Mechanism of efficient electroreduction of CO2 to CO at Ag electrode in imidazolium-based ionic liquids/acetonitrile solution

Imidazolium-based ionic liquids (Imim-ILs) have great application potential in catalyzing the electrochemical CO reduction reaction (CORR). However, the microscopic mechanism by which imidazolium-based cations promote CORR remains unclear. In this study, we observe that despite the structural differences between [Bmmim] and [Bmim], both exhibit high catalytic activity during the electrochemical CORR. Electrochemical and in situ spectroscopic analyses, as well as Quantum Theory of Atomic in Molecules (QTAIM), reveal that the pivotal step in the CORR mechanism facilitated by [Bmmim] and [Bmim] involves the formation of [Bmmim]···CO or [Bmim]···CO complexes via hydrogen bond. These complexes enhance the electrochemical reduction of CO or ·CO on electrode, facilitating efficient CO production. Specifically, the [Bmmim]···CO complex forms at the C4-H position of the imidazole ring, while in the [Bmim]···CO complex, it forms at the C2-H position.