Electrochemical CO₂ reduction (eCO₂RR) toward n-propanol (n-PrOH) is a promising strategy for the efficient utilization of renewable electricity and the achievement of carbon neutrality. However, both the catalytic activity and selectivity for n-PrOH production are still unsatisfactory and the underlying mechanism remains to be fully elucidated. Herein, we demonstrate phase boundary-rich copper catalysts (Cu(T)-600-320) for enhanced eCO₂RR-to-n-PrOH performance via facilitating the coupling between key intermediates of *CO and *OC₂H₅. Catalytically active sites at Cu(111)/Cu₂O(111) phase boundaries on Cu(T)-600-320 are ultrastable for the eCO₂RR under industrial-level current density conditions, even without any external regulators. In the flow cell, the n-PrOH Faradaic efficiency reaches 19.3% with a high partial current density of 77.2 mA·cm⁻² at −0.88 V versus reversible hydrogen electrode, outperforming the performance of most reported catalysts. In situ spectroscopy studies, control experiments, and density functional theory calculations unambiguously elucidate that n-PrOH is generated via the *CO + *OC₂H₅ → *OCHCH₂CH₃ pathway over Cu(T)-600-320. This work offers new insights into the rational design of high-performance copper-based catalysts targeting C₃ products generation via eCO₂RR.