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 (|j_C2+|) 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.