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. Copper catalyses electrochemical reduction of CO2 to valuable multicarbon products, but its selectivity depends on the local microenvironment near the catalyst surface. Here, the authors explore and optimize this environment to improve performance using bilayer ionomer coatings to control the local pH and CO2/H2O ratio.