Electrocatalytic CO2 reduction reaction (CO2RR) to produce multi-carbon products (C2+) is one of the most sustainable manners to achieve net-zero carbon emissions. Among many approaches, enriching grain boundaries (GBs) in copper (Cu) catalysts has been demonstrated to enable enhancement for C2+ production. However, it still lacks effective strategies to controllably synthesize abundant GBs, rendering efficient C2+ production a persistent challenge, especially at ampere-level current density. Herein, we propose a novel strategy, which can achieve unconventional grain fragmentation during thermal annealing and thus create controllable GB densities. The catalyst with the utmost GB density exhibits a peak C2+ faradaic efficiency (FE) of ca. 70.0% in an H-type cell and 68.2% in a flow cell; even more impressively, it delivers an ultra-high C2+ current density of 0.768 A cm-2, outperforming most recently reported results. A combination of in situ spectroscopies and theoretical calculations reveal that the enrichment of GBs yields more active sites for a higher ⁎CO coverage, leading to promotion of the ⁎CO-⁎CO coupling process and ultimately high C2+ production performance.

Unconventional Grain Fragmentation Creates High-Density Boundaries for Efficient CO2-to-C2+ Electro-conversion at Ampere-Level Current Density