Oxygen Vacancy Tuning toward Efficient Electrocatalytic CO 2 Reduction to C 2 H 4

Electrochemical reduction of carbon dioxide (CO 2 ) is a promising approach to solve both renewable energy storage and carbon‐neutral energy cycles, while the capability of selective reduction to C 2+ products has still been quite limited. In this work, partially reduced copper oxide nanodendrites with rich surface oxygen vacancies (CuO x –Vo) are developed, serving as excellent Lewis base sites for enhanced CO 2 adsorption and subsequent electrochemical reduction. Theoretical calculations reveal that these oxygen vacancy‐rich CuO x surfaces provide strong binding affinities to the intermediates of *CO and *COH, but weak affinity to *CH 2 , thus leading to efficient formation of C 2 H 4 . As a result, the partially reduced CuO x nanodendrites exhibit one of the highest C 2 H 4 production Faradaic efficiencies of 63%. The electrochemical stability test further shows that the C 2 H 4 Faradaic efficiency strongly depends on the oxygen vacancy density in CuO x , which can further be regenerated for several cycles, thus suggesting the critical role of oxygen vacancies for the C 2 product selectivity.