Tethered Alkylammonium Dications as Electrochemical Interface Modifiers: Chain Length Effect on CO 2 Reduction Selectivity at Industry-Relevant Current Density.

The electrochemical reduction of CO 2 (CO 2 RR) has the potential to be an economically viable method to produce platform chemicals synergistically with renewable energy sources. Copper is one of the most commonly used electrocatalysts for this purpose, as it allows C-C bond formation, yielding a broad product distribution. Controlling selectivity is a stepping stone on the way to its industrial application. The kinetics of the reaction can be modified to favor the rates of certain products quickly and inexpensively by applying additives such as ionic liquids and coelectrolytes that directly affect the electrocatalytic interface. In this work, we propose tethered tetraalkylammonium salts as double-charged cationic modifiers of the electrochemical double layer to control CO 2 RR product selectivity. A novel setup comprising a gas diffusion electrode (GDE) flow cell coupled with real-time mass spectroscopy was used to study the effect of a library of the selected salts. We emphasize how the length of an alkyl linker effectively controls the selectivity of the reaction toward C 1 , C 2 , or C 3 products at high relevant current densities ( J total = -400 mA cm -2 ) along with the inhibition of the parasitic hydrogen evolution reaction. Standard long-term experiments were performed for quantitative validation and stability evaluation. These results have broad implications for further tailoring an effective catalytic system for selective CO 2 reduction reaction.