogen Bonding in Electrocatalysis of CO₂." Journal of the American Chemical Society 2024, 146 (34), 23775-23785.

5. Nkurunziza, F.; Dongare, S.; Chatterjee, S.; Shah, B.; Gautam, M.; Muchharla, B.; Kumar, B.; Janik, M. J.; Gurkan, B.; Sacci, R. L.; Spurgeon, J. M., "Alkali Cation Inhibition of Imidazolium-Mediated Electrochemical CO₂ Reduction on Silver." Journal of the American Chemical Society 2025, 147 (9), 7564-7577.

6. Dongare, S.; Coskun, O. K.; Cagli, E.; Stanley, J. S.; Mir, A. Q.; Brower, R. S.; Velázquez, J. M.; Yang, J. Y.; Sacci, R. L.; Gurkan, B., "Key Experimental Considerations When Evaluating Functional Ionic Liquids for Combined Capture and Electrochemical Conversion of CO₂." Langmuir 2024, 40 (18), 9426–9438.