The electrochemical reduction of CO₂ has been extensively studied over the past decades. Nevertheless, this topic has been tackled so far only by using a very fundamental approach and mostly by trying to improve kinetics and selectivities toward specific products in half-cell configurations and liquid-based electrolytes. The main drawback of this approach is that, due to the low solubility of CO₂ in water, the maximum CO₂ reduction current which could be drawn falls in the range of 0.01–0.02 A cm^–2. This is at least an order of magnitude lower current density than the requirement to make CO₂-electrolysis a technically and economically feasible option for transformation of CO₂ into chemical feedstock or fuel thereby closing the CO₂ cycle. This work attempts to give a short overview on the status of electrochemical CO₂ reduction with respect to challenges at the electrolysis cell as well as at the catalyst level. We will critically discuss possible pathways to increase both operating current density and conversion efficiency in order to close the gap with established energy conversion technologies.

Room‐temperature ionic liquids (RTILs) are promising new electrolytes for efficient carbon dioxide reduction. However, due to their high viscosity, the mass transport of CO₂ in RTILs is typically slow, at least one order of magnitude slower than in aqueous systems. One possibility to improve mass transport in RTILs is to decrease their viscosity through dilution with water. Herein, defined amounts of water are added to 1‐butyl‐3methylimidazolium tetrafluoroborate ([BMIm][BF₄]), which is a hydrophilic RTIL. Electrochemical measurements on quiescent and hydrodynamic systems both indicate enhanced CO₂ electroreduction. This enhancement has its origin in thermodynamic/kinetic effects (the addition of water increases the availability of H⁺, which is a reaction partner of CO₂ electroreduction) and in an increased rate of transport due to lower viscosity. Electrochemically determined diffusion coefficients for CO₂ in [BMIm][BF₄]/water systems agree well with values determined by NMR spectroscopy.