Organic–Inorganic Grain Boundary Engineering for Highly Selective and Stable CO 2 Electroreduction to Ethylene

Electrocatalytic conversion of CO 2 to ethylene (C 2 H 4 ), the cornerstone of the chemical industry, offers a sustainable alternative to conventional energy‐intensive steam cracking but remains limited by inefficient C‐C coupling and competing hydrogen evolution reaction. Here, we report an organic‐inorganic grain‐boundary (OIGB) catalyst by embedding CuO nanodomains within a Cu‐based metal‐organic framework matrix, which creates well‐defined electronically integrated interfaces that enable cooperative stabilization of *CO and *COH intermediates. The OIGB structure achieves a high Faradaic efficiency of ∼81% for CO 2 electroreduction to C 2 H 4 at an industrially relevant current density of 300 mA cm − 2 , together with stable operation for over 100 h. Operando spectroscopy combined with computational calculations reveals a synergistic mechanism in which CuO nanodomains serve as local *CO generation sites while Cu–N coordination sites stabilize *COH species, associated with formation of the key *COH‐CO intermediate for CO 2 electroreduction to C 2 H 4 .