Electrocatalytic reduction of CO₂ in neat and water-containing imidazolium-based ionic liquids

Energetically efficient electrochemical reduction of CO2 would offer the possibility of storing electricity from renewables in the form of fuels and other valuable chemicals. It may also help mitigate the increase of atmospheric CO2 associated with global warming. However, the process suffers from a low energy efficiency due to the large overpotentials required. In aqueous electrolytes, the competing hydrogen evolution reaction also decreases the faradaic efficiency (which contributes to the low energy efficiency of the process). Recent claims of high faradaic efficiency and low overpotentials for the reduction of CO2 in room temperature ionic liquids (RTILs) and RTIL-water mixtures have spurred considerable research. Here, we offer a critical review of those claims and of recent work aimed at understanding the details of this important reaction in these non-conventional electrolytes.