Tailoring Electrochemical CO₂ Reduction on Copper by Reactive Ionic Liquid and Native Hydrogen Bond Donors

Abstract

Electrochemical CO2 reduction (CO2RR) on copper (Cu) shows promise for higher‐value products beyond CO. However, challenges such as the limited CO2 solubility, high overpotentials, and the competing hydrogen evolution reaction (HER) in aqueous electrolytes hinder the practical realization. We propose a functionalized ionic liquid (IL) which generates ion‐CO2 adducts and a hydrogen bond donor (HBD) upon CO2 absorption to modulate CO2RR on Cu in a non‐aqueous electrolyte. As revealed by transient voltammetry, electrochemical impedance spectroscopy (EIS), and in‐situ surface‐enhanced Raman spectroscopy (SERS) complemented with image charge augmented quantum‐mechanical/molecular mechanics (IC‐QM/MM) computations, a unique microenvironment is constructed. In this microenvironment, the catalytic activity is primarily governed by the IL and HBD concentrations; former controlling the double layer thickness and the latter modulating the local proton availability. This translates to ample CO2 availability, reduced overpotential, and suppressed HER where C4 products are obtained. This study deepens the understanding of electrolyte effects in CO2RR and the role of IL ions towards electrocatalytic microenvironment design.

Understanding the Electrode–Electrolyte Interfaces of Ionic Liquids and Deep Eutectic Solvents

“…This shift underscores the necessity of comprehensively understanding the mechanisms of CO 2 binding and the processes away from the equilibrium as the dynamic nature of the interface presents an electron transfer reaction in parallel to other chemical reactions such as hydrogen transfer among the IL ions and CO 2 chemisorption by both the anion and the cation. Recently, we reported on the reduction of the onset potential of CO 2 RR on Ag and Cu electrodes with a CO 2 -reactive [EMIM]­[2-CNpyr] IL in non-aqueous electrolyte where the microenvironment and the catalytic role of the IL were examined through the interfacial structure and surface species as investigated by EIS and in situ SERS. While CO was obtained as the only product over Ag (>95% Faradaic efficiency), various C 2+ products were reported over Cu owing to the stabilization of the reaction intermediates on the electrode surface and the hydrogen bonding among the interfacial species.…”

Modulating Interfacial Hydrogen-Bond Environment by Electrolyte Engineering Promotes Acidic CO2 Electrolysis

“…The electrocatalytic reaction occurs in the narrow nanoscale region at the electrode–electrolyte interface. − Modifying the components of electrolytes is a significant strategy to regulate the interfacial hydrogen-bond (H-bond) environment and steer the kinetics of hydrogen-related reactions, e.g., HER and CO 2 RR. − For instance, Li et al discovered that alkali-metal cations can modulate proton transfer kinetics by reducing the connectivity of the H-bond network in the electric double layer (EDL) . Xu and co-workers demonstrated that bulky organic cations, such as tetrapropyl ammonium, can foster the formation and lifetime of H-bonds among interfacial water molecules, thereby enhancing the kinetics of HER and hydrogen oxidation reactions (HOR).…”

Deciphering the role of aromatic cations in electrochemical CO2 reduction: interfacial ion assembly governs reaction pathways

“…Ionic liquids have highly tunable ion structures, high intrinsic conductivity, wide electrochemical windows, and can be designed to be proton donors or acceptors. 30–33 These properties provide many avenues for using ionic liquids as co-catalytic promoters in electrocatalysis. Further, ionic liquids are soluble in nonaqueous and aprotic solvents, circumventing competing water reduction and providing opportunities for detailed mechanistic study of proton-coupled electron transfers in electrochemical CO 2 reduction by introducing external proton donors.…”