The Effect of Salts on the CO 2 Reduction Product Distribution in an Aprotic Electrolyte

Electrochemical CO reduction in non-aqueous solvents is promising due to the increased CO solubility of organic-based electrolytes compared to aqueous electrolytes. Here the effect of nine different salts in propylene carbonate (PC) on the CO reduction product distribution of polycrystalline Cu is investigated. Three different cations (tetraethylammonium (TEA), tetrabutylammonium (TBA), and tetrahexylammonium (THA)) and three different anions (chloride (Cl), tetrafluoroborate (BF ), and hexafluorophosphate (PF )) were used. Chronoamperometry and in-situ FTIR measurements show that the size of the cation has a crucial role in the selectivity. A more hydrophobic surface is obtained when employing a larger cation with a weaker hydration shell. This stabilizes the CO radical and promotes the formation of ethylene. CO reduction in 0.7 M THACl/PC shows the highest hydrocarbon formation. Lastly, we hypothesize that the hydrocarbon formation pathway is not through C-C coupling, as the CO solubility in PC is very high, but through the dimerization of the COH intermediate.