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 CO2 reduction reaction (CO2RR). However, the microscopic mechanism by which imidazolium-based cations promote CO2RR remains unclear. In this study, we observe that despite the structural differences between [Bmmim](+) and [Bmim](+), both exhibit high catalytic activity during the electrochemical CO2RR. Electrochemical and in situ spectroscopic analyses, as well as Quantum Theory of Atomic in Molecules (QTAIM), reveal that the pivotal step in the CO2RR mechanism facilitated by [Bmmim](+) and [Bmim](+) involves the formation of [Bmmim]center dot center dot center dot CO2 or [Bmim]center dot center dot center dot CO2 complexes via hydrogen bond. These complexes enhance the electrochemical reduction of CO2 or center dot CO2- on electrode, facilitating efficient CO production. Specifically, the [Bmmim]center dot center dot center dot CO2 complex forms at the C4-H position of the imidazole ring, while in the [Bmim]center dot center dot center dot CO2 complex, it forms at the C-2-H position.