Orderly Coating of Bilayer Polymer to Tailor Microenvironment for Efficient C−N Coupling Toward Highly Selective Urea Electrosynthesis

Abstract Electrosynthesis of urea from co‐reduction of carbon dioxide and nitrate is a promising alternative to the industrial process. However, the overwhelming existence of proton and nitrate as well as the insufficient supply of CO 2 at the reaction interface usually result in complex product distributions from individual nitrate reduction or hydrogen evolution, instead of C−N coupling. In this work, we systematically optimize this microenvironment through orderly coating of bilayer polymer to specifically tackle the above challenges. Polymer of intrinsic microporosity is chosen as the upper polymer to achieve physical sieving, realizing low water diffusivity for suppressing hydrogen evolution and high gas permeability for smooth mass transfer of CO 2 at the same time. Polyaniline with abundant basic amino groups is capable of triggering chemical interaction with acidic CO 2 molecules, so that is used as the underlying polymer to serve as CO 2 concentrator and facilitate the carbon source supply for C−N coupling. Within this tailored microenvironment, a maximum urea generation yield rate of 1671.6 μg h −1 mg −1 and a high Faradaic efficiency of 75.3 % are delivered once coupled with efficient electrocatalyst with neighboring active sites, which is among the most efficient system of urea electrosynthesis.