Tailored catalyst microenvironments for CO2 electroreduction to multicarbon products on copper using bilayer ionomer coatings

Electrochemical carbon dioxide reduction (CO₂R) provides a promising pathway for sustainable generation of fuels and chemicals. Copper (Cu) electrocatalysts catalyse CO₂R to valuable multicarbon (C₂₊) products, but their selectivity depends on the local microenvironment near the catalyst surface. Here we systematically explore and optimize this microenvironment using bilayer cation- and anion-conducting ionomer coatings to control the local pH (via Donnan exclusion) and CO₂/H₂O ratio (via ionomer properties), respectively. When this tailored microenvironment is coupled with pulsed electrolysis, further enhancements in the local ratio of CO₂/H₂O and pH are achieved, leading to selective C₂₊ production, which increases by 250% (with 90% Faradaic efficiency and only 4% H₂) compared with static electrolysis over bare Cu. These results underscore the importance of tailoring the catalyst microenvironment as a means of improving overall performance in electrochemical syntheses.