The electrochemical double layer (EDL) at the catalyst–electrolyte interface plays a pivotal yet often overlooked role in governing the reaction pathways of electrocatalytic CO 2 reduction (eCO 2 RR). Previous efforts have predominantly focused on precise engineering of catalytic active sites to promote multi‑carbon (C 2+ ) product formation, while the interplay between catalyst design and EDL regulation has received far less attention. Herein, we report a Na + -assisted surface engineering strategy to precisely tailor the local interfacial microenvironment of grain-boundary-rich Cu 2 O catalysts. Alkaline etching and thermal treatment induce electrostatically stabilized anchoring of Na + on the topmost atomic layers of the catalyst surface, while preserving the bulk intrinsic active sites. In situ spectroscopic analyses further reveal that this configuration promotes the accumulation of hydroxyl species on the catalyst surface, thus establishing a locally alkaline microenvironment within the EDL that facilitates C C coupling toward C 2+ products. As a result, the catalyst exhibits exceptional C 2+ selectivity across a wide current density window, maintaining ~90% C 2+ Faradaic efficiency at 250 mA cm −2 (1.25 A) and ~ 75% even at 400 mA cm −2 (2 A). This work demonstrates that surface structural modification can be leveraged to modulate the EDL, offering an effective strategy to regulate the interfacial microenvironment and enabling efficient formation of C 2+ products. • Na + -assisted surface engineering tailor the local interfacial microenvironment of grain-boundary-rich Cu 2 O catalysts. • Stably anchored Na + promotes hydroxyl accumulation and accelerates C C coupling toward C 2+ products. • The catalyst achieves 90% C 2+ selectivity at 250 mA cm −2 , demonstrating a scalable strategy for efficient eCO 2 RR.
Wang et al. (Wed,) studied this question.