Potassium ion modulation of the Cu electrode-electrolyte interface with ionomers enhances CO2 reduction to C2+ products

Ionomers have shown promise as organic coatings on Cu electrodes to increase the CO2 reduction (CO2R) selectivity toward multi-carbon (C2+) products. However, the effects of systematic polymer structure modification on electrocatalytic performance have been seldom reported. Herein, we report on a series of polystyrene-based ionomers to probe the effect of local [K+] in the Cu electrode microenvironment on CO2R performance. Partial current density toward C2+ products (|jC2+|) increases with [K+] in ionomers, up to 225 mA cm−2. Replacing K+ with [Me4N]+ lowers performance to the level of bare Cu, highlighting the crucial role of K+ in improving C2+ product selectivity. Molecular dynamics simulations show that CO2 diffusivity increases with [K+], implicating CO2 transport to the electrode as a potential mechanism for improved CO2R performance. Our results highlight the intersection of synthetic polymer chemistry and electrocatalysis as a promising strategy in electrode modification toward achieving high selectivity of value-added chemicals.