Insight into the island-sea effect of Cu-N-C for enhanced CO2 eletroreduction selectively towards C2H4

The electrochemical reduction of CO2 into C2H4 with a high energy density and added value is a promising and desirable strategy for addressing carbon neutrality and energy shortage. However, the intricate peculiarity of the reaction limits the selectivity of atomically dispersed copper catalysts (ADCCs) towards C2H4, primarily due to the excessive number of electron transfer steps and the singular reactivity resulting from the presence of isolated single atoms or atom clusters. Herein, the Cu-N - C catalyst with a precisely controlled Island-sea structure (Island of atom cluster surrounded by the Sea with single atoms, namely CuSA/AC- C3N4) delivered outstanding C2H4 selectivity of up to 80.35 % (carbonaceous product ratio exceeding 99.4 %) and enhanced activity (a 56fold increase in current density). Experimental and theoretical investigation further unveiled that the crucial intermediate *CHO was generated at the Sea of single-atoms and then transferred to the Island of atom cluster with high reductive activity via the electron bridge, facilitating subsequent C-C coupling and deep reduction towards C2H4. Importantly, the Island-sea effect not only coupled the electron transfer processes but also facilitated the synergistic functionalization reactions involving the supply of *H and C-C bond formation. This study provides novel insights and avenues for the development of enhanced M-N - C catalysts.